WO2022163176A1 - 窒化物半導体発光素子 - Google Patents
窒化物半導体発光素子 Download PDFInfo
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- WO2022163176A1 WO2022163176A1 PCT/JP2021/045852 JP2021045852W WO2022163176A1 WO 2022163176 A1 WO2022163176 A1 WO 2022163176A1 JP 2021045852 W JP2021045852 W JP 2021045852W WO 2022163176 A1 WO2022163176 A1 WO 2022163176A1
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- 150000004767 nitrides Chemical class 0.000 title claims abstract description 351
- 239000004065 semiconductor Substances 0.000 title claims abstract description 289
- 230000000903 blocking effect Effects 0.000 claims abstract description 6
- 229910052738 indium Inorganic materials 0.000 claims description 5
- 229910052758 niobium Inorganic materials 0.000 claims description 5
- 229910052718 tin Inorganic materials 0.000 claims description 5
- 229910052719 titanium Inorganic materials 0.000 claims description 5
- 229910052725 zinc Inorganic materials 0.000 claims description 5
- 229910052726 zirconium Inorganic materials 0.000 claims description 5
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- 229910004298 SiO 2 Inorganic materials 0.000 description 18
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
- H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/14—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
- H01L33/145—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure with a current-blocking structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/36—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
- H01L33/40—Materials therefor
- H01L33/42—Transparent materials
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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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/005—Processes
- H01L33/0062—Processes for devices with an active region comprising only III-V compounds
- H01L33/0075—Processes for devices with an active region comprising only III-V compounds comprising nitride compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/44—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the coatings, e.g. passivation layer or anti-reflective coating
Definitions
- the present invention relates to a nitride semiconductor light emitting device.
- Patent Document 1 discloses a method of sequentially forming a p-type GaN guide layer, a p-type AlGaN clad layer and a p-type GaN contact layer on an active layer.
- a p-type GaN contact layer is provided for making contact with the p-side electrode.
- the vertical transverse mode of the laser light is pulled toward the p-type GaN contact layer, resulting in a decrease in the amplification efficiency of the laser light.
- the p-type AlGaN cladding layer is thin, the vertical transverse mode of the laser light is applied to the p-side electrode, resulting in optical loss.
- the resistance and optical loss will increase accordingly.
- the heat generation increased and the slope efficiency decreased.
- an object of the present invention is to provide a nitride semiconductor light emitting device capable of reducing heat generation and improving slope efficiency.
- a nitride semiconductor light emitting device a nitride semiconductor layer of a first conductivity type, an active layer positioned on the nitride semiconductor layer of the first conductivity type, and an active layer positioned on the active layer a nitride semiconductor layer of a second conductivity type; a current constriction layer located in a portion of the nitride semiconductor layer of the second conductivity type; and a transparent conductive layer that is transparent to light.
- the vertical transverse mode in the direction perpendicular to the light propagation direction with the transparent conductive layer while suppressing thickening of the second conductivity type nitride semiconductor layer.
- the current injected into the active layer can be confined by the current confinement layer, and the current can be efficiently injected into the light emitting region. can be confined to Therefore, it is possible to reduce the heat generation of the nitride semiconductor light emitting device, reduce the light loss during light propagation, and improve the slope efficiency.
- a and an end face protective film are provided.
- the guided light can be reflected while maintaining the vertical transverse mode distribution, and the optical loss can be reduced.
- the lower surface of the current confinement layer is set at a position lower than the upper surface of the second conductivity type nitride semiconductor layer.
- the current injected into the active layer can be confined by the current confinement layer, and the current can be efficiently injected into the light emitting region. It becomes possible to confine it between layers.
- the current confinement layer is formed to have an opening along the waveguide direction of light generated in the active layer, A biconductivity type nitride semiconductor layer is embedded in the opening.
- the transparent conductive layer As a result, it becomes possible to confine the vertical transverse mode in the direction perpendicular to the light propagation direction with the transparent conductive layer while suppressing an increase in the thickness of the nitride semiconductor layer of the second conductivity type. Guided light can be reflected by the facet protection film while maintaining the distribution. Moreover, it is not necessary to provide a contact layer on the transparent conductive layer for making contact with the electrode, and the resistance of the current injected into the active layer through the transparent conductive layer can be reduced. Furthermore, the current injected into the active layer can be confined by the current confinement layer without performing crystal growth again after forming the current confinement layer, and the current can be efficiently injected into the light emitting region. Therefore, it is possible to reduce the heat generation of the nitride semiconductor light-emitting device while suppressing an increase in the number of steps, reduce the light loss during light propagation, and improve the slope efficiency.
- the transparent conductive layer is used as at least one of a guide layer and a clad layer on the active layer.
- the guide layer or the clad layer of the nitride semiconductor layer of the second conductivity type can be removed while allowing the vertical transverse mode during light propagation to be confined in the transparent conductive layer. It is possible to reduce the resistance of the current injected into the active layer through the semiconductor layer.
- the current confinement layer is also located on the light emitting portion of the active layer on the end face side of the second conductivity type nitride semiconductor layer.
- the current confinement layer is positioned along the light guiding direction and is continuous with the end face side of the nitride semiconductor layer of the second conductivity type. do.
- the horizontal lateral mode can be confined between the current confinement layers based on one patterning of the current confinement layer, and the current non-injection region can be formed on the facet side. An increase in the number of manufacturing steps can be suppressed.
- the nitride semiconductor layer of the second conductivity type extends between the current confinement layer and the active layer.
- the first conductivity type is n-type
- the second conductivity type is p-type
- the thickness of the p-type nitride semiconductor layer at the position where the current constriction layer does not exist is 40 nm or more and 550 nm or less.
- the thickness of the p-type nitride semiconductor layer is set to 40 nm or more, a depletion layer necessary for recombination can be secured in the p-type nitride semiconductor layer, and a decrease in luminous efficiency can be prevented. can.
- the thickness of the p-type nitride semiconductor layer is set to 550 nm or less, it is possible to reduce the resistance of the current injected into the active layer through the p-type nitride semiconductor layer, thereby reducing the heat generation of the nitride semiconductor light emitting device. can be reduced.
- the first conductivity type is p-type
- the second conductivity type is n-type
- the thickness of the n-type nitride semiconductor layer at the position where the current confinement layer does not exist is 5 nm or more and 150 nm or less.
- the thickness of the n-type nitride semiconductor layer is set to 5 nm or more, a depletion layer necessary for recombination can be secured in the n-type nitride semiconductor layer, and a decrease in luminous efficiency can be prevented. can.
- the thickness of the n-type nitride semiconductor layer is set to 150 nm or less, the resistance of the current injected into the active layer through the n-type nitride semiconductor layer can be reduced, and heat generation of the nitride semiconductor light-emitting element can be reduced. can be reduced.
- the transparent conductive layer contains at least one element selected from In, Sn, Zn, Ti, Nb and Zr.
- the transparent conductive layer is thinned within a range capable of confining the vertical transverse mode during light propagation.
- the transparent conductive layer has a thickness of 80 nm or more and 120 nm or less.
- the thickness of the transparent conductive layer is 80 nm or more, it becomes possible to confine the vertical transverse mode in the direction perpendicular to the light propagation direction with the transparent conductive layer.
- the thickness of the transparent conductive layer is 120 nm or less, the resistance of the current injected into the active layer through the transparent conductive layer can be reduced.
- the heat generation of the nitride semiconductor light-emitting device can be reduced and the slope efficiency can be improved.
- FIG. 1 is a cross-sectional view showing the configuration of a nitride semiconductor light emitting device according to a first embodiment cut perpendicularly to the optical waveguide direction;
- FIG. (a) is a sectional view showing the configuration of the nitride semiconductor light emitting device according to the first embodiment cut along the optical waveguide direction, and
- (b) is each layer of the nitride semiconductor light emitting device according to the first embodiment. is a diagram showing the refractive index of .
- FIG. 4 is a cross-sectional view showing an example of a method for manufacturing the nitride semiconductor light emitting device according to the first embodiment;
- FIG. 4 is a cross-sectional view showing an example of a method for manufacturing the nitride semiconductor light emitting device according to the first embodiment
- FIG. 2 is a plan view showing a configuration example of a current confinement layer of the nitride semiconductor light emitting device according to the first embodiment
- FIG. 4 is a cross-sectional view showing an example of a method for manufacturing the nitride semiconductor light emitting device according to the first embodiment
- FIG. 3 is a diagram showing an example of a simplified model for obtaining the built-in potential of the nitride semiconductor light emitting device according to the first embodiment
- FIG. 5 is a diagram showing simulation results of the propagation mode of the nitride semiconductor light emitting device according to the first embodiment.
- FIG. 4 is a diagram showing; It is a figure which shows an example of the simulation result of the propagation mode of the nitride semiconductor light-emitting device which concerns on a comparative example.
- FIG. 10 is a diagram showing another example of the simulation result of the propagation mode of the nitride semiconductor light emitting device according to the comparative example;
- 1 is a cross-sectional view showing a mounting example of a nitride semiconductor light emitting device according to a first embodiment;
- FIG. FIG. 5 is a cross-sectional view showing the configuration of a nitride semiconductor light emitting device according to a second embodiment, cut perpendicularly to the optical waveguide direction;
- FIG. 10 is a cross-sectional view showing the configuration of a nitride semiconductor light emitting device according to a third embodiment, cut perpendicularly to the optical waveguide direction; It is sectional drawing which shows an example of the manufacturing method of the nitride semiconductor light-emitting device which concerns on 3rd Embodiment. It is sectional drawing which shows an example of the manufacturing method of the nitride semiconductor light-emitting device which concerns on 3rd Embodiment.
- FIG. 1 is a cross-sectional view showing the configuration of the nitride semiconductor light emitting device according to the first embodiment cut perpendicularly to the optical waveguide direction
- FIG. FIG. 2(b) which is a sectional view showing the configuration cut along the optical waveguide direction, is a diagram showing the refractive index of each layer of the nitride semiconductor light emitting device according to the first embodiment.
- the semiconductor laser LA includes an n-type nitride semiconductor layer N1, an active layer 15, a p-type nitride semiconductor layer N2, a current confinement layer 19 and a transparent conductive layer 20.
- the active layer 15 is laminated on the n-type nitride semiconductor layer N1.
- the p-type nitride semiconductor layer N2 is laminated on the active layer 15.
- the thickness of the p-type nitride semiconductor layer N2 is preferably 40 nm or more and 550 nm or less.
- the nitride semiconductor can have a composition of, for example, InxAlyGa1 -xyN ( 0 ⁇ x ⁇ 1 , 0 ⁇ y ⁇ 1 , 0 ⁇ x+y ⁇ 1).
- a non-doped nitride guide layer 14 may be provided between the n-type nitride semiconductor layer N1 and the active layer 15.
- a non-doped nitride guide layer 16 may be provided between the p-type nitride semiconductor layer N2 and the active layer 15 in order to suppress diffusion of impurities from the p-type nitride semiconductor layer N2 to the active layer 15 .
- the current confinement layer 19 is located in part of the p-type nitride semiconductor layer N2.
- the current confinement layer 19 can be arranged in a part of the p-type nitride semiconductor layer N2 so as to configure at least one of the refractive index-guided and gain-guided resonators.
- the lower surface of the current confinement layer 19 can be set at a position lower than the upper surface of the p-type nitride semiconductor layer N2.
- the lower surface of the current confinement layer 19 can be set at a position lower than the lower surface of the transparent conductive layer 20 .
- the current confinement layer 19 can also be positioned on the light emitting portion of the active layer 15 on the end face side of the p-type nitride semiconductor layer N2. Further, the current confinement layer 19 can be arranged such that the p-type nitride semiconductor layer N2 extends between the current confinement layer 19 and the active layer 15. As shown in FIG. A high resistance layer made of AlN, for example, can be used for the current confinement layer 19 . The thickness of the current confinement layer 19 can be set to 100 nm, for example.
- the transparent conductive layer 20 is a conductive layer transparent to light generated in the active layer 15 .
- the transparent conductive layer 20 may have a Fermi level in the conduction band.
- the transparent conductive layer 20 is used as at least one of a guide layer and a clad layer on the active layer 15 .
- the transparent conductive layer 20 can contain at least one element selected from In, Sn, Zn, Ti, Nb and Zr, and can be an oxide of these elements.
- the transparent conductive layer 20 may be an ITO film, a ZnO film, an SnO film, or a TiO film. It is preferable that the transparent conductive layer 20 be thin within a range capable of confining the vertical transverse mode MA.
- the vertical transverse mode MA is a propagation mode perpendicular to the direction of light propagation.
- the thickness of the transparent conductive layer 20 is preferably 80 nm or more and 120 nm or less.
- the p-type nitride semiconductor layer N2 and the transparent conductive layer 20 are sometimes collectively referred to as a p-side layer.
- the n-type nitride semiconductor layer N1 includes an n-type nitride cladding layer 12 and an n-type nitride guide layer 13.
- the n-type nitride cladding layer 12 and the n-type nitride guide layer 13 are sequentially laminated on the n-type nitride semiconductor substrate 11 .
- the p-type nitride semiconductor layer N2 includes a p-type carrier block layer 17 and a p-type nitride guide layer 18.
- a p-type carrier block layer 17 and a p-type nitride guide layer 18 are sequentially laminated on the non-doped nitride guide layer 16 .
- an opening KA is formed in the current confinement layer 19, and a portion of the p-type nitride guide layer 18 is p-type nitrided.
- the material guide layer 18A may be embedded in the opening KA.
- An electrode 21 for injecting current into the active layer 15 is formed on the transparent conductive layer 20 through the transparent conductive layer 20 and the p-type nitride semiconductor layer N2.
- the electrode 21 can have a laminated structure of Ti/Pt/Au.
- the thickness of Ti/Pt/Au can be set to 100/50/300 nm, for example.
- a facet protection film 22 is formed on the facet EF of the semiconductor laser LA.
- the facet protection film 22 can have a laminated structure of AlN/SiO 2 .
- the thickness of AlN/SiO 2 can be set to 30/300 nm, for example.
- a facet protective film 23 is formed on the facet ER of the semiconductor laser LA.
- the facet protection film 23 can have a laminated structure of AlN/(SiO 2 /Ta 2 O 5 ) 6 /SiO 2 .
- the thickness of AlN/(SiO 2 /Ta 2 O 5 ) 6 /SiO 2 can be set to 30/(60/40) 6 /10 nm, for example.
- the facet protection films 22 and 23 cover not only the facets of the n-type nitride semiconductor layer N1, the active layer 15, the p-type nitride semiconductor layer N2 and the current confinement layer 19, but also the facets of the transparent conductive layer 20. can be done.
- the nitride guide layers 18 and 18A include an n-type GaN substrate, an n-type Al 0.02 Ga 0.98 N layer, an n-type GaN layer, an In 0.02 Ga 0.99 N layer, and an In 0.02 Single quantum well layer composed of Ga0.98N layer/In0.08Ga0.88N layer / In0.02Ga0.98N layer , In0.02Ga0.99N layer , p-type Al A 0.22 Ga 0.78 N layer and a p-type GaN layer can be used, respectively.
- the thickness of the n-type nitride cladding layer 12 can be set to, for example, 700 nm, and the donor concentration N D can be set to 1 ⁇ 10 17 cm ⁇ 3 .
- the thickness of the n-type nitride guide layer 13 can be set to, for example, 50 nm, and the donor concentration N D can be set to 1 ⁇ 10 17 cm ⁇ 3 .
- the thickness of the non-doped nitride guide layer 14 can be set to 136 nm, for example.
- the thicknesses of the barrier layer/well layer/barrier layer of the quantum well layers of the active layer 15 can be set to 10/9/10 nm, for example.
- the thickness of the non-doped nitride guide layer 16 can be set to 135 nm, for example.
- the thickness of the p-type carrier block layer 17 can be set to, for example, 4 nm, and the acceptor concentration N A can be set to 1 ⁇ 10 18 cm ⁇ 3 .
- the total thickness of the p-type nitride guide layers 18, 18A can be set to, for example, 50 nm, and the acceptor concentration N A can be set to 1 ⁇ 10 18 cm ⁇ 3 .
- the refractive index of the n-type nitride cladding layer 12 is made smaller than the refractive index of the n-type nitride guide layer 13, and the refractive index of the n-type nitride guide layer 13 is , the refractive index of the non-doped nitride guide layer 14, and the refractive index of the non-doped nitride guide layer 14 can be smaller than the refractive index of the active layer 15.
- the refractive index of the transparent conductive layer 20 is made smaller than the refractive index of the p-type nitride guide layer 18, the refractive index of the p-type nitride guide layer 18 is made smaller than the refractive index of the non-doped nitride guide layer 16,
- the refractive index of the non-doped nitride guide layer 16 can be made smaller than the refractive index of the active layer 15 .
- the refractive index of the transparent conductive layer 20 can be made smaller than the refractive index of the p-type carrier block layer 17
- the refractive index of the p-type carrier block layer 17 can be made smaller than the refractive index of the p-type nitride guide layer 18 . can.
- the vertical transverse mode MA during laser oscillation of the semiconductor laser LA is applied to the transparent conductive layer 20 .
- the refractive index of the transparent conductive layer 20 smaller than the refractive index of the p-type nitride guide layer 18, the thickness of the p-type nitride semiconductor layer N2 is suppressed, and the vertical transverse mode MA becomes transparent conductive. Confinement in layer 20 becomes possible. Further, by stacking the transparent conductive layer 20 on the p-type nitride semiconductor layer N2, it is not necessary to provide a p-type nitride semiconductor contact layer for making contact with the electrode 21 on the transparent conductive layer 20.
- the resistance of the current injected into the active layer 15 through the conductive layer 20 can be reduced. Furthermore, by providing the current confinement layer 19 in a part of the p-type nitride semiconductor layer N2, the current injected into the active layer 15 can be confined by the current confinement layer 19, and the current can be efficiently injected into the light emitting region. , and the horizontal transverse mode in the direction horizontal to the light propagation direction can be confined between the current confinement layers 19 . Therefore, it is possible to reduce the heat generation of the semiconductor laser LA, reduce the optical loss during light propagation, and improve the slope efficiency.
- the end surface protection films 22 and 23 are also applied to the end surfaces EF and ER of the transparent conductive layer 20.
- the guided light can be reflected while maintaining the distribution of the vertical transverse mode MA, and the optical loss can be reduced.
- the thickness of the p-type nitride semiconductor layer N2 is set to 40 nm or more, a depletion layer necessary for recombination can be secured in the p-type nitride semiconductor layer N2, thereby preventing a decrease in luminous efficiency. can be done.
- the thickness of the p-type nitride semiconductor layer N2 is set to 550 nm or less, the resistance of the current injected into the active layer 15 via the p-type nitride semiconductor layer N2 can be reduced, and the heat generation of the semiconductor laser LA can be reduced. can be reduced.
- the thickness of the transparent conductive layer 20 is set to 80 nm or more, it becomes possible to confine the vertical transverse mode MA in the transparent conductive layer 20 .
- the thickness of the transparent conductive layer 20 is set to 120 nm or less, the resistance of current injected into the active layer 15 through the transparent conductive layer 20 can be reduced.
- FIG. 3A, 3B, and 3D are cross-sectional views showing an example of a method for manufacturing the nitride semiconductor light emitting device according to the first embodiment
- FIG. 3C is a current confinement layer of the nitride semiconductor light emitting device according to the first embodiment.
- 1 is a plan view showing a configuration example of FIG.
- an n-type nitride cladding layer 12, an n-type nitride guide layer 13, an undoped nitride guide layer 14, an active layer 15, an undoped nitride guide layer 16, a p-type carrier block layer 17 and a p-type are grown by epitaxial growth.
- Nitride guide layers 18 are sequentially stacked on n-type nitride semiconductor substrate 11 . Furthermore, a current confinement layer 19 is laminated on the p-type nitride guide layer 18 by epitaxial growth, sputtering, or the like.
- the current confinement layer 19 is patterned by photolithography and dry etching to form an opening KA in the current confinement layer 19 .
- the opening KA can be formed so that the current confinement layer 19 is also located above the light emitting portion of the active layer 15 on the side of the end faces EF and ER of the semiconductor laser LA.
- the current confinement layers 19 are positioned on both sides of the resonator through which the laser light is guided, and the opening KA is formed so that the current confinement layers 19 are continuous on the end faces EF and ER on the light emitting portion of the active layer 15 . can do.
- the horizontal lateral mode can be confined between the current confinement layers 19 based on one patterning of the current confinement layer 19, and the current non-injection regions can be formed on the end faces EF and ER. , it is possible to suppress an increase in the number of steps required to fabricate the current non-injection region.
- a p-type nitride guide layer 18A is selectively formed on the p-type nitride guide layer 18 by epitaxial growth so as to fill the opening KA.
- a transparent conductive layer 20 is formed on the p-type nitride guide layer 18A and the current constriction layer 19 by a method such as sputtering.
- an electrode 21 is formed on the transparent conductive layer 20 by a method such as vapor deposition.
- the n-type nitride semiconductor substrate 11 is cleaved to form end faces EF and ER having cleaved surfaces.
- end face protective films 22 and 23 are formed on the end faces EF and ER by a method such as sputtering.
- the thickness of the p-type nitride semiconductor layer N2 must be greater than or equal to the depletion layer thickness w P of the depletion layer formed in the p-type nitride semiconductor layer N2 so as to obtain sufficient diode characteristics.
- This depletion layer thickness wP is obtained as follows.
- the nitride semiconductor light-emitting device of this embodiment has a semiconductor layer structure of p-type-i-type-n-type.
- the built-in potential ⁇ of this pin junction is given by the following equation (1).
- ⁇ 1 , ⁇ 2 and ⁇ 3 are given by the following equations (2) to (4).
- z is the coordinate indicating the position of the pin junction in the thickness direction
- ⁇ p and ⁇ n are the amount of charge per unit volume of the depletion layers of the p-type semiconductor layer and the n-type semiconductor layer
- ⁇ is the dielectric constant
- ⁇ 0 is the dielectric constant of vacuum
- w1 is the z - coordinate at the boundary between the p-type semiconductor layer and the i-type semiconductor layer
- w2 is the z - coordinate at the boundary between the n-type semiconductor layer and the i-type semiconductor layer
- wP is the p
- w n is the depletion layer thickness of the n-type semiconductor layer.
- the depletion layer thickness WP formed in the P -type semiconductor can be obtained.
- the built-in potential ⁇ can be calculated using a simplified model.
- FIG. 4 is a diagram showing an example of a simplified model for obtaining the built-in potential of the nitride semiconductor light emitting device according to the first embodiment.
- the acceptor concentration NA of the p - type semiconductor layer and the donor concentration ND of the p-type semiconductor layer are constant with respect to the z coordinate.
- the thickness w intr of the i-type semiconductor layer is given by w 1 +w 2 .
- the built-in potential ⁇ is obtained for this model, the built-in potential ⁇ is given by the following equation (6).
- the depletion layer thickness wn is given by the following equation (8).
- Mg is used as a dopant for the p-type semiconductor. Since the impurity level of Mg is deep, it is hardly activated, and even 10% activation is enough. However, the n-type semiconductor uses Si as a dopant and is almost 100% activated. Therefore, if the activation rate of Mg is ⁇ , the equations (7) and (8) are modified as the following equations (9) and (10).
- Equation (12) the intrinsic carrier density ni is given by Equation (12) below.
- Nc is the effective density of states in the conductor and Nv is the effective density of states in the valence band.
- the thickness of the p-type nitride semiconductor layer N2 may be set with a margin of about 150 nm in order to ensure the ease of handling of the device and the reliability of its operation.
- formulas (9) and (10) were calculated assuming that the p-type and n-type impurity concentrations are spatially uniform. In the case of uniform distribution, the spatially averaged impurity concentration may be applied to equations (9) and (10). In order to make a more accurate estimate, the calculation should be performed using the formulas (1) to (5).
- the refractive index of the p-type clad layer is n 3
- the refractive index of the core layer is n 1
- the refractive index of the n-type clad layer is n 2 -.
- Equation (14) the distribution E(y) of light toward the outermost p-type cladding layer side is given by Equation (14) below.
- the thickness of the outermost clad layer preferably satisfies the following formula (16) in order to prevent disturbance of the waveguide mode.
- the active layer and the guide layer generally correspond to the core layer (total thickness is 500 nm), and its refractive index is n core ⁇ 2.52 (in the case of GaN) at 405 nm, and the refractive index of the p-side layer is The rate n clad is ⁇ 2.11. Therefore, it is preferable to set the layer thickness of the transparent conductive layer 20 to 94 nm or more.
- the above estimation is for the case of using a three-layer dielectric slab waveguide, but empirically, it is possible to estimate the outermost clad layer in the same way even in the case of multiple layers of three or more layers. I know. Also, since the oscillation wavelength may vary toward the longer wavelength side, it is preferable to set the thickness of the transparent conductive layer 20 to about 100 nm with some allowance. In addition, it can be similarly estimated when the propagating light is a TM (Transverse Magnetic) wave.
- TM Transverse Magnetic
- FIG. 5 is a diagram showing simulation results of the propagation mode of the nitride semiconductor light emitting device according to the first embodiment.
- a simulation was performed with the p-side layer thickness set to 100 nm for the structure of FIG. 2(a). It was found that if the p-side layer thickness is about 100 nm, the light propagation mode is sufficiently confined in the longitudinal direction. Therefore, even if the p-side layer is thin, the light propagation mode can be sufficiently confined in the vertical direction, and the resistance and optical loss of the semiconductor laser LA can be reduced.
- FIG. 6(a) is a sectional view showing the configuration of a nitride semiconductor light emitting device according to a comparative example cut along the optical waveguide direction
- FIG. 6(b) shows each layer of the nitride semiconductor light emitting device according to the comparative example.
- the semiconductor laser LB includes a p-type nitride semiconductor layer N2' instead of the p-type nitride semiconductor layer N2 of the semiconductor laser LA in FIG. 2A.
- a current confinement layer 33 is provided in a portion of the p-type nitride semiconductor layer N2'.
- An electrode 35 is formed on the p-type nitride semiconductor layer N2'.
- a facet protection film 36 is formed on the facet EF of the semiconductor laser LB, and a facet protection film 37 is formed on the facet ER of the semiconductor laser LB.
- the p-type nitride semiconductor layer N2' includes a p-type carrier block layer 17, a p-type nitride guide layer 31, a p-type nitride cladding layer 32 and a p-type nitride contact layer .
- a p-type carrier block layer 17 , a p-type nitride guide layer 31 , a p-type nitride cladding layer 32 and a p-type nitride contact layer 34 are sequentially laminated on the non-doped nitride guide layer 16 .
- the p-type nitride cladding layer 32 and the p-type nitride contact layer 34 for example, a p-type GaN layer, a p-type Al 0.02 Ga 0.98 N layer and a p-type GaN layer are used. Each can be used.
- the refractive index of the p-type nitride cladding layer 32 can be made smaller than the refractive indices of the p-type nitride guide layer 31 and the p-type nitride contact layer 34 .
- FIG. 7A is a diagram showing an example of simulation results of propagation modes of a nitride semiconductor light emitting device according to a comparative example.
- the simulation was performed by setting the thickness of the p-type nitride semiconductor layer N2' to 700 nm for the structure of FIG. 6(a). In this case, since the p-type nitride semiconductor layer N2' is thick, the resistance is increased and the light propagation mode slightly seeps out to the electrode 35 side.
- FIG. 7B is a diagram showing another example of simulation results of the propagation mode of the nitride semiconductor light emitting device according to the comparative example.
- a simulation was performed with the thickness of the p-type nitride semiconductor layer N2' set to 100 nm for the structure of FIG. 6(a). In this case, it is expected that the light propagation mode will be applied to the electrode 35, resulting in an increase in propagation loss.
- FIG. 8 is a cross-sectional view showing a mounting example of the nitride semiconductor light emitting device according to the first embodiment.
- the semiconductor laser LA is mounted on the submount MT by junction down bonding.
- the material of the submount MT is SiC, for example.
- Au—Sn solder HD for example, can be used to connect the semiconductor laser LA and the submount MT.
- the inner stripe type semiconductor laser LA can planarize the electrode 21 in FIG. Therefore, even when the semiconductor laser LA is mounted by junction-down bonding, it is possible to alleviate the concentration of external stress on a specific region of the semiconductor laser LA, thereby improving the reliability. Moreover, by mounting the semiconductor laser LA by junction down bonding, the heat dissipation of the semiconductor laser LA can be improved, and the laser output can be improved.
- FIG. 9 is a cross-sectional view showing the configuration of the nitride semiconductor light emitting device according to the second embodiment, cut perpendicularly to the optical waveguide direction.
- the semiconductor laser LC includes a p-type nitride semiconductor layer N11, an active layer 35, an n-type nitride semiconductor layer N12, a current confinement layer 39 and a transparent conductive layer .
- the active layer 35 is laminated on the p-type nitride semiconductor layer N11.
- the n-type nitride semiconductor layer N12 is laminated on the active layer 35.
- the thickness of the n-type nitride semiconductor layer N12 is preferably 5 nm or more and 150 nm or less.
- a non-doped nitride guide layer 37 may be provided between the n-type nitride semiconductor layer N12 and the active layer 35 in order to suppress diffusion of impurities from the n-type nitride semiconductor layer N12 to the active layer 35. .
- the current confinement layer 39 is located in part of the n-type nitride semiconductor layer N12.
- the current confinement layer 39 may extend from the n-type nitride semiconductor layer N12 to the non-doped nitride guide layer 37.
- the current confinement layer 39 is part of the n-type nitride semiconductor layer N12 and the non-doped nitride guide layer 37 so as to form at least one of the refractive index-guided and gain-guided resonators. can be placed in
- the planar shape of the current confinement layer 39 can be set as shown in FIG. 3C.
- a high resistance layer made of AlN, for example, can be used for the current confinement layer 39 .
- the thickness of the current confinement layer 39 can be made equal to the sum of the thickness of the n-type nitride semiconductor layer N12 and the thickness of the non-doped nitride guide layer 37, for example.
- the thickness of the current confinement layer 39 can be set to 150 nm.
- the transparent conductive layer 40 is a conductive layer transparent to light generated in the active layer 35 .
- the transparent conductive layer 40 may have a Fermi level in the conduction band.
- the transparent conductive layer 40 is used as at least one of a guide layer and a clad layer on the active layer 45 .
- the transparent conductive layer 40 can contain at least one element selected from In, Sn, Zn, Ti, Nb and Zr, and can be an oxide of these elements.
- the transparent conductive layer 40 is preferably thin enough to confine a vertical transverse mode, which is a propagation mode perpendicular to the light propagation direction. At this time, the thickness of the transparent conductive layer 40 is preferably 80 nm or more and 120 nm or less.
- the n-type nitride semiconductor layer N12 and the transparent conductive layer 40 are sometimes collectively referred to as an n-side layer.
- the p-type nitride semiconductor layer N11 includes a p-type nitride cladding layer 32, a p-type nitride guide layer 33 and a p-type carrier block layer .
- a p-type nitride cladding layer 32 , a p-type nitride guide layer 33 and a p-type carrier block layer 34 are sequentially laminated on the p-type nitride semiconductor substrate 31 .
- the n-type nitride semiconductor layer N12 includes an n-type nitride guide layer 38.
- An n-type nitride guide layer 38 is laminated on the non-doped nitride guide layer 37 .
- an opening KC is formed in the current confinement layer 39, and the non-doped nitride guide layer 37 and The n-type nitride guide layers 38 may be sequentially embedded in the openings KC.
- An electrode 41 for injecting current into the active layer 35 is formed on the transparent conductive layer 40 through the transparent conductive layer 40 and the p-type nitride semiconductor layer N12.
- the electrode 41 can have a laminated structure of Ti/Pt/Au.
- the thickness of Ti/Pt/Au can be set to 100/50/300 nm, for example.
- Facet protection films are formed on the front facet and the rear facet of the semiconductor laser LC.
- a facet protective film on the front facet of the semiconductor laser LC can have a laminated structure of AlN/SiO 2 .
- the thickness of AlN/SiO 2 can be set to 30/300 nm, for example.
- a facet protective film on the rear facet of the semiconductor laser LC can have a laminated structure of AlN/(SiO 2 /Ta 2 O 5 ) 6 /SiO 2 .
- the thickness of AlN/(SiO 2 /Ta 2 O 5 ) 6 /SiO 2 can be set to 30/(60/40) 6 /10 nm, for example.
- the facet protective film can cover not only the facets of the p-type nitride semiconductor layer N11, the active layer 35, the n-type nitride semiconductor layer N12 and the current constriction layer 39, but also the facets of the transparent conductive layer 40.
- p-type nitride semiconductor substrate 31 As p-type nitride semiconductor substrate 31, p-type nitride cladding layer 32, p-type nitride guide layer 33, p-type carrier block layer 34, active layer 35, non-doped nitride guide layer 37 and n-type nitride guide layer 38 , for example, p-type GaN substrate, p-type Al 0.02 Ga 0.98 N layer, p-type GaN layer, p-type Al 0.22 Ga 0.78 N layer, In 0.02 Ga 0.98 N layer/ In 0.08 Ga 0.88 N layer/In 0.02 Ga 0.98 N layer/In 0.08 Ga 0.88 N layer/In 0.02 Ga 0.98 N layer/In 0.08 Ga 0 A multiple quantum well layer consisting of .88N layer/ In0.02Ga0.98N layer, a GaN layer and a p-type GaN layer can be used, respectively.
- the thickness of the p-type nitride cladding layer 32 can be set to, for example, 500 nm, and the acceptor concentration N A can be set to 1 ⁇ 10 18 cm ⁇ 3 .
- the thickness of the n-type nitride guide layer 33 can be set to, for example, 36 nm, and the acceptor concentration N A can be set to 1 ⁇ 10 18 cm ⁇ 3 .
- the thickness of the p-type carrier blocking layer 34 can be set to, for example, 4 nm, and the acceptor concentration N A can be set to 1 ⁇ 10 18 cm ⁇ 3 .
- the thicknesses of the barrier layer/well layer/barrier layer/well layer/barrier layer/well layer/barrier layer/well layer/barrier layer of the quantum well layer of the active layer 35 are set to 10/9/10/9/10/9/10 nm, for example. can do.
- the thickness of the non-doped nitride guide layer 37 can be set to 33 nm, for example.
- the thickness of the p-type nitride guide layer 38 can be set to, for example, 117 nm, and the donor concentration N D can be set to 1 ⁇ 10 17 cm ⁇ 3 . Note that the thicknesses of the n-type nitride semiconductor layer N12 and the transparent conductive layer 40 can be obtained by the same method as in the first embodiment.
- the refractive index of the p-type nitride cladding layer 32 can be made smaller than the refractive index of the p-type nitride guide layer 33 .
- the refractive index of p-type carrier blocking layer 34 can be smaller than the refractive index of p-type nitride cladding layer 32 .
- the refractive index of the transparent conductive layer 40 is made smaller than the refractive index of the n-type nitride guide layer 38
- the refractive index of the n-type nitride guide layer 38 is made smaller than the refractive index of the non-doped nitride guide layer 36
- the refractive index of the non-doped nitride guide layer 37 can be smaller than that of the active layer 35 .
- the refractive index of the transparent conductive layer 40 is made smaller than the refractive index of the n-type nitride guide layer 38, the thickness of the n-type nitride semiconductor layer N12 is suppressed and the vertical transverse mode is controlled by the transparent conductive layer. At 40 it becomes possible to confine.
- the transparent conductive layer 40 by laminating the transparent conductive layer 40 on the n-type nitride semiconductor layer N12, it is not necessary to provide an n-type nitride semiconductor contact layer for making contact with the electrode 41 on the transparent conductive layer 40. The resistance of the current injected into the active layer 35 through the conductive layer 40 can be reduced.
- the current confinement layer 39 in a part of the n-type nitride semiconductor layer N12, the current injected into the active layer 35 can be confined by the current confinement layer 39, and the current can be efficiently injected into the light emitting region. and confine the horizontal transverse mode in the direction horizontal to the light propagation direction between the current confinement layers 39 . Therefore, it is possible to reduce the heat generation of the semiconductor laser LC, reduce the optical loss during light propagation, and improve the slope efficiency.
- the thickness of the n-type nitride semiconductor layer N12 is set to 5 nm or more, a depletion layer necessary for recombination can be secured in the n-type nitride semiconductor layer N12, thereby preventing a decrease in luminous efficiency. can be done.
- the thickness of the n-type nitride semiconductor layer N12 is set to 150 nm or less, the resistance of the current injected into the active layer 35 via the n-type nitride semiconductor layer N12 can be reduced, and the heat generation of the semiconductor laser LC can be reduced. can be reduced.
- FIG. 10 is a cross-sectional view showing the configuration of the nitride semiconductor light emitting device according to the third embodiment, cut perpendicularly to the optical waveguide direction.
- the semiconductor laser LD has an active layer 55, a p-type nitride semiconductor layer instead of the active layer 15, the p-type nitride semiconductor layer N2, the current constriction layer 19 and the transparent conductive layer 20 of the semiconductor laser LA of FIG. It comprises a layer N22, a current confinement layer 59 and a transparent conductive layer 60.
- FIG. The active layer 55 is laminated on the n-type nitride semiconductor layer N1.
- the p-type nitride semiconductor layer N22 is laminated on the active layer 15. As shown in FIG.
- a non-doped nitride guide layer 14 may be provided between the n-type nitride semiconductor layer N1 and the active layer 55.
- a non-doped nitride guide layer 56 may be provided between the p-type nitride semiconductor layer N12 and the active layer 55 in order to suppress the diffusion of impurities from the p-type nitride semiconductor layer N22 to the active layer 55.
- the current confinement layer 59 is located on part of the transparent conductive layer 60 . At this time, the current confinement layer 59 can be arranged in a part of the transparent conductive layer 60 so as to form a gain guided resonator. The current confinement layer 59 can also be positioned on the light emitting portion of the active layer 55 on the end surface side of the p-type nitride semiconductor layer N22. A high resistance layer made of AlN, for example, can be used for the current confinement layer 59 . The thickness of the current confinement layer 59 can be set to 100 nm, for example.
- the transparent conductive layer 60 is a conductive layer transparent to light generated in the active layer 55 .
- the transparent conductive layer 60 may have a Fermi level in the conduction band.
- the transparent conductive layer 60 is used as at least one of a guide layer and a clad layer on the active layer 55 .
- the transparent conductive layer 60 can contain at least one element selected from In, Sn, Zn, Ti, Nb and Zr, and can be an oxide of these elements.
- the transparent conductive layer 60 is preferably thin enough to confine the vertical transverse mode.
- an opening KD may be formed in the current confinement layer 59 and the transparent conductive layer 60D may be embedded in the opening KD.
- the p-type nitride semiconductor layer N22 includes a p-type carrier block layer 57 and a p-type nitride guide layer 58.
- a p-type carrier block layer 57 and a p-type nitride guide layer 58 are sequentially laminated on the non-doped nitride guide layer 56 .
- An electrode 61 for injecting current into the active layer 55 is formed on the transparent conductive layer 60 through the transparent conductive layer 60 and the p-type nitride semiconductor layer N22.
- the electrode 61 can have a laminated structure of Ti/Pt/Au.
- the thickness of Ti/Pt/Au can be set to 100/50/300 nm, for example.
- Facet protection films are formed on the front facet and the rear facet of the semiconductor laser LD.
- a facet protective film on the front facet of the semiconductor laser LD may have a laminated structure of AlN/SiO 2 .
- the thickness of AlN/SiO 2 can be set to 30/300 nm, for example.
- a facet protective film on the rear facet of the semiconductor laser LD may have a laminated structure of AlN/(SiO 2 /Ta 2 O 5 ) 6 /SiO 2 .
- the thickness of AlN/(SiO 2 /Ta 2 O 5 ) 6 /SiO 2 can be set to 30/(60/40) 6 /10 nm, for example.
- the facet protective film can cover not only the facets of the p-type nitride semiconductor layer N1, the active layer 55, the n-type nitride semiconductor layer N22 and the current confinement layer 59, but also the facets of the transparent conductive layer 60.
- the active layer 55, the non-doped nitride guide layer 56, the p-type carrier block layer 57 and the p-type nitride guide layer 58 for example, In 0.02 Ga 0.98 N layer/In 0.08 Ga 0.88 N layer /In0.02Ga0.98N layer / In0.08Ga0.88N layer / In0.02Ga0.98N layer , In0.02Ga0.99N layers, a p-type Al 0.22 Ga 0.78 N layer and a p-type GaN layer, respectively.
- the thicknesses of the barrier layer/well layer/barrier layer/well layer/barrier layer of the quantum well layer of the active layer 55 can be set to 10/9/10/9/10 nm, for example.
- the thickness of the non-doped nitride guide layer 16 can be set to 126 nm, for example.
- the thickness of the p-type carrier blocking layer 17 can be set to, for example, 4 nm, and the acceptor concentration N A can be set to 1 ⁇ 10 18 cm ⁇ 3 .
- the thickness of the p-type nitride guide layer 18 can be set to, for example, 150 nm, and the acceptor concentration N A can be set to 1 ⁇ 10 18 cm ⁇ 3 .
- the refractive index of the transparent conductive layer 60 is made smaller than the refractive index of the p-type nitride guide layer 58, and the refractive index of the p-type nitride guide layer 58 is made smaller than the refractive index of the non-doped nitride guide layer 56.
- the refractive index of the non-doped nitride guide layer 56 can be smaller than that of the active layer 55 .
- the refractive index of the p-type carrier blocking layer 57 can be smaller than the refractive index of the p-type nitride guiding layer 58 .
- the p-type nitride semiconductor layer N2 is It is possible to confine the vertical transverse mode in the transparent conductive layer 60 while suppressing the thickening of the film, and to reflect guided light on the facet protective film while maintaining the distribution of the vertical transverse mode. Further, by stacking the transparent conductive layer 60 on the p-type nitride semiconductor layer N22, it is not necessary to provide a p-type nitride semiconductor contact layer for making contact with the electrode 61 on the transparent conductive layer 60.
- the resistance of the current injected into the active layer 55 through the conductive layer 60 can be reduced. Furthermore, by providing the current confinement layer 59 in a part of the transparent conductive layer 60, the current injected into the active layer 55 can be blocked by the current confinement layer 59 without performing crystal growth again after the formation of the current confinement layer 60. It becomes possible to inject a current efficiently into the light emitting region by constricting the region. Therefore, it is possible to reduce the heat generation of the semiconductor laser LD while suppressing an increase in the number of steps, reduce the light loss during light propagation, and improve the slope efficiency.
- FIG. 11A and 11B are cross-sectional views showing an example of a method for manufacturing a nitride semiconductor light emitting device according to the third embodiment.
- an n-type nitride cladding layer 52, an n-type nitride guide layer 53, an undoped nitride guide layer 54, an active layer 55, an undoped nitride guide layer 56, a p-type carrier block layer 57 and p-type are grown by epitaxial growth.
- a nitride guide layer 58 is sequentially stacked on the n-type nitride semiconductor substrate 51 .
- a current confinement layer 59 is laminated on the p-type nitride guide layer 58 by epitaxial growth, sputtering, or the like. Note that the thicknesses of the p-type nitride semiconductor layer N22 and the transparent conductive layer 60 can be obtained by the same method as in the first embodiment.
- the current confinement layer 59 is patterned to form an opening KD in the current confinement layer 59 based on photolithography technology and dry etching technology.
- the planar shape of the current confinement layer 59 can be set as shown in FIG. 3C.
- a transparent conductive layer 60D is formed on the p-type nitride guide layer 58 and the current constriction layer 59 by a method such as sputtering so as to fill the opening KD.
- an electrode 61 is formed on the transparent conductive layer 60 by a method such as vapor deposition.
- the n-type nitride semiconductor substrate 11 is cleaved to form an end surface having a cleaved surface.
- a facet protection film is formed on each facet by a method such as sputtering.
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Abstract
Description
特許文献1には、p型GaNガイド層、p型AlGaNクラッド層およびp型GaNコンタクト層を活性層上に順次形成する方法が開示されている。
また、特許文献1に開示された構成では、p型AlGaNクラッド層が薄いと、レーザ光の垂直横モードがp側電極にかかり、光損失を招いていた。
また、電流狭窄層19は、図2(a)に示すように、p型窒化物半導体層N2の端面側において、活性層15の発光部上にも位置することができる。また、電流狭窄層19は、電流狭窄層19と活性層15との間にp型窒化物半導体層N2が延在するように配置することができる。電流狭窄層19は、例えば、AlNからなる高抵抗層を用いることができる。電流狭窄層19の厚さは、例えば、100nmに設定することができる。
AlN/SiO2の厚さは、例えば、30/300nmに設定することができる。
半導体レーザLAの端面ERには、端面保護膜23が形成されている。端面保護膜23は、AlN/(SiO2/Ta2O5)6/SiO2の積層構造とすることができる。AlN/(SiO2/Ta2O5)6/SiO2の厚さは、例えば、30/(60/40)6/10nmに設定することができる。
端面保護膜22、23は、n型窒化物半導体層N1、活性層15、p型窒化物半導体層N2および電流狭窄層19のそれぞれの端面だけでなく、透明導電層20の端面も被覆することができる。
また、透明導電層20の屈折率は、p型窒化物ガイド層18の屈折率より小さくし、p型窒化物ガイド層18の屈折率は、ノンドープ窒化物ガイド層16の屈折率より小さくし、ノンドープ窒化物ガイド層16の屈折率は、活性層15の屈折率より小さくすることができる。また、透明導電層20の屈折率は、p型キャリアブロック層17の屈折率より小さくし、p型キャリアブロック層17の屈折率は、p型窒化物ガイド層18の屈折率より小さくすることができる。
図3Aにおいて、エピタキシャル成長によって、n型窒化物クラッド層12、n型窒化物ガイド層13、ノンドープ窒化物ガイド層14、活性層15、ノンドープ窒化物ガイド層16、p型キャリアブロック層17およびp型窒化物ガイド層18をn型窒化物半導体基板11上に順次積層する。さらに、エピタキシャル成長やスパッタなどの方法によって、電流狭窄層19をp型窒化物ガイド層18上に積層する。
このとき、図3Cに示すように、半導体レーザLAの端面EF、ER側において活性層15の発光部上にも電流狭窄層19が位置するように開口部KAを形成することができる。
これにより、ウェハから切り出す際の端面EF、ERの劈開異常を低減することが可能となるとともに、端面EF、ERの発熱を抑制し、端面破壊を抑制することができる。
p型窒化物半導体層N2の厚さは、ダイオードとして十分な特性が得られるように、p型窒化物半導体層N2内に形成される空乏層の空乏層厚wP以上にする必要がある。
本実施形態の窒化物半導体発光素子はp型-i型-n型という半導体の層構造をもつ。
このpinジャンクションの内蔵電位Φは、以下の式(1)で与えられる。
図4において、このモデルでは、p型半導体層のアクセプタ濃度NAおよびp型半導体層のドナー濃度NDはz座標に対して一定とした。i型半導体層の厚さwintrはw1+w2で与えられる。
そこで、上式より、具体的な空乏層厚wP(温度T=25℃)を求める。温度TにおけるバンドギャップEgは、以下の式(11)で与えられる。
また、実際の使用環境において、ハンドリングなどで多少逆バイアスが印加されるような状況も想定され、内蔵電位Φが大きくなる方向に働く。このため、素子の扱い易さおよび動作の信頼性を確保するため、p型窒化物半導体層N2の厚さは150nm程度になるように余裕を持たせて設定してもよい。
p型クラッド層、コア層およびn型クラッド層の3層の誘電体スラブ型導波路を考える。ここで、p型クラッド層の屈折率をn3、コア層の屈折率をn1、n型クラッド層の屈折率をn2-とする。このとき、n1=ncore>n2=nn-cladかつn1=ncore>n3=np-cladとなる3層の誘電体スラブ型導波路を伝搬する光波は、
コア層周辺をピークに概ね山型の分布をする。TE(Transverse Electric)波の場合、最外のp型クラッド層側への光の分布E(y)は、以下の式(14)で与えられる。
ただし、k0は発光光の波数であり、定数である。このことから、導波モードの乱れを防止するには、経験的に最外のクラッド層厚は、以下の式(16)を満たすのが好ましい
図5において、図2(a)の構造についてp側層厚を100nmに設定してシミュレーションを行った。p側層厚が100nm程度あれば、光の伝搬モードが縦方向に十分閉じ込められることが判った。このため、p側層厚が薄いままでも光の伝搬モードが縦方向に十分閉じ込めることができ、半導体レーザLAの低抵抗化および低光損失化を図ることができる。
図6(a)において、半導体レーザLBは、図2(a)の半導体レーザLAのp型窒化物半導体層N2の代わりにp型窒化物半導体層N2´を備える。p型窒化物半導体層N2´の一部には、電流狭窄層33が設けられている。
図7Aにおいて、図6(a)の構造についてp型窒化物半導体層N2´の厚さを700nmに設定してシミュレーションを行った。この場合、p型窒化物半導体層N2´の厚さが厚いため、抵抗が増大するとともに、光の伝搬モードが電極35側に若干染み出している。
図7Bにおいて、図6(a)の構造についてp型窒化物半導体層N2´の厚さを100nmに設定してシミュレーションを行った。この場合、光の伝搬モードが電極35にかかり、伝搬損失の増大を招くことが予想される。
図8において、半導体レーザLAは、サブマウントMT上にジャンクションダウンボンディング実装されている。サブマウントMTの材料は、例えば、SiCである。半導体レーザLAとサブマウントMTとの接続には、例えば、Au-SnハンダHDを用いることができる。
図9において、半導体レーザLCは、p型窒化物半導体層N11、活性層35、n型窒化物半導体層N12、電流狭窄層39および透明導電層40を備える。活性層35は、p型窒化物半導体層N11上に積層されている。n型窒化物半導体層N12は、活性層35上に積層されている。n型窒化物半導体層N12の厚さは、5nm以上150nm以下であるのが好ましい。
このとき、電流狭窄層39は、屈折率導波型および利得導波型のいずれか少なくとも1つの共振器が構成されるようにn型窒化物半導体層N12およびノンドープ窒化物ガイド層37の一部に配置することができる。電流狭窄層39の平面形状は、図3Cに示したように設定することができる。電流狭窄層39は、例えば、AlNからなる高抵抗層を用いることができる。電流狭窄層39の厚さは、例えば、n型窒化物半導体層N12の厚さとノンドープ窒化物ガイド層37の厚さの合計と等しくすることができる。例えば、電流狭窄層39の厚さは、150nmに設定することができる。
また、透明導電層40の屈折率は、n型窒化物ガイド層38の屈折率より小さくし、n型窒化物ガイド層38の屈折率は、ノンドープ窒化物ガイド層36の屈折率より小さくし、ノンドープ窒化物ガイド層37の屈折率は、活性層35の屈折率より小さくすることができる。
図10において、半導体レーザLDは、図1の半導体レーザLAの活性層15、p型窒化物半導体層N2、電流狭窄層19および透明導電層20の代わりに、活性層55、p型窒化物半導体層N22、電流狭窄層59および透明導電層60を備える。活性層55は、n型窒化物半導体層N1上に積層されている。p型窒化物半導体層N22は、活性層15上に積層されている。
電流狭窄層59は、p型窒化物半導体層N22の端面側において、活性層55の発光部上にも位置することができる。電流狭窄層59は、例えば、AlNからなる高抵抗層を用いることができる。電流狭窄層59の厚さは、例えば、100nmに設定することができる。
図11Aにおいて、エピタキシャル成長によって、n型窒化物クラッド層52、n型窒化物ガイド層53、ノンドープ窒化物ガイド層54、活性層55、ノンドープ窒化物ガイド層56、p型キャリアブロック層57およびp型窒化物ガイド層58をn型窒化物半導体基板51上に順次積層する。さらに、エピタキシャル成長やスパッタなどの方法によって、電流狭窄層59をp型窒化物ガイド層58上に積層する。なお、p型窒化物半導体層N22および透明導電層60の厚さは、第1実施形態と同様な方法によって求めることができる。
次に、蒸着などの方法によって、電極61を透明導電層60上に形成する。次に、n型窒化物半導体基板11の劈開によって、劈開面を持つ端面を形成する。次に、スパッタなどの方法によって、各端面に端面保護膜を形成する。
N2 p型窒化物半導体層
11 n型窒化物半導体基板
12 第n型窒化物クラッド層
13 n型窒化物ガイド層
14、16 ノンドープ窒化物ガイド層
15 活性層
17 p型キャリアブロック層
18 p型窒化物ガイド層
19 電流狭窄層
20 透明導電層
21 電極
22 端面保護膜
Claims (16)
- 第1導電型窒化物半導体層と、
前記第1導電型窒化物半導体層上に位置する活性層と、
前記活性層上に位置する第2導電型窒化物半導体層と、
前記第2導電型窒化物半導体層の一部に位置する電流狭窄層と、
前記第2導電型窒化物半導体層上に位置し、前記活性層で発生される光に透明な透明導電層とを備えることを特徴とする窒化物半導体発光素子。 - 前記第1導電型窒化物半導体層、前記活性層、第2導電型窒化物半導体層および前記透明導電層の各端面に形成された端面保護膜をさらに備えることを特徴とする請求項1に記載の窒化物半導体発光素子。
- 前記電流狭窄層の下面は、前記第2導電型窒化物半導体層の上面より低い位置に設定されていることを特徴とする請求項1または2に記載の窒化物半導体発光素子。
- 前記電流狭窄層は、前記活性層で発生される光の導波方向に沿った開口部を有するように形成され、前記第2導電型窒化物半導体層は前記開口部に埋め込まれていることを特徴とする請求項1から3のいずれか1項に記載の窒化物半導体発光素子。
- 第1導電型窒化物半導体層と、
前記第1導電型窒化物半導体層上に位置する活性層と、
前記活性層上に位置する第2導電型窒化物半導体層と、
前記第2導電型窒化物半導体層上に位置し、前記活性層で発生される光に透明な透明導電層と、
前記透明導電層の一部に位置する電流狭窄層と、
前記第1導電型窒化物半導体層、前記活性層、第2導電型窒化物半導体層および前記透明導電層の各端面に形成された端面保護膜とを備えることを特徴とする窒化物半導体発光素子。 - 前記透明導電層は、前記活性層上のガイド層またはクラッド層の少なくともいずれか1つとして用いられることを特徴とする請求項1から5のいずれか1項に記載の窒化物半導体発光素子。
- 前記電流狭窄層は、前記第2導電型窒化物半導体層の端面側において、前記活性層の発光部上にも位置することを特徴とする請求項1から6のいずれか1項に記載の窒化物半導体発光素子。
- 前記電流狭窄層は、光の導波方向に沿うように位置し、前記第2導電型窒化物半導体層の端面側に連続することを特徴とする請求項7に記載の窒化物半導体発光素子。
- 前記第2導電型窒化物半導体層は、前記電流狭窄層と前記活性層との間に延在することを特徴とする請求項1から8のいずれか1項に記載の窒化物半導体発光素子。
- 前記第1導電型はn型、前記第2導電型はp型であることを特徴とする請求項1から9のいずれか1項に記載の窒化物半導体発光素子。
- 前記電流狭窄層が存在しない位置におけるp型窒化物半導体層の厚さは、40nm以上550nm以下であることを特徴とする請求項10に記載の窒化物半導体発光素子。
- 前記第1導電型はp型、前記第2導電型はn型であることを特徴とする請求項1から9のいずれか1項に記載の窒化物半導体発光素子。
- 前記電流狭窄層が存在しない位置におけるn型窒化物半導体層の厚さは、5nm以上150nm以下であることを特徴とする請求項12に記載の窒化物半導体発光素子。
- 前記透明導電層は、In、Sn、Zn、Ti、NbおよびZrから選択される少なくともいずれか1つの元素を含むことを特徴とする請求項1から13のいずれか1項に記載の窒化物半導体発光素子。
- 前記透明導電層は、光伝搬時の垂直横モードを閉じ込め可能な範囲内で薄膜化されていることを特徴とする請求項1から14のいずれか1項に記載の窒化物半導体発光素子。
- 前記透明導電層の厚さは、80nm以上120nm以下であることを特徴とする請求項1から15のいずれか1項に記載の窒化物半導体発光素子。
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