Semiconductor light emitting device and method for manufacturing the same

Abstract

To provide a semiconductor light-emitting element capable of increasing a coupling coefficient between waveguide light and a diffraction grating.SOLUTION: A semiconductor light-emitting element comprises: a first conductivity type semiconductor layer; an active layer provided on the first conductivity type semiconductor layer; a second conductivity type semiconductor layer provided on the active layer; a waveguide layer which is provided in the second conductivity type semiconductor layer and guides waveguide light in the active layer while concealing the waveguide light in a lateral direction of a waveguide direction of the waveguide light; a diffraction grating which is provided in the second conductivity type semiconductor layer in the waveguide direction of the waveguide light; and a concealment layer which is provided on the waveguide layer and on the diffraction grating and conceals the waveguide light which is guided in the active layer in a longitudinal direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a semiconductor light-emitting device and a method for manufacturing the same. [Background technology]

[0002] In order to stabilize the oscillation wavelength of a semiconductor laser, a distributed feedback (DFB) structure is often used. Non-Patent Document 1 discloses an optical element in which a first-order diffraction grating is formed between an AlInGaN-based n-wave guiding layer and an n-cladding layer. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Japanese Journal of Applied Physics Vol.45,No.46,2006,pp00.L1223-L1225 Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a semiconductor light emitting device capable of increasing the coupling coefficient between guided light and a diffraction grating, and a method for manufacturing the semiconductor light emitting device. [Means for solving the problem]

[0005] A semiconductor light-emitting device according to one aspect of the present invention includes a first conductivity type semiconductor layer, an active layer provided on the first conductivity type semiconductor layer, a second conductivity type semiconductor layer provided on the active layer, a waveguide layer provided in the second conductivity type semiconductor layer and guiding the guided light while confining the guided light in a horizontal direction of a waveguide direction of the guided light guided through the active layer, a diffraction grating provided in the second conductivity type semiconductor layer along the waveguide direction of the guided light, and a confinement layer provided on the waveguide layer and the diffraction grating and confining the guided light guided through the active layer in a vertical direction.

[0006] This allows the diffraction grating to be located close to the active layer while confining the guided light in the active layer in both the horizontal and vertical directions, thereby increasing the coupling coefficient between the guided light and the diffraction grating while suppressing a decrease in the light emission efficiency, and stabilizing the oscillation wavelength while suppressing a decrease in the output of the semiconductor light emitting element.

[0007] In addition, in the semiconductor light emitting device according to one aspect of the present invention, the confinement layer is a second conductivity type semiconductor layer having a smaller refractive index than the waveguide layer.

[0008] This makes it possible to vertically confine the guided light that propagates through the active layer while suppressing mismatch between the lattice constant of the confinement layer and the lattice constant of the waveguide layer, thereby suppressing a decrease in the light emission efficiency and a decrease in the reliability of the semiconductor light emitting device.

[0009] In addition, in the semiconductor light emitting device according to one aspect of the present invention, the confinement layer is a transparent conductive layer that is transparent to guided light that is guided through the active layer.

[0010] This makes it possible to confine the perpendicular transverse mode perpendicular to the waveguide direction (resonator direction) of the guided light in the transparent conductive layer while suppressing the thickening of the second conductive type semiconductor layer. In addition, it is not necessary to provide a contact layer on the transparent conductive layer for contacting the electrode, and the resistance of the current injected into the active layer via the transparent conductive layer can be reduced. This makes it possible to reduce heat generation in the semiconductor light emitting element, reduce optical loss during optical propagation, and improve slope efficiency.

[0011] In addition, in the semiconductor light emitting device according to one aspect of the present invention, the confinement layer is used as at least one of a guide layer and a cladding layer on the active layer.

[0012] This makes it possible to confine the perpendicular transverse mode during light propagation while locating the diffraction grating close to the active layer, thereby improving the light emission efficiency and stabilizing the oscillation wavelength.

[0013] Furthermore, in a semiconductor light-emitting element according to one aspect of the present invention, the diffraction grating includes a resistive layer that is located in a portion of the second conductive type semiconductor layer and has a smaller refractive index and a larger resistance than the second conductive type semiconductor layer.

[0014] This allows the current injected into the active layer to be confined by the resistive layer while providing a DFB structure on the active layer, and also allows the refractive index difference between the second conductive type semiconductor layer and the diffraction grating to be increased while suppressing an increase in crystal defects in the second conductive type semiconductor layer. This allows the current to be efficiently injected into the light emitting region while confining the horizontal transverse mode in the horizontal direction to the light propagation direction. Furthermore, the coupling coefficient between the guided light and the diffraction grating can be increased. This allows the heat generation of the semiconductor light emitting device to be reduced, the output of the semiconductor light emitting device to be increased, and the oscillation wavelength to be stabilized.

[0015] In the semiconductor light emitting device according to one aspect of the present invention, the diffraction grating is located on both sides of the waveguide layer.

[0016] This makes it possible to ensure a refractive index difference between the second conductive type semiconductor layer and the diffraction grating. Also, it becomes possible to laterally confine the guided light that is guided through the active layer and place the diffraction grating close to the active layer. This makes it possible to increase the coupling coefficient between the guided light and the diffraction grating while ensuring the reliability of the semiconductor light emitting element, and to stabilize the oscillation wavelength.

[0017] Furthermore, in a semiconductor light-emitting device according to one aspect of the present invention, the resistive layer includes a first resistive layer in which the diffraction grating is formed on both sides of a first opening in which the waveguide layer is embedded, and a second resistive layer stacked on the first resistive layer and in which a second opening in which the waveguide layer is embedded is formed.

[0018] This allows the diffraction grating to be located close to the active layer while laterally confining the guided light guided through the active layer, and also allows the current injected into the active layer to be constricted while ensuring the refractive index difference between the second conductive type semiconductor layer and the diffraction grating while suppressing the increase in crystal defects in the second conductive type semiconductor layer. Therefore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating while ensuring the reliability of the semiconductor light emitting device, and it is possible to reduce the threshold current of the semiconductor light emitting device while suppressing heat generation of the semiconductor light emitting device. As a result, it is possible to increase the output of the semiconductor light emitting device while suppressing deterioration of the characteristics of the semiconductor light emitting device, and it is possible to stabilize the oscillation wavelength.

[0019] In addition, in a semiconductor light emitting device according to one aspect of the present invention, the diffraction grating is set back from an end face of the active layer by a distance equal to or greater than the period of the diffraction grating.

[0020] This makes it possible to provide a current non-injection region in the vicinity of the end face of the active layer, thereby making it possible to suppress heat generation at the end face of the active layer and protect the end face of the active layer.

[0021] In addition, in the semiconductor light emitting device according to one aspect of the present invention, the diffraction grating includes a phase shift portion.

[0022] This makes it possible to improve the SMSR (Side Mode Suppression Ratio) of the diffraction grating while dealing with the variation in characteristics depending on the cleavage position, and thus improve the light emission efficiency of a desired oscillation wavelength.

[0023] In addition, in a semiconductor light emitting device according to one aspect of the present invention, the length of the phase shift portion is expressed by N being a positive integer, and the effective refractive index of the diffraction grating is expressed by n eff , where λ is the Bragg wavelength, λ / (4·n eff )·(2N-1) relationship is satisfied.

[0024] This allows the phase shift sections to be arranged at positions where the centers of the peaks, valleys, or peaks of the standing waves formed by the diffraction grating coincide with each other, thereby improving the SMSR.

[0025] In addition, in a semiconductor light emitting device according to one aspect of the present invention, the center of the phase shift portion is located at a distance between 60% and 80% of the distance from the end face with a lower reflectance to the end face of the active layer.

[0026] As a result, even when the reflectivities of the two end faces used in the resonator are different from each other, it is possible to improve the SMSR while lowering the threshold, and to stabilize the oscillation wavelength while improving the output.

[0027] Furthermore, in the semiconductor light emitting device according to one aspect of the present invention, the condition 1≦κ·L≦3 is satisfied, where κ is a coupling coefficient of the diffraction grating and L is a cavity length.

[0028] This makes it possible to lower the threshold voltage and increase the efficiency of the semiconductor light emitting device, while stabilizing the oscillation wavelength.

[0029] In the semiconductor light emitting device according to one aspect of the present invention, the reflectance of the first end facet of the active layer is set to 2% or less, and the reflectance of the second end facet of the active layer is set to 90% or more.

[0030] This makes it possible to reduce the variation in characteristics of the semiconductor light emitting element while suppressing the decrease in light emitting efficiency.

[0031] In addition, in the semiconductor light emitting device according to one aspect of the present invention, the waveguide layer is made of GaN, and the diffraction grating is made of AlN.

[0032] This makes it possible to realize a blue-violet laser diode, and to ensure the refractive index difference between the second conductive type semiconductor layer and the diffraction grating while suppressing the increase in crystal defects in the second conductive type semiconductor layer. In addition, it is possible to constrict the current injected into the active layer while suppressing the increase in thermal resistance, and to suppress heat generation in the semiconductor light emitting element. Furthermore, it is possible to laterally confine the guided light that is guided through the active layer, and it is possible to stabilize the oscillation wavelength while increasing the output of the semiconductor light emitting element.

[0033] In addition, in a semiconductor light emitting device according to an aspect of the present invention, the diffraction grating includes a plurality of high-order diffraction gratings having a greatest common divisor of 1 and different orders.

[0034] This allows the period of the diffraction grating to be increased while matching the diffraction condition of the diffraction grating with the guide direction of the guided light in the active layer. This makes it possible to stabilize the oscillation wavelength while suppressing the decrease in oscillation efficiency. Furthermore, it is possible to realize a blue-violet laser diode with a stable oscillation wavelength while mitigating the manufacturing difficulties associated with miniaturizing the diffraction grating.

[0035] In addition, in a semiconductor light-emitting element according to one aspect of the present invention, the multiple high-order diffraction gratings have an area in which at least one of the centers of the convex portions and the centers of the concave portions and the centers of the convex portions and the concave portions coincide.

[0036] This increases the difference in energy density of the electric field of the standing wave formed by the high-order diffraction grating, and increases the stop band width, which in turn increases the SMSR of the high-order diffraction grating and the coupling coefficient between the guided light and the high-order diffraction grating.

[0037] In addition, in the semiconductor light emitting device according to one aspect of the present invention, the duties of the multiple high-order diffraction gratings are different from one another.

[0038] By optimizing the concavo-convex pattern of the high-order diffraction grating, the coupling coefficient between the guided light and the high-order diffraction grating can be maximized. Also, the number of steps in the manufacturing process of the semiconductor light emitting device can be reduced while stabilizing the oscillation wavelength.

[0039] In addition, in the semiconductor light emitting device according to one aspect of the present invention, the multiple high-order diffraction gratings are arranged so that the coupling coefficients are equal to each other.

[0040] As a result, even when a plurality of high-order diffraction gratings are used in forming a DFB structure, it is possible to suppress a decrease in the coupling coefficient between the guided light and the high-order diffraction grating.

[0041] Furthermore, a method for manufacturing a semiconductor light-emitting element according to one aspect of the present invention includes the steps of sequentially stacking an active layer and a second conductivity type semiconductor layer on a first conductivity type semiconductor layer, forming irregularities in the second conductivity type semiconductor layer, stacking a resistive layer having a smaller refractive index and a larger resistance than the second conductivity type semiconductor layer on the second conductivity type semiconductor layer so as to cover the irregularities, thereby forming a diffraction grating fitted into the irregularities, forming an opening in the resistive layer in which the diffraction grating is formed, and regrowing the second conductivity type semiconductor layer so as to fill the openings.

[0042] This makes it possible to laterally confine the guided light guided through the active layer based on the formation of the resistive layer once, and to place the diffraction grating close to the active layer. Furthermore, it is possible to improve the confinement of the current injected into the active layer while ensuring the refractive index difference between the second conductive type semiconductor layer and the diffraction grating. Therefore, it is possible to suppress the increase in crystal defects in the second conductive type semiconductor layer while suppressing the complication of the manufacturing process. Furthermore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating, and it is possible to reduce the threshold current of the semiconductor light emitting element while suppressing heat generation from the semiconductor light emitting element. As a result, it is possible to stabilize the oscillation wavelength, and it is possible to increase the output while ensuring the reliability of the semiconductor light emitting element.

[0043] Furthermore, a method for manufacturing a semiconductor light-emitting element according to one embodiment of the present invention includes the steps of sequentially stacking an active layer, a second conductivity type semiconductor layer, and a resistive layer having a higher resistance than the second conductivity type semiconductor layer on the first conductivity type semiconductor layer, forming an opening in the resistive layer with a diffraction grating on both sides, and re-growing the second conductivity type semiconductor layer so that the diffraction grating and the opening are embedded.

[0044] This makes it possible to form a waveguide layer that laterally confines the guided light in the active layer at the opening and simultaneously form a diffraction grating on both sides of the waveguide layer. Also, it is possible to increase the refractive index difference between the second conductive type semiconductor layer and the diffraction grating while suppressing an increase in crystal defects in the second conductive type semiconductor layer. Therefore, it is possible to stably form an inner stripe type semiconductor laser having a DFB structure while suppressing an increase in the number of steps. Effect of the Invention

[0045] In one aspect of the present invention, the coupling coefficient between the guided light and the diffraction grating can be increased. [Brief description of the drawings]

[0046] [Figure 1] 1 is a perspective view illustrating a configuration of a semiconductor light emitting device according to a first embodiment. [Diagram 2] FIG. 1A is a plan view showing the configuration of a resistive layer of a semiconductor light-emitting element according to a first embodiment; FIG. 1B is a cross-sectional view showing the configuration of the semiconductor light-emitting element according to the first embodiment cut along a horizontal direction of the waveguiding direction; and FIG. 1C is a diagram showing the refractive index of each layer of the semiconductor light-emitting element according to the first embodiment. [Diagram 3] 1A is a cross-sectional view showing the configuration of a semiconductor light-emitting element according to a comparative example taken along a lateral direction of the waveguide direction, and FIG. 1B is a cross-sectional view showing the configuration of a semiconductor light-emitting element according to a comparative example taken along the waveguide direction. [Figure 4] 4 is a diagram showing the relationship between the height of the diffraction grating and the coupling coefficient of the semiconductor light emitting device according to the first embodiment in comparison with a semiconductor light emitting device of a comparative example. FIG. [Diagram 5] FIG. 1(a) is a plan view showing the configuration of a resistive layer of a semiconductor light-emitting element according to a second embodiment; FIG. 1(b) is a cross-sectional view showing the configuration of the semiconductor light-emitting element according to the second embodiment cut along the horizontal direction of the waveguiding direction; and FIG. 1(c) is a diagram showing the refractive index of each layer of the semiconductor light-emitting element according to the second embodiment. [Figure 6] 10(a1) and (b1) are plan views showing an example of a manufacturing method of a semiconductor light-emitting element according to a third embodiment, (a2) is a cross-sectional view cut along the waveguide direction of (a1), and (b2) is a cross-sectional view cut along the waveguide direction of (b1). [Figure 7] FIG. 11(a1) is a plan view showing an example of a manufacturing method for a semiconductor light-emitting element according to a third embodiment, FIG. 11(a2) is a cross-sectional view taken along the waveguiding direction at the position of the diffraction grating in FIG. 11(a1), and FIG. 11(a3) is a cross-sectional view taken along the waveguiding direction at the position of the waveguide in FIG. [Figure 8] FIG. 11(a1) is a plan view showing an example of a manufacturing method for a semiconductor light-emitting element according to a third embodiment, FIG. 11(a2) is a cross-sectional view taken along the waveguiding direction at the position of the diffraction grating in FIG. 11(a1), and FIG. 11(a3) is a cross-sectional view taken along the waveguiding direction at the position of the waveguide in FIG. [Figure 9A] FIG. 11 is a perspective view showing a configuration of a semiconductor light emitting device according to a fourth embodiment. [Figure 9B]10A is a plan view showing the configuration of a semiconductor light emitting device according to a fourth embodiment, and FIG. 10B is a cross-sectional view taken along the line X1-X1 in FIG. [Figure 10] 11(a1) and (b1) are plan views showing an example of a manufacturing method of a semiconductor light-emitting element according to a fifth embodiment, (a2) is a cross-sectional view cut along the waveguide direction of (a1), and (b2) is a cross-sectional view cut along the waveguide direction of (b1). [Figure 11] 11(a1) and (b1) are plan views showing an example of a manufacturing method of a semiconductor light-emitting element according to a fifth embodiment, (a2) is a cross-sectional view cut along the waveguide direction of (a1), and (b2) is a cross-sectional view cut along the waveguide direction of (b1). [Figure 12] FIG. 11(a1) is a plan view showing an example of a manufacturing method of a semiconductor light-emitting element according to a fifth embodiment, FIG. 11(a2) is a cross-sectional view taken along the waveguiding direction at the position of the diffraction grating in FIG. 11(a1), and FIG. 11(a3) is a cross-sectional view taken along the waveguiding direction at the position of the waveguide in FIG. [Figure 13] FIG. 11(a1) is a plan view showing an example of a manufacturing method of a semiconductor light-emitting element according to a fifth embodiment, FIG. 11(a2) is a cross-sectional view taken along the waveguiding direction at the position of the diffraction grating in FIG. 11(a1), and FIG. 11(a3) is a cross-sectional view taken along the waveguiding direction at the position of the waveguide in FIG. [Figure 14] 13(a) is a plan view showing the configuration of a resistive layer of a semiconductor light-emitting element according to a sixth embodiment, and (b) is a cross-sectional view showing the configuration of the semiconductor light-emitting element according to the sixth embodiment cut along a horizontal direction of the waveguide direction. [Figure 15] FIG. 13 is a plan view showing a configuration of a resistive layer of the semiconductor light emitting device according to the seventh embodiment. [Figure 16] 13 is a cross-sectional view of the configuration of the semiconductor light emitting device according to the seventh embodiment, taken along the waveguiding direction at the position of the second-order diffraction grating. FIG. [Figure 17] 16(a) and (b) are diagrams showing the refractive index distribution of the diffraction grating in FIG. 15, and (c) and (d) are diagrams showing the relationship between the phase and energy of a standing wave formed in the waveguide in FIG. 15. [Figure 18]FIG. 16 is a relationship diagram between the refractive index and the position in the waveguiding direction, showing as examples the second-order diffraction grating and the third-order diffraction grating shown in FIG. 15, as parameters that can be adjusted when changing the relative positional relationship between a plurality of diffraction gratings. [Figure 19A] FIG. 13 is a diagram showing the relationship between the grating shift and the stop band width when the duty of the diffraction grating of the semiconductor light emitting device according to the seventh embodiment is changed. [Figure 19B] 13A to 13C are diagrams illustrating a method for maximizing the stop band width of the semiconductor light emitting device according to the seventh embodiment. [Figure 20] 13 is a plan view showing a configuration of a resistive layer of the semiconductor light emitting device according to the eighth embodiment. FIG. [Figure 21] 13(a) and (b) are diagrams showing the refractive index distribution of a diffraction grating of a semiconductor light-emitting element according to the ninth embodiment, and (c) and (d) are diagrams showing the relationship between the phase and energy of a standing wave formed in a waveguide of the semiconductor light-emitting element according to the ninth embodiment. [Figure 22] FIG. 13 is a diagram showing the relationship between the grating shift and the stop band width when the duty of the diffraction grating of the semiconductor light emitting device according to the ninth embodiment is changed. [Diagram 23] FIG. 23 is a plan view showing the configuration of a resistive layer of the semiconductor light emitting device according to the tenth embodiment. [Figure 24] FIG. 13 is a diagram showing the relationship between the height of a diffraction grating and a coupling coefficient. [Diagram 25] FIG. 11(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to an eleventh embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). [Figure 26] FIG. 11(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to an eleventh embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). [Figure 27] FIG. 11(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to an eleventh embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). [Figure 28] FIG. 11(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to an eleventh embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). [Figure 29]FIG. 11(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to an eleventh embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). [Diagram 30] FIG. 23(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to a twelfth embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). [Diagram 31] FIG. 23(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to a twelfth embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). [Diagram 32] FIG. 23(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to a twelfth embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). [Diagram 33] FIG. 23(a) is a plan view showing a method for manufacturing a semiconductor light emitting device according to a twelfth embodiment, and (b) is a cross-sectional view taken along the waveguide direction of (a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the present invention, and not all of the combinations of features described in the embodiments are necessarily essential to the configuration of the present invention. The configuration of the embodiments may be appropriately modified or changed depending on the specifications of the device to which the present invention is applied and various conditions (conditions of use, environment of use, etc.). The technical scope of the present invention is determined by the claims, and is not limited by the individual embodiments below. Also, the drawings used in the following description may differ in scale and shape from the actual structure in order to make each configuration easier to understand.

[0048] In addition, in the following description, a nitride semiconductor laser capable of emitting blue laser light in the 444 nm wavelength band will be taken as an example, but it may be an AlGaInN semiconductor laser capable of emitting blue laser light in the 405 nm wavelength band, or an AlGaN semiconductor laser capable of emitting near-ultraviolet laser light with an emission wavelength of 390 nm or less.

[0049] FIG. 1 is a perspective view showing the configuration of the semiconductor light emitting device according to the first embodiment, FIG. 2(a) is a plan view showing the configuration of the resistance layer of the semiconductor light emitting device according to the first embodiment, FIG. 2(b) is a cross-sectional view showing the configuration of the semiconductor light emitting device according to the first embodiment cut along the lateral direction of the waveguiding direction, and FIG. 2(c) is a diagram showing the refractive index of each layer of the semiconductor light emitting device according to the first embodiment. Note that FIG. 2(b) shows the configuration cut at the position of the X1-X1 line in FIG. 2(a). Also, from the viewpoint of ease of understanding, the end face reflective film in FIG. 2(a) and the electrode in FIG. 2(b) are omitted in FIG. 1.

[0050] 1, 2(a) and 2(b), the semiconductor laser LA includes an n-type nitride semiconductor layer E1, an active layer 15, a p-type nitride semiconductor layer E2, a resistive layer RA and a confinement layer E3. The active layer 15 is stacked on the n-type nitride semiconductor layer E1. The p-type nitride semiconductor layer E2 is stacked on the active layer 15. The nitride semiconductor is, for example, In x Al y Ga 1-x-y N (0≦x≦1, 0≦y≦1, 0≦x+y≦1).

[0051] In order to suppress diffusion of impurities from the n-type nitride semiconductor layer E1 to the active layer 15, an undoped nitride guide layer 14 may be provided between the n-type nitride semiconductor layer E1 and the active layer 15. In order to suppress diffusion of impurities from the p-type nitride semiconductor layer E2 to the active layer 15, an undoped nitride guide layer 16 may be provided between the p-type nitride semiconductor layer E2 and the active layer 15.

[0052] The n-type nitride semiconductor layer E1 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 stacked on the n-type nitride semiconductor substrate 11 in this order.

[0053] The p-type nitride semiconductor layer E2 includes a p-type carrier block layer 17 and p-type nitride guide layers 18, 18A. The p-type carrier block layer 17 and the p-type nitride guide layers 18, 18A are sequentially stacked on the undoped nitride guide layer 16. The p-type nitride guide layers 18, 18A can be made of the same material. The p-type nitride semiconductor layer E2 includes a waveguide layer WA. The waveguide layer WA guides the guided light while confining the guided light in a lateral direction D2 of the guide direction D1 of the guided light guided through the active layer 15. The waveguide layer WA can be made of the p-type nitride guide layer 18A on the p-type nitride guide layer 18.

[0054] The resistive layer RA is located in a part of the p-type nitride semiconductor layer E2. The position of the resistive layer RA in the p-type nitride semiconductor layer E2 in the vertical direction D3 of the waveguiding direction D1 is not particularly limited. For example, the position of the top surface of the resistive layer RA may be equal to the position of the top surface of the p-type nitride guide layer 18, or may be lower than the position of the top surface of the p-type nitride guide layer 18. The position of the bottom surface of the resistive layer RA may be equal to the position of the bottom surface of the p-type nitride guide layer 18, or may be higher than the position of the bottom surface of the p-type nitride guide layer 18.

[0055] The resistive layer RA has a smaller refractive index and a larger resistance than the p-type nitride semiconductor layer E2. The resistive layer RA can configure at least one of a refractive index guided type and a gain guided type Fabry-Perot resonator, and can be disposed in a part of the p-type nitride semiconductor layer E2 so as to have a DFB structure. The resistive layer RA can be, for example, a high-resistance layer made of AlN.

[0056] The resistive layer RA includes an opening KA and a diffraction grating EA. The pitch Λ1 of the diffraction grating EA can be matched to the oscillation period of the laser light guided through the waveguide layer WA. The diffraction grating EA is located on both sides of the waveguide layer WA. At this time, unevenness is formed on both sides of the waveguide layer WA, and the unevenness of the diffraction grating EA can be fitted into the unevenness on both sides of the waveguide layer WA. At this time, by embedding the p-type nitride guide layer 18A in the recesses and the opening KA of the diffraction grating EA, the waveguide layer WA can be formed in the p-type nitride semiconductor layer E2 while increasing the refractive index difference between the projections and recesses of the diffraction grating EA.

[0057] The opening KA and the diffraction grating EA are recessed from the end faces MA, MB of the active layer 15. The diffraction grating EA can be recessed from the end faces MA, MB of the active layer 15 by a distance equal to or greater than the period of the diffraction grating EA. Here, by recessing the opening KA and the diffraction grating EA from the end faces MA, MB of the active layer 15, a non-current injection region NJ can be provided in the vicinity of the end faces MA, MB of the active layer 15. This makes it possible to suppress heat generation at the end faces MA, MB of the active layer 15 and protect the end faces MA, MB of the active layer 15.

[0058] If the coupling coefficient of the diffraction grating EA is κ and the cavity length of the semiconductor laser LA is L, it is preferable to satisfy the condition 1≦κ·L≦3. This makes it possible to stabilize the oscillation wavelength while lowering the threshold value and increasing the efficiency of the semiconductor laser LA.

[0059] The confinement layer E3 is provided on the p-type nitride semiconductor layer E2. In this case, the confinement layer E3 can be located on the diffraction grating EA and the waveguide layer WA. The confinement layer E3 has a lower refractive index than the p-type nitride semiconductor layer E2. In this case, the confinement layer E3 can confine the guided light guided through the active layer 15 in the vertical direction E3. The confinement layer E3 can include, for example, a p-type nitride cladding layer 20.

[0060] A p-type nitride contact layer 21 is laminated on the p-type nitride cladding layer 20. The p-type nitride contact layer 21 can make ohmic contact with an electrode 22 that injects a current into the active layer 15.

[0061] An electrode 22 for injecting a current into the active layer 15 through the opening KA is formed on the p-type nitride contact layer 21. The electrode 22 may have a layered structure of Ti / Pt / Au. The thicknesses of the Ti / Pt / Au layers may be set to, for example, 100 / 50 / 300 nm.

[0062] Examples of materials that can be used for each layer include the following: an n-type GaN substrate as the n-type nitride semiconductor substrate 11, an n-type Al as the n-type nitride cladding layer 12, and an n-type GaN substrate as the n-type nitride cladding layer 13. 0.02 Ga 0.98 The n-type nitride guide layer 13 is an n-type GaN layer, and the undoped nitride guide layer 14 is an In 0.02 Ga 0.99 The active layer 15 includes an InN layer. 0.02 Ga 0.98 N barrier layer / In 0.15 Ga 0.88 N well layer / In 0.02 Ga 0.98 A single quantum well layer made of an InN barrier layer can be used for the undoped nitride guide layer 16. 0.02 Ga 0.99 The N layer and the p-type carrier block layer 17 are made of p-type Al 0.22 Ga 0.78 The N layer, the p-type nitride guide layer 18, 18A, the p-type GaN layer, the p-type nitride cladding layer 20, and the p-type nitride contact layer 21 are p-type Al 0.02 Ga 0.98 An N-type layer and a p-type GaN layer can be used, respectively.

[0063] The thickness of the n-type nitride cladding layer 12 is, for example, 700 nm, and the donor concentration N D is 1 x 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 ND is 1 x 10 17 cm -3 The thickness of the undoped nitride guide layer 14 can be set to, for example, 136 nm. The thicknesses of the barrier layer / well layer / barrier layer of the quantum well layer of the active layer 15 can be set to, for example, 10 / 9 / 10 nm. The thickness of the undoped nitride guide layer 16 can be set to, for example, 135 nm. The thickness of the p-type carrier block layer 17 can be set to, for example, 4 nm, and the acceptor concentration N A is 1 x 10 18 cm -3 The total thickness of the p-type nitride guide layers 18 and 18A can be set to, for example, 150 nm, and the acceptor concentration N A is 1 x 10 18 cm -3 The thickness of the p-type nitride cladding layer 20 can be set to, for example, 700 nm, and the acceptor concentration N A is 1 x 10 18 cm -3 The thickness of the p-type nitride contact layer 21 can be set to, for example, 60 nm, and the acceptor concentration N A is 1 x 10 18 cm -3 can be set to.

[0064] 2(c), the refractive index of the n-type nitride cladding layer 12 is smaller than the refractive index of the n-type nitride guide layer 13. In addition, the refractive index of the n-type nitride guide layer 13 is smaller than the refractive index of the undoped nitride guide layer 14, which can be smaller than the refractive index of the active layer 15. The refractive index of the p-type nitride contact layer 21 is greater than that of the p-type nitride cladding layer 20. The refractive index of the p-type nitride cladding layer 20 is smaller than that of the p-type nitride guide layer 18, which is smaller than that of the undoped nitride guide layer 16. The refractive index of the undoped nitride guide layer 16 can be smaller than that of the active layer 15. The refractive index of the p-type carrier block layer 17 can be smaller than that of the p-type nitride guide layer 18.

[0065] As shown in Fig. 2(a), end face reflective films 24, 25 are formed on the end faces MA, MB of the semiconductor laser LA. In this case, it is preferable to set the reflectance of the end face MA to 2% or less, and the reflectance of the end face MB to 90% or more. This makes it possible to reduce the variation in the characteristics of the semiconductor laser LA while suppressing the decrease in the light emission efficiency of the semiconductor laser LA.

[0066] In this case, the end face reflection film 24 can be a laminated structure of AlN / SiO2. Here, the thickness of AlN / SiO2 can be set to, for example, 30 / 300 nm. The end face reflection film 25 can be an AlN / (SiO2 / Ta2O5) 6 / SiO2 laminate structure. Here, AlN / (SiO2 / Ta2O5) 6 / SiO2 thickness is, for example, 30 / (60 / 40) 6 / 10nm.

[0067] Moreover, by providing the opening KA and the diffraction grating EA in the resistive layer RA under the p-type nitride cladding layer 20, it is possible to provide the diffraction grating EA on both sides of the waveguide layer WA. Therefore, it is possible to confine the guided light guided in the active layer 15 in the horizontal direction D2 and the vertical direction D3. It is also possible to arrange the diffraction grating EA close to the active layer 15, and to increase the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating EA while suppressing an increase in crystal defects in the p-type nitride guide layer 18A. Therefore, it is possible to improve the light emission efficiency of the semiconductor laser LA and increase the output of the semiconductor laser LA. Furthermore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating EA while suppressing a decrease in the reliability of the semiconductor laser LA, and to stabilize the oscillation wavelength.

[0068] Moreover, by forming the waveguide layer WA from GaN and the resistive layer RA from AlN, it is possible to suppress the decrease in the thermal conductivity of the resistive layer RA while suppressing the deviation between the lattice constant of the resistive layer RA and the lattice constant of the waveguide layer WA. In addition, it is possible to secure the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating EA while constricting the current injected into the active layer 15. Therefore, it is possible to realize a blue-violet laser diode with a stable oscillation wavelength while suppressing the decrease in the heat dissipation from the active layer 15. Furthermore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating EA while suppressing the increase in crystal defects in the p-type nitride guide layer 18A. As a result, it is possible to increase the light emission efficiency while suppressing the heat generation of the semiconductor laser LA, and it is possible to increase the output of the semiconductor laser LA, and it is possible to stabilize the oscillation wavelength while suppressing the decrease in the reliability of the semiconductor laser LA.

[0069] For example, if the waveguide layer WA is made of GaN and the resistive layer RA is made of AlN, the refractive index of the waveguide layer WA is 2.49 and the refractive index of the resistive layer RA is 2.18 at a laser oscillation wavelength of 444 nm. By using such materials, the stop band width of the diffraction grating EA can be expanded and the SMSR can be increased. Specifically, an SMSR of about 30 to 40 dB can be ensured. In contrast, if the diffraction grating is made of an AlInGaN-based semiconductor with a high concentration of Al or In, the stop band width of the diffraction grating is about 0.23 nm and the SMSR is only about 10 dB.

[0070] FIG. 3(a) is a cross-sectional view showing the configuration of a semiconductor light-emitting element according to a comparative example cut along the horizontal direction of the waveguide direction, and FIG. 3(b) is a cross-sectional view showing the configuration of a semiconductor light-emitting element according to a comparative example cut along the waveguide direction. 3(a) and 3(b), the semiconductor laser LA' has a ridge RA and a diffraction grating EA' instead of the resistive layer RA, the opening KA, and the diffraction grating EA of the semiconductor laser LA in Fig. 2(b). The other components of the semiconductor laser LA' can be configured in the same way as the semiconductor laser LA.

[0071] The diffraction grating EA' in this comparative example is located below the active layer 15. In this case, the diffraction grating EA' can be formed in the n-type nitride cladding layer 12A on the n-type nitride cladding layer 12. The n-type nitride cladding layers 12 and 12A can be integrally formed of the same material. The diffraction grating EA' can be covered with the n-type nitride guide layer 13.

[0072] When forming a diffraction grating EA', for example, an n-type Al 0.02 Ga 0.98 On the surface of the N layer, a pattern with a period (pitch: Λ) of 89.2 nm and a duty of 0.5 is formed using photolithography and etching techniques, and an n-type GaN layer is then regrown on top of the pattern. The duty is the ratio of the width of the convex portion to the width of one period of the diffraction grating.

[0073] A p-type nitride cladding layer 20A is formed on the p-type nitride cladding layer 20. The p-type nitride cladding layers 20 and 20A can be made of the same material. The p-type nitride cladding layer 20A includes a ridge RA. The ridge RA is provided across the end faces of the semiconductor laser LA' along the guiding direction D1 of the guided light guided through the active layer 15. At this time, the ridge RA can confine the guided light guided through the active layer 15 in the lateral direction D2 and the vertical direction D3 of the guiding direction D1. In this configuration, the p-type nitride contact layer 21 is formed on the top surface of the ridge RA.

[0074] 4 is a diagram showing the relationship between the height of the diffraction grating and the coupling coefficient of the semiconductor light emitting device according to the first embodiment in comparison with a semiconductor light emitting device of a comparative example. Note that H1 shows the relationship between the height of the diffraction grating and the coupling coefficient in the configuration of FIG. 2(b), and H2 shows the relationship between the height of the diffraction grating and the coupling coefficient in the configuration of FIG. 3.

[0075] In Fig. 4, the coupling coefficients of the comparative example in Fig. 3 and the configuration in Fig. 2(b) were compared in the case of a rectangular diffraction grating using a method similar to that described in the literature (IEEE J. Quantum Electron. QE-11, p867, 1975). According to this literature, for example, in the case of the TE mode, the coupling coefficient κ is given by the following equation:

[0076]

number

[0077]

number

[0078]

number

[0079] where β is the propagation constant. In the configuration of Fig. 2(b) and the comparative example of Fig. 3, when the heights of the diffraction gratings EA and EA' are equal, the configuration of Fig. 2(b) has a larger coupling coefficient than the comparative example of Fig. 3. As a result, in the configuration of Fig. 2(b), the stop band width can be made larger, making it easier to obtain a larger side mode suppression ratio (SMSR). Also, in the configuration of Fig. 2(b), when the height of the diffraction grating EA is 100 nm, κ·L is ~1.4.

[0080] The refractive indices used in the estimation by the method described in the above-mentioned document were n1=2.48, n2=2.49, and n3=2.48 in the comparative example of Fig. 3, and n1=2.18, n2=2.49, and n3=2.48 in the configuration of Fig. 2(b). In addition, the variables common to the configuration of Fig. 2(b) and the comparative example of Fig. 3 were t=3 μm, λ0=444 nm, and duty=0.4.

[0081] This semiconductor laser LA can be used as a light source that generates 222 nm SHG (Second Harmonic Generation) waves. 222 nm ultraviolet light is safer for humans than 254 nm ultraviolet light, which is used for sterilization, and can prevent the onset of skin cancer and keratitis.

[0082] Fig. 5(a) is a plan view showing the configuration of a resistive layer of a semiconductor light emitting device according to a second embodiment, Fig. 5(b) is a cross-sectional view showing the configuration of the semiconductor light emitting device according to the second embodiment cut along the lateral direction of the waveguiding direction, and Fig. 5(c) is a diagram showing the refractive indexes of each layer of the semiconductor light emitting device according to the second embodiment. Note that Fig. 5(b) shows the configuration cut along the line X1-X1 in Fig. 5(a).

[0083] 5(a) and 5(b), the semiconductor laser LB has a transparent conductive layer 23 instead of the p-type nitride cladding layer 20 and the p-type nitride contact layer 21 of the semiconductor laser LA of Fig. 2(b). Other than that, the semiconductor laser LB can be configured in the same way as the semiconductor laser LA of Fig. 2(b).

[0084] The transparent conductive layer 23 is a conductive layer transparent to the light generated in the active layer 15. The transparent conductive layer 23 is used as at least one of the guide layer and the cladding layer on the active layer 15. The transparent conductive layer 23 may contain at least one element selected from In, Sn, Zn, Ti, Nb, and Zr, and may be an oxide of these elements. For example, the transparent conductive layer 23 may be an ITO film, a ZnO film, an SnO film, or a TiO film. Here, as shown in FIG. 5(c), the refractive index of the transparent conductive layer 23 may be smaller than the refractive index of the p-type nitride guide layer 18. The transparent conductive layer 23 is preferably thinned within a range in which light can be confined in the perpendicular transverse mode. The perpendicular transverse mode is a propagation mode in the longitudinal direction D3 of the waveguiding direction D1. At this time, the thickness of the transparent conductive layer 23 is preferably 80 nm or more and 120 nm or less. An electrode 21 is formed on the transparent conductive layer 23. The transparent conductive layer 23 can make direct ohmic contact with the electrode 21 .

[0085] Here, by making the refractive index of the transparent conductive layer 23 smaller than that of the p-type nitride guide layer 18, it becomes possible to confine the vertical transverse mode in the transparent conductive layer 23 while suppressing the thickening of the p-type nitride semiconductor layer E2. Furthermore, by stacking the transparent conductive layer 23 on the p-type nitride semiconductor layer E2, it becomes unnecessary to provide a p-type nitride semiconductor contact layer on the transparent conductive layer 23 for contacting the electrode 22, and it is possible to reduce the resistance of the current injected into the active layer 15 via the transparent conductive layer 23. Therefore, it becomes possible to reduce the heat generation of the semiconductor laser LB, reduce the optical loss during optical propagation, and improve the slope efficiency.

[0086] Figures 6(a1), 6(b1), 7(a1), and 8(a1) are plan views showing an example of a method for manufacturing a semiconductor light-emitting device according to the third embodiment. Also, Figures 6(a2) and 6(b2) are cross-sectional views cut along the waveguiding direction of Figures 6(a1) and 6(b1), respectively. Also, Figures 7(a2) and 8(a2) are cross-sectional views cut along the waveguiding direction at the position of the diffraction grating of Figures 7(a1) and 8(a1), respectively. Also, Figures 7(a3) and 8(a3) are cross-sectional views cut along the waveguiding direction at the position of the waveguide of Figures 7(a1) and 8(a1), respectively. Note that Figures 6(a2), 6(b2), 7(a2) and 8(a2) show configurations cut along line A1-A1 in Figures 6(a1), 6(b1), 7(a1) and 8(a1), respectively, and Figures 7(a3) and 8(a3) show configurations cut along line B1-B1 in Figures 7(a1) and 8(a1), respectively.

[0087] This third embodiment can be applied to the manufacture of the semiconductor laser LA of Fig. 2(b). Note that in Fig. 6(a2), Fig. 6(b2), Fig. 7(a2), Fig. 7(a3), Fig. 8(a2) and Fig. 8(a3), the n-type nitride semiconductor substrate 11, the n-type nitride cladding layer 12, the n-type nitride guide layer 13 and the undoped nitride guide layer 14 of Fig. 2(b) are omitted.

[0088] 6(a1) and 6(a2), 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 nitride guide layer 18 are sequentially laminated on an n-type nitride semiconductor substrate 11 by epitaxial growth. Furthermore, a resistive layer RA is laminated on the p-type nitride guide layer 18 by a method such as epitaxial growth or sputtering. The epitaxial growth may be MOCVD (Metal Organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), or HVPE (Hydride Vapor Phase Epitaxy).

[0089] Next, as shown in Fig. 6(b1) and Fig. 6(b2), the resistive layer RA is patterned based on photolithography and dry etching techniques to form an opening KA in the resistive layer RA, with a diffraction grating EA on both sides along the waveguide direction D1. At this time, the concave and convex portions of the diffraction grating EA can be arranged on both sides of the opening KA along the waveguide direction D1 with a period of the oscillation wavelength.

[0090] Next, as shown in Figures 7(a1), 7(a2) and 7(a3), a p-type nitride guide layer 18A is selectively formed on the p-type nitride guide layer 18 by epitaxial growth so as to be embedded in the opening KA. At this time, the p-type nitride guide layer 18A can be embedded in the recesses of the diffraction grating EA, and the refractive index difference between the recesses and protrusions of the diffraction grating EA can be determined by the refractive index of the resistive layer RA. In addition, a waveguide layer WA is formed in the opening KA, with the diffraction grating EA provided on both sides along the waveguiding direction D1.

[0091] Next, as shown in Figures 8(a1), 8(a2) and 8(a3), the p-type nitride cladding layer 20 and the p-type nitride contact layer 21 are successively formed by epitaxial growth on the p-type nitride guide layer 18A and the resistive layer RA.

[0092] 2(a) in the aperture KA, the diffraction grating EA can be formed on both sides of the waveguide layer WA at the same time, and the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating EA can be increased. Therefore, an inner stripe type semiconductor laser having a DFB structure can be stably formed while suppressing an increase in the number of steps.

[0093] FIG. 9A is a perspective view showing the configuration of a semiconductor light emitting device according to a fourth embodiment. 9A and 9B, the semiconductor laser LC has a p-type nitride semiconductor layer E2' instead of the p-type nitride semiconductor layer E2 of the semiconductor laser LA of Fig. 2(b). Other than that, the semiconductor laser LC can be configured in the same way as the semiconductor laser LA of Fig. 2(b).

[0094] As shown in FIG. 9A and FIG. 9B, the p-type nitride semiconductor layer E2′ includes a p-type carrier block layer 17 and p-type nitride guide layers 18, 18A, and 18A′. The p-type carrier block layer 17 and the p-type nitride guide layers 18, 18A, and 18A′ are sequentially stacked on the undoped nitride guide layer 16. The p-type nitride guide layers 18, 18A, and 18A′ can be made of the same material. The p-type nitride semiconductor layer E2′ includes waveguide layers WA and WA′. The waveguide layers WA and WA′ guide the guided light while confining the guided light in the lateral direction D2 of the guide direction D1 of the guided light guided through the active layer 15. The waveguide layer WA′ can be made of a p-type nitride guide layer 18A′ on the p-type nitride guide layer 18A.

[0095] The resistive layers RA, RA' are located in a part of the p-type nitride semiconductor layer E2'. The resistive layers RA, RA' may be made of the same material. The resistive layers RA, RA' may be integrated with each other. The positions of the resistive layers RA, RA' in the p-type nitride semiconductor layer E2' in the vertical direction D3 of the waveguide direction D1 are not particularly limited.

[0096] The resistive layers RA, RA' have a smaller refractive index and a larger resistance than the p-type nitride semiconductor layer E2'. The resistive layer RA' is laminated on the resistive layer RA. The resistive layers RA, RA' can form at least one of a refractive index guided type and a gain guided type Fabry-Perot resonator, and can be disposed in a part of the p-type nitride semiconductor layer E2' so as to have a DFB structure. The resistive layers RA, RA' can be, for example, high resistance layers made of AlN.

[0097] Moreover, by forming the waveguide layers WA, WA' from GaN and the resistive layers RA, RA' from AlN, it is possible to suppress the deviation between the lattice constant of the resistive layers RA, RA' and the lattice constant of the waveguide layers WA, WA' while suppressing the decrease in the thermal conductivity of the resistive layers RA, RA'. Furthermore, even if the diffraction grating EA is present, it is possible to ensure the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating EA while improving the confinement of the current injected into the active layer 15. Therefore, it is possible to realize a blue-violet laser diode while suppressing the heat generation of the semiconductor laser LC. In addition, it is possible to increase the coupling coefficient between the guided light and the diffraction grating EA while suppressing the increase in crystal defects of the p-type nitride guide layer 18A and the decrease in the heat dissipation from the active layer 15. As a result, it is possible to increase the light emission efficiency while suppressing the temperature rise of the semiconductor laser LC, and to increase the output of the semiconductor laser LC. As a result, it is possible to stabilize the oscillation wavelength while suppressing the decrease in the reliability of the semiconductor laser LC.

[0098] In the semiconductor laser LC of FIGS. 9A and 9B, an example is shown in which a waveguide layer WA' having no diffraction gratings on both sides is laminated on a waveguide layer WA having diffraction gratings EA on both sides, as in the case of the semiconductor laser LB shown in FIG. 5. However, a waveguide layer WA having diffraction gratings EA on both sides may be laminated on a waveguide layer WA' having no diffraction gratings on both sides.

[0099] 10(a1), 10(b1), 11(a1), 11(b1), 12(a1), and 13(a1) are plan views showing an example of a method for manufacturing a semiconductor light-emitting device according to the fifth embodiment. Also, FIG. 10(a2), FIG. 10(b2), FIG. 11(a2), and FIG. 11(b2) are cross-sectional views cut along the waveguiding direction of FIG. 6(a1) and FIG. 6(b1), respectively. Also, FIG. 12(a2) and FIG. 13(a2) are cross-sectional views cut along the waveguiding direction at the position of the diffraction grating of FIG. 12(a1) and FIG. 13(a1), respectively. Furthermore, FIG. 12(a3) and FIG. 13(a3) are cross-sectional views cut along the waveguiding direction at the position of the waveguide of FIG. 12(a1) and FIG. 13(a1), respectively. 10(a2), 10(b2), 11(a2), 12(a2) and 13(a2) show configurations cut along line A1-A1 in 10(a1), 10(b1), 11(a1), 12(a1) and 13(a1), respectively. Also, 11(b2), 12(a3) and 13(a3) show configurations cut along line B1-B1 in 11(b1), 12(a1) and 13(a1), respectively.

[0100] This fifth embodiment can be applied to the manufacture of the semiconductor laser LC of Fig. 9. Note that in Fig. 10(a2), Fig. 10(b2), Fig. 11(a2), Fig. 11(b2), Fig. 12(a2), Fig. 12(a3), Fig. 13(a2) and Fig. 13(a3), the n-type nitride semiconductor substrate 11, the n-type nitride cladding layer 12, the n-type nitride guide layer 13 and the undoped nitride guide layer 14 of Fig. 9 are omitted.

[0101] 10(a1) and 10(a2), 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 p-type nitride guide layers 18, 18A are sequentially stacked on an n-type nitride semiconductor substrate 11 by epitaxial growth.

[0102] Next, as shown in Figures 10(b1) and 10(b2), the p-type nitride guiding layer 18A is patterned based on photolithography and dry etching techniques to form convex portions QT and concave portions QB alternately in the p-type nitride guiding layer 18A at a period of the oscillation wavelength along the waveguide direction D1.

[0103] Next, as shown in Figures 11(a1) and 11(a2), resistive layers RA, RA' are formed in sequence on the p-type nitride guide layers 18, 18A by epitaxial growth or sputtering. The resistive layers RA, RA' can be formed collectively in a single film formation process. At this time, the resistive layer RA can be formed so as to fill the recessed portion QB of the p-type nitride guide layer 18A, and the resistive layer RA' can be formed so as to cover the protruding portion QT of the p-type nitride guide layer 18A and the resistive layer RA.

[0104] 11(b1) and 11(b2), the resistive layers RA, RA' are patterned by photolithography and dry etching to form openings KA, KA' in the resistive layers RA, RA' along the waveguide direction D1. At this time, the resistive layers RA, RA' are removed in the openings KA, KA', and the protrusions QT and recesses QB of the p-type nitride guide layer 18' are exposed from the resistive layers RA, RA'.

[0105] Next, as shown in Figures 12(a1), 12(a2) and 12(a3), a p-type nitride guide layer 18A' is selectively formed by epitaxial growth on the p-type nitride guide layers 18, 18A so as to fill the openings KA, KA'. At this time, a waveguide layer WA having diffraction gratings EA on both sides along the waveguiding direction D1 is formed in the opening KA, as shown in Figure 5. Also, a waveguide layer WA' without diffraction gratings on both sides is formed in the opening KA'.

[0106] Next, as shown in Figures 13(a1), 13(a2) and 13(a3), the p-type nitride cladding layer 20 and the p-type nitride contact layer 21 are successively formed by epitaxial growth on the p-type nitride guide layer 18A' and the resistive layer RA'.

[0107] This allows the diffraction grating KA to be located close to the active layer 15 while laterally confining the guided light guided through the active layer 15 based on a single deposition of the resistive layers RA and RA'. Also, the current injected into the active layer 15 can be constricted at the position of the opening KA' while ensuring the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating KA. This makes it possible to increase the coupling coefficient between the guided light and the diffraction grating KA while suppressing the increase in crystal defects in the p-type nitride guide layers 18A and 18A', while suppressing the complication of the manufacturing process. Also, it is possible to reduce the threshold current of the semiconductor laser LC while suppressing the heat generation of the semiconductor laser LC. As a result, it is possible to stabilize the oscillation wavelength while suppressing an increase in the cost, and to increase the output while ensuring the reliability of the semiconductor laser LC.

[0108] Fig. 14(a) is a plan view showing the configuration of a resistive layer of a semiconductor light emitting device according to a sixth embodiment, and Fig. 14(b) is a cross-sectional view showing the configuration of the semiconductor light emitting device according to the sixth embodiment cut along the lateral direction of the waveguiding direction. Fig. 14(b) shows the configuration cut at the position of line X1-X1 in Fig. 14(a).

[0109] In Figures 14(a) and 14(b), the semiconductor laser LD has a resistive layer RD instead of the resistive layer RA of the semiconductor laser LA of Figure 2(b). Other points of the semiconductor laser LD can be configured in the same way as the semiconductor laser LA of Figure 2(b).

[0110] The resistive layer RD can be configured in the same manner as the resistive layer RA, except that the position in the vertical direction D3 in the p-type nitride guide layer 18 is different from the position in the vertical direction D3 of the resistive layer RA. That is, the top surface of the resistive layer RD can be disposed at a position lower than the top surface of the p-type nitride guide layer 18. This allows the diffraction grating EA to be closer to the active layer 15, and the coupling coefficient between the guided light and the diffraction grating EA can be improved.

[0111] Fig. 15 is a plan view showing the configuration of the resistive layer of the semiconductor light emitting device according to the seventh embodiment, and is a diagram showing the state of a standing wave formed in the semiconductor light emitting device for the purpose of explanation. Fig. 16 is a cross-sectional view of the configuration of the semiconductor light emitting device according to the seventh embodiment cut along the waveguiding direction at the position of the second-order diffraction grating. Fig. 16 shows the configuration cut at the position of the A1-A1 line in Fig. 15.

[0112] In FIG. 15, the semiconductor laser LE has a p-type nitride semiconductor layer E2" instead of the p-type nitride semiconductor layer E2 of the semiconductor laser LB of FIG. 5(b). The p-type nitride semiconductor layer E2" has a resistive layer RE instead of the resistive layer RA. Other than that, the semiconductor laser LE can be configured in the same way as the semiconductor laser LB of FIG. 5(b).

[0113] The resistive layer RE is located in a part of the p-type nitride semiconductor layer E2''. The position of the resistive layer RE in the p-type nitride semiconductor layer E2'' in the longitudinal direction D3 of the waveguide direction D1 is not particularly limited. The resistive layer RE has a smaller refractive index and a larger resistance than the p-type nitride semiconductor layer E2''. Here, the resistive layer RE can configure at least one of a refractive index guided type and a gain guided type Fabry-Perot resonator. In addition, the resistive layer RE can be disposed in a part of the p-type nitride semiconductor layer E2'' so as to have a high-order DFB structure. The resistive layer RE includes a plurality of high-order diffraction gratings having a greatest common denominator of 1 and different orders. The resistive layer RE can be, for example, a high-resistance layer made of AlN.

[0114] As shown in FIG. 15, the resistive layer RE has an opening KE, a second-order diffraction grating EE2, and a third-order diffraction grating EE3. A waveguide layer WE is provided in the opening KE. The pitch Λ2 of the second-order diffraction grating EE2 can be matched to a length that is twice the oscillation period of the laser light guided through the waveguide layer WE. The pitch Λ3 of the third-order diffraction grating EE3 can be matched to a length that is three times the oscillation period of the laser light guided through the waveguide layer WE. The second-order diffraction grating EE2 and the third-order diffraction grating EE3 are located on both sides of the waveguide layer WE. At this time, a concavo-convex shape with a pitch Λ2 is formed on one side of the waveguide layer WE, and the concavo-convex shape of the second-order diffraction grating EE2 can be fitted into the concavo-convex shape of one side of the waveguide layer WE. The concavo-convex shape with a pitch Λ3 is formed on the other side of the waveguide layer WE, and the concavo-convex shape of the third-order diffraction grating EE3 can be fitted into the concavo-convex shape of the other side of the waveguide layer WE. At this time, by embedding the p-type nitride guide layer 18A in the recesses of the second-order diffraction grating EE2 (the grey part of the diffraction grating formation part in the figure), the recesses of the third-order diffraction grating EE3 (the grey part of the diffraction grating formation part in the figure), and the opening KE (the part in the figure where the diffraction grating and the waveguide layer WE are surrounded by a white line), it is possible to form the waveguide layer WE in the p-type nitride semiconductor layer E2'' (see FIG. 16) while increasing the refractive index difference between the protrusions and recesses of the second-order diffraction grating EE2 and the third-order diffraction grating EE3.

[0115] Here, the second-order diffraction grating EE2 and the third-order diffraction grating EE3 have regions in which at least one of the following portions coincide with each other. 1) the center of the convex portion ST2 of the second-order diffraction grating EE2 and the center of the convex portion ST3 of the third-order diffraction grating EE3, 2) the center of the concave portion SB2 of the second-order diffraction grating EE2 and the center of the concave portion SB3 of the third-order diffraction grating EE3, 3) the center of the convex portion ST2 of the second-order diffraction grating EE2 and the center of the concave portion SB3 of the third-order diffraction grating EE3, 4) the center of the concave portion SB2 of the second-order diffraction grating EE2 and the center of the convex portion ST3 of the third-order diffraction grating EE3

[0116] For example, at positions PC1, PC3, and PC5 in the waveguide direction D1, the center of the protrusion ST2 of the second-order diffraction grating EE2 coincides with the center of the protrusion ST3 of the third-order diffraction grating EE3. At positions PC2, PC4, and PC6 in the waveguide direction D1, the center of the recess SB2 of the second-order diffraction grating EE2 coincides with the center of the protrusion ST3 of the third-order diffraction grating EE3.

[0117] The opening KE, the second-order diffraction grating EE2, and the third-order diffraction grating EE3 are formed at positions recessed from the end faces MA, MB of the active layer 15. The second-order diffraction grating EE2 and the third-order diffraction grating EE3 can be recessed from the end faces MA, MB of the active layer 15 by a distance equal to or greater than the periodicity of the second-order diffraction grating EE2 and the third-order diffraction grating EE3, respectively.

[0118] Here, by setting the greatest common divisor of the orders of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 to 1, it is possible to increase the periods of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 while matching the diffraction condition with the guide direction D1 of the guided light guided through the active layer 15. This makes it possible to stabilize the oscillation wavelength while suppressing a decrease in the oscillation efficiency. Furthermore, it is possible to realize a blue-violet laser diode with a highly stable oscillation wavelength while mitigating the manufacturing difficulties associated with miniaturization of the second-order diffraction grating EE2 and the third-order diffraction grating EE3.

[0119] That is, the second-order diffraction grating EE2 diffracts the emitted light not only in the in-plane direction (180° direction: D1 direction in the cross-sectional view of FIG. 16 and the direction perpendicular to the paper surface direction) but also in the 90° direction (D3 direction in FIG. 16). The third-order diffraction grating EE3 diffracts the emitted light not only in the in-plane direction (180°) but also in directions of approximately 70° and approximately 110° with respect to the D1 axis in FIG. 16. However, since the greatest common denominator of the orders of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 is 1, diffraction only occurs in the in-plane direction (180°), and the pitch is increased compared to the first-order diffraction grating, while providing the same effect as the first-order diffraction grating.

[0120] Furthermore, by providing a region in which at least one of the centers of the convex portions, the centers of the concave portions, and the centers of the convex portions and the concave portions of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 coincide, it is possible to increase the difference in energy density of the electric field of the standing wave VE formed by the second-order diffraction grating EE2 and the third-order diffraction grating EE3, and to increase the stop band width. As a result, it is possible to increase the SMSR of multiple high-order diffraction gratings formed by the second-order diffraction grating EE2 and the third-order diffraction grating EE3, and to increase the coupling coefficient between the guided light and the high-order diffraction grating.

[0121] 17(a) and 17(b) show the refractive index distribution of the diffraction grating shown in FIG. 15. The horizontal axis of the figure shows the position in the light guide direction, and the vertical axis shows the magnitude of the refractive index. FIG. 17(c) and 17(d) show the relationship between the phase and energy of the standing wave formed in the waveguide of FIG. 15. The horizontal axis of the figure shows the position in the light guide direction, and the vertical axis shows the magnitude of the amplitude. Note that FIG. 17(a) shows the refractive index distribution in the waveguiding direction D1 of the second-order diffraction grating EE2 of FIG. 15 when the period (pitch: Λ2) is 178.3 nm and the duty is 0.2, and FIG. 17(b) shows the refractive index distribution in the waveguiding direction D1 of the third-order diffraction grating EE3 of FIG. 15 when the period (pitch: Λ3) is 267.5 nm and the duty is 0.2.

[0122] 17(a) and 17(b), the second-order diffraction grating EE2 and the third-order diffraction grating EE3 have points PC12 and PC14 where the centers of the convex portions coincide with each other, and points PC11 and PC13 where the centers of the concave portions coincide with each other. In this case, even if the wavelength is the same, the energy density u=1 / 2εE of the electric field E, which is indicated by the magnitude of the amplitude depending on the position of the waveguiding direction D1 of the standing waves VE1 and VE2 relative to the diffraction grating, is 2are different. ε is the refractive index of the medium in which the electric field E is formed. The difference in energy density u between the standing waves VE1 and VE2 corresponds to the stop band width. At this time, at points PC12 and PC14 where the center of the convex part of the second-order diffraction grating EE2 and the center of the convex part of the third-order diffraction grating EE3 coincide, and at points PC11 and PC13 where the center of the concave part of the second-order diffraction grating EE2 and the center of the convex part of the third-order diffraction grating EE3 coincide, the difference in amplitude between the standing waves VE1 and VE2 increases. That is, the difference in energy density u between the standing waves VE1 and VE2 increases. In other words, by providing points PC12 and PC14 where the center of the convex part of the second-order diffraction grating EE2 and the center of the convex part of the third-order diffraction grating EE3 coincide, and points PC11 and PC13 where the center of the concave part of the second-order diffraction grating EE2 and the center of the convex part of the third-order diffraction grating EE3 coincide, the stop band width can be increased, and the coupling coefficient between the guided light and the high-order diffraction grating can be increased.

[0123] FIG. 18 is a relationship diagram between the refractive index and the position in the waveguiding direction, showing as examples the second-order diffraction grating and the third-order diffraction grating shown in FIG. 15, as parameters that can be adjusted when changing the relative positional relationship between multiple diffraction gratings. In Fig. 18, there are countless ways to select the relative positional relationship of the concaves and convexes of the second-order diffraction grating EE2 and the third-order diffraction grating EE3. When changing the relative positional relationship of the concaves and convexes of the second-order diffraction grating EE2 and the third-order diffraction grating EE3, the inter-grating shift FK between the second-order diffraction grating EE2 and the third-order diffraction grating EE3 may be changed, the duty DY2 of the second-order diffraction grating EE2 may be changed, the duty DY3 of the third-order diffraction grating EE3 may be changed, or these changes may be combined. The inter-grating shift FK is the difference in physical distance from the end face of the resonator between the second-order diffraction grating and the third-order diffraction grating, and this inter-grating shift creates a phase shift of the wave formed in the resonator.

[0124] FIG. 19A is a diagram showing the relationship between the inter-grating shift and the stop band width when the duty of the diffraction grating of the semiconductor light emitting device according to the seventh embodiment is changed. 19A, the stop band width was estimated when the duty DY2 of the second-order diffraction grating EE2 and the duty DY3 of the third-order diffraction grating EE3 were set to the same value and the inter-grating shift FK was changed between 0.1 and 0.5. Here, for the duty DY2 of the second-order diffraction grating and the duty DY3 of the third-order diffraction grating, the ◆ mark indicates the case of 0.1, the ■ mark indicates the case of 0.2, the ▲ mark indicates the case of 0.3, the × mark indicates the case of 0.4, and the asterisk indicates the case of 0.5.

[0125] From this result, it was found that the stop band width changes depending on the relative positions of multiple diffraction gratings. In this estimation, the largest stop band value was obtained when the duty DY2 of the second-order diffraction grating EE2 and the duty DY3 of the third-order diffraction grating EE3 were 0.2 and the grating shift FK was 0.5.

[0126] FIG. 19B is a diagram showing a method for maximizing the stop band width of the semiconductor light emitting device according to the seventh embodiment. In Figure 19B, when the duty DY2 of the second-order diffraction grating EE2 and the duty DY3 of the third-order diffraction grating EE3 are changed, it has been found that when the duty DY2 of the second-order diffraction grating EE2 is 0.3, the duty DY3 of the third-order diffraction grating EE3 is 0.5, and the inter-grating shift FK is 0, a larger stop band width can be obtained than when the duty DY2 of the second-order diffraction grating EE2 and the duty DY3 of the third-order diffraction grating EE3 are both set to the same value of 0.2.

[0127] FIG. 20 is a plan view showing the configuration of a resistive layer of the semiconductor light emitting device according to the eighth embodiment. 20, the semiconductor laser LF includes a resistive layer RF instead of the resistive layer RE of the semiconductor laser LE of FIG 15. Other points of the semiconductor laser LF can be configured similarly to the semiconductor laser LE of FIG 15.

[0128] The resistive layer RF includes an opening KF, a second-order diffraction grating EF2, and a third-order diffraction grating EF3. A waveguide layer WF is provided in the opening KF. The second-order diffraction grating EF2 and the third-order diffraction grating EF3 are provided on both sides of the waveguide layer WF along the waveguiding direction D1. The second-order diffraction grating EF2 is provided with a phase shift portion SF2, and the third-order diffraction grating EF3 is provided with a phase shift portion SF3.

[0129] Here, the semiconductor laser LF is an end face reflection type laser, and the reflection surface is formed by crystal cleavage, but the characteristics vary depending on the cleavage position. In this case, by providing a phase shift portion SF2 on the second-order diffraction grating EF2 and a phase shift portion SF3 on the third-order diffraction grating EF3, it is possible to improve the SMSR of the diffraction grating while dealing with the variation in characteristics depending on the cleavage position, and to improve the light emission efficiency of the desired oscillation wavelength.

[0130] In such a phase-shifted distributed feedback laser diode, a larger SMSR can be easily obtained compared to a laser diode having a diffraction grating without a phase shift portion. In addition, the threshold gain can be lowered, and the characteristics of the nitride semiconductor light-emitting device can be further improved.

[0131] The center of the phase shift part is preferably located at a distance L1 between the end face MA with the lower reflectance and 60% to 80% of the distance (L1+L2) between the end faces MA and MB. In particular, the distance L1 from the end face MA to the center of the phase shift part is preferably set to 70% (L1:L2=7:3) of the distance (L1+L2) between the end faces MA and MB. This allows the phase shift part to be located at a position that coincides with the centers of the peaks, valleys, or peaks of the standing waves formed by the diffraction grating, improving the SMSR.

[0132] In addition, if N is a natural number (positive integer), the effective refractive index of the diffraction grating is neff, and λ is the Bragg wavelength, the length of the phase shift part is λ / (4 n eff)·(2N-1) is preferably satisfied. This allows the phase shift sections to be arranged at positions that coincide with the centers of the peaks and valleys, or the centers of the peaks and valleys, of the standing waves formed by the diffraction grating, thereby improving the SMSR.

[0133] Fig. 21(a) and Fig. 21(b) are diagrams showing the refractive index distribution of the diffraction grating of the semiconductor light emitting device of the ninth embodiment. Fig. 21(c) and Fig. 21(d) are diagrams showing the relationship between the phase and energy of a standing wave formed in the waveguide of the semiconductor light emitting device of the ninth embodiment. In this ninth embodiment, a combination of a third-order diffraction grating and a fifth-order diffraction grating is used instead of the combination of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 of Fig. 15.

[0134] In Figures 21(a) and 21(b), the pitch of the third-order diffraction grating can be matched to three times the oscillation period of the laser light. The pitch of the fifth-order diffraction grating can be matched to five times the oscillation period of the laser light. Even in the case of a combination of a third-order diffraction grating and a fifth-order diffraction grating, the greatest common divisor of the orders of these diffraction gratings is 1, so only diffraction occurs in the in-plane direction (180°). This provides the effect of efficiently achieving stable laser oscillation.

[0135] FIG. 21(a) shows the refractive index distribution of the third-order diffraction grating, where the low refractive index portion corresponds to the concave portion of the third-order diffraction grating, and the high refractive index portion corresponds to the convex portion. Similarly, FIG. 21(b) shows the refractive index distribution of the fifth-order diffraction grating. In the combination of the third-order diffraction grating and the fifth-order diffraction grating, there are points PC21 and PC23 where the center of the concave portion of the third-order diffraction grating and the center of the convex portion of the fifth-order diffraction grating coincide, and points PC22 and PC24 where the center of the convex portion of the third-order diffraction grating and the center of the concave portion of the fifth-order diffraction grating coincide. In this case, at points PC21 and PC23 where the center of the concave portion of the third-order diffraction grating and the center of the convex portion of the fifth-order diffraction grating coincide, and points PC22 and PC24 where the center of the convex portion of the third-order diffraction grating and the center of the concave portion of the fifth-order diffraction grating coincide, the difference in amplitude between the standing waves VE3 and VE4 increases, and the difference in energy density u between the standing waves VE3 and VE4 increases. Therefore, by providing points PC21 and PC23 where the centers of the recesses of the third-order diffraction grating and the protrusions of the fifth-order diffraction grating coincide with each other, and points PC22 and PC24 where the centers of the protrusions of the third-order diffraction grating and the recesses of the fifth-order diffraction grating coincide with each other, the stop band width can be increased. As a result, the coupling coefficient between the guided light and the high-order diffraction grating can be increased.

[0136] FIG. 22 is a diagram showing the relationship between the grating shift and the stop band width when the duty of the diffraction grating of the semiconductor light emitting device according to the ninth embodiment is changed. In Fig. 22, the stop band width was estimated when the duty of the third-order diffraction grating and the duty of the fifth-order diffraction grating were set to the same value and the inter-grating shift was changed between 0.1 and 0.5. Here, for the duty DY3 of the third-order diffraction grating and the duty DY5 of the fifth-order diffraction grating, the ◆ mark indicates the case of 0.1, the ■ mark indicates the case of 0.2, the ▲ mark indicates the case of 0.3, the × mark indicates the case of 0.4, and the asterisk indicates the case of 0.5.

[0137] From this result, it was found that the stop band width changes depending on the relative positions of multiple diffraction gratings. In this estimation, the largest stop band value was obtained when the duty of the third-order diffraction grating and the duty of the fifth-order diffraction grating were 0.5 and the grating shift was 0.5.

[0138] The duty of the third-order diffraction grating and the duty of the fifth-order diffraction grating may be different from each other. For example, under the condition that the duty of the third-order diffraction grating is 0.5, the duty of the fifth-order diffraction grating is 0.1, and the inter-grating shift is 0.5, and under the condition that the duty of the third-order diffraction grating is 0.5, the duty of the fifth-order diffraction grating is 0.3, and the inter-grating shift is 0, the stop band value was obtained similar to the condition under which the stop band value was the largest in FIG. 22 (the duty of the third-order diffraction grating and the fifth-order diffraction grating is 0.5, and the inter-grating shift is 0.5).

[0139] FIG. 23 is a plan view showing the configuration of a resistive layer of the semiconductor light emitting device according to the tenth embodiment. In Fig. 23, the semiconductor laser LG includes a resistive layer RG instead of the resistive layer RF of the semiconductor laser LF in Fig. 20. Other points of the semiconductor laser LG can be configured in the same way as the semiconductor laser LF in Fig. 20.

[0140] The resistive layer RG includes an opening KG, second-order diffraction gratings EG2, EG2', and third-order diffraction gratings EG3, EG3', instead of the opening KE, second-order diffraction grating EE2, and third-order diffraction grating EE3 of FIG.

[0141] A waveguide layer WG is provided within the opening KG. The second-order diffraction gratings EG2, EG2' and the third-order diffraction gratings EG3, EG3' are located on both sides of the waveguide layer WG along the waveguiding direction L1. In this case, the third-order diffraction gratings EG3, EG3' can be arranged closer to the waveguide layer WG than the second-order diffraction gratings EG2, EG2'. This allows the high-order diffraction gratings to be arranged closer to the light distribution of the emitted light, and the low-order diffraction gratings to be arranged farther from the light distribution. This allows the coupling coefficients of the low-order diffraction gratings and the high-order diffraction gratings to be roughly the same, allowing the emitted light to be efficiently diffracted in the 180° direction.

[0142] FIG. 24 is a diagram showing the relationship between the height of the diffraction grating and the coupling coefficient. In FIG. 24, according to the literature (IEEE J. Quantum Electron. QE-11, p867, 1975), the coupling coefficient decreases as the order increases even if the height of the diffraction grating is the same. Using a method similar to that described in this literature, the coupling coefficients of diffraction gratings of different orders were estimated for the TE mode and rectangular diffraction grating. As a result, as shown in FIG. 24, it can be seen that the coupling coefficient decreases even if the height of the diffraction grating is the same as the order (the number represented by "m" in the figure) increases. Here, the refractive indices used to estimate the coupling coefficients were n1 = 2.48, n2 = 2.49, and n3 = 2.48. In addition, the variables common to the method in this literature were guide layer thickness t = 3 μm, oscillation wavelength λ0 = 444 nm, and duty = 0.4.

[0143] 25 to 29 show a method for manufacturing a semiconductor light-emitting device according to an eleventh embodiment. In each figure, (a) is a plan view showing the method for manufacturing a semiconductor light-emitting device according to the eleventh embodiment, and (b) is a cross-sectional view cut along the waveguide direction corresponding to (a) in each figure. Note that Fig. 25(b) to Fig. 27(b) and Fig. 29(b) show configurations cut along the line A1-A1 in the corresponding figures (a), and Fig. 28(b) shows a configuration cut along the line B1-B1 in Fig. 28(a).

[0144] 25(a) and 25(b), 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 p-type nitride guide layers 18, 18A are sequentially stacked on an n-type nitride semiconductor substrate 11 by epitaxial growth.

[0145] 26(a) and 26(b), the p-type nitride guiding layer 18A is patterned based on photolithography and dry etching techniques to alternately form protrusions QT2 and recesses QB2 in the p-type nitride guiding layer 18A at a period twice the oscillation wavelength along the waveguide direction D1, and to alternately form protrusions QT3 and recesses QB3 in the p-type nitride guiding layer 18A at a period three times the oscillation wavelength along the waveguide direction D1. At this time, the arrangement of the protrusions QT2 and recesses QB2 and the arrangement of the protrusions QT3 and recesses QB3 can be arranged adjacent to each other in the lateral direction D2 of the waveguide direction D1.

[0146] Next, as shown in Figures 27(a) and 27(b), resistive layers RH and RH' are formed in sequence on the p-type nitride guide layers 18 and 18A by epitaxial growth or sputtering to form the second-order diffraction grating EH2 and the third-order diffraction grating EH3. The resistive layers RH and RH' can be formed collectively in a single film formation process. At this time, the resistive layer RH can be formed so as to fill the recesses QB2 and QB3 of the p-type nitride guide layer 18A, and the resistive layer RH' can be formed so as to cover the protrusions QT2 and QT3 of the p-type nitride guide layer 18A and the resistive layer RH.

[0147] 28(a) and 28(b), the resistive layers RH, RH' are patterned by photolithography and dry etching to form openings KH, KH' in the resistive layers RH, RH' along the waveguide direction D1. At this time, the resistive layers RH, RH' are removed in the openings KH, KH', and the protrusions QT2, QT3 and recesses QB2, QB3 of the p-type nitride guide layer 18' are exposed from the resistive layers RH, RH'.

[0148] Next, as shown in Figures 29(a) and 29(b), a p-type nitride guide layer 18A' is selectively formed by epitaxial growth on the p-type nitride guide layers 18, 18A and on the resistive layer RH' so as to fill the openings KH, KH'. At this time, a waveguide layer WH having a second-order diffraction grating EH2 and a third-order diffraction grating EH3 on both sides along the waveguiding direction D1 is formed in the opening KH. Also, a waveguide layer WH' not having a second-order diffraction grating EH2 and a third-order diffraction grating EH3 on both sides is formed in the opening KH'.

[0149] Next, the p-type nitride cladding layer 20 and the p-type nitride contact layer 21 are successively formed on the p-type nitride guide layer 18A' by epitaxial growth.

[0150] This allows the second-order diffraction grating EH2 and the third-order diffraction grating EH3 to be located close to the active layer 15 while the guided light guided through the active layer 15 can be laterally confined based on a single film formation process of the resistive layers RH and RH'. Furthermore, the current injected into the active layer 15 can be constricted at the position of the opening KH' while ensuring the refractive index difference between the p-type nitride guide layer 18A and the second-order diffraction grating EH2 and the third-order diffraction grating EH3. This allows the coupling coefficient between the guided light and the second-order diffraction grating EH2 and the third-order diffraction grating EH3 to be increased, and the threshold current of the semiconductor laser can be reduced while suppressing heat generation of the semiconductor laser. As a result, the pitch can be enlarged compared to the first-order diffraction grating, and the oscillation wavelength can be stabilized, and the output can be increased while ensuring the reliability of the semiconductor laser.

[0151] Figures 30(a) to 33(a) are plan views showing a method for manufacturing a semiconductor light-emitting device according to the twelfth embodiment, and Figures 30(b) to 33(b) are cross-sectional views taken along the waveguide direction of Figures 30(a) to 33(a), respectively. Note that Figures 30(b) to 33(b) show configurations taken along the lines A1-A1 of Figures 30(a) to 33(a), respectively.

[0152] 30(a) and 30(b), 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 nitride guide layer 18 are sequentially laminated by epitaxial growth on an n-type nitride semiconductor substrate 11. Furthermore, a resistive layer RI is laminated on the p-type nitride guide layer 18 by a method such as epitaxial growth or sputtering.

[0153] Next, as shown in Figures 31(a) and 31(b), the resistive layer RI is patterned based on photolithography and dry etching techniques to form an opening KI in the resistive layer RI, with a second-order diffraction grating EI2 and a third-order diffraction grating EI3 on ​​either side thereof along the waveguide direction D1.

[0154] Next, as shown in Figures 32(a) and 32(b), a p-type nitride guide layer 18A is selectively formed on the p-type nitride guide layer 18 by epitaxial growth so as to be embedded in the opening KI. At this time, the p-type nitride guide layer 18A can be embedded in the recesses of the second-order diffraction grating EI2 and the recesses of the third-order diffraction grating EI3, and the refractive index difference between the recesses and protrusions of the second-order diffraction grating EI2 and the refractive index difference between the recesses and protrusions of the third-order diffraction grating EI3 can be determined by the refractive index of the resistive layer RI. Also, a waveguide layer WI is formed in the opening KI, on both sides of which the second-order diffraction grating EI2 and the third-order diffraction grating EI3 are provided along the waveguiding direction D1.

[0155] Next, as shown in FIGS. 33(a) and 33(b), the p-type nitride cladding layer 20 and the p-type nitride contact layer 21 are successively formed on the p-type nitride guide layer 18A by epitaxial growth.

[0156] This makes it possible to form the second-order grating EI2 and the third-order grating EI3 on ​​both sides of the waveguide layer WI at the same time as forming the waveguide layer WI in the aperture KI. Also, it is possible to increase the refractive index difference between the p-type nitride guide layer 18A and the second-order grating EI2 and the third-order grating EI3. Therefore, it is possible to stably form an inner stripe type semiconductor laser having a DFB structure with a larger pitch than that of a first-order grating while suppressing an increase in the number of steps. [Explanation of symbols]

[0157] E1 n-type nitride semiconductor layer E2 p-type nitride semiconductor layer E3 Confinement layer 11 n-type nitride semiconductor substrate 12 n-type nitride cladding layer 13 n-type nitride guide layer 14, 16 Undoped nitride guide layer 15 Active layer 17 p-type carrier blocking layer 18 p-type nitride guide layer RA resistance layer 20 p-type nitride cladding layer 21 p-type nitride contact layer

Claims

1. A first conductivity type semiconductor layer; an active layer provided on the first conductive type semiconductor layer; a second conductive type semiconductor layer provided on the active layer; a waveguide layer provided in the second conductive type semiconductor layer, for guiding the guided light while confining the guided light in a lateral direction of a guide direction of the guided light in the active layer; a diffraction grating provided in the second conductive type semiconductor layer along a guide direction of the guided light; a confinement layer provided on the waveguide layer and the diffraction grating, for vertically confining guided light guided through the active layer, the grating comprises a resistive layer; the resistive layer is located in a portion of the second conductive type semiconductor layer, and has a smaller refractive index and a larger resistance than the second conductive type semiconductor layer; The semiconductor light emitting device is characterized in that the diffraction grating is located on both sides of the waveguide layer.

2. 2. The semiconductor light emitting device according to claim 1, wherein the confinement layer is a second conductive type semiconductor layer having a refractive index smaller than that of the waveguide layer.

3. 2. The semiconductor light emitting device according to claim 1, wherein the confinement layer is a transparent conductive layer that is transparent to light guided through the active layer.

4. The semiconductor light-emitting device according to claim 1 , wherein the confinement layer is used as at least one of a guide layer and a cladding layer on the active layer.

5. The diffraction grating is recessed from the end face of the active layer by a distance equal to or greater than the period of the diffraction grating. The semiconductor light emitting device according to claim 1 .

6. The semiconductor light emitting device according to claim 1 , wherein the diffraction grating comprises a phase shift portion.

7. The length of the phase shift portion is a positive integer N, and the effective refractive index of the diffraction grating is n ｅｆｆ , where λ is the Bragg wavelength, λ / (4·n ｅｆｆ 7. The semiconductor light emitting device according to claim 6, wherein the relationship of (2N-1) is satisfied.

8. 7. The semiconductor light emitting device according to claim 6, wherein the center of the phase shift portion is located at a distance between 60% and 80% of the distance between the end face having a lower reflectance and the end face of the active layer.

9. 2. The semiconductor light emitting device according to claim 1, wherein the coupling coefficient of the diffraction grating is κ and the length of the resonator is L, and the condition 1≦κ·L≦3 is satisfied.

10. 2. The semiconductor light emitting device according to claim 1, wherein the waveguide layer is made of GaN, and the diffraction grating is made of AlN.

11. The semiconductor light emitting device according to claim 1 , wherein the diffraction grating comprises a plurality of high-order diffraction gratings having different orders, the greatest common denominator of which is 1.

12. The semiconductor light-emitting element according to claim 11, characterized in that the multiple high-order diffraction gratings have areas in which at least one of the centers of the convex portions and the centers of the concave portions and the centers of the convex portions and the concave portions coincide with each other.

13. The semiconductor light emitting device according to claim 11 , wherein the duties of the multiple high-order diffraction gratings are different from each other.

14. The semiconductor light emitting device according to claim 11 , wherein the plurality of high-order diffraction gratings are arranged so that the coupling coefficients are equal to each other.

15. A first conductivity type semiconductor layer; an active layer provided on the first conductive type semiconductor layer; a second conductive type semiconductor layer provided on the active layer; a waveguide layer provided in the second conductive type semiconductor layer, for guiding the guided light while confining the guided light in a lateral direction of a guide direction of the guided light in the active layer; a diffraction grating provided in the second conductive type semiconductor layer along a guide direction of the guided light; a confinement layer provided on the waveguide layer and the diffraction grating, for vertically confining guided light guided through the active layer, the grating comprises a resistive layer; the resistive layer is located in a portion of the second conductive type semiconductor layer, and has a smaller refractive index and a larger resistance than the second conductive type semiconductor layer; The resistive layer is a first resistive layer in which the diffraction grating is formed on both sides of a first opening in which the waveguide layer is embedded; a second resistive layer laminated on the first resistive layer, the second resistive layer having a second opening in which the waveguide layer is embedded.

16. a step of sequentially stacking an active layer and a second conductive type semiconductor layer on the first conductive type semiconductor layer; forming projections and recesses on the second conductive type semiconductor layer; a step of laminating a resistive layer having a smaller refractive index and a larger resistance than the second conductive type semiconductor layer on the second conductive type semiconductor layer so as to cover the irregularities, thereby forming a diffraction grating fitted to the irregularities; forming an opening in the resistive layer on which the diffraction grating is formed; and re-growing the second conductive type semiconductor layer so as to fill the opening.

17. A process of sequentially stacking an active layer, a second conductive type semiconductor layer, and a resistive layer having a resistance higher than that of the second conductive type semiconductor layer on a first conductive type semiconductor layer; forming an aperture in the resistive layer flanked by a diffraction grating; and re-growing the second conductive type semiconductor layer so that the diffraction grating and the opening are buried.

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