CN113745967B - Semiconductor laser and preparation method thereof - Google Patents

Semiconductor laser and preparation method thereof Download PDF

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Publication number
CN113745967B
CN113745967B CN202110992957.9A CN202110992957A CN113745967B CN 113745967 B CN113745967 B CN 113745967B CN 202110992957 A CN202110992957 A CN 202110992957A CN 113745967 B CN113745967 B CN 113745967B
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layer
substrate
epitaxial
sub
laser
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CN113745967A (en
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吴猛
李淼
刘朝明
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Yinlin Photoelectric Technology Suzhou Co ltd
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Yinlin Photoelectric Technology Suzhou Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
    • H01S5/1231—Grating growth or overgrowth details
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2004—Confining in the direction perpendicular to the layer structure
    • H01S5/2018—Optical confinement, e.g. absorbing-, reflecting- or waveguide-layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure

Abstract

The embodiment of the invention discloses a semiconductor laser and a preparation method thereof, wherein the laser comprises the following components: the laser epitaxial structure comprises a substrate, and a grating structure and a ridge structure which are sequentially positioned on one side of the substrate; the substrate comprises a plurality of step structures which are sequentially arranged along a first direction; the grating structure comprises a step structure and a first sub-epitaxial structure arranged between two adjacent step structures, and the refractive indexes of the step structure and the first sub-epitaxial structure are different; the ridge structure at least comprises an upper light field limiting layer, an upper contact layer and a first electrode layer which are arranged in a laminated mode, wherein the first electrode layer is positioned on one side, far away from the substrate, of the upper contact layer; and the second electrode layer is positioned on one side of the substrate away from the grating structure. The semiconductor laser and the preparation method thereof provided by the embodiment of the invention have the advantages of low grating loss, high coupling efficiency, small series resistance, low cost and the like, and can obviously improve the performance and reliability of the semiconductor laser.

Description

Semiconductor laser and preparation method thereof
Technical Field
The embodiment of the invention relates to the technical field of semiconductor photoelectricity, in particular to a semiconductor laser and a preparation method thereof.
Background
The semiconductor laser, also called laser diode, uses semiconductor material, such as gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), aluminium nitride (AlN), cadmium sulfide (CdS), zinc sulfide (ZnS) etc. as working substance, and has the advantages of small volume, high efficiency and long service life. The distributed feedback laser (Distributed Feedback Laser, abbreviated as DFB) has the advantages of good single-mode characteristic, half-width of spectrum, high modulation rate and the like, and has important application in various aspects such as laser communication, laser storage, laser printing, laser gyro, laser display, laser ranging, laser radar and the like, and is widely paid attention to the industry and academia.
DFB lasers require the preparation of gratings to select the mode. Typically the grating of the laser is made on the inner or upper surface of the laser. For the internal grating, multiple epitaxial growth is needed, so that the preparation process is complex, the cost is high, contamination such as carbon, oxygen and silicon is easy to occur at a secondary epitaxial growth interface, and the performance and the reliability of the device are seriously affected. Therefore, most DFB lasers use surface gratings, i.e. the gratings are manufactured on the upper surface of the laser, and the surface gratings are generally manufactured by dry etching, and the dry etching not only affects current injection to cause non-uniform current injection, but also can generate surface states such as dangling bonds to cause non-radiative recombination, thereby affecting the efficiency of the device. Furthermore, for the ridge surface grating, the light field and the grating are overlapped very greatly, so that the light loss of the device is large, and furthermore, the etched part in the ridge grating is difficult to form ohmic contact, so that the current injection of the laser is uneven, and the performance of the device is seriously affected. In order to reduce the influence of etching damage, some DFB lasers adopt a ridge-shaped side wall grating structure, and the grating is made on the side wall of the ridge, however, because the optical field is mainly distributed below the ridge, the coupling efficiency of the grating is low, multimode is easy to appear in the laser, and in addition, the influence of etching damage still exists, and the performance of the device can still be influenced. In addition, the fabrication of gratings on both the ridge sidewalls and the ridge upper surface reduces the current injection area, resulting in an increase in the device series resistance.
Therefore, the grating structure in the prior art has the problems of larger optical loss, low coupling efficiency, larger series resistance, complex preparation process of multiple epitaxial growth, higher cost and serious influence on the device performance of the laser caused by the grating structure in the device or on the upper surface.
Disclosure of Invention
In view of the above, the embodiment of the invention provides a semiconductor laser and a preparation method thereof, which are used for solving the problems of large optical loss, low coupling efficiency, large series resistance, complex preparation process of multiple epitaxial growth, high cost and serious influence on the device performance of the laser caused by a grating structure in the device or on the upper surface in the prior art.
In a first aspect, an embodiment of the present invention provides a semiconductor laser, including:
the laser epitaxial structure comprises a substrate, and a grating structure and a ridge structure which are sequentially positioned on one side of the substrate;
the substrate comprises a plurality of step structures which are sequentially arranged along a first direction, wherein the first direction is parallel to a plane where the substrate is positioned and is intersected with a direction of the substrate pointing to the ridge structure;
the grating structure comprises the step structures and first sub-epitaxial structures arranged between two adjacent step structures, and refractive indexes of the step structures and the first sub-epitaxial structures are different;
The ridge structure at least comprises an upper light field limiting layer, an upper contact layer and a first electrode layer which are arranged in a laminated mode, wherein the first electrode layer is positioned on one side, away from the substrate, of the upper contact layer;
and a second electrode layer positioned on one side of the substrate away from the grating structure.
Optionally, a plurality of the step structures are periodically arranged.
Optionally, the step structure includes a first surface near one side of the ridge structure and a sidewall connected to the first surface;
the included angle between the first surface and the side wall is a right angle;
alternatively, the included angle between the first surface and the side wall is an obtuse angle.
Optionally, the first sub-epitaxial structure includes at least a portion of the lower optical field confinement layer.
Optionally, the laser epitaxial structure further includes at least one common epitaxial layer, and the common epitaxial layer is located on a side of the first sub-epitaxial structure away from the substrate;
the common epitaxial layer and the step structure have a first effective refractive index, the common epitaxial layer and the first sub-epitaxial structure have a second effective refractive index, and the first effective refractive index is different from the second effective refractive index.
Optionally, the first sub-epitaxial structure includes at least a portion of the lower optical field confinement layer; the common epitaxial layer at least comprises a lower waveguide layer, an active region, an upper waveguide layer, the upper light field limiting layer and the upper contact layer which are arranged in a laminated manner, wherein the upper contact layer is positioned on one side far away from the substrate;
Alternatively, the first sub-epitaxial structure includes the lower optical field confinement layer and at least a portion of the lower waveguide layer arranged in a stack; the common epitaxial layer at least comprises an active region, an upper waveguide layer, an upper light field limiting layer and an upper contact layer which are arranged in a laminated mode, wherein the upper contact layer is positioned on one side far away from the substrate;
alternatively, the first sub-epitaxial structure includes the lower optical field confinement layer, the lower waveguide layer, and at least a portion of the active region in a stacked arrangement; the common epitaxial layer at least comprises an upper waveguide layer, an upper light field limiting layer and an upper contact layer which are arranged in a laminated mode, wherein the upper contact layer is positioned on one side far away from the substrate;
alternatively, the first sub-epitaxial structure includes the lower optical field confinement layer, the lower waveguide layer, the active region, and at least a portion of the upper waveguide layer in a stacked arrangement; the common epitaxial layer at least comprises the upper light field limiting layer and the upper contact layer which are arranged in a lamination mode, and the upper contact layer is arranged on one side away from the substrate;
alternatively, the first sub-epitaxial structure includes the lower optical field confinement layer, the lower waveguide layer, the active region, the upper waveguide layer, and at least a portion of the upper optical field confinement layer in a stacked arrangement; the common epitaxial layer comprises at least the upper contact layer, which is located on a side away from the substrate.
Optionally, the first sub-epitaxial structure includes the lower optical field confinement layer, the lower waveguide layer, the active region, the upper waveguide layer, the upper optical field confinement layer, and the upper contact layer that are stacked, and the upper contact layer is located on a side away from the substrate;
the ridge structure includes a portion of the upper light field confining layer, the upper contact layer, and the first electrode layer.
Optionally, the first effective refractive index satisfies:
the second effective refractive index satisfies:
wherein ,i is more than or equal to 1 and less than or equal to k, j is more than or equal to 1 and less than or equal to m, and i, j, m, k is a positive integer;
P i n is the ratio of the light intensity of the ith layer of the common epitaxial layer in the lasing mode to the total light intensity of the lasing mode i Refractive index of the ith layer in the common epitaxial layer; p (P) a N is the ratio of the light intensity of the laser excitation mode in the step structure to the total light intensity of the laser excitation mode a Refractive index of the step structure; p (P) bj N is the ratio of the light intensity of the j-th layer of the first sub-epitaxy structure of the laser lasing mode to the total light intensity of the laser lasing mode bj And the refractive index of the j-th layer of the first sub-epitaxial structure.
Optionally, the semiconductor laser further includes a connection electrode located on a side of the first electrode layer away from the substrate;
The thickness of the connecting electrode is larger than that of the first electrode layer, and the vertical projection of the connecting electrode on the plane of the substrate covers the vertical projection of the ridge structure on the plane of the substrate.
In a second aspect, an embodiment of the present invention further provides a method for preparing a semiconductor laser, which is used for preparing the semiconductor laser in the first aspect, where the preparation method includes:
preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate, and a grating structure and a ridge structure which are sequentially positioned on one side of the substrate;
preparing a plurality of step structures which are sequentially arranged along a first direction on one side surface of the substrate, wherein the first direction is parallel to a plane where the substrate is positioned and intersects with a direction of the substrate pointing to the ridge structure;
preparing a grating structure on one side of the substrate, wherein the grating structure comprises the step structures and first sub-epitaxial structures arranged between two adjacent step structures, and refractive indexes of the step structures and the first sub-epitaxial structures are different;
preparing a ridge structure on one side of the grating structure far away from the substrate, and etching at least part of the upper light field limiting layer, the upper contact layer and the first electrode layer which are arranged in a lamination manner to form the ridge structure, wherein the first electrode layer is positioned on one side of the upper contact layer far away from the substrate;
Preparing a second electrode layer on one side of the substrate away from the grating structure;
and carrying out scribing, cleavage, film plating and splitting processes on the epitaxial structure to form the semiconductor laser.
According to the semiconductor laser and the preparation method thereof provided by the embodiment of the invention, the plurality of step structures are sequentially arranged on the surface of the substrate along the first direction, the grating structure comprises the step structures and the first sub-epitaxial structures positioned between the two adjacent step structures, the step structures are utilized to realize the regulation and control of the thickness of the first sub-epitaxial structures of the laser, the grating structure comprising the step structures on the surface of the substrate and the first sub-epitaxial structures is formed, the grating is arranged below the laser, the separation of the grating and the ridge shape on the upper surface of the laser is realized, and the regulation and the selection of the laser mode are realized. The semiconductor laser and the preparation method thereof provided by the embodiment of the invention have the advantages of low grating loss, high grating coupling efficiency, small series resistance, low cost and the like, and can remarkably improve the performance, reliability and market competitiveness of the semiconductor laser.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
Fig. 1 is a schematic surface structure of a semiconductor laser according to an embodiment of the present invention;
FIG. 2 is a schematic cross-sectional view taken along the direction AA' of FIG. 1;
FIG. 3 is a schematic cross-sectional view taken along the BB' direction in FIG. 1;
FIG. 4 is a schematic cross-sectional view taken along the direction AA' of the alternative embodiment of FIG. 1;
fig. 5 is a flowchart of a method for manufacturing a semiconductor laser according to an embodiment of the present invention;
FIG. 6 is a schematic view of the surface structure of a prepared patterned substrate;
FIG. 7 is a schematic cross-sectional view of the prepared patterned substrate along AA';
FIG. 8 is a schematic cross-sectional view of the epitaxial wafer along AA' after the growth of the laser structure;
fig. 9 is a schematic diagram of a surface structure of an epitaxial wafer after etching to prepare a ridge structure;
FIG. 10 is a schematic cross-sectional view of the epitaxial wafer along BB' after etching to prepare the ridge structure;
FIG. 11 is a schematic cross-sectional view of the epitaxial wafer along BB' after deposition of the dielectric layer;
FIG. 12 is a schematic cross-sectional view of the epitaxial wafer along BB' after stripping the dielectric layer;
FIG. 13 is a schematic cross-sectional view of the epitaxial wafer along BB' after the connection electrodes are prepared;
FIG. 14 is a schematic cross-sectional view of the epitaxial wafer along BB' after preparation of the second electrode on the substrate side;
fig. 15 is a flowchart of another method for manufacturing a semiconductor laser according to an embodiment of the present invention.
The following is a reference numeral description:
101-substrate, 102-lower optical field confinement layer, 103-lower waveguide layer, 104-active region, 105-upper waveguide layer, 106-upper optical field confinement layer, 107-upper contact layer, 108-first electrode layer, 109-photoresist, 110-dielectric layer, 111-connection electrode, 112-second electrode layer, 201-step structure, 202-first sub-epitaxial structure, 20-grating structure, 30-ridge structure, 40-common epitaxial layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be fully described below by way of specific embodiments with reference to the accompanying drawings in the examples of the present invention. It is apparent that the described embodiments are some, but not all, embodiments of the present invention, and that all other embodiments, which a person of ordinary skill in the art would obtain without making inventive efforts, are within the scope of this invention.
An optical device composed of a large number of equally wide, equally spaced parallel slits is called a grating. The common grating is made by carving a large number of parallel scores on a glass sheet, wherein the scores are opaque parts, a smooth part between the two scores can transmit light and is equivalent to a slit, and the requirements of grating mode selection are met due to the refractive index difference between the opaque part and the transparent part. In the prior art, the grating is usually prepared in the laser or on the surface of the laser, and the internal grating is complicated in process and high in cost because of multiple epitaxial growth, and is easy to pollute, so that the performance and the reliability of the device are affected. The surface grating is usually prepared by dry etching, and the dry etching can influence current injection to cause current injection non-uniformity, and surface states such as suspension bonds and the like are generated to cause non-radiative recombination so as to influence the efficiency of the device, and also can cause larger grating loss; in order to reduce the influence of etching damage, a ridge-shaped side wall grating structure is adopted, so that the coupling efficiency of the grating is low, multiple modes are easy to appear in a laser, and the performance of a device is influenced. In addition, the fabrication of gratings on both the ridge sidewalls and the ridge upper surface reduces the current injection area, resulting in an increase in the device series resistance. In order to solve the problems, in the embodiment of the invention, a plurality of step structures are sequentially arranged on the surface of a substrate along a first direction, a grating structure comprises the step structures and a first sub-epitaxial structure positioned between two adjacent step structures, the step structures are utilized to realize the regulation and control of the thickness of the first sub-epitaxial structure of a laser, a grating structure comprising the step structures on the surface of the substrate and the first sub-epitaxial structure is formed, and the grating is arranged below the laser, so that the separation of the grating and the ridge shape on the upper surface of the laser is realized, and the regulation and the selection of the laser mode are realized. The semiconductor laser provided by the embodiment of the invention has the advantages of low grating loss, high grating coupling efficiency, small series resistance, low cost and the like, and can remarkably improve the performance, reliability and market competitiveness of the semiconductor laser.
Specifically, fig. 1 is a schematic surface structure of a semiconductor laser according to an embodiment of the present invention, fig. 2 is a schematic cross-sectional view along AA 'in fig. 1, and fig. 3 is a schematic cross-sectional view along BB' in fig. 1. As shown in fig. 1 to 3, a semiconductor laser provided in an embodiment of the present invention includes: a laser epitaxial structure comprising a substrate 101, a grating structure 20 and a ridge structure 30 located on one side of the substrate 101 in sequence; the substrate 101 comprises a plurality of step structures 201 arranged in sequence along a first direction X, wherein the first direction X is parallel to the plane of the substrate 101 and intersects the direction of the substrate 101 pointing to the ridge structure 30; the grating structure 20 comprises a step structure 201 and a first sub-epitaxial structure 202 arranged between two adjacent step structures 201, wherein the refractive indexes of the step structure 201 and the first sub-epitaxial structure 202 are different; the ridge structure 30 at least comprises an upper light field limiting layer 106, an upper contact layer 107 and a first electrode layer 108 which are arranged in a stacked manner, wherein the first electrode layer 108 is positioned on one side of the upper contact layer 107 away from the substrate 101; a second electrode layer 112 on the side of the substrate 101 remote from the grating structure 20.
1-3, a semiconductor laser according to an embodiment of the present invention includes a laser epitaxial structure, which is a main light emitting structure of a laser, and the laser epitaxial structure includes a grating structure 20 and a ridge structure 30 sequentially disposed on one side of a substrate 101 with the substrate 101. Wherein the substrate 101 material comprises any one or a combination of more than two of GaAs, inP, gaN, alGaN, inGaN, alN, sapphire, siC, si and SOI.
As shown in fig. 2, a first direction X is defined parallel to the plane of the substrate 101 and intersects the direction of the substrate 101 pointing towards the ridge structure 30 (as shown in the Y-direction). Along the first direction X, a plurality of step structures 201 are sequentially disposed on the surface of the substrate 101, and the alternately disposed step structures 201 and the first sub-epitaxial structures 202 form the grating structure 20. The first sub-epitaxial structure 202 may be a single-layer epitaxial layer or a multi-layer epitaxial layer stacked along the Y direction, and when the first sub-epitaxial structure 202 is a single-layer epitaxial layer, the first sub-epitaxial structure may be a single-layer epitaxial layerThe epitaxial structure 202 may include a portion of the single-layer epitaxial layer, and referring to fig. 2, the first sub-epitaxial structure 202 in fig. 2 is a single-layer epitaxial layer, and a portion of the single-layer epitaxial layer is located between two adjacent step structures 201. Optionally, the material of the first sub-epitaxial structure 202 includes Al x1 In y1 Ga 1-x1-y1 As x2 P y2 N 1-x2-y2 The method is satisfied that x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, x2 is more than or equal to 0 and less than or equal to 1, y2 is more than or equal to 0 and less than or equal to 1, (x 1+ y 1) is more than or equal to 0 and less than or equal to 1, and (x 2+ y 2) is more than or equal to 0 and less than or equal to 1. Those skilled in the art may select different epitaxial layer semiconductor materials according to the characteristics of the distributed feedback laser, which is not limited by the embodiment of the present invention.
Specifically, the refractive index n of the step structure 201 on the surface of the substrate 101 is achieved by reasonably selecting the materials of the substrate 101 and the first sub-epitaxial structure 202 1 And refractive index n of first sub-epitaxial structure 202 2 Different, the condition of grating structure formation is satisfied. Illustratively, by controlling the refractive index n 1 And refractive index n 2 The index of refraction delta n of the grating structure 20 can be effectively controlled to select a mode, single mode laser or multimode laser output. When the refractive index n 1 And refractive index n 2 When the refractive index difference delta n is larger, the reflectivity of the grating structure can be effectively improved, so that single-mode operation is better realized. Setting the width L of the adjacent step structures 201 in the first direction X 1 And a width L of the first sub-epitaxial structure 202 in the first direction X 2 The sum is the grating period L of the grating structure 20, and the grating equation of the grating structure 20 meeting the single laser wavelength lambda is realized by adjusting the grating period L, so that the requirement of single-mode operation with only one laser excitation mode lambda is met. Compared with the traditional method for preparing the surface grating by dry etching, the method for preparing the surface grating by the dry etching has the advantages that the grating is formed by adjusting and controlling the thickness of the first sub-epitaxial structure 202 of the laser, the first sub-epitaxial structure 202 is prepared by epitaxial growth, and the grating loss is lower because the defects of semiconductor materials which are grown by epitaxy are fewer and far fewer than the defects caused by dry etching. In addition, the step structure 201 is formed on the surface of the substrate 101, so that impurities are not introduced, other film layers above the substrate 101 are not affected, the material quality can be improved, and the device performance is further improved.
Meanwhile, the grating structure 20 and the ridge structure 30 form a plurality of epitaxial layers on one side of the substrate 101, the ridge structure 30 at least comprises an upper light field limiting layer 106, an upper contact layer 107 and a first electrode layer 108 which are grown in a lamination mode on the side, away from the substrate 101, of the grating structure 20, and current limitation and light field limitation in the semiconductor laser can be enhanced by adopting the ridge structure 30. In a conventional semiconductor grating structure, in order to reduce the influence of grating etching damage, a ridge-shaped side wall grating structure is generally adopted as a surface grating, and because an optical field is mainly distributed below a ridge shape, the coupling efficiency of the grating is low, multimode is easy to appear in a laser, and a grating structure 20 formed by a surface step structure 201 of a substrate 101 and a first sub-epitaxy structure 202 is arranged right below a ridge structure 30, so that the overlapping of the grating structure 20 and a laser optical field in the laser epitaxy structure can be effectively increased, and the coupling efficiency of the grating is improved. Meanwhile, the current injection area is reduced no matter the grating is prepared on the ridge side wall or the ridge, so that the series resistance of the device is increased, the ridge structure 30 is separated from the grating by the structure provided by the embodiment, the influence of the grating structure 20 on the current injection area can be effectively avoided, the ridge area is increased, the ridge current injection area is further increased, the series resistance of the device is reduced, and the device performance is improved. In addition, the grating structure 20 proposed in the embodiment of the present invention is of high conductivity, and does not affect the injection and conduction of current, and therefore does not affect the efficiency of the active region and the device performance. Further, the grating structure 20 formed by the step structure 201 on the surface of the substrate 101 and the first sub-epitaxial structure 202 only needs to be subjected to one epitaxial growth, so that the device cost can be effectively reduced, and when the laser is grown, the substrate 101 with the step structure 201 on the surface is almost indistinguishable from a flat substrate, the epitaxial growth area is the same as that of the flat substrate, the growth rate, doping and the like are not affected, and therefore, the device is completely the same as a conventional laser growing program on a flat substrate, and additional debugging cost is not required to be increased.
The first electrode layer 108 is arranged on the side, far away from the substrate 101, of the upper contact layer 107, so that good ohmic contact is achieved between the first electrode layer 108 and the upper contact layer 107, and improvement of carrier injection efficiency is facilitated. The material of the first electrode layer 108 may include any one or a combination of two or more of Ni, ti, pd, pt, au, al, cr, tiN, ITO, auGe, auGeNi and IGZO.
In summary, unlike the conventional DFB laser grating structure in the device or on the upper surface, the semiconductor laser provided in the embodiment of the present invention sequentially sets a plurality of step structures on the surface of the substrate along the first direction, where the grating structure includes a step structure and a first sub-epitaxy structure located between two adjacent step structures, and the step structure is used to regulate the thickness of the first sub-epitaxy structure of the laser, so as to form a grating structure including a step structure on the surface of the substrate and the first sub-epitaxy structure, and the grating is made below the laser, thereby realizing the separation of the grating and the ridge on the upper surface of the laser, and thus realizing regulation and selection of the laser mode. The semiconductor laser provided by the embodiment of the invention has the advantages of low grating loss, high grating coupling efficiency, small series resistance, low cost and the like, and can remarkably improve the performance, reliability and market competitiveness of the semiconductor laser.
Specifically, a plurality of step structures 201 are periodically arranged.
As shown in fig. 2, along a first direction X, the surface of the substrate 101 is provided with periodic step structures 201, where periodic means that the width L of all step structures 201 in the first direction X 1 Equal, the heights H of all the step structures 201 in the Y direction are equal, and the widths L of all the first sub-epitaxial structures 202 in the first direction X 2 Equal, i.e. all the step structures 201 are the same size and the distance between two adjacent step structures 201 is equal. The thickness of the first sub-epitaxial structure 201 of the laser can be regulated and controlled by reasonably setting the height H of the periodical step structure 201 in the Y direction, and the refractive index difference of the grating is improved, so that the reflectivity of the grating is improved, and single-mode operation is better realized. Alternatively, the height H of the step structure 201 of the surface of the substrate 101 in the Y direction satisfies 0 μm < H.ltoreq.5 μm, for example 3 μm. In this embodiment, the first sub-epitaxy structure of the laser is implemented by using the step structure 201 by providing the periodic step structure 201 along the first direction X on the surface of the substrate202, a periodic grating structure 20 comprising a step structure 201 and a first sub-epitaxial structure 202 on the surface of the substrate 101 is formed, thereby realizing the regulation and selection of the laser mode.
Optionally, the step structure 201 includes a first surface adjacent to one side of the ridge structure 30 and a sidewall connected to the first surface; the included angle alpha between the first surface and the side wall is a right angle; alternatively, the angle α between the first surface and the sidewall is an obtuse angle.
Fig. 4 is a schematic cross-sectional view along AA' of another embodiment of fig. 1, and referring to fig. 2 and 4, a step structure 201 on a surface of a substrate 101 includes a first surface adjacent to one side of a ridge structure 30, and a sidewall connected to the first surface. As shown in fig. 2, the width L of the step structure 201 in the first direction X along the Y direction 1 All are equal, namely the included angle alpha between the first surface of the step structure 201 and the side wall is a right angle, the step structure 201 is of a mutant type in the Y direction, and the process of the mutant type step structure 201 is simple. As shown in fig. 4, the step structure 201 is in a trapezoid shape with a narrow top and a wide bottom along the Y direction, that is, an included angle α between the first surface of the step structure 201 and the side wall is an obtuse angle, and the step structure 201 is in a gradual shape along the Y direction. When another material is grown on one material, lattice mismatch and thermal mismatch are generated, and compared with the mutant step structure 201, the graded step structure 201 can reduce defects, improve material quality, and further improve device performance.
Optionally, the first sub-epitaxial structure 202 includes at least a portion of the lower optical field confinement layer 102.
As shown in fig. 2, the first sub-epitaxial structure 202 may include a portion of the lower optical field limiting layer 102, and in other embodiments, the first sub-epitaxial structure 202 may include all of the lower optical field limiting layer 102, i.e., a single epitaxial layer, or may be a stacked arrangement of multiple epitaxial layers. Illustratively, referring to fig. 2, taking the example that the first sub-epitaxial structure 202 includes a portion of the lower optical field-limiting layer 102, the first sub-epitaxial structure 202 and the step structure 201 form the grating structure 20 due to the different materials and refractive indices of the lower optical field-limiting layer 102 and the substrate 101.
Optionally, with continued reference to fig. 2, the laser epitaxial structure further includes at least one common epitaxial layer 40, the common epitaxial layer 40 being located on a side of the first sub-epitaxial structure 202 remote from the substrate 101; the common epitaxial layer 40 and the step structure 201 have a first effective refractive index N1, and the common epitaxial layer 40 and the first sub-epitaxial structure 202 have a second effective refractive index N2, the first effective refractive index N1 being different from the second effective refractive index N2.
Illustratively, with continued reference to fig. 2, the laser epitaxial structure is relatively complex, with the multilayer epitaxial structure layered to form a laser resonator structure that stabilizes the single mode output. Specifically, the laser epitaxial structure further includes at least one common epitaxial layer 40, which has the functions of exciting light waves and limiting light field distribution, and the common epitaxial layer 40 is disposed in a stacked manner along a side of the first sub-epitaxial structure 202 away from the substrate 101. The optical fields of the laser waveguide are not uniformly distributed in the common epitaxial layer 40, the step structure 201 and the first sub-epitaxial structure 202, and the laser waveguide has optical loss in the process of multiple oscillation excitation output in the laser resonator. By providing the structural combination of the common epitaxial layer 40 and the step structure 201 with the first effective refractive index N1, the structural group of the common epitaxial layer 40 and the first sub-epitaxial structure 202 has the second effective refractive index N2, such that the first effective refractive index N1 and the second effective refractive index N2 have refractive index differences, when the refractive index differences are larger, the reflectivity of the grating structure 20 is larger, the grating optical loss is smaller, and thus better single-mode operation is achieved.
Optionally, the first effective refractive index N1 satisfies:
the second effective refractive index N2 satisfies:
wherein ,i is more than or equal to 1 and less than or equal to k, j is more than or equal to 1 and less than or equal to m, and i, j, m, k is a positive integer; p (P) i In the lasing modeThe ratio of the light intensity of the ith layer of the common epitaxial layer 40 to the total light intensity of the lasing modes, n i Refractive index of the i-th layer in the common epitaxial layer 40; p (P) a N is the ratio of the light intensity of the lasing mode in the step structure 201 to the total light intensity of the lasing mode a Is the refractive index of the step structure 201; p (P) bj N is the ratio of the light intensity of the j-th layer of the first sub-epitaxy structure 202 in the lasing mode to the total light intensity of the lasing mode bj Is the refractive index of the j-th layer of the first sub-epitaxial structure 202.
Illustratively, with continued reference to fig. 2, the first effective refractive index N1 of the combined structure providing the common epitaxial layer 40 and the step structure 201 satisfies the proportional relationship:
and the second effective refractive index N2 of the structural combination of the common epitaxial layer 40 and the first sub-epitaxial structure 202 satisfies:
wherein ,i is more than or equal to 1 and less than or equal to k, j is more than or equal to 1 and less than or equal to m, and i, j, m, k is a positive integer.
The common epitaxial layer 40 is at least one epitaxial layer, wherein P i N is the ratio of the light intensity of the ith layer of the common epitaxial layer 40 in the lasing mode to the total light intensity of the lasing mode i For the refractive index of the i-th layer in the common epitaxial layer 40, the refractive index difference between the first effective refractive index N1 and the second effective refractive index N2 affects the distribution of light intensity in the common epitaxial layer 40 and the grating structure 20 due to the difference of the refractive indexes of different materials, and directly affects the reflectivity, optical loss and mode selection of the grating. Referring to the formulas of the first effective refractive index N1 and the second effective refractive index N2, it can be seen that by reasonably arranging the common epitaxial layer structure40 and the grating structure 20, specifically, the grating structure 20 includes a step structure 201 and a first sub-epitaxy structure 202 which are alternately arranged along the first direction X, semiconductor epitaxial layers of different materials are selected, and refractive index difference values of the step structure 201 and the first sub-epitaxy structure 202 are adjusted, so that the reflectivity of the grating structure 20 to light can be increased, the light loss is reduced, and then the single-mode operation of the laser is affected.
It should be noted that, when the first sub-epitaxial structure 202 is a single epitaxial layer, as illustrated in fig. 2, by way of example, the first sub-epitaxial structure 202 includes a portion of the lower optical field confinement layer 102, and then the second effective refractive index N2 satisfies:
n b1 for the refractive index of the lower light field confinement layer 102, P b1 The ratio of the light intensity of the lower light field confinement layer 102 to the total light intensity of the lasing mode.
When the first sub-epitaxial structure 202 is an epitaxial layer of a plurality of stacked layers, the second effective refractive index N2 satisfies, illustratively, when the first sub-epitaxial structure 202 includes the lower optical field confinement layer 102 and at least a portion of the lower waveguide layer 103:
wherein ,nb1 For the refractive index of the lower light field confinement layer 102, P b1 N is the ratio of the light intensity of the lower light field confinement layer 102 in the lasing mode to the total light intensity of the lasing mode b2 P, the refractive index of the lower waveguide layer 103 b2 Is the ratio of the light intensity of the lower waveguide layer 103 in the lasing mode to the total light intensity of the lasing mode. By analogy, when the first sub-epitaxial structure 202 comprises m stacked arrangements of epitaxial layers, the second effective refractive index N2 of the structural combination of the common epitaxial layer 40 and the first sub-epitaxial structure 202 satisfies:
optionally, the first sub-epitaxial structure 202 includes at least a portion of the lower optical field confinement layer 102; the common epitaxial layer 40 includes at least a lower waveguide layer 103, an active region 104, an upper waveguide layer 105, an upper optical field confinement layer 106, and an upper contact layer 107 which are stacked, the upper contact layer 107 being located on a side away from the substrate 101 (refer to fig. 2);
Alternatively, the first sub-epitaxial structure includes a lower optical field confinement layer and at least a portion of a lower waveguide layer disposed in a stack; the common epitaxial layer comprises at least an active region, an upper waveguide layer, an upper optical field confinement layer and an upper contact layer which are arranged in a stacked manner, wherein the upper contact layer is positioned on one side away from the substrate (not shown in the structure diagram);
alternatively, the first sub-epitaxial structure includes a lower optical field confinement layer, a lower waveguide layer, and at least a portion of an active region disposed in a stack; the common epitaxial layer comprises at least an upper waveguide layer, an upper optical field confinement layer and an upper contact layer arranged in a stack, the upper contact layer being located on a side remote from the substrate (not shown in this block diagram);
alternatively, the first sub-epitaxial structure includes a lower optical field confinement layer, a lower waveguide layer, an active region, and at least a portion of an upper waveguide layer disposed in a stack; the common epitaxial layer comprises at least an upper optical field confinement layer and an upper contact layer arranged in a stack, the upper contact layer being located on a side remote from the substrate (not shown in this block diagram);
alternatively, the first sub-epitaxial structure includes a lower optical field confinement layer, a lower waveguide layer, an active region, an upper waveguide layer, and at least a portion of the upper optical field confinement layer disposed in a stack; the common epitaxial layer comprises at least an upper contact layer, which is located on the side remote from the substrate (not shown in this block diagram).
Illustratively, by reasonably configuring the film structure of the first sub-epitaxial structure 202 in the grating structure 20, there are a plurality of deep grating structures formed by the step structure 201 on the surface of the substrate 101 and the first sub-epitaxial structure 202, and specifically, taking the first sub-epitaxial structure 202 including at least a part of the lower optical field confinement layer 102, the common epitaxial layer 40 includes at least the lower waveguide layer 103, the active region 104, the upper waveguide layer 105, the upper optical field confinement layer 106 and the upper contact layer 107 which are stacked in a stacked manner. As shown in fig. 2, the first sub-epitaxial structure 202 includes a portion of the lower optical field-limiting layer 102, and the common epitaxial layer 40 includes a stacked portion of the lower optical field-limiting layer 102, the lower waveguide layer 103, the active region 104, the upper waveguide layer 105, the upper optical field-limiting layer 106, and the upper contact layer 107; or the first sub-epitaxial structure includes a lower optical field confining layer and the common epitaxial layer includes a lower waveguide layer, an active region, an upper waveguide layer, an upper optical field confining layer, and an upper contact layer (not shown in this block diagram) in a stacked arrangement. The grating structure formed by the first sub-epitaxial structure 202 and the step structure 201 increases the overlapping area of the grating structure 20 and the optical field of the laser, so that the coupling efficiency of the grating can be effectively improved. Similarly, as the epitaxial layer structure of the first sub-epitaxial structure 202 gradually increases, the depth of the grating structure 20 in the Y direction can be further increased, a deep grating structure formed by the step structure 201 on the surface of the substrate 101 and the first sub-epitaxial structure 202 is obtained, and the overlap of the laser light field in the grating structure 20 and the laser epitaxial structure is increased, so that the coupling efficiency of the grating is effectively improved. Other specific configurations are not specifically recited herein.
Optionally, the first sub-epitaxial structure includes a lower optical field confinement layer, a lower waveguide layer, an active region, an upper waveguide layer, an upper optical field confinement layer, and an upper contact layer disposed in a stacked manner, the upper contact layer being located on a side away from the substrate; the ridge structure includes a portion of an upper light field confining layer, an upper contact layer, and a first electrode layer.
Illustratively, the first sub-epitaxial structure is further configured to include a lower optical field confinement layer, a lower waveguide layer, an active region, an upper waveguide layer, an upper optical field confinement layer, and an upper contact layer disposed in a stack such that the grating structure extends through all of the optical field regions of the laser epitaxial structure, and the ridge structure includes a portion of the upper optical field confinement layer, the upper contact layer, and the first electrode layer, the grating structure and the ridge structure being disposed with a portion of overlap in a direction away from the substrate. Compared with the traditional ridge side wall grating structure, the ridge structure is not influenced by the side wall grating, on one hand, the ridge area can be increased, the ridge current injection area can be increased, the series resistance of the device can be reduced, and the performance of the device can be improved; on the other hand, the distribution of the laser waveguides in the grating structure and the ridge structure is increased, so that the laser field in the grating structure can be effectively increased, and the coupling efficiency of the grating is effectively improved.
Optionally, referring to fig. 2 and 3, the semiconductor laser further includes a connection electrode 111 located on a side of the first electrode layer 108 remote from the substrate 101; the thickness of the connection electrode 111 is greater than the thickness of the first electrode layer 108, and the perpendicular projection of the connection electrode 111 onto the plane of the substrate 101 covers the perpendicular projection of the ridge structure 30 onto the plane of the substrate 101.
Referring to fig. 3, the semiconductor laser may optionally further comprise a dielectric layer 110 between the first electrode layer 108 and the connection electrode 111.
Illustratively, the ridge structure 30 is generally narrow in width and the first electrode layer 108 is relatively thin, which is disadvantageous for practical production of electrical connection, and in order to increase conductivity of the first electrode layer 108 on the upper surface of the ridge structure 30 and operability of electrical connection, a connection electrode 111 having a thickness greater than that of the first electrode layer 108 is deposited on a side of the first electrode layer 108 away from the substrate 101, as a thickened electrode, to facilitate electrical connection preparation of the laser. The vertical projection of the connection electrode 111 on the plane of the substrate 101 covers the vertical projection of the ridge structure 30 on the plane of the substrate 101, so that the first electrode layer 108 and the second electrode layer 112 form an electrode pair for injecting carriers, and the injection efficiency of carriers is improved. The connection electrode 111 may include any one or a combination of two or more of Ni, ti, pd, pt, au, al, cr, tiN, ITO, auGe, auGeNi and IGZO.
Specifically, in order to avoid the electrical short between the first electrode layer 108 and the connection electrode 111, a dielectric layer 110 is formed by adding a dielectric film between the first electrode layer 108 and the connection electrode 111, and the dielectric layer 110 covers the optical field limiting layer 108 and the sidewalls of the ridge structure 30 on the remaining portion, so as to electrically insulate the first electrode layer 108 from the connection electrode 111. Wherein the dielectric film material of the dielectric layer 110 comprises HfO 2 、Si、SiO 2 、SiN x 、SiON、Al 2 O 3 、AlON、SiAlON、TiO 2 、Ta 2 O 5 、ZrO 2 、MgO、MgF 2 And one or more of polysilicon and the likeAnd (5) combining.
In summary, the semiconductor laser including the grating structure formed by the substrate surface step structure and the first sub-epitaxial structure provided by the embodiment of the invention has the advantages of low grating loss, high grating coupling efficiency, small series resistance, low cost and the like, and can remarkably improve the performance, reliability and market competitiveness of the semiconductor laser.
Based on the same conception, the embodiment of the invention also provides a preparation method of the semiconductor laser, which is used for preparing the semiconductor laser provided by any embodiment. Fig. 5 is a flowchart of a method for manufacturing a semiconductor laser according to an embodiment of the present invention; FIG. 6 is a schematic view of the surface structure of a prepared patterned substrate; FIG. 7 is a schematic cross-sectional view of the prepared patterned substrate along AA'; FIG. 8 is a schematic cross-sectional view of the epitaxial wafer along AA' after the growth of the laser structure; fig. 9 is a schematic diagram of a surface structure of an epitaxial wafer after etching to prepare a ridge structure; FIG. 10 is a schematic cross-sectional view of the epitaxial wafer along BB' after etching to prepare the ridge structure; FIG. 11 is a schematic cross-sectional view of the epitaxial wafer along BB' after deposition of the dielectric layer; FIG. 12 is a schematic cross-sectional view of the epitaxial wafer along BB' after stripping the dielectric layer; FIG. 13 is a schematic cross-sectional view of the epitaxial wafer along BB' after the connection electrodes are prepared; fig. 14 is a schematic cross-sectional view of the epitaxial wafer along BB' after preparation of the second electrode on the substrate side. As shown in fig. 5 to 14, the method for manufacturing the semiconductor laser includes:
S101, preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate, a grating structure and a ridge structure, wherein the grating structure and the ridge structure are sequentially arranged on one side of the substrate, a plurality of step structures which are sequentially arranged along a first direction are prepared on one side surface of the substrate, and the first direction is parallel to a plane of the substrate and is intersected with the direction of the substrate pointing to the ridge structure; and preparing a grating structure on one side of the substrate, wherein the grating structure comprises a step structure and a first sub-epitaxial structure arranged between two adjacent step structures, and the refractive indexes of the step structure and the first sub-epitaxial structure are different.
Specifically, photoresist is spin-coated on the substrate 101, a plurality of step structures 201 sequentially arranged along the first direction X are photo-etched by using a photolithography technique, and dry etching or wet etching is usedEtching transfers the step structure 201 to the substrate 101, forming a patterned substrate 101, as shown in fig. 6 and 7. Wherein the substrate material comprises any one or more than two of GaAs, inP, gaN, alGaN, inGaN, alN, sapphire, siC, si and SOI. Illustratively, in connection with FIG. 2, along a first direction X, the surface of the substrate 101 is provided with a periodic step structure 201, and the step structure 201 has a width L 1 The distance between two adjacent step structures 201 is L 2 。
Taking the first sub-epitaxial structure 202 comprising part of the lower optical field limiter layer 102 as an example, the laser structure epitaxial structure further comprises a lower waveguide layer 103 on the side of the lower optical field limiter layer 102 remote from the substrate 101, an active region 104, an upper waveguide layer 105, an upper optical field limiter layer 106 and an upper contact layer 107. Specifically, as shown in fig. 8, the patterned substrate 101 is cleaned, and then placed in a reaction chamber, and a lower optical field limiting layer 102, a lower waveguide layer 103, an active region 104, an upper waveguide layer 105, an upper optical field limiting layer 106 and an upper contact layer 107 are sequentially grown on the patterned substrate 101 by adopting a one-time epitaxial growth method, so as to form a laser structure. In connection with fig. 2, the step structure 201 and the first sub-epitaxial structure 202 form the grating structure 20. Compared with the prior art, the grating structure and the multi-layer epitaxial layer can be prepared by adopting one-time epitaxial growth, so that the device cost can be effectively reduced, the substrate 101 with the step structure 201 arranged on the surface is almost indistinguishable from a flat substrate when the laser is grown, the epitaxial growth area is the same as that of the flat substrate, the growth rate, doping and the like are not influenced, and therefore, the method is completely the same as that of a conventional laser growing program on the flat substrate, and additional debugging cost is not required to be increased. With continued reference to fig. 2, the grating period is adjusted by setting the widths of the step structure 201 and the first sub-epitaxial structure 202 in the first direction X, thereby achieving the output of different lasing modes. The materials of the step structure 201 and the first sub-epitaxy structure 202 are selected to have a larger refractive index difference, so that the reflectivity of the grating structure 20 to the laser waveguide is improved, and single-mode operation is better realized.
Illustratively, depending on the laser epitaxial structure, the first sub-epitaxial structure 202 may include at least a portion of the lower optical field confinement layer 102, or the firstThe sub-epitaxial structure 202 includes the lower optical field confinement layer 102, the lower waveguide layer 103, the active region 104 and the upper waveguide layer 107, and further first sub-epitaxial structure 202 structures are not listed here, and may be set according to the laser structure and actual working requirements. Wherein. The materials of the laser epitaxial structure include: al (Al) x1 In y1 Ga 1-x1-y1 As x2 P y2 N 1-x2-y2 The epitaxial layer of the semiconductor material has the advantages that x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, x2 is more than or equal to 0 and less than or equal to 1, y2 is more than or equal to 0 and less than or equal to 1, (x 1+y1) is more than or equal to 0 and less than or equal to 1, and x2+y2 is more than or equal to 0 and less than or equal to 1, so that the epitaxial layer has various semiconductor materials.
S102, preparing a ridge structure on one side of the grating structure far away from the substrate, and etching at least an upper light field limiting layer, an upper contact layer and a first electrode layer which are arranged in a laminated mode to form the ridge structure, wherein the first electrode layer is located on one side of the upper contact layer far away from the substrate.
Specifically, referring to fig. 9-10, the prepared laser epitaxial wafer is cleaned, a first electrode layer 108 is deposited on the surface of one side of the epitaxial wafer far away from the substrate 101, and is annealed, the first electrode layer 108 and the upper contact layer 107 form ohmic contact, and the first electrode layer 108 is used as a first electrode of a semiconductor laser for carrier injection of stimulated radiation work of the laser. Further, photoresist 109 is spin-coated on the surface of the epitaxial wafer, a ridge pattern is photo-etched by using a photolithography technique, and then dry etching or wet etching is performed to etch the ridge structure 30 formed by the upper light field limiting layer 106, the upper contact layer 107 and the first electrode layer 108 in the stacked portion. Wherein the etched photoresist 109 is retained and the epitaxial structure is further prepared.
S103, preparing a second electrode layer on one side of the substrate far away from the grating structure.
Specifically, the prepared epitaxial structure is thinned, ground and polished, and a second electrode layer 112 is deposited on a side of the substrate 101 away from the grating structure 20, so as to prepare a second electrode of the semiconductor laser, and referring to fig. 14, the second electrode layer 112 is disposed opposite to the first electrode layer 108. Wherein the materials of the first electrode layer 108 and the second electrode layer 112 include any one or a combination of two or more of Ni, ti, pd, pt, au, al, cr, tiN, ITO, auGe, auGeNi and IGZO.
S104, scribing, cleaving, coating and splitting the epitaxial structure to form the semiconductor laser.
Specifically, according to the production requirement of the laser, reasonable scribing, cleaving, coating and splitting processes are further carried out on the epitaxial structure, and the required semiconductor laser is prepared.
In summary, in the method for manufacturing a semiconductor laser according to the embodiment of the present invention, a plurality of step structures are sequentially disposed on a surface of a substrate along a first direction, and a grating structure includes the step structures and a first sub-epitaxial structure located between two adjacent step structures, and the step structures are used to regulate and control a thickness of the first sub-epitaxial structure of the laser, so as to form a grating structure including the step structures on the surface of the substrate and the first sub-epitaxial structure, and the grating is formed below the laser, thereby realizing separation of the grating and a ridge on an upper surface of the laser, and further realizing regulation and selection of a laser mode. The preparation method provided by the embodiment of the invention has the advantages of low grating loss, high grating coupling efficiency, small series resistance, low cost and the like, and can remarkably improve the performance, reliability and market competitiveness of the semiconductor laser.
Fig. 15 is a flowchart of another method for manufacturing a semiconductor laser according to an embodiment of the present invention, where, as shown in fig. 15, the method for manufacturing a semiconductor laser includes:
s201, preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate, a grating structure and a ridge structure, wherein the grating structure and the ridge structure are sequentially arranged on one side of the substrate, a plurality of step structures which are sequentially arranged along a first direction are prepared on one side surface of the substrate, and the first direction is parallel to a plane of the substrate and is intersected with the direction of the substrate pointing to the ridge structure; and preparing a grating structure on one side of the substrate, wherein the grating structure comprises a step structure and a first sub-epitaxial structure arranged between two adjacent step structures, and the refractive indexes of the step structure and the first sub-epitaxial structure are different.
S202, preparing a ridge structure on one side of the grating structure far away from the substrate, and at least etching an upper light field limiting layer, an upper contact layer and a first electrode layer which are arranged in a laminated mode to form the ridge structure, wherein the first electrode layer is located on one side of the upper contact layer far away from the substrate.
And S203, preparing a dielectric layer on one side of the first electrode layer away from the substrate.
Specifically, referring to fig. 10-12, after the ridge structure is prepared, a dielectric layer 110 is deposited on the surface of the epitaxial wafer, and then the photoresist 109 above the ridge structure is used for stripping, so that the photoresist 109 is remained, the effect of protecting the first electrode layer 108 is achieved in the process of removing the dielectric layer 110 on the surface of the ridge structure, and then the photoresist 109 on the upper surface of the ridge structure is stripped, so that the formed dielectric layer 110 covers the upper surface of the optical field limiting layer 106 on the rest and the side wall of the ridge structure. Wherein the material of the dielectric layer 110 comprises HfO 2 、Si、SiO 2 、SiN x 、SiON、Al 2 O 3 、AlON、SiAlON、TiO 2 、Ta 2 O 5 、ZrO 2 Any one or a combination of more than two of MgO, polysilicon and the like.
S204, preparing a connecting electrode on one side of the first electrode layer far away from the substrate, wherein the thickness of the connecting electrode is larger than that of the first electrode layer, and the vertical projection of the connecting electrode on the plane of the substrate covers the vertical projection of the ridge structure on the plane of the substrate, and the dielectric layer is positioned between the first electrode layer and the connecting electrode.
Referring to fig. 13, in order to increase the conductivity of the ridge structure upper surface first electrode layer 108 and the operability of electrical connection, a connection electrode 111 is further prepared. Specifically, photoresist is spin-coated on the surface of the epitaxial wafer for photoetching, then, a coating film technology, a stripping technology and the like are combined, a connecting electrode 111 with the thickness larger than that of the first electrode layer 108 is prepared on the upper surface of the laser epitaxial wafer, and the vertical projection of the connecting electrode 111 on the plane of the substrate 101 is arranged to cover the vertical projection of the ridge structure on the plane of the substrate 101. The connection electrode 111 forms an electrode pair for injecting carriers between the first electrode layer 108 and the second electrode layer 112, thereby improving the injection efficiency of carriers; on the other hand, the electrode is used as a thickening electrode, so that the laser is convenient to prepare by electric connection.
S205, preparing a second electrode layer on one side of the substrate far away from the grating structure.
S206, scribing, cleaving, coating and splitting the epitaxial structure to form the semiconductor laser.
According to the preparation method of the semiconductor laser, the plurality of step structures are sequentially arranged on the surface of the substrate along the first direction, the grating structure comprises the step structures and the first sub-epitaxial structures positioned between the two adjacent step structures, the step structures are used for regulating and controlling the thickness of the first sub-epitaxial structures of the laser, the grating structure comprising the step structures on the surface of the substrate and the first sub-epitaxial structures is formed, the grating is arranged below the laser, the separation of the grating and the ridge shape on the upper surface of the laser is achieved, and therefore regulation and selection of a laser mode are achieved. The preparation method provided by the embodiment of the invention has the advantages of low grating loss, high grating coupling efficiency, small series resistance, low cost and the like, and can remarkably improve the performance, reliability and market competitiveness of the semiconductor laser.
As a possible embodiment, a specific example is exemplified, and a gallium nitride (GaN) -based semiconductor laser is prepared based on the preparation method provided in the above example, and referring to fig. 6 to 14, the specific preparation method is as follows:
Step 1, spin coating photoresist on the surface of an n-GaN substrate, and photoetching a periodical step structure by adopting a photoetching technology.
Step 2, transferring the periodic step structure onto the substrate by Inductively Coupled Plasma (ICP) etching, and then removing the photoresist, as shown in fig. 6 and 7.
And 3, cleaning the n-GaN substrate, and then placing the n-GaN substrate into a reaction chamber of a Metal Organic Chemical Vapor Deposition (MOCVD) device, epitaxially growing an n-AlGaN lower light field limiting layer, a GaN lower waveguide layer, 4 pairs of InGaN/GaN multiple quantum wells, a GaN upper waveguide layer, a p-AlGaN upper light field limiting layer and a p-GaN contact layer, as shown in figure 8.
And step 4, cleaning the epitaxial wafer, depositing a first electrode Ti/Au on the surface of the epitaxial wafer, and performing thermal annealing to form ohmic contact with the p-GaN of the upper contact layer.
And step 5, spin coating photoresist on the surface of the epitaxial wafer, photoetching a ridge pattern by adopting a photoetching technology, and then performing Inductively Coupled Plasma (ICP) etching to form an other ridge structure, as shown in fig. 9 and 10.
Step 6, depositing a dielectric layer SiN on the surface of the epitaxial wafer at low temperature, as shown in FIG. 11; the photoresist over the ridge is then used for lift-off, as shown in fig. 12.
And 7, spin-coating photoresist on the surface of the epitaxial wafer for photoetching, and then preparing a thickened electrode Cr/Au of the first electrode on the upper surface of the laser epitaxial wafer by combining a coating and stripping technology. As shown in fig. 13.
Step 8, thinning, grinding and polishing the epitaxial wafer, then preparing a second electrode Ni/AuGe/Ni/Au on the back surface of the epitaxial wafer, and performing thermal annealing to form better ohmic contact, as shown in fig. 14.
And 9, scribing, cleaving, coating and splitting to form the semiconductor laser tube core.
By adopting the preparation method of the semiconductor laser provided by the embodiment of the invention, the gallium nitride (GaN) base laser with the grating structure comprising the substrate surface step structure and the first sub-epitaxial structure is prepared, and the grating is arranged below the laser, so that the separation of the grating and the ridge shape on the upper surface of the laser is realized, and the preparation method has the advantages of low grating loss, high grating coupling efficiency, small series resistance, low cost and the like, and can remarkably improve the performance and reliability of the semiconductor laser.
Note that the above is only a preferred embodiment of the present invention and the technical principle applied. Those skilled in the art will appreciate that the invention is not limited to the specific embodiments described herein, and that features of the various embodiments of the invention may be partially or fully coupled or combined with each other and may be co-operated and technically driven in various ways. Various obvious changes, rearrangements, combinations and substitutions can be made by those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.

Claims (8)

1. A semiconductor laser, comprising:
the laser epitaxial structure comprises a substrate, and a grating structure and a ridge structure which are sequentially positioned on one side of the substrate;
the substrate comprises a plurality of step structures which are sequentially arranged along a first direction, wherein the first direction is parallel to a plane where the substrate is positioned and is intersected with a direction of the substrate pointing to the ridge structure;
the grating structure comprises the step structures and first sub-epitaxial structures arranged between two adjacent step structures, and refractive indexes of the step structures and the first sub-epitaxial structures are different;
the ridge structure at least comprises an upper light field limiting layer, an upper contact layer and a first electrode layer which are arranged in a laminated mode, wherein the first electrode layer is positioned on one side, away from the substrate, of the upper contact layer;
a second electrode layer positioned on one side of the substrate away from the grating structure;
the laser epitaxial structure further comprises at least one common epitaxial layer, and the common epitaxial layer is positioned on one side of the first sub-epitaxial structure far away from the substrate;
the common epitaxial layer and the step structure have a first effective refractive index, the common epitaxial layer and the first sub-epitaxial structure have a second effective refractive index, and the first effective refractive index is different from the second effective refractive index;
The first effective refractive index satisfies:
the second effective refractive index satisfies:
wherein ,i is more than or equal to 1 and less than or equal to k, j is more than or equal to 1 and less than or equal to m, and i, j, m, k is a positive integer;
P i n is the ratio of the light intensity of the ith layer of the common epitaxial layer in the lasing mode to the total light intensity of the lasing mode i Refractive index of the ith layer in the common epitaxial layer; p (P) a N is the ratio of the light intensity of the laser excitation mode in the step structure to the total light intensity of the laser excitation mode a Refractive index of the step structure; p (P) bj N is the ratio of the light intensity of the j-th layer of the first sub-epitaxy structure of the laser lasing mode to the total light intensity of the laser lasing mode bj And the refractive index of the j-th layer of the first sub-epitaxial structure.
2. The semiconductor laser of claim 1, wherein a plurality of said step structures are periodically arranged.
3. The semiconductor laser of claim 1, wherein the step structure includes a first surface adjacent a side of the ridge structure and a sidewall connected to the first surface;
the included angle between the first surface and the side wall is a right angle;
alternatively, the included angle between the first surface and the side wall is an obtuse angle.
4. The semiconductor laser of claim 1, wherein the first sub-epitaxial structure comprises at least a portion of a lower optical field confinement layer.
5. The semiconductor laser of claim 4, wherein the first sub-epitaxial structure comprises at least a portion of the lower optical field confinement layer; the common epitaxial layer at least comprises a lower waveguide layer, an active region, an upper waveguide layer, the upper light field limiting layer and the upper contact layer which are arranged in a laminated manner, wherein the upper contact layer is positioned on one side far away from the substrate;
alternatively, the first sub-epitaxial structure includes the lower optical field confinement layer and at least a portion of the lower waveguide layer arranged in a stack; the common epitaxial layer at least comprises an active region, an upper waveguide layer, an upper light field limiting layer and an upper contact layer which are arranged in a laminated mode, wherein the upper contact layer is positioned on one side far away from the substrate;
alternatively, the first sub-epitaxial structure includes the lower optical field confinement layer, the lower waveguide layer, and at least a portion of the active region in a stacked arrangement; the common epitaxial layer at least comprises an upper waveguide layer, an upper light field limiting layer and an upper contact layer which are arranged in a laminated mode, wherein the upper contact layer is positioned on one side far away from the substrate;
Alternatively, the first sub-epitaxial structure includes the lower optical field confinement layer, the lower waveguide layer, the active region, and at least a portion of the upper waveguide layer in a stacked arrangement; the common epitaxial layer at least comprises the upper light field limiting layer and the upper contact layer which are arranged in a lamination mode, and the upper contact layer is arranged on one side away from the substrate;
alternatively, the first sub-epitaxial structure includes the lower optical field confinement layer, the lower waveguide layer, the active region, the upper waveguide layer, and at least a portion of the upper optical field confinement layer in a stacked arrangement; the common epitaxial layer comprises at least the upper contact layer, which is located on a side away from the substrate.
6. The semiconductor laser of claim 4, wherein the first sub-epitaxial structure comprises the lower optical field confining layer, lower waveguide layer, active region, upper waveguide layer, upper optical field confining layer, and upper contact layer disposed in a stack, the upper contact layer being located on a side away from the substrate;
the ridge structure includes a portion of the upper light field confining layer, the upper contact layer, and the first electrode layer.
7. The semiconductor laser of claim 1, further comprising a connection electrode on a side of the first electrode layer remote from the substrate;
The thickness of the connecting electrode is larger than that of the first electrode layer, and the vertical projection of the connecting electrode on the plane of the substrate covers the vertical projection of the ridge structure on the plane of the substrate.
8. A method for manufacturing a semiconductor laser, for manufacturing the semiconductor laser according to any one of claims 1 to 7, comprising:
preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate, and a grating structure and a ridge structure which are sequentially positioned on one side of the substrate;
preparing a plurality of step structures which are sequentially arranged along a first direction on one side surface of the substrate, wherein the first direction is parallel to a plane where the substrate is positioned and intersects with a direction of the substrate pointing to the ridge structure;
preparing a grating structure on one side of the substrate, wherein the grating structure comprises the step structures and first sub-epitaxial structures arranged between two adjacent step structures, and refractive indexes of the step structures and the first sub-epitaxial structures are different;
preparing a ridge structure on one side of the grating structure far away from the substrate, and etching at least part of the upper light field limiting layer, the upper contact layer and the first electrode layer which are arranged in a lamination manner to form the ridge structure, wherein the first electrode layer is positioned on one side of the upper contact layer far away from the substrate;
Preparing a second electrode layer on one side of the substrate away from the grating structure;
and carrying out scribing, cleavage, film plating and splitting processes on the epitaxial structure to form the semiconductor laser.
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