WO2004105202A1 - Laser diode device - Google Patents
Laser diode device Download PDFInfo
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- WO2004105202A1 WO2004105202A1 PCT/JP2004/005821 JP2004005821W WO2004105202A1 WO 2004105202 A1 WO2004105202 A1 WO 2004105202A1 JP 2004005821 W JP2004005821 W JP 2004005821W WO 2004105202 A1 WO2004105202 A1 WO 2004105202A1
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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
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
- H01S5/323—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/32308—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm
- H01S5/32341—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm blue laser based on GaN or GaP
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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
- H01S5/20—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
- H01S5/223—Buried stripe structure
- H01S5/2231—Buried stripe structure with inner confining structure only between the active layer and the upper electrode
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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
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/02208—Mountings; Housings characterised by the shape of the housings
- H01S5/02212—Can-type, e.g. TO-CAN housings with emission along or parallel to symmetry axis
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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
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0225—Out-coupling of light
- H01S5/02253—Out-coupling of light using lenses
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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
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0233—Mounting configuration of laser chips
- H01S5/0234—Up-side down mountings, e.g. Flip-chip, epi-side down mountings or junction down mountings
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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
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
- H01S5/0651—Mode control
- H01S5/0653—Mode suppression, e.g. specific multimode
- H01S5/0654—Single longitudinal mode emission
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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
- H01S5/1082—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 with a special facet structure, e.g. structured, non planar, oblique
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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
- H01S5/20—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
- H01S5/2205—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 comprising special burying or current confinement layers
- H01S5/2218—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 comprising special burying or current confinement layers having special optical properties
Definitions
- the present invention relates to a group III nitride compound semiconductor laser diode device. More specifically, the present invention relates to improvement of a ridge waveguide type group III nitride compound semiconductor laser diode device.
- GaN laser diode devices made of group III nitride compound semiconductors are considered promising as capable of emitting short-wavelength laser light, and research and development for practical use are underway. It has been done energetically.
- the basic structure of a GaN-based laser diode element is a structure in which an n-type semiconductor layer and a p-type semiconductor layer are laminated on an sapphire substrate with an active layer sandwiched between them, and various types of optical waveguides have been proposed. I have.
- a typical optical waveguide structure is a ridge waveguide structure having a ridge for horizontal current confinement and light confinement (hereinafter, also referred to as a “ridge structure”). Many improvements have been made on this ridge structure.For example, a GaN-based buried layer that absorbs oscillation light is formed on both sides in the width direction of the ridge to increase the ridge width without reducing the ridge width. A structure that avoids the generation of the next mode and obtains oscillation in the fundamental mode (Japanese Patent Laid-Open No.
- JP-A-2002-374035 a waveguide of perfect refractive index and a waveguide of effective refractive index as the waveguide region on the stripe.
- the ridge waveguide structure has a relatively simple structure and is easy to fabricate.
- the light confinement ratios of the fundamental mode (0th mode) and the higher mode (1st mode) are close ( That is, since the gain difference between the modes is small), the mode is easily shifted, and the kink is easily generated.
- An object of the present invention is to provide a ridge waveguide type III-nitride-based compound semiconductor laser diode device capable of stabilizing the horizontal and lateral modes without increasing the threshold current density and operating voltage.
- a ridge waveguide type group III nitride compound semiconductor laser diode device comprising: a first region including a central portion and continuing in a longitudinal direction; and a first region sandwiching the first region from both sides and having an average layer thickness of A laser diode element having a ridge structure including a second region smaller than the average layer thickness of the first region is provided.
- a ridge structure in which a first region having a relatively large average layer thickness is sandwiched by a second region.
- the effective refractive index in the central portion directly involved in the fundamental mode oscillation becomes higher than that in the peripheral portion, and light is efficiently confined in the central portion. That is, the light confinement rate of the fundamental mode increases, and the light confinement rate of the higher-order mode decreases. Therefore, the stability of the horizontal and horizontal modes is increased, and the occurrence of kinks is suppressed.
- the threshold current density and the operating voltage do not increase. Also, the light confinement rate of the fundamental mode Increase leads to a decrease in fight current density and operating voltage.
- the average layer thickness of the first region and the second region means the average thickness of each region in the stacking direction of the P-type contact layers constituting the first region and the second region.
- the second region is defined as a region (consisting of a P-type contact layer) having an average thickness smaller than that of the p-type contact layer constituting the first region.
- FIG. 1 is a sectional view showing an example of a ridge structure employed in a laser diode device of the present invention.
- FIG. 2 is a sectional view showing another example of the ridge structure employed in the laser diode device of the present invention.
- FIG. 3 is a sectional view showing another example of the ridge structure employed in the laser diode device of the present invention.
- FIG. 4 is a sectional view showing a configuration of a laser diode element according to an embodiment of the present invention.
- FIG. 5 is a diagram showing a semiconductor laser device using the laser diode element 1 of the embodiment.
- FIG. 6A is a schematic view showing a ridge structure of an element used for a simulation.
- FIG. 6B is a table showing the thickness and refractive index of each layer in the element used for the simulation.
- FIG. 7A is a graph showing light output characteristics in the basic mode.
- FIG. 7B is a graph showing light output characteristics in a higher-order mode.
- the laser diode element of the present invention has a basic structure in which a plurality of semiconductor layers made of a group III nitride compound semiconductor are stacked on a substrate, and has a ridge structure.
- a laser diode element ridge waveguide type laser diode element having such a ridge structure, current confinement and light confinement in the horizontal direction are realized by the ridge structure.
- the semiconductor layers stacked on the substrate include an n-type contact layer, an n-type clad layer, an n-type guide layer, an active layer (single quantum well structure, multiple quantum well structure, etc.), a p-type guide layer, Includes a mold cladding layer and a P-type contact layer.
- the substrate is not particularly limited as long as a Group III nitride compound semiconductor layer can be grown thereon, and is preferably GaN, sapphire, spinel, silicon carbide, zinc oxide, gallium phosphide, gallium arsenide, oxide magnetic Shiumu, manganese oxide, YS Z (stabilized zirconate Nia yttria), can be used a substrate made of Z r B 2 (zirconium di Po fluoride) or the like.
- a sapphire substrate is preferable, and in that case, its c-plane is particularly preferably used. This is for growing a group III nitride compound semiconductor layer having good crystallinity.
- a buffer layer can be provided between the substrate and the crystal layer made of a group III nitride compound semiconductor.
- the puffer layer is provided for the purpose of improving the crystallinity of the group III nitride compound semiconductor grown thereon.
- the buffer layer can be formed of a group III nitride compound semiconductor such as AIN, InN, GaN, AlGaN, InGaN, and A1InGaN.
- the group III nitride-based compound semiconductor has the general formula A 1 X G a Y I n! - ⁇ . ⁇ 0 (0 ⁇ X ⁇ 1, 0 ⁇ Y ⁇ 1, 0 ⁇ X + Y ⁇ 1) So-called binary system of A 1 N, G a ⁇ and I ⁇ ⁇ , A l x G a ⁇ X N, A 1 x I n i- x N, G a x I n X _ X N (or more , Including the so-called ternary system of 0 ⁇ ⁇ 1).
- At least a part of the group III element may be replaced by boron (B), lithium (T 1), or the like, and at least a part of nitrogen (N) may be replaced by phosphorus (P), arsenic (A s), It can be replaced by antimony (Sb), bismuth (Bi), etc.
- the group III nitride-based compound semiconductor may contain any dopant. Silicon (S i), germanium (G e), selenium (S e), tellurium (T e), carbon (C), or the like can be used as the n-type impurity.
- the P-type impurities magnesium (Mg), zinc (Zn), beryllium (Be), calcium (Ca), strontium (Sr), and balium (Ba) can be used.
- the Group III nitride-based compound semiconductor can be exposed to electron beam irradiation, plasma irradiation, or heating by a furnace or the like, but is not essential.
- These semiconductor layers can be formed by a known film formation method.
- MOCVD metal organic chemical vapor deposition
- MBE molecular beam crystal growth
- HVPE halide vapor deposition
- sputtering and ion plating can be used. it can.
- the ridge structure is a stripe-shaped convex portion and is typically constituted by a part of a p-type contact layer and a part of a p-type cladding layer.
- Such a ridge structure can be formed by growing each semiconductor layer on a substrate and then removing a part of the P-type semiconductor layer by etching or the like.
- the width of the entire ridge structure can be, for example, 1 im to 10 m.
- the first region including the center portion and continuing in the longitudinal direction, and the first region is located so as to sandwich the first region, and the average layer thickness is larger than the average layer thickness of the first region.
- a ridge structure including a small second region is provided.
- the effective refractive index of the central portion (first region) is larger than that of the regions located on both sides (second region). This increases the light confinement rate in the fundamental mode, and consequently improves the stability in the horizontal and transverse modes.
- FIG. 1 shows an example of a ridge structure employed in the laser diode device of the present invention.
- FIG. 1 is a cross-sectional view of the ridge structure 40 perpendicular to the longitudinal direction.
- a specific example satisfying the above conditions may be a ridge structure 40 in which both sides (second regions) 42 of the central portion (first region) 41 are lower by one step toward the substrate than the central portion (first region) 41. .
- the first region 4 The ratio of the width 41 of 1: the second region (one side) 42 and the width 42 of 42 can be set to 1:10 to 10: 1.
- the ratio of the height 41b of the first region 41 to the height 42b of the second region 42 can be set to 2: 1 to 11: 1.
- the second region 42 is formed symmetrically on both sides of the first region 41. Such symmetry contributes to the improvement of the horizontal and transverse mode characteristics.
- the first region 41 and the second region 42 each have a uniform layer thickness (height) over the entire area, but the layer thickness (height) in each region is continuous or stepwise. May be changed.
- FIG. 2 (a) shows an example in which the layer thickness (height) in the first region changes continuously.
- the first region 41 is tapered on both sides with the center as a boundary. That is, the layer thickness of the first region 41 decreases continuously at a constant rate of change from the center to the periphery. The rate of change of the layer thickness need not be constant.
- FIG. 2 (b) shows an example in which the layer thickness (height) in the first region changes stepwise.
- the layer thickness of the first region 41 changes stepwise.
- the layer thickness of the first region 41 may be formed by using both a continuous change and a stepwise change.
- FIG. 3 (a) shows an example in which the layer thickness (height) changes stepwise in the second region.
- the second region 42 has a tapered shape so that its layer thickness is continuously reduced as the distance from the first region 41 is increased. That is, the layer thickness of the second region 42 continuously decreases at a constant rate of change in the direction away from the first region 41.
- the rate of change of the layer thickness may not be constant.
- FIG. 3 (b) shows an example in which the layer thickness (height) in the second region changes stepwise.
- the layer thickness of the second region 42 changes stepwise.
- the upper surface is stepped, so that the second layer thickness changes gradually.
- the region 42 ie, the second region 42 including two or more regions having different layer thicknesses can be formed.
- the layer thickness of the second region 42 may be formed by using both continuous change and stepwise change.
- the ridge structure is generally constituted by a part of a P-type cladding layer and a P-type contact layer.
- both the first region and the second region constituting the ridge structure include a p-type contact layer.
- a p-electrode can be formed on the first region and the second region. That is, it is possible to secure a sufficiently large electrode surface.
- a laser diode element having a low threshold current density and a low operating voltage is formed.
- the method of manufacturing the ridge structure including the first region 41 and the second region 42 is, for example, as follows.
- a striped protective film is formed on the surface of the p-type contact layer so as to cover the region where the ridge structure is to be formed. It is formed by lithography.
- Protective film is, for example, made of silicon oxide such as S i 0 2.
- the region where the protective film is not formed is etched partway through the P-type cladding layer.
- RIE reactive ion etching method
- the protective film covering the other portion (second region) is removed so that the protective film remains only in the portion (center portion) where the first region 41 is formed.
- etching is performed in the same manner as described above to etch a part of the P-type contact layer that is not covered with the protective film.
- FIG. 4 shows a semiconductor laser diode device (hereinafter, also referred to as “LD device”) 1 according to an embodiment of the present invention. Details of each layer of the LD element 1 are as follows.
- the first n-type layer 13 is an n-type contact layer
- the second n-type layer 14 is an n-type cladding layer
- the third n-type layer 15 is an n-type guide layer
- the MQW layer 16 is light emitting Layer, the first!
- the type layer 17 functions as a type guide layer
- the second p-type layer 18 functions as a p-type cladding layer
- the third p-type layer 19 functions as a p-type contact layer.
- the buffer layer 12 may be composed of GaN, InN, AlGaN, InGaN and A1InGaN.
- the n-type layers 13, 14, 15 may be composed of G aN, A1 G aN, In G aN or A 1 In G aN.
- the n-type layers 13, 14, and 15 are doped with Si as an n-type impurity.
- Ge, Se, Te, and C are also doped as n-type impurities. You may want to
- the MQW layer 16 may have a multiple quantum well structure such as A1GaN / A1GaInN, in addition to the multiple quantum well structure of InGaNZNZaN.
- the number of quantum well layers is preferably 1 to 30.
- the P-type layers 17, 18, 19 can be made of GaN, AlGaN, InGaN or InA1GaN.
- the p-type impurity may be Zn, .Be, Ca, Sr, Ba instead of Mg.
- the resistance of the p-type layer can be reduced by a known method such as electron beam irradiation, plasma irradiation, heating by a furnace or the like.
- the group III nitride compound semiconductor layer above the first n-type layer 13 is formed by MOCVD, molecular beam crystal growth (MBE), or halide vapor deposition. (HVPE method), a sputtering method, an ion plating method, or the like.
- a ridge structure 20 is formed.
- the ridge structure 20 is formed by photolithography and etching.
- a protective film (S i 0 2) on the entire surface of the third p-type layer 1 9.
- a part of the protective film is removed by photolithography to form a stripe-shaped protective film having a desired width (width of the ridge structure 20).
- portions exposed without being covered with the protective film are sequentially removed by reactive ion etching from the third p-type layer 19. This etching process is continued until part of the second p-type layer 18 is removed.
- the convex portion (ridge structure 20) formed by the above process is processed to form a first region 20a and a second region 20b.
- the protective film covering the other portions is removed so that the protective film remains only in the portion where the first region 20a is to be formed (that is, in the center of the ridge structure 20). I do.
- a stripe-shaped protective film covering the central portion of the ridge structure 20 is formed.
- reactive ion etching is performed again to etch a part of the third p-type layer 19 that is not covered with the protective film.
- the protective film is removed.
- both the first region 20a and the second region 20b include the third p-type layer 19.
- the n-electrode 22 and the p-electrode 23 are formed.
- the n-electrode 22 is made of a material including A 1, Ti and the like, and after forming the ridge structure 20, the third p-type layer to the second n-type layer, and the first n-type layer 1 Exposed by removing part of 3 by etching It is formed on the first n-type layer 13 by vapor deposition.
- the p-electrode 23 is made of a material including Ni, Pi; and Au, and is formed by vapor deposition.
- a light reflecting film (not shown) is formed on the end surface (rear end surface) on the light reflecting side of the obtained laminate by sputtering.
- FIG. 5 shows an example of a semiconductor laser device using the LD element 1 manufactured through the above steps.
- some elements such as a p-electrode and an n-electrode are omitted in FIG.
- the LD element 1 is installed on a stem 71 erected on a support 70 via a heat sink (conductive substrate) 72.
- the LD element 1 is mounted on the heat sink 72 with the electrode side down.
- An insulating material layer is formed on a part of the surface of the heat sink 72, and the insulating material layer prevents a short circuit between the n-electrode and the p-electrode.
- the cap 75 has a condenser lens 77, and the laser light generated by the LD element 1 is emitted to the outside via the condenser lens 77.
- FIG. 6A and 6B show conditions for simulating the optical output characteristics of the laser diode device manufactured by the above-described method.
- FIG. 6A schematically shows a ridge structure used for the simulation.
- the ridge width is 1.8 m in the area shown in Fig. 6A (a).
- the ridge width is 0.6 m in part (first region) and 0.6 m in part (second region) shown in FIG.
- 0.6 X 3 1.8 ⁇ .
- Fig. 6 (4) shows the equivalent refractive index nefi calculated in each part (1) to (3) of the ridge structure.
- the equivalent refractive index neff is calculated by a calculation formula: nefi r ⁇ r + r ⁇ ⁇ 2 + n 3 ⁇ 3 +- ⁇ + ⁇ ⁇ ⁇ ⁇ . ⁇ , ⁇ ⁇ ⁇ ]! Is the refractive index of each layer, and ⁇ is the proportion of light present in each layer, which can be determined by simulation.
- FIGS. 7A and 7B show the simulation results.
- Fig. 7A is a graph showing the light output characteristics of the fundamental mode
- Fig. 7B is the higher order mode
- 5 is a graph showing the light output characteristics of the optical device.
- the peak of the fundamental mode is higher in the structure of the present example, and the peak in the higher-order mode is lower than that of the conventional structure. That is, the structure of the present embodiment has a higher light confinement ratio in the fundamental mode and a lower light confinement ratio in the higher-order mode. Therefore, in the structure of this embodiment, the horizontal
- a ridge waveguide type III-nitride-based compound semiconductor laser diode device capable of stabilizing a horizontal / lateral mode without increasing a threshold current density and an operating voltage.
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Abstract
A group III nitride compound semiconductor laser diode device of ridge waveguide type is disclosed which has a ridge structure comprising a first region which includes the central portion of the structure and continuously extends in the longitudinal direction and a second region which extends on both sides of the first region and has an average layer thickness thinner than that of the first region.
Description
明細書 レーザダイォ一ド素子 本出願は、 日本特許出願番号 2003— 1451 37に基づいており、 この日本出願の全内容は、 本出願において参照され導入される。 技術分野 Description Laser diode device The present application is based on Japanese Patent Application No. 2003-145137, and the entire contents of this Japanese application are referred to and incorporated in the present application. Technical field
本発明は III族窒化物系化合物半導体レーザダイォード素子に関する。 詳しくは、 リッジ導波路型 III族窒化物系化合物半導体レーザダイォー ド素子の改良に関する。 背景技術 The present invention relates to a group III nitride compound semiconductor laser diode device. More specifically, the present invention relates to improvement of a ridge waveguide type group III nitride compound semiconductor laser diode device. Background art
III族窒化物系化合物半導体を材料としたレーザダイォード素子 (G a N系レーザダイオード素子) は、 短波長レーザ光の発振を可能とする ものとして有望視され、 実用化に向けた研究開発が精力的に行われてき た。 G aN系レーザダイオード素子の基本的な構造は、 サファイア基 板上に活性層を挟むようにして n型半導体層及び p型半導体層が積層 されたものであり、 様々な構成の光導波路が提案されている。 Laser diode devices (GaN laser diode devices) made of group III nitride compound semiconductors are considered promising as capable of emitting short-wavelength laser light, and research and development for practical use are underway. It has been done energetically. The basic structure of a GaN-based laser diode element is a structure in which an n-type semiconductor layer and a p-type semiconductor layer are laminated on an sapphire substrate with an active layer sandwiched between them, and various types of optical waveguides have been proposed. I have.
代表的な光導波路の構造として、 水平方向の電流狭窄と光閉じ込めのた めのリッジを備えるリッジ導波路構造 (以下、 「リッジ構造」 ともいう) がある。 このリッジ構造については多くの改良研究が行われており、 例 えば、 リッジの幅方向の両側に発振光を吸収する G a N系の埋込み層を '形成することでリッジ幅を狭めることなく高次モードの発生を回避し、 基本モードの発振を得る構造 (特開 2000— 3 1 59 9号公報) や、 ストライプ上の導波路領域として完全屈折型の導波路と実効屈折率型 の導波路を有することで素子信頼性及びビーム特性を向上させた構造 (特開 2002— 374035号公報) 等が提案されている。
リッジ導波路構造は、 構造が比較的単純であって作製が容易である反面、 水平横モードにおいて基本モード (0次モード) と高次モード ( 1次モ ード) の光閉じ込め率が近い (即ちモード間利得差が小さい) ためモー ド移行し易く、 キンク (kink) が発生し易い。 リッジ幅を狭めることに よって水平横モードの安定化を図ることも可能であるが、 このような構 造は P電極における高抵抗化を伴い、 動作電圧の上昇を引き起こす。 ま た水平方向の光閉じ込め係数が減少するので、 閾電流密度の上昇を引き 起こす。 発明の開示 A typical optical waveguide structure is a ridge waveguide structure having a ridge for horizontal current confinement and light confinement (hereinafter, also referred to as a “ridge structure”). Many improvements have been made on this ridge structure.For example, a GaN-based buried layer that absorbs oscillation light is formed on both sides in the width direction of the ridge to increase the ridge width without reducing the ridge width. A structure that avoids the generation of the next mode and obtains oscillation in the fundamental mode (Japanese Patent Laid-Open No. 2000-31599), a waveguide of perfect refractive index and a waveguide of effective refractive index as the waveguide region on the stripe There has been proposed a structure (JP-A-2002-374035) in which the device reliability and beam characteristics are improved by having the structure described above. The ridge waveguide structure has a relatively simple structure and is easy to fabricate. On the other hand, in the horizontal and transverse modes, the light confinement ratios of the fundamental mode (0th mode) and the higher mode (1st mode) are close ( That is, since the gain difference between the modes is small), the mode is easily shifted, and the kink is easily generated. Although it is possible to stabilize the horizontal and transverse modes by reducing the ridge width, such a structure involves an increase in the resistance of the P electrode and an increase in operating voltage. Also, the horizontal light confinement factor decreases, causing an increase in the threshold current density. Disclosure of the invention
本発明は、 閾電流密度及び動作電圧の上昇を伴うことなく水平横モー ドの安定化を図ることができるリッジ導波路型 I I I族窒化物系化合物半 導体レーザダイォ一ド素子を提供することを目的とする。 An object of the present invention is to provide a ridge waveguide type III-nitride-based compound semiconductor laser diode device capable of stabilizing the horizontal and lateral modes without increasing the threshold current density and operating voltage. And
本発明により、 According to the present invention,
リッジ導波路型の I I I族窒化物系化合物半導体レーザダイォード素子 であって 中央部を含み且つ長手方向に連続する第 1領域と、 該第 1領 域を両側から挟み且つその平均層厚が該第 1領域の平均層厚よりも小 さい第 2領域とを含むリッジ構造を備えるレ一ザダイォ一ド素子が提 供される。 A ridge waveguide type group III nitride compound semiconductor laser diode device, comprising: a first region including a central portion and continuing in a longitudinal direction; and a first region sandwiching the first region from both sides and having an average layer thickness of A laser diode element having a ridge structure including a second region smaller than the average layer thickness of the first region is provided.
この構成では、 相対的に大きな平均層厚を有する第 1領域が、 第 2領 域に挾まれたリッジ構造が備えられる。 これによつて、 リッジ構造にお いて基本モードの発振に直接関与する中央部の実効屈折率が周縁部の それよりも高くなり、 当該中央部への効率的な光の閉じ込めが行われる。 即ち、 基本モードの光閉じ込め率が増大し、 且つ高次モードの光閉じ込 め率は減少する。従って、水平横モ一ドの安定性が増加し、キンク(kink) の発生が抑制される。 In this configuration, a ridge structure is provided in which a first region having a relatively large average layer thickness is sandwiched by a second region. As a result, in the ridge structure, the effective refractive index in the central portion directly involved in the fundamental mode oscillation becomes higher than that in the peripheral portion, and light is efficiently confined in the central portion. That is, the light confinement rate of the fundamental mode increases, and the light confinement rate of the higher-order mode decreases. Therefore, the stability of the horizontal and horizontal modes is increased, and the occurrence of kinks is suppressed.
一方、 トータルのリッジ幅を十分に確保できることから、 閾電流密度及 び動作電圧の上昇を伴うことがない。 また、 基本モードの光閉じ込め率
が増大することによって闘電流密度及び動作電圧の低下がもたらされ る。 On the other hand, since the total ridge width can be sufficiently secured, the threshold current density and the operating voltage do not increase. Also, the light confinement rate of the fundamental mode Increase leads to a decrease in fight current density and operating voltage.
なお、 第 1領域および第 2領域の平均層厚は、 第 1領域および第 2領 域を構成する P型コンタクト層の積層方向における各領域の平均膜厚 を意味する。 第 2領域は、 第 1領域を構成する p型コンタクト層よりも 小さい平均膜厚を有する (P型コンタクト層から成る) 領域と定義され る。 図面の簡単な説明 The average layer thickness of the first region and the second region means the average thickness of each region in the stacking direction of the P-type contact layers constituting the first region and the second region. The second region is defined as a region (consisting of a P-type contact layer) having an average thickness smaller than that of the p-type contact layer constituting the first region. BRIEF DESCRIPTION OF THE FIGURES
第 1図は本発明のレーザダイォ一ド素子において採用されるリッジ構 造の一例を示した断面図である。 FIG. 1 is a sectional view showing an example of a ridge structure employed in a laser diode device of the present invention.
第 2図は本発明のレーザダイォード素子において採用されるリッジ 構造の他の例を示した断面図である。 FIG. 2 is a sectional view showing another example of the ridge structure employed in the laser diode device of the present invention.
第 3図は本発明のレーザダイォ一ド素子において採用されるリッジ 構造の他の例を示した断面図である。 FIG. 3 is a sectional view showing another example of the ridge structure employed in the laser diode device of the present invention.
第 4図は本発明の実施例であるレーザダイォード素子の構成を示す 断面図である。 FIG. 4 is a sectional view showing a configuration of a laser diode element according to an embodiment of the present invention.
第 5図は実施例のレーザダイォード素子 1を使用した半導体レーザ 装置を示す図である。 FIG. 5 is a diagram showing a semiconductor laser device using the laser diode element 1 of the embodiment.
第 6 A図はシミュレーションに使用される素子のリッジ構造を示す 模式図である。 FIG. 6A is a schematic view showing a ridge structure of an element used for a simulation.
第 6 B図はシミュレーションに使用される素子における各層の膜厚、 屈 折率を示す表である。 FIG. 6B is a table showing the thickness and refractive index of each layer in the element used for the simulation.
第 7 A図は基本モ一ドにおける光出力特性を示すグラフである。 FIG. 7A is a graph showing light output characteristics in the basic mode.
第 7 B図は高次モードにおける光出力特性を示すグラフである。 発明を実施するための最良の形態 FIG. 7B is a graph showing light output characteristics in a higher-order mode. BEST MODE FOR CARRYING OUT THE INVENTION
以下、 本発明の各要素について説明する
本発明のレーザダイォード素子は、 基板上に III族窒化物系化合物半導 体からなる複数の半導体層が積層された基本構造を有し、 かつリッジ構 造を備える。 このようなリッジ構造を備えるレーザダイオード素子 (リ ッジ導波路型レーザダイォ一ド素子) ではリッジ構造によって水平方向 の電流狭窄と光閉じ込めが実現される。 基板上に積層される各半導体層 には、 n型コンタクト層、 n型クラッド層、 n型ガイ ド層、 活性層 (単 一量子井戸構造、 多重量子井戸構造など) 、 p型ガイド層、 p型クラッ ド層、 及び P型コンタクト層が含まれる。 Hereinafter, each element of the present invention will be described. The laser diode element of the present invention has a basic structure in which a plurality of semiconductor layers made of a group III nitride compound semiconductor are stacked on a substrate, and has a ridge structure. In a laser diode element (ridge waveguide type laser diode element) having such a ridge structure, current confinement and light confinement in the horizontal direction are realized by the ridge structure. The semiconductor layers stacked on the substrate include an n-type contact layer, an n-type clad layer, an n-type guide layer, an active layer (single quantum well structure, multiple quantum well structure, etc.), a p-type guide layer, Includes a mold cladding layer and a P-type contact layer.
基板は、 その上に ΙΠ族窒化物系化合物半導体層を成長させることが できるものであれば特に限定されず、 G aN、 サファイア、 スピネル、 炭化シリコン、 酸化亜鉛、 リン化ガリウム、 ヒ化ガリウム、 酸化マグネ シゥム、 酸化マンガン、 YS Z (安定化ジルコニァイットリア) 、 Z r B2 (ジルコニウムジポライド) 等からなる基板を用いることができる。 半導体基板を用いない場合にはサファイア基板が好ましく、 その場合に は特にその c面を用いることが好ましい。 結晶性のよい III族窒化物系 化合物半導体層を成長させるためである。 The substrate is not particularly limited as long as a Group III nitride compound semiconductor layer can be grown thereon, and is preferably GaN, sapphire, spinel, silicon carbide, zinc oxide, gallium phosphide, gallium arsenide, oxide magnetic Shiumu, manganese oxide, YS Z (stabilized zirconate Nia yttria), can be used a substrate made of Z r B 2 (zirconium di Po fluoride) or the like. When a semiconductor substrate is not used, a sapphire substrate is preferable, and in that case, its c-plane is particularly preferably used. This is for growing a group III nitride compound semiconductor layer having good crystallinity.
基板と III族窒化物系化合物半導体からなる結晶層の間にはバッファ 層を設けることができる。 パッファ層はその上に成長される III族窒化 物系化合物半導体の結晶性を向上する目的で設けられる。 バッファ層は AIN、 I nN、 G aN、 A l G aN、 I n G aN、 A 1 I n G aN等 の III族窒化物系化合物半導体で形成することができる。 A buffer layer can be provided between the substrate and the crystal layer made of a group III nitride compound semiconductor. The puffer layer is provided for the purpose of improving the crystallinity of the group III nitride compound semiconductor grown thereon. The buffer layer can be formed of a group III nitride compound semiconductor such as AIN, InN, GaN, AlGaN, InGaN, and A1InGaN.
ここに、 III族窒化物系化合物半導体は、 一般式として A 1 XG aY I n !-χ.γΝ ( 0≤X≤ 1 , 0≤Y≤ 1、 0≤X + Y≤ 1 )で表され、 A 1 N、 G a Ν及び I η Νのいわゆる 2元系、 A l xG aい XN、 A 1 x I n i-xN, G a x I n X_XN (以上において 0<χ< 1) のいわゆる 3 元系を包含する。 III族元素の少なくとも一部をボロン (B) 、 夕リウ ム (T 1 ) 等で置換しても良く、 また、 窒素 (N) の少なくとも一部も リン (P) 、 ヒ素 (A s ) 、 アンチモン (S b) 、 ビスマス (B i ) 等 で置換できる。
III族窒化物系化合物半導体は任意のドーパントを含むものであっても 良い。 n型不純物として、 シリコン (S i ) 、 ゲルマニウム (G e ) 、 セレン (S e ) 、 テルル (T e ) 、 力一ボン (C) 等を用いることがで きる。 P型不純物として、 マグネシウム (M g) 、 亜鉛 (Z n) 、 ベリ リウム (B e ) 、 カルシウム (C a) 、 ストロンチウム (S r ) 、 バリ ゥム (B a) 等を用いることができる。 なお、 p型不純物をドープした 後に ΙΠ族窒化物系化合物半導体を電子線照射、 プラズマ照射若しくは 炉等による加熱にさらすことができるが必須ではない。 Here, the group III nitride-based compound semiconductor has the general formula A 1 X G a Y I n! -Χ.γ 0 (0≤X≤ 1, 0≤Y≤ 1, 0≤X + Y≤ 1) So-called binary system of A 1 N, G a Ν and I η 、, A l x G a いX N, A 1 x I n i- x N, G a x I n X _ X N (or more , Including the so-called ternary system of 0 <χ <1). At least a part of the group III element may be replaced by boron (B), lithium (T 1), or the like, and at least a part of nitrogen (N) may be replaced by phosphorus (P), arsenic (A s), It can be replaced by antimony (Sb), bismuth (Bi), etc. The group III nitride-based compound semiconductor may contain any dopant. Silicon (S i), germanium (G e), selenium (S e), tellurium (T e), carbon (C), or the like can be used as the n-type impurity. As the P-type impurities, magnesium (Mg), zinc (Zn), beryllium (Be), calcium (Ca), strontium (Sr), and balium (Ba) can be used. After doping with the p-type impurity, the Group III nitride-based compound semiconductor can be exposed to electron beam irradiation, plasma irradiation, or heating by a furnace or the like, but is not essential.
これら半導体層は周知の成膜方法で形成することができる。 例えば、 有機金属気相成長法 (MO CVD法) のほか、 分子線結晶成長法 (MB E法) 、 ハライド系気相成長法 (HVP E法) 、 スパッ夕法、 イオンプ レーティング法を用いることができる。 These semiconductor layers can be formed by a known film formation method. For example, in addition to metal organic chemical vapor deposition (MOCVD), molecular beam crystal growth (MBE), halide vapor deposition (HVPE), sputtering, and ion plating can be used. it can.
リッジ構造は、 ストライプ状の凸部であって典型的には p型コンタク ト層及び P型クラッド層の一部によって構成される。 このようなリッジ 構造は、 基板上に各半導体層を成長させた後に P型半導体層の一部をェ ツチング処理などで除去することによって形成することができる。 リッ ジ構造全体の幅は例えば 1 im〜 1 0 mとすることができる。 The ridge structure is a stripe-shaped convex portion and is typically constituted by a part of a p-type contact layer and a part of a p-type cladding layer. Such a ridge structure can be formed by growing each semiconductor layer on a substrate and then removing a part of the P-type semiconductor layer by etching or the like. The width of the entire ridge structure can be, for example, 1 im to 10 m.
本発明のレーザダイォ一ド素子では、 中央部を含み且つ長手方向に連 続する第 1領域と、 この第 1領域を挟むように位置し且つその平均層厚 が第 1領域の平均層厚よりも小さい第 2領域とを含むリッジ構造が備 えられる。 このような構成では中央部 (第 1領域) の実効屈折率がその 両側に位置する領域 (第 2領域) のそれよりも大きくなる。 これによつ て基本モードの光閉じ込め率が高まり、 その結果水平横モードの安定性 が向上する。 In the laser diode device of the present invention, the first region including the center portion and continuing in the longitudinal direction, and the first region is located so as to sandwich the first region, and the average layer thickness is larger than the average layer thickness of the first region. A ridge structure including a small second region is provided. In such a configuration, the effective refractive index of the central portion (first region) is larger than that of the regions located on both sides (second region). This increases the light confinement rate in the fundamental mode, and consequently improves the stability in the horizontal and transverse modes.
第 1図は本発明のレーザダイォード素子において採用されるリッジ 構造の一例を示す。 第 1図はリッジ構造 4 0の長手方向に垂直な断面 図である。上記条件を満たす具体例は、第 1図に示すように、 中央部(第 1領域) 4 1よりもその両側 (第 2領域) 4 2が基板側に一段下がった リッジ構造 4 0であり得る。 このリッジ構造 4 0において、 第 1領域 4
1の幅 4 1 a :第 2領域 (片側) 4 2の幅 4 2 aの比率は、 1 : 1 0〜 1 0 : 1に設定することができる。 一方、 第 1領域 4 1の高さ 4 1 b : 第 2領域 4 2の高さ 4 2 bの比率は、 2 : 1〜 1 1 : 1に設定すること ができる。 FIG. 1 shows an example of a ridge structure employed in the laser diode device of the present invention. FIG. 1 is a cross-sectional view of the ridge structure 40 perpendicular to the longitudinal direction. As shown in FIG. 1, a specific example satisfying the above conditions may be a ridge structure 40 in which both sides (second regions) 42 of the central portion (first region) 41 are lower by one step toward the substrate than the central portion (first region) 41. . In this ridge structure 40, the first region 4 The ratio of the width 41 of 1: the second region (one side) 42 and the width 42 of 42 can be set to 1:10 to 10: 1. On the other hand, the ratio of the height 41b of the first region 41 to the height 42b of the second region 42 can be set to 2: 1 to 11: 1.
第 1図の例では、 第 1領域 4 1の両側に左右対称.となるように第 2領 域 4 2が形成されている。 このような対称性は水平横モード特性の向上 に貢献する。 第 1図の例では第 1領域 4 1及び第 2領域 4 2がそれぞれ 全体に亘つて均一な層厚 (高さ) を有するが、 各領域における層厚 (高 さ) は連続的または段階的に変化してもよい。 In the example of FIG. 1, the second region 42 is formed symmetrically on both sides of the first region 41. Such symmetry contributes to the improvement of the horizontal and transverse mode characteristics. In the example of FIG. 1, the first region 41 and the second region 42 each have a uniform layer thickness (height) over the entire area, but the layer thickness (height) in each region is continuous or stepwise. May be changed.
第 2図 (a ) は、 第 1領域における層厚 (高さ) が連続的に変化する 例を示す。 この例では、 第 1領域 4 1がその中心を境として両側にテー パ状となっている。 即ち、 中心から周縁に向かって一定の変化率で連続 的に第 1領域 4 1の層厚が小さくなる。 層厚の変化率は一定でなくても よい。 FIG. 2 (a) shows an example in which the layer thickness (height) in the first region changes continuously. In this example, the first region 41 is tapered on both sides with the center as a boundary. That is, the layer thickness of the first region 41 decreases continuously at a constant rate of change from the center to the periphery. The rate of change of the layer thickness need not be constant.
第 2図 (b ) は、 第 1領域における層厚 (高さ) が段階的に変化する 例を示す。 この例では、 第 1領域 4 1の層厚が段階的に変化する。 図示 されるように上面を階段状とすることで、 段階的に層厚が変化する第 1 領域 4 1 (即ち、層厚の互いに異なる二以上の領域を含む第 1領域 4 1 ) を構成できる。 FIG. 2 (b) shows an example in which the layer thickness (height) in the first region changes stepwise. In this example, the layer thickness of the first region 41 changes stepwise. By forming the upper surface in a stepped shape as shown in the figure, the first region 4 1 in which the layer thickness changes stepwise (that is, the first region 41 including two or more regions having different layer thicknesses) can be configured. .
また、 第 1領域 4 1の層厚は連続的な変化及び段階的な変化を併用し て形成してもよい。 Further, the layer thickness of the first region 41 may be formed by using both a continuous change and a stepwise change.
第 3図 (a ) は、 第 2領域において層厚 (高さ) が段階的に変化する 例を示す。 この例では、 第 2領域 4 2が、 第 1領域 4 1から遠ざかるに つれて連続的にその層厚が小さくなるようにテーパ状となっている。 即 ち、 第 1領域 4 1から遠ざかる方向に一定の変化率で連続的に第 2領域 4 2の層厚が小さくなる。 層厚の変化率は一定でなくてもよい。 FIG. 3 (a) shows an example in which the layer thickness (height) changes stepwise in the second region. In this example, the second region 42 has a tapered shape so that its layer thickness is continuously reduced as the distance from the first region 41 is increased. That is, the layer thickness of the second region 42 continuously decreases at a constant rate of change in the direction away from the first region 41. The rate of change of the layer thickness may not be constant.
第 3図 (b ) は、 第 2領域における層厚 (高さ) が段階的に変化する 例を示す。 この例では、 第 2領域 4 2の層厚が段階的に変化する。 図示 されるように上面を階段状とすることで、 段階的に層厚が変化する第 2
領域 4 2 (即ち、層厚の互いに異なる二以上の領域を含む第 2領域 4 2 ) を構成できる。 FIG. 3 (b) shows an example in which the layer thickness (height) in the second region changes stepwise. In this example, the layer thickness of the second region 42 changes stepwise. As shown in the figure, the upper surface is stepped, so that the second layer thickness changes gradually. The region 42 (ie, the second region 42 including two or more regions having different layer thicknesses) can be formed.
また、 第 2領域 4 2の層厚は連続的な変化及び段階的な変化を併用し て形成してもよい。 Further, the layer thickness of the second region 42 may be formed by using both continuous change and stepwise change.
リッジ構造は一般に、 P型クラッド層の一部及び P型コンタクト層に よって構成される。 本発明では、 リッジ構造を構成する第 1領域及び第 2領域のいずれもが p型コン夕クト層を含むことが好ましい。 かかる構 造では第 1領域上及び第 2領域上に p電極を形成することができる。 即 ち、 十分に広い面積の電極面を確保することが可能となる。 これによつ て低閾電流密度及び低動作電圧のレーザダイォ一ド素子が構成される。 上記の第 1領域 4 1及び第 2領域 4 2を含むリッジ構造の製造方法 は例えば次の通りである。 The ridge structure is generally constituted by a part of a P-type cladding layer and a P-type contact layer. In the present invention, it is preferable that both the first region and the second region constituting the ridge structure include a p-type contact layer. In such a structure, a p-electrode can be formed on the first region and the second region. That is, it is possible to secure a sufficiently large electrode surface. As a result, a laser diode element having a low threshold current density and a low operating voltage is formed. The method of manufacturing the ridge structure including the first region 41 and the second region 42 is, for example, as follows.
まず、 基板上に各半導体層 (n型コンタクト層〜 p型コンタクト層) を成長させた後、 p型コンタクト層表面のリッジ構造を形成する領域を 被覆するように、 ストライプ状の保護膜をフォトリソグラフィで形成す る。 保護膜は、 例えば、 S i 0 2などのシリコン酸化物からなる。 次に、 保護膜が形成されない領域を P型クラッド層の途中までエッチングす る。 エッチング方法としては反応性イオンエッチング法 (R I E ) を好 適に利用できる。 次に、 第 1領域 4 1を形成する部分 (中央部) のみに 保護膜が残存するように、 その他の部分 (第 2領域) を被覆している保 護膜を除去する。 その後、 上記と同様の方法でエッチング処理し、 保護 膜で被覆されていない P型コンタクト層の一部をエッチングする。 以上 の工程によって、 周縁部 (第 2領域) が中央部 (第 1領域) よりも基板 側へと一段下がったリッジ構造が形成される。 First, after growing each semiconductor layer (n-type contact layer to p-type contact layer) on the substrate, a striped protective film is formed on the surface of the p-type contact layer so as to cover the region where the ridge structure is to be formed. It is formed by lithography. Protective film is, for example, made of silicon oxide such as S i 0 2. Next, the region where the protective film is not formed is etched partway through the P-type cladding layer. As an etching method, a reactive ion etching method (RIE) can be suitably used. Next, the protective film covering the other portion (second region) is removed so that the protective film remains only in the portion (center portion) where the first region 41 is formed. Thereafter, etching is performed in the same manner as described above to etch a part of the P-type contact layer that is not covered with the protective film. Through the above steps, a ridge structure in which the peripheral portion (second region) is one step lower than the central portion (first region) toward the substrate is formed.
[実施例] [Example]
第 4図は、本発明の実施例である半導体レーザダイォ一ド素子(以下、 「LD素子」 ともいう) 1を示す。 LD素子 1の各層の詳細は次の通りで ある。 FIG. 4 shows a semiconductor laser diode device (hereinafter, also referred to as “LD device”) 1 according to an embodiment of the present invention. Details of each layer of the LD element 1 are as follows.
層 : 組成
第 3の p型層 1 G a N : M g Layer: Composition Third p-type layer 1 G a N: Mg
第 2の p型層 1 A 1 G a N : M g Second p-type layer 1 A 1 G a N: Mg
第 1の p型層 1 G a N : M g First p- type layer 1 G a N: Mg
MQW層 1 6 I n G a N/G a N MQW layer 1 6 I n G a N / G a N
第 3の n型層 1 G a N : S Third n-type layer 1 G a N: S
第 2の n型層 1 A I G a N : S i 2nd n-type layer 1 A I G a N: S i
第 1の n型層 1 G a N : S i 1st n-type layer 1 G a N: S i
バッファ層 1 2 A 1 N Buffer layer 1 2 A 1 N
基板 1 1 サファイア Substrate 1 1 Sapphire
第 1の n型層 1 3は n型コンタクト層、 第 2の n型層 1 4は n型クラ ッド層、 第 3の n型層 1 5は n型ガイド層、 MQW層 1 6は発光層、 第 1の!)型層 17は 型ガィド層、 第 2の p型層 1 8は p型クラッド層、 第 3の p型層 1 9は p型コンタクト層としてそれぞれ機能する。 The first n-type layer 13 is an n-type contact layer, the second n-type layer 14 is an n-type cladding layer, the third n-type layer 15 is an n-type guide layer, and the MQW layer 16 is light emitting Layer, the first! The type layer 17 functions as a type guide layer, the second p-type layer 18 functions as a p-type cladding layer, and the third p-type layer 19 functions as a p-type contact layer.
ノ ッファ層 1 2は、 G aN、 I nN、 A l G aN、 I n G aN及び A 1 I n G a N等からなり得る。 The buffer layer 12 may be composed of GaN, InN, AlGaN, InGaN and A1InGaN.
ここで n型層 1 3、 14、 1 5は、 G aN、 A l G aN、 I n G aN 若しくは A 1 I n G a Nからなり得る。 Here, the n-type layers 13, 14, 15 may be composed of G aN, A1 G aN, In G aN or A 1 In G aN.
また, n型層 1 3、 14、 1 5は、 n型不純物として S iをド一プし たが、 このほかに n型不純物として、 G e、 S e、 T e、 C等をド一プ してもよい。 The n-type layers 13, 14, and 15 are doped with Si as an n-type impurity. In addition, Ge, Se, Te, and C are also doped as n-type impurities. You may want to
MQW層 1 6は、 I n G a NZG a Nの多重量子井戸構造の他、 A 1 G a N/A 1 G a I n N等の多重量子井戸構造を有してもよい。 量子井 戸層の数は 1〜30とすることが好ましい。 The MQW layer 16 may have a multiple quantum well structure such as A1GaN / A1GaInN, in addition to the multiple quantum well structure of InGaNZNZaN. The number of quantum well layers is preferably 1 to 30.
P型層 1 7、 1 8、 1 9は、 G aN、 A l G aN、 I n G aN又は I n A 1 G aNからなり得る。 また、 p型不純物は、 Mgの代わりに、 Z n、. B e、 C a、 S r、 B aであり得る。 p型層は、 p型不純物の導入 後に、 電子線照射、 プラズマ照射、 炉等による加熱等の周知の方法によ り低抵抗化することができる。
上記構成の LD素子 1において、 第 1の n型層 1 3より上の I I I族窒 化物系化合物半導体層は、 M O C V D法の他、 分子線結晶成長法 (M B E法) 、 ハライド系気相成長法 (H V P E法) 、 スパッタ法、 イオンプ レーティング法等の方法で形成することができる。 The P-type layers 17, 18, 19 can be made of GaN, AlGaN, InGaN or InA1GaN. Also, the p-type impurity may be Zn, .Be, Ca, Sr, Ba instead of Mg. After the introduction of the p-type impurity, the resistance of the p-type layer can be reduced by a known method such as electron beam irradiation, plasma irradiation, heating by a furnace or the like. In the LD device 1 having the above configuration, the group III nitride compound semiconductor layer above the first n-type layer 13 is formed by MOCVD, molecular beam crystal growth (MBE), or halide vapor deposition. (HVPE method), a sputtering method, an ion plating method, or the like.
各半導体層を積層した後、 リッジ構造 2 0を形成する。 リッジ構造 2 0はフォトリソグラフィ及びエッチングによって形成される。 まず、 第 3の p型層 1 9の全面に保護膜 (S i 0 2 ) を形成する。 次にフォトリ ソグラフィによって一部の保護膜を除去し、 所望の幅 (リッジ構造 2 0 の幅) を有するストライプ状の保護膜とする。 続いて、 残存する保護膜 をマスクとして、 保護膜に被覆されずに露出した部分を第 3の p型層 1 9から順に反応性イオンエッチングで除去する。 このエッチング処理は 第 2の p型層 1 8の一部が除去されるまで継続される。 After stacking the semiconductor layers, a ridge structure 20 is formed. The ridge structure 20 is formed by photolithography and etching. First, a protective film (S i 0 2) on the entire surface of the third p-type layer 1 9. Next, a part of the protective film is removed by photolithography to form a stripe-shaped protective film having a desired width (width of the ridge structure 20). Subsequently, using the remaining protective film as a mask, portions exposed without being covered with the protective film are sequentially removed by reactive ion etching from the third p-type layer 19. This etching process is continued until part of the second p-type layer 18 is removed.
次に、 上記工程によって形成された凸状部 (リッジ構造 2 0 ) に加工 を施し第 1領域 2 0 a及び第 2領域 2 0 bを形成する。 まずフォトリソ グラフィを利用して、 第 1領域 2 0 aを形成する部分 (即ちリッジ構造 2 0の中央部) のみに保護膜が残存するように、 その他の部分を被覆し ている保護膜を除去する。 これによつて、 リッジ構造 2 0の中央部を被 覆するストライプ状の保護膜が形成される。 続いて再度反応性イオンェ ツチングを実施し、 保護膜が被覆されていない第 3の p型層 1 9の一部 をエッチングする。 最後に保護膜を除去する。 以上の工程によって、 第 1図に示されるように、 中央部 (第 1領域 2 0 a ) よりも周縁部 (第 2 領域 2 0 b ) が基板 1 1側へと一段下がったリッジ構造 2 0が形成され る。 尚、 本実施例では第 1領域 2 0 a及び第 2領域 2 0 bのいずれもが 第 3の p型層 1 9を含む。 Next, the convex portion (ridge structure 20) formed by the above process is processed to form a first region 20a and a second region 20b. First, using photolithography, the protective film covering the other portions is removed so that the protective film remains only in the portion where the first region 20a is to be formed (that is, in the center of the ridge structure 20). I do. As a result, a stripe-shaped protective film covering the central portion of the ridge structure 20 is formed. Subsequently, reactive ion etching is performed again to etch a part of the third p-type layer 19 that is not covered with the protective film. Finally, the protective film is removed. By the above steps, as shown in FIG. 1, the ridge structure 20 in which the peripheral portion (the second region 20 b) is lower by one step toward the substrate 11 than the central portion (the first region 20 a). Is formed. In this embodiment, both the first region 20a and the second region 20b include the third p-type layer 19.
以上の手順でリッジ構造 2 0を形成した後、 n電極 2 2及び p電極 2 3を形成する。 n電極 2 2は、 A 1や T i等を含む材料からなり、 リツ ジ構造 2 0を形成した後に、 第 3の p型層〜第 2の n型層、 及び第 1の n型層 1 3の一部をエッチングにより除去することによって表出する
第 1の n型層 1 3上に蒸着で形成される。 p電極 2 3は N iや P i;、 A u等を含む材料で構成されており、 蒸着により形成される。 After forming the ridge structure 20 by the above procedure, the n-electrode 22 and the p-electrode 23 are formed. The n-electrode 22 is made of a material including A 1, Ti and the like, and after forming the ridge structure 20, the third p-type layer to the second n-type layer, and the first n-type layer 1 Exposed by removing part of 3 by etching It is formed on the first n-type layer 13 by vapor deposition. The p-electrode 23 is made of a material including Ni, Pi; and Au, and is formed by vapor deposition.
続いて、 エッチング等の常法でチップ化した後、 得られた積層体におい て光反射側となる端面 (後端面) に光反射膜 (図示せず) をスパッ夕で 形成する。 Subsequently, after chipping is performed by a conventional method such as etching, a light reflecting film (not shown) is formed on the end surface (rear end surface) on the light reflecting side of the obtained laminate by sputtering.
第 5図は、 上記各工程を経て作製された LD素子 1を使用した半導体 レーザ装置の例を示す。 説明の便宜上、 第 5図では、 p電極や n電極な ど、 一部の要素を省略する。 FIG. 5 shows an example of a semiconductor laser device using the LD element 1 manufactured through the above steps. For convenience of explanation, some elements such as a p-electrode and an n-electrode are omitted in FIG.
LD素子 1は、 支持体 7 0に立設されたステム 7 1上にヒートシンク (導電性基板) 7 2を介して設置される。 LD素子 1は電極側を下にし てヒートシンク 7 2にマウン卜されている。 ヒートシンク 7 2の表面の 一部には絶縁性材料層が形成されており、 この絶縁材料層によって n電 極と P電極間の短絡が防止される。 The LD element 1 is installed on a stem 71 erected on a support 70 via a heat sink (conductive substrate) 72. The LD element 1 is mounted on the heat sink 72 with the electrode side down. An insulating material layer is formed on a part of the surface of the heat sink 72, and the insulating material layer prevents a short circuit between the n-electrode and the p-electrode.
キヤップ 7 5は集光レンズ 7 7を備えており、 LD素子 1で生成された レーザ光は当該集光レンズ 7 7を介して外部に放出される。 The cap 75 has a condenser lens 77, and the laser light generated by the LD element 1 is emitted to the outside via the condenser lens 77.
第 6 A図および第 6 B図は、 上述の方法によって作製されるレーザダ ィォード素子の光出力特性をシミュレ一卜するための条件を示す。 第 6 A図はシミュレーションに用いられるリッジ構造を模式的に示す。 従来 のリッジ構造において、 リッジ幅は、 第 6 A図 (a) に示される①部で 1. 8 mである。 本実施例のリッジ構造において、 リッジ幅は、 第 6 A図 (b) に示される①部 (第 1領域) で 0. 6 m、 ②部 (第 2領域) で 0. 6 m (片側) とし、 ト一タルで、 0. 6 X 3 = 1. 8 ΠΙであ る。 第 6 Β図は、 リッジ構造の各部①〜③において算出される等価屈折 率 nefiを示す。 等価屈折率 neff は、 計算式: nefi r^ r + r^ Γ 2 + n 3 Γ 3 + - · · +ηηΓη によって算出される。 伹し、 η丄〜]!。 は各層の屈折率であり、 Γは各層に存在する光の割合であってシミュレ —ションによって求められる。 6A and 6B show conditions for simulating the optical output characteristics of the laser diode device manufactured by the above-described method. FIG. 6A schematically shows a ridge structure used for the simulation. In the conventional ridge structure, the ridge width is 1.8 m in the area shown in Fig. 6A (a). In the ridge structure of the present embodiment, the ridge width is 0.6 m in part (first region) and 0.6 m in part (second region) shown in FIG. In total, 0.6 X 3 = 1.8 ΠΙ. Fig. 6 (4) shows the equivalent refractive index nefi calculated in each part (1) to (3) of the ridge structure. The equivalent refractive index neff is calculated by a calculation formula: nefi r ^ r + r ^ Γ 2 + n 3 Γ 3 +-· + η η Γ η .伹, η 丄 ~]! Is the refractive index of each layer, and Γ is the proportion of light present in each layer, which can be determined by simulation.
第 7 A図および第 7 B図は、 シミュレーション結果を示す。 第 7 A図 は基本モードの光出力特性を示すグラフであり、 第 7 B図は高次モード
の光出力特性を示すグラフである。 これらのグラフから明らかなように、 従来の構造に比較して本実施例の構造では基本モードにおけるピーク が高く、 これとは逆に高次モードにおけるピークが低い。 即ち、 本実施 例の構造の方が基本モードにおける光閉じ込め率が高く、 且つ高次モー ドにおける光閉じ込め率が低い。 従って、 本実施例の構造では水平横モFIGS. 7A and 7B show the simulation results. Fig. 7A is a graph showing the light output characteristics of the fundamental mode, and Fig. 7B is the higher order mode. 5 is a graph showing the light output characteristics of the optical device. As is clear from these graphs, the peak of the fundamental mode is higher in the structure of the present example, and the peak in the higher-order mode is lower than that of the conventional structure. That is, the structure of the present embodiment has a higher light confinement ratio in the fundamental mode and a lower light confinement ratio in the higher-order mode. Therefore, in the structure of this embodiment, the horizontal
—ドがより一層安定化し、 キンクレベル (kink l evel) が向上するとい える。 また、 本実施例の構造では基本モードにおいて光閉じ込め率が増 大し、 閾電流密度が減少する。 本発明は完全で明確な開示のための特定の実施例に関して記載され ているが、 添付の請求の範囲は、 当該記載に限定されるべきではなく、 本明細書に記載される基本的な教示に正当に含まれ、 当業者が想到し得 る全ての変更態様および代替構成を含むものとして解釈されるべきで ある。 産業上の利用の可能性 -It is said that the stabilization is further stabilized and the kink level (kink level) is improved. In the structure of this embodiment, the light confinement ratio increases in the fundamental mode, and the threshold current density decreases. Although the invention has been described with respect to particular embodiments for a complete and clear disclosure, the appended claims should not be limited to the description but include the basic teachings described herein. And should be construed as including all modifications and alternatives that are within the reach of those skilled in the art. Industrial potential
本発明によれば、 閾電流密度及び動作電圧の上昇を伴うことなく水平 横モードの安定化を図ることができるリッジ導波路型 I I I族窒化物系化 合物半導体レーザダイォード素子が提供される。
According to the present invention, there is provided a ridge waveguide type III-nitride-based compound semiconductor laser diode device capable of stabilizing a horizontal / lateral mode without increasing a threshold current density and an operating voltage. .
Claims
1 . リッジ導波路型の I I I族窒化物系化合物半導体レ一ザダイォ一ド素 子であって、 1. A ridge waveguide type II I-nitride-based compound semiconductor laser diode,
中央部を含み且つ長手方向に連続する第 1領域と、 該第 1領域を両側 から挟み且つその平均層厚が該第 1領域の平均層厚よりも小さい第 2 領域とを含むリッジ構造を備える、 レーザダイオード素子。 A ridge structure including a first region including a central portion and continuing in the longitudinal direction, and a second region sandwiching the first region from both sides and having an average layer thickness smaller than the average layer thickness of the first region. , Laser diode element.
2 . 前記第 2領域が、 前記長手方向に垂直な断面において左右対称の形 状を有する、 請求項 1に記載のレ一ザダイオード素子。 2. The laser diode element according to claim 1, wherein the second region has a symmetrical shape in a cross section perpendicular to the longitudinal direction.
3 . 前記第 1領域の層厚が全体に亘つて均一である、 請求項 1又は 2に 記載のレーザダイォード素子。 3. The laser diode device according to claim 1, wherein a layer thickness of the first region is uniform throughout.
4 . 中心から周縁に向かって連続的又は段階的に層厚が小さくなるよう に、 前記第 1領域の上面が階段状又はテーパ状に形成されている、 請求 項 1又は 2に記載のレーザダイォ一ド素子。 4. The laser diode according to claim 1, wherein the upper surface of the first region is formed in a stepped or tapered shape so that the layer thickness decreases continuously or stepwise from the center to the periphery. Element.
5 . 前記第 2領域の層厚が全体に亘つて均一である、 請求項 1〜4のい ずれかに記載のレーザダイオード素子。 5. The laser diode device according to any one of claims 1 to 4, wherein a layer thickness of the second region is uniform throughout.
6 . 前記第 2領域が、 平均層厚が互いに異なる二以上の領域を含む、 請 求項 1〜4のいずれかに記載のレ一ザダイォード素子。 6. The laser diode device according to claim 1, wherein the second region includes two or more regions having different average layer thicknesses.
7 . 前記第 1領域から遠ざかるにつれて連続的又は段階的に層厚が小さ くなるように、 前記第 2領域の上面が階段状又はテーパ状に形成されて いる、 請求項 1〜 4のいずれかに記載のレーザダイォード素子。
7. The upper surface of the second region is formed in a stepped or tapered shape so that the layer thickness decreases continuously or stepwise as the distance from the first region increases. 14. A laser diode element according to item 1.
8 . 前記第 1領域及び前記第 2領域がそれぞれ p型コンタクト層を含み、 両領域上に p電極が形成される、 請求項 1〜 7のいずれかに記載のレー ザダイォード素子。
8. The laser diode device according to claim 1, wherein the first region and the second region each include a p-type contact layer, and p electrodes are formed on both regions.
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JP2002237661A (en) * | 2000-12-07 | 2002-08-23 | Nichia Chem Ind Ltd | Nitride semiconductor laser device |
JP2002246692A (en) * | 2001-02-20 | 2002-08-30 | Toshiba Corp | Semiconductor laser and method of manufacturing the same |
JP2002299763A (en) * | 2001-04-03 | 2002-10-11 | Sony Corp | Semiconductor laser element and method of manufacturing the same |
-
2003
- 2003-05-22 JP JP2003145137A patent/JP2004349485A/en not_active Withdrawn
-
2004
- 2004-04-22 WO PCT/JP2004/005821 patent/WO2004105202A1/en active Application Filing
- 2004-05-04 TW TW093112514A patent/TWI237431B/en not_active IP Right Cessation
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
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JPH10233556A (en) * | 1997-02-20 | 1998-09-02 | Mitsubishi Electric Corp | Ridge-type semiconductor laser diode and its manufacturing method |
JP2000286504A (en) * | 1999-01-26 | 2000-10-13 | Sanyo Electric Co Ltd | Nitride semiconductor laser element |
JP2001274514A (en) * | 2000-03-24 | 2001-10-05 | Sony Corp | Semiconductor laser light emitting device |
JP2002237661A (en) * | 2000-12-07 | 2002-08-23 | Nichia Chem Ind Ltd | Nitride semiconductor laser device |
JP2002246692A (en) * | 2001-02-20 | 2002-08-30 | Toshiba Corp | Semiconductor laser and method of manufacturing the same |
JP2002299763A (en) * | 2001-04-03 | 2002-10-11 | Sony Corp | Semiconductor laser element and method of manufacturing the same |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US11967802B2 (en) * | 2017-09-14 | 2024-04-23 | Mitsubishi Electric Corporation | Semiconductor laser device |
US11398713B2 (en) * | 2017-12-04 | 2022-07-26 | Mitsubishi Electric Corporation | Electro-absorption modulator, optical semiconductor device and optical module |
Also Published As
Publication number | Publication date |
---|---|
TW200427165A (en) | 2004-12-01 |
TWI237431B (en) | 2005-08-01 |
JP2004349485A (en) | 2004-12-09 |
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