Semiconductor laser and forming method thereof

Abstract

Semiconductor lasers and methods of forming the same are disclosed. A semiconductor laser includes a substrate and an epitaxial structure. The epitaxial structure grows on a substrate along a first direction and comprises an active region stacking structure and a photonic crystal structure. Wherein the active region stacking structure comprises a plurality of active regions stacked in the first direction, and the photonic crystal structure is located on the side, away from the substrate, of the active region stacking structure in the first direction. Laser generated by the semiconductor laser is emitted from the substrate or from one side far away from the substrate along a first direction.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor lasers. Background Art

[0002] Semiconductor lasers have the characteristics of miniaturization, high energy efficiency, durability, etc., and are widely used in various fields.

[0003] In the field of lidar (light detection and ranging), two types of lasers are often used: vertical-cavity surface-emitting lasers (VCSELs) and edge-emitting lasers (EELs).

[0004] VCSELs can adopt single-junction or multi-junction structures, with low packaging and testing costs, a divergence angle shape that makes the emitted light spot circular without additional optical packaging, and good reliability. In addition, multi-junction VCSELs can achieve high output power and high power conversion efficiency (PCE). However, due to the large light-emitting aperture, multimode lasing will occur in high-power VCSEL devices, resulting in a large divergence angle.

[0005] EELs emit laser light in a wide wavelength range and have high output power. However, the reliability of EELs is lower than that of VCSELs, and the emitted light spot is non-circular, so additional optical packaging is required, resulting in high packaging and testing costs. In addition, EELs cannot achieve wafer-level testing.

[0006] As a new type of laser, the photonic crystal surface-emitting laser (PCSEL) realizes vertical surface emission through a photonic crystal (PC), combining the advantages of a wide wavelength range of EELs and high reliability and low packaging and testing costs of VCSELs.

[0007] There is a need in the art for semiconductor lasers with further improved performance. Summary of the Invention

[0008] In order to provide a semiconductor laser with improved performance, the present invention is provided.

[0009] A first aspect of the present invention provides a semiconductor laser, which includes: a substrate; and an epitaxial structure grown on the substrate along a first direction, the epitaxial structure including: an active region stack structure including a plurality of active regions stacked along the first direction; a photonic crystal structure located on a side away from the substrate relative to the active region stack structure along the first direction, wherein the laser generated by the semiconductor laser exits along the first direction from the substrate or from a side away from the substrate.

[0010] Optionally, the active region stack structure includes a plurality of active regions and one or more tunneling junctions alternately arranged along the first direction, wherein each tunneling junction connects adjacent active regions.

[0011] Optionally, the epitaxial structure is configured such that the optical field intensity of the excited mode of the semiconductor laser reaches a minimum value at the one or more tunneling junctions and a maximum value at each active region.

[0012] Optionally, the epitaxial structure is further configured such that the optical field intensity of the excited mode of the semiconductor laser reaches 70% or more of the maximum optical field intensity at the photonic crystal structure.

[0013] Optionally, the semiconductor laser is configured to emit in a single mode.

[0014] Optionally, the tunneling junction includes two first portions adjacent to the active regions on the two connected sides and a second portion between the two first portions, wherein the materials of the two first portions have a first refractive index, the material of the second portion has a second refractive index, and the first refractive index is different from the second refractive index.

[0015] Optionally, the epitaxial structure includes a semiconductor material layer grown on a side away from the substrate of the active region stack structure along the first direction, and the epitaxial structure further includes: a cladding layer grown on the semiconductor material layer on a side away from the substrate along the first direction, and the photonic crystal structure includes: a hole structure formed by etching the semiconductor material layer and forming the cladding layer on the semiconductor material layer.

[0016] Optionally, the photonic crystal structure includes a pillar structure, and the epitaxial structure further includes: a cladding layer grown on the active region stack structure on a side away from the substrate along the first direction, wherein the pillar structure is formed by at least partially etching the cladding layer along the first direction.

[0017] Optionally, the epitaxial structure further includes: a reflective layer formed on a side of the active region stack structure facing away from the laser output.

[0018] Another aspect of the present invention provides a method for forming a semiconductor laser, which includes: providing a substrate; and growing an epitaxial structure on the substrate along a first direction, wherein growing the epitaxial structure includes: growing an active region stack structure, the active region stack structure including a plurality of active regions stacked along the first direction; and forming a photonic crystal structure on a side away from the substrate relative to the active region stack structure along the first direction, wherein the laser generated by the semiconductor laser exits along the first direction from the substrate or from the side away from the substrate.

[0019] Optionally, growing the active region stack structure includes: growing a plurality of active regions and one or more tunneling junctions arranged alternately along the first direction, wherein each tunneling junction connects adjacent active regions.

[0020] Optionally, the epitaxial structure is configured such that the optical field intensity of the excited mode of the semiconductor laser reaches a minimum value at the one or more tunneling junctions and reaches a maximum value at each active region.

[0021] Optionally, the epitaxial structure is further configured such that the optical field intensity of the excited mode of the semiconductor laser reaches 70% or more of the maximum value of the optical field intensity at the photonic crystal structure.

[0022] Optionally, the semiconductor laser is configured to emit in a single mode.

[0023] Optionally, the tunneling junction includes two first portions adjacent to the active regions on the two connected sides and a second portion between the two first portions, wherein the materials of the two first portions have a first refractive index, the material of the second portion has a second refractive index, and the first refractive index is different from the second refractive index.

[0024] Optionally, forming the photonic crystal structure includes: forming a semiconductor material layer on a side away from the substrate of the active region stack structure along the first direction; etching the semiconductor material layer; and growing a cladding layer on a side away from the substrate of the semiconductor material layer along the first direction by epitaxial regrowth.

[0025] Optionally, forming the photonic crystal structure includes: growing a cladding layer on a side away from the substrate of the active region stack structure along the first direction; and at least partially etching the cladding layer along the first direction.

[0026] Optionally, growing the epitaxial structure further includes: forming a reflective layer on a side of the active region stack structure facing away from the laser output.

[0027] A semiconductor laser according to an embodiment of the present invention, as a PCSEL, improves the shape of the emitted light spot and reduces the packaging and testing cost compared to an EEL, and optimizes the divergence angle of the emitted light spot compared to a VCSEL. In addition, as a multi-junction PCSEL, it further improves the peak power compared to a conventional PCSEL including a single active region, and improves the PCE under high-power operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Cross-sectional views showing two PCSEL examples are presented.

[0029] Figure 2 Cross-sectional views showing examples of semiconductor lasers according to some embodiments of the present invention are presented.

[0030] Figure 3 Cross-sectional views showing examples of semiconductor lasers including a hole-type PC structure according to some embodiments of the present invention are presented.

[0031] Figure 4 Cross-sectional views showing examples of semiconductor lasers including a column-type PC structure according to some embodiments of the present invention are presented.

[0032] Figure 5 Schematic diagrams showing the optical field intensity distribution and material refractive index distribution of examples of semiconductor lasers according to some embodiments of the present invention are presented.

[0033] Figure 6 Flowcharts showing examples of methods for forming semiconductor lasers according to some embodiments of the present invention are presented.

[0034] Figure 7 Flowcharts showing examples of processes for forming a hole-type PC structure according to some embodiments of the present invention are presented.

[0035] Figure 8 Flowcharts showing examples of processes for forming a column-type PC structure according to some embodiments of the present invention are presented.

[0036] Figures 9 - 10 Schematic diagrams showing examples of processes for forming a hole-type PC structure according to some embodiments of the present invention are presented.

[0037] Figures 11 - 12 Schematic diagrams showing examples of processes for forming a hole-type PC structure according to some embodiments of the present invention are presented. DETAILED DESCRIPTION

[0038] In the present disclosure, the "first direction" is used to represent the extending direction of the semiconductor laser, which is substantially consistent with the epitaxial growth direction or the thickness direction of the semiconductor laser.

[0039] The terms "first", "second", etc. in the description and claims of the present disclosure do not imply any order, quantity, or importance, but are only used to distinguish different components or features.

[0040] The embodiments of the present disclosure are exemplary implementations or examples. References in the description to "embodiment", "one embodiment", "some embodiments", "alternative embodiments", or "other embodiments" mean that the specific features, structures described in connection with the embodiments are included in at least some embodiments of the present technology, but not necessarily all embodiments. The various occurrences of "embodiment", "one embodiment", or "some embodiments" do not necessarily refer to the same embodiment. Elements or aspects from one embodiment may be combined with elements or aspects of another embodiment.

[0041] In the description of the present disclosure, the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", "left", "right", "vertical", "horizontal", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present disclosure, rather than indicating or implying that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present disclosure. In other embodiments where the placement direction of the device or component is opposite to or different from the direction shown in the drawings, these position descriptions may change accordingly.

[0042] In the description of the present disclosure, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0043] Figure 1A cross-sectional view showing two PCSEL examples is presented. PCSEL 100 includes a hole-type PC structure. PCSEL 100 includes a substrate 101 and a cladding layer 102, an active region 103, a PC layer 104, a cladding layer 105, and a contact layer 106 that grow upward. Among them, the PC layer 104 may include a hole structure 105. PCSEL 100 also includes an electrode 108 formed on the substrate 101 and an electrode 107 formed on the contact layer 106. PCSEL 150 includes a pillar-type PC structure. PCSEL 150 includes a substrate 151 and a cladding layer 152, an active region 153, a cladding layer 154, a contact layer 155, and an indium tin oxide (ITO) layer 156 that grow upward. The pillar structure 157 is at least partially formed in the cladding layer 154 and the contact layer 155 through deep etching. PCSEL 100 also includes an electrode 159 formed on the substrate 151 and an electrode 158 formed on the ITO layer 156.

[0044] Current PCSELs all include a single active region. For example, Chinese Patent Application CN 115882333 A discloses such a laser. By forming an etching layer on the light-emitting layer and forming a resonant unit in the etching layer to form a PC region. However, the current PCSELs including a single active region have a relatively low output optical power.

[0045] According to one aspect of the present invention, a semiconductor laser is provided.

[0046] Figure 2 A cross-sectional view showing an example of a semiconductor laser according to some embodiments of the present invention is presented.

[0047] The semiconductor laser 200 may include a substrate 210 and an epitaxial structure 220. The substrate may include any suitable semiconductor substrate. As an example, for a semiconductor laser emitting laser light in the wavelength range of 800 - 1000 nm, the substrate may include gallium arsenide (GaAs). As another example, for a semiconductor laser emitting laser light in the wavelength range of 1450 - 1650 nm, the substrate 210 may include indium phosphide (InP). The epitaxial structure 220 grows on the substrate along a first direction (e.g., Figure 2 the longitudinal direction in

[0048] The active region stack structure 230 may include active regions 231, 232,..., 233 stacked along the first direction. Although in Figure 2Three active regions 231, 232, and 233 are shown, but the active region stack structure 230 may include any other number of active regions, as indicated by the ellipsis in the figure. By providing the active region stack structure 230 including multiple active regions, the power of the semiconductor laser 200 is effectively increased.

[0049] As an example, the active region may include a quantum well (QW) structure or a multiple quantum wells (MQWs) structure.

[0050] In some embodiments, the active region stack structure 230 may include a plurality of active regions and one or more tunneling junctions arranged alternately in a first direction, wherein each tunneling junction connects adjacent active regions. By using one or more tunneling junctions to connect adjacent active regions, the power of the light emitted from each active region can be coupled. In some embodiments, a periodic active region - tunneling junction structure in the first direction may be used to improve the uniformity of the light field peak.

[0051] The PC structure 240 is on a side away from the substrate 210 with respect to the active region stack structure 230 in the first direction. The PC structure 240 may be configured to cause the light emitted from the active region stack structure 230 to be amplified by stimulated emission. The PC structure 240 may also be configured to cause the light of some modes to lase in the direction of the PC plane defined by the PC structure through Bragg diffraction. In some embodiments, the laser generated by the semiconductor laser 200 may exit from the substrate 210 in the first direction (e.g., Figure 2 downward in the figure). In other embodiments, the laser generated by the semiconductor laser 200 may exit from a side away from the substrate 210 (e.g., Figure 2 upward in the figure).

[0052] In some embodiments, the tunneling junction may include two first portions adjacent to the active regions on both sides connected thereto and a second portion between the two first portions. The refractive index of the material of the two first portions may be different from the refractive index of the material of the second portion to achieve the corresponding light field design. As an example, the refractive index of the material of the first portion may be greater than or less than the refractive index of the material of the second portion. The following combines Figure 5 to describe such a material distribution of the tunneling junction.

[0053] In some embodiments, the PC structure 240 may include a periodically arranged hole structure, which will be discussed below in combination with Figure 3 In some embodiments, the PC structure 240 may include a periodically arranged column structure, which will be discussed below in combination with Figure 4 As is known to those skilled in the art, the PC structure 240 may be formed by processing one or more semiconductor material layers of the epitaxial structure 220, as described below in combination withFigure 3 , Figure 4 as discussed

[0054] In some embodiments, the optical field of the semiconductor laser 200 can be designed by setting the positions of the active region, the tunneling junction, and the PC structure 240 in the first direction, thereby improving the coupling efficiency of the PC structure 240. This will be further discussed below in conjunction with Figure 5 further discussion

[0055] In some embodiments, a semiconductor material layer 250 may be included between the substrate 210 and the active region stack structure 230. In some embodiments, a semiconductor material layer 260 may be included on the side of the PC structure 240 away from the substrate. In some embodiments, each of the semiconductor material layers 250 and 260 may include one or more layers, as indicated by the ellipsis in Figure 2 The following will further discuss some possible compositions of the semiconductor material layers 250 and 260 in conjunction with Figure 3 , Figure 4 further discussion

[0056] Figure 3 shows a cross-sectional view of an example of a semiconductor laser including a hole-type PC structure according to some embodiments of the present invention. In Figure 3 , the general direction of light emission is indicated by an arrow

[0057] Figure 3 shows top-emitting semiconductor lasers 310 and 330, where the semiconductor laser 330 includes a reflective layer Figure 3 Also shown are bottom-emitting semiconductor lasers 350 and 370, where the semiconductor laser 370 includes a reflective layer

[0058] In some embodiments, the semiconductor laser 310 may include a substrate 310 and an active region stack structure 313, a semiconductor material layer 314, and a contact layer 316 formed on the substrate in the first direction. In other embodiments, the semiconductor laser 310 may include a substrate 311 and a first cladding layer 312, an active region stack structure 313, a semiconductor material layer 314, a second cladding layer 315, and a contact layer 316 formed on the substrate in the first direction

[0059] In some embodiments, the semiconductor laser 310 may further include an electrode 317 formed on the substrate 311 and an electrode 318 formed on the contact layer 316. In some embodiments, the active region stack structure 313 may be similar to the active region stack structure 230 discussed above in conjunction with Figure 2 discussion

[0060] The semiconductor material layer 314 may include a periodically arranged pore structure. In some embodiments, the pores may include air holes. In other embodiments, the pores may be filled with other materials, and the refractive indices of these filled materials may be different from the refractive index of the semiconductor material layer 314. In some embodiments, the semiconductor material layer 314 may be formed on the active region stack structure 313, the semiconductor material layer 314 may be selectively etched to form a plurality of periodically arranged pores, and a second cladding layer 315 may be formed on the semiconductor material layer 314, thereby forming a pore-type PC structure.

[0061] In some embodiments, for a semiconductor laser that emits laser light in the wavelength range of 800 - 1000 nm, the substrate 311 may include GaAs, and the first cladding layer 312 and the second cladding layer 315 may include aluminum gallium arsenide (AlGaAs). The doping type (e.g., P-type or N-type) of the first cladding layer 312 may be the same as that of the substrate 311, the doping type of the second cladding layer 315 may be the same as the doping type of the contact layer 316, and the doping type of the first cladding layer 312 may be opposite to the doping type of the second cladding layer 315. In other embodiments, for a semiconductor laser that emits laser light in the wavelength range of 1450 - 1650 nm, the substrate 311 may include InP.

[0062] As an example, the substrate 311 includes an N-type substrate, the first cladding layer 312 includes an N-type cladding layer, the second cladding layer 315 includes a P-type cladding layer, and the contact layer 316 includes a P-type contact layer.

[0063] In some embodiments, the doping concentration of the substrate 311 (e.g., N + ) may be greater than the doping concentration of the first cladding layer 312 (e.g., N - ). In some embodiments, the doping concentration of the contact layer 316 (e.g., P + ) may be greater than the doping concentration of the second cladding layer 315 (e.g., P - ).

[0064] As an example, the substrate 311 includes a P-type substrate, the first cladding layer 312 includes a P-type cladding layer, the second cladding layer 315 includes an N-type cladding layer, and the contact layer 316 includes an N-type contact layer.

[0065] In some embodiments, the doping concentration of the substrate 311 (e.g., P + ) may be greater than the doping concentration of the first cladding layer 312 (e.g., P - ). In some embodiments, the doping concentration of the contact layer 316 (e.g., N + ) may be greater than the doping concentration of the second cladding layer 315 (e.g., N - ).

[0066] Turn to semiconductor laser 330. In some embodiments, semiconductor laser 330 may include a substrate 331, a reflective layer 332, an active region stack structure 334, a semiconductor material layer 335, and a contact layer 337 formed on the substrate along a first direction. In other embodiments, semiconductor laser 330 may include a substrate 331, a reflective layer 332, a first cladding layer 333, an active region stack structure 334, a semiconductor material layer 335, a second cladding layer 336, and a contact layer 337 formed on the substrate along a first direction.

[0067] In some embodiments, semiconductor laser 330 may further include an electrode 338 formed on substrate 331 and an electrode 339 formed on contact layer 337. In some embodiments, the active region stack structure 334 may be similar to the active region stack structure 230 discussed above in connection with Figure 2 the discussion.

[0068] The semiconductor material layer 335 may include periodically arranged hole structures. In some embodiments, the holes may include air holes. In other embodiments, the holes may be filled with other materials, and the refractive index of these filled materials may be different from the refractive index of the semiconductor material layer 314. In some embodiments, the semiconductor material layer 335 may be formed on the active region stack structure 334, selectively etched to form a plurality of periodically arranged holes, and a second cladding layer 336 may be formed on the semiconductor material layer 335 to form a hole-shaped PC structure.

[0069] In some embodiments, for a semiconductor laser that emits laser light in the wavelength range of 800 - 1000 nm, substrate 331 may include GaAs, reflective layer 332 may include AlGaAs, and the first cladding layer 333 and the second cladding layer 336 may include AlGaAs. As an example, the reflective layer 332 may include a first AlGaAs material with a high Al content and a second AlGaAs material with a low Al content arranged periodically. In other embodiments, for a semiconductor laser that emits laser light in the wavelength range of 1450 - 1650 nm, substrate 331 may include InP.

[0070] The doping type (e.g., P-type or N-type) of the first cladding layer 333 may be the same as that of the substrate 331 and the reflective layer 332, the doping type of the second cladding layer 336 may be the same as the doping type of the contact layer 337, and the doping type of the first cladding layer 333 may be opposite to the doping type of the second cladding layer 336.

[0071] As an example, substrate 331 includes an N-type substrate, reflective layer 332 includes an N-type reflective layer, the first cladding layer 333 includes an N-type cladding layer, the second cladding layer 336 includes a P-type cladding layer, and the contact layer 337 includes a P-type contact layer.

[0072] In some embodiments, the doping concentration of the substrate 331 (e.g., N + ) may be greater than the doping concentration of the reflective layer 332 (e.g., N - ) and may be greater than the doping concentration of the first cladding layer 333 (e.g., N - ). In some embodiments, the doping concentration of the contact layer 337 (e.g., P + ) may be greater than the doping concentration of the second cladding layer 336 (e.g., P - ).

[0073] As an example, the substrate 331 includes a P-type substrate, the reflective layer 332 includes a P-type reflective layer, the first cladding layer 333 includes a P-type cladding layer, the second cladding layer 336 includes an N-type cladding layer, and the contact layer 337 is an N-type contact layer.

[0074] In some embodiments, the doping concentration of the substrate 331 (e.g., P + ) may be greater than the doping concentration of the reflective layer 332 (e.g., P - ) and may be greater than the doping concentration of the first cladding layer 333 (e.g., P - ). In some embodiments, the doping concentration of the contact layer 337 (e.g., N + ) may be greater than the doping concentration of the second cladding layer 336 (e.g., N - ).

[0075] The semiconductor laser 330 improves the light output efficiency by providing the reflective layer 332 on the side of the active region stack structure 334 away from the laser output direction. As an example, the reflective layer 332 may include a Distributed Bragg Reflector (DBR), a metal reflective layer, or the like.

[0076] Turning to the semiconductor laser 350. In some embodiments, the semiconductor laser 350 may include a substrate 351 and an active region stack structure 353, a semiconductor material layer 354, and a contact layer 356 formed on the substrate along a first direction. In other embodiments, the semiconductor laser 350 may include a substrate 351 and a first cladding layer 352, an active region stack structure 353, a semiconductor material layer 354, a second cladding layer 355, and a contact layer 356 formed on the substrate along a first direction.

[0077] In some embodiments, the semiconductor laser 350 may further include an electrode 357 formed on the substrate 351 and an electrode 358 formed on the contact layer 356.

[0078] In some embodiments, the layers and composition of the semiconductor laser 350 may be similar to those of the semiconductor laser 310 discussed above, except that, in the semiconductor laser 350 , light is emitted from the substrate side through optical design.

[0079] Turning to the semiconductor laser 370. In some embodiments, the semiconductor laser 370 may include a substrate 371 and an active region stack structure 373, a semiconductor material layer 374, a reflective layer 376, and a contact layer 377 formed on the substrate along a first direction. In other embodiments, the semiconductor laser 370 may include a substrate 371 and a first cladding layer 372, an active region stack structure 373, a semiconductor material layer 374, a second cladding layer 375, a reflective layer 376, and a contact layer 377 formed on the substrate along a first direction.

[0080] In some embodiments, the semiconductor laser 370 may further include an electrode 378 formed on the substrate 371 and an electrode 379 formed on the contact layer 377 .

[0081] The semiconductor laser 370 improves light extraction efficiency by disposing a reflective layer 376 on the side of the active region stack structure 373 that is away from the laser emission direction. As an example, the reflective layer 376 may include a DBR or a metal reflective layer.

[0082] In some embodiments, the layers and composition of the semiconductor laser 370 may be similar to those of the semiconductor laser 330 discussed above, except that, in the semiconductor laser 370, light is emitted from the substrate side through optical design.

[0083] Figure 4 A cross-sectional view of an example of a semiconductor laser including a pillar-type PC structure according to some embodiments of the present invention is shown. Figure 4 In the figure, the approximate direction of light emission is shown by arrows.

[0084] Figure 4 Top emitting semiconductor lasers 410 , 430 are shown, wherein the semiconductor laser 430 comprises a reflective layer. Figure 4 A bottom emitting semiconductor laser 450 is also shown.

[0085] The semiconductor laser 410 may include a substrate 411 and a first cladding layer 412, an active region stacking structure 413, a second cladding layer 414, and a transparent electrode layer 416 formed on the substrate 411 along a first direction. As an example, the transparent electrode layer 416 may include an ITO layer. In some embodiments, the semiconductor laser 410 may further include an electrode 417 formed on the substrate 411 and an electrode 418 formed on the transparent electrode layer 416. In some embodiments, the active region stacking structure 413 may be combined with the above. Figure 2Similar to the active region stack structure 230 discussed.

[0086] The semiconductor laser 410 may include periodically arranged pillar structures. In some embodiments, the pillars may include air pillars. In other embodiments, the pillars may be filled with other materials, and the refractive indices of these filled materials may be different from the refractive index of the second cladding 414. In some embodiments, a plurality of periodically arranged pillar structures may be formed by at least partially etching the second cladding 414. As an example, Figure 4 FIG. shows that the second cladding 414 includes an upper portion 415 having a pillar structure and includes a lower portion.

[0087] In some embodiments, for a semiconductor laser that emits laser light in the wavelength range of 800 - 1000 nm, the substrate 411 may include GaAs, and the first claddings 412, 414 may include AlGaAs. The doping type (e.g., P-type or N-type) of the first cladding 412 may be the same as that of the substrate 411, and may be opposite to the doping type of the second cladding 414. In other embodiments, for a semiconductor laser that emits laser light in the wavelength range of 1450 - 1650 nm, the substrate 411 may include InP.

[0088] As an example, the substrate 411 includes an N-type substrate, the first cladding 412 includes an N-type cladding, and the second cladding 414 includes a P-type cladding.

[0089] In some embodiments, the doping concentration of the substrate 411 (e.g., N + ) may be greater than the doping concentration of the first cladding 412 (e.g., N - ), and greater than the doping concentration of the second cladding 414 (e.g., P - ).

[0090] As an example, the substrate 411 includes a P-type substrate, the first cladding 412 includes a P-type cladding, and the second cladding 414 includes an N-type cladding.

[0091] In some embodiments, the doping concentration of the substrate 411 (e.g., P + ) may be greater than the doping concentration of the first cladding 412 (e.g., P - ), and greater than the doping concentration of the second cladding 414 (e.g., N - ).

[0092] Turn to semiconductor laser 430. In some embodiments, semiconductor laser 430 may include a substrate 431, a reflective layer 432, a first cladding layer 433, an active region stack structure 434, a second cladding layer 435, and a transparent electrode layer 437 formed on the substrate 431 along a first direction. As an example, the transparent electrode layer 437 may include an ITO layer. In some embodiments, semiconductor laser 430 may further include an electrode 438 formed on the substrate 431 and an electrode 439 formed on the transparent electrode layer 437. In some embodiments, the active region stack structure 434 may be similar to the active region stack structure 230 discussed above in conjunction with Figure 2 the active region stack structure 230 discussed above.

[0093] Semiconductor laser 430 may include periodically arranged column structures. In some embodiments, the columns may include air columns. In other embodiments, other materials may be filled in the columns, and the refractive indices of these filled materials may be different from the refractive index of the second cladding layer 435. In some embodiments, the column structure may be formed by at least partially etching the second cladding layer 435. As an example, Figure 4 FIG. shows that the second cladding layer 435 includes an upper portion 436 having a column structure and includes a lower portion.

[0094] In some embodiments, for a semiconductor laser that emits laser light in the wavelength range of 800 - 1000 nm, the substrate 431 may include GaAs, the first cladding layer 433 and the second cladding layer 435 may include AlGaAs, and the reflective layer 432 may include AlGaAs. As an example, the reflective layer 432 may be formed by periodically arranging a first AlGaAs material with a high Al content and a second AlGaAs material with a low Al content. The doping type (e.g., P-type or N-type) of the first cladding layer 433 may be the same as that of the substrate 431, the doping type of the second cladding layer 435 may be the same as the doping type of the contact layer 436, and may be opposite to the doping type of the second cladding layer 435. In other embodiments, for a semiconductor laser that emits laser light in the wavelength range of 1450 - 1650 nm, the substrate 431 may include InP.

[0095] As an example, the substrate 431 includes an N-type substrate, the first cladding layer 433 includes an N-type cladding layer, and the second cladding layer 435 includes a P-type cladding layer.

[0096] In some embodiments, the doping concentration of the substrate 431 (e.g., N + ) may be greater than the doping concentration of the first cladding layer 433 (e.g., N-), and greater than the doping concentration of the second cladding layer 435 (e.g., P-).

[0097] As an example, the substrate 431 includes a P-type substrate, the first cladding layer 433 includes a P-type cladding layer, and the second cladding layer 435 includes an N-type cladding layer.

[0098] In some embodiments, the doping concentration of the substrate 431 (eg, P + ) may be greater than the doping concentration of the first cladding layer 433 (eg, P-), and greater than the doping concentration of the second cladding layer 435 (eg, N-).

[0099] The semiconductor laser 430 improves light extraction efficiency by disposing a reflective layer 432 on a side of the active region stack structure 434 that is away from the laser emission direction. As an example, the reflective layer 432 may include a DBR or a metal reflective layer.

[0100] Turning to the semiconductor laser 450. In some embodiments, the semiconductor laser 450 may include a substrate 451 and a first cladding layer 452, an active region stacked structure 453, a second cladding layer 454, and a transparent electrode layer 456 formed on the substrate 451 along a first direction. As an example, the transparent electrode layer 456 may include an ITO layer. In some embodiments, the semiconductor laser 450 may also include an electrode 457 formed on the substrate 451 and an electrode 458 formed on the transparent electrode layer 456.

[0101] In some embodiments, the layers and composition of the semiconductor laser 450 may be similar to those of the semiconductor laser 410 discussed above, except that, in the semiconductor laser 450 , light is emitted from the substrate side through optical design.

[0102] Figure 5 Schematic diagram of light field intensity distribution and material refractive index distribution of a semiconductor laser according to an embodiment of the present invention. Figure 5 The semiconductor laser (for example, Figure 3 The results of the semiconductor lasers 330, 370 in FIG.

[0103] Figure 5 The abscissa in represents thickness (eg, a distance extending along a first direction in a semiconductor laser), the ordinate on the left represents the normalized electric field intensity of an excited mode of the semiconductor laser, and the ordinate on the right represents the refractive index.

[0104] In some embodiments, through epitaxial structure design, the semiconductor laser is arranged so that the light field intensity of the excited mode reaches a minimum value at each tunnel junction along the first direction, such as Figure 5 In some embodiments, through epitaxial structure design, the semiconductor laser is arranged so that the light field intensity of the excited mode reaches a maximum value at each active region along the first direction, such as Figure 5as indicated by "QW" in Figure 5 as indicated by "PC" in

[0105] Figure 5 An enlarged view of the dash-dotted box in the curve is also shown. 510 and 520 indicate the positions where the refractive index of the material of the semiconductor laser reaches a maximum value along the first direction, which may correspond to the position of the active region of the semiconductor laser. 530 and 540 indicate the positions adjacent to 510 and 520 respectively, and 550 indicates the position between 510 and 520. 530, 540, and 550 may correspond to the positions of the tunneling junctions between two adjacent active regions of the semiconductor laser. In some embodiments, the refractive index of the material of the tunneling junction at the positions indicated by 530 and 540 may be less than the refractive index of the material at the position indicated by 550, and less than the refractive index of the material of the active region at the positions indicated by 510 and 520. Figure 5 This "low-high-low" setting of the refractive index of the tunneling junction of the semiconductor laser shown in Figure 5 is only an example along the first direction. Other types of tunneling junction material combinations can also be used. For example, tunneling junctions with material combinations of "low-high", "high-low", "high-low-high", "low-high-low-high", "high-low-high-low", etc. can be used. Tunneling junctions with different refractive index material combinations help to achieve the optical field design. Although

[0106] The semiconductor laser according to some embodiments of the present invention, as a PCSEL, improves the shape of the output light spot and reduces the packaging and testing cost compared to the EEL, and optimizes the divergence angle of the output light spot compared to the VCSEL. In addition, as a multi-junction PCSEL, it further increases the peak power compared to the PCSEL including a single active region, and increases the PCE under high-power operating conditions.

[0107] According to another aspect of the present disclosure, a method for forming a semiconductor laser is provided.

[0108] Figure 6 A flowchart showing an example of a method for forming a semiconductor laser according to some embodiments of the present invention is shown. Method 600 can be used to form the semiconductor laser 200 described above in conjunction with Figure 2 described, or the semiconductor lasers 310, 330, 350, 370 described in conjunction with Figure 3 described, or the semiconductor lasers 410, 430, 450 described in conjunction with Figure 4 described.

[0109] Method 600 may include: at block 610, providing a substrate. The substrate may include any suitable semiconductor substrate. As an example, for a semiconductor laser that emits laser light in the range of 800 - 1000 nm, the substrate may include GaAs. As another example, for a semiconductor laser that emits laser light in the range of 1450 - 1650 nm, the substrate may include InP.

[0110] Method 600 may include: at block 630, growing an epitaxial structure on the substrate along a first direction.

[0111] In some embodiments, the step at block 630 may include: at block 631, growing an active region stack structure, where the active region stack structure includes a plurality of active regions stacked along the first direction. By forming an active region stack structure including a plurality of active regions, the power of the semiconductor laser is effectively increased. As an example, the active region may include a QW structure or an MQWs structure.

[0112] In some embodiments, the step at block 631 may include: growing a plurality of alternately arranged active regions and one or more tunneling junctions along the first direction, where each tunneling junction connects adjacent active regions. By using one or more tunneling junctions to connect adjacent active regions, the power of the light emitted by each active region is effectively coupled. In some embodiments, a periodic active region - tunneling junction structure may be formed along the first direction to improve the uniformity of the light field peak.

[0113] In some embodiments, the tunneling junction may include two first portions adjacent to the active regions on both sides to which it is connected and a second portion between the two first portions. The refractive index of the material of the two first portions may be lower than the refractive index of the material of the second portion and lower than the refractive index of the materials of the active regions on both sides to achieve the corresponding light field design.

[0114] In some embodiments, the step at block 630 may further include: at block 632, forming a PC structure on the side away from the substrate with respect to the active region stack structure along the first direction. The photonic PC may include a hole - type PC structure and a column - type PC structure. The following will be described in conjunction withFigure 7 , Figures 9 - 10 Describe the formation process of the hole-type PC structure and, in combination with Figure 8 , Figures 11 - 12 describe the formation process of the columnar PC structure.

[0115] As described above in combination with Figure 5 In some embodiments, the epitaxial structure can be grown such that the optical field intensity of the excited mode of the semiconductor laser reaches a minimum value at each tunneling junction along a first direction. In some embodiments, the epitaxial structure can be grown such that the optical field intensity of the excited mode of the semiconductor laser reaches a maximum value at each active region along the first direction. In some embodiments, the epitaxial structure can be grown such that the optical field intensity of the excited mode of the semiconductor laser reaches a relatively high value at the PC structure. As an example, the relatively high value can be that the normalized electric field intensity reaches 0.7 or higher, 0.8 or higher, 0.9 or higher, 0.95 or higher, or 0.99 or higher, etc. In some embodiments, the semiconductor laser can also be configured to perform single-mode lasing with the above-described excited mode.

[0116] Optionally, in some embodiments, the step at block 630 can include: at block 633, forming a cladding layer. The formation of the PC structure is at least partially based on forming and / or processing at least a portion of the cladding layer, which will be described below in combination with Figures 7 - 12 . Optionally, in some embodiments, the step at block 630 can include: at block 634, forming a contact layer. Optionally, in some embodiments, the step at block 630 can include: at block 635, forming a reflective layer. The reflective layer is formed on the side of the active region stack structure facing away from the laser output. As an example, the reflective layer can include a DBR or a metal reflective layer, etc.

[0117] Optionally, in some embodiments, method 600 can include: at block 650, forming electrodes. The electrodes can be formed on opposite sides of the substrate and the opposing contact layer that face away from each other.

[0118] Figure 6 The method 600 shown in

[0119] Figure 7 does not require including all the shown steps, and the steps are not limited to being executed in the order shown. Those skilled in the art can add, subtract steps, and execute them in different orders according to the implementation of the semiconductor laser to be formed.

[0119] Figure 7 shows a flowchart of an example process for forming a hole-type PC structure according to some embodiments of the present invention.

[0120] Process 700 can include: at block 710, forming a semiconductor material layer on the side of the active region stack structure away from the substrate along a first direction.

[0121] Process 700 may include: at block 730, selectively etching a semiconductor material layer to form a plurality of periodically arranged hole-type PC structures.

[0122] Process 700 may include: at block 750, growing a cladding layer on a side of the semiconductor material layer away from the substrate along a first direction by epitaxial regrowth.

[0123] This will be further described in conjunction with Figures 9 - 10 Process 700.

[0124] Figure 8 A flowchart showing an example of a process for forming columnar PC structures according to some embodiments of the present invention.

[0125] Process 800 may include: at block 810, growing a cladding layer on a side of the active region stack structure away from the substrate along a first direction.

[0126] Process 800 may include: at block 850, at least partially etching the cladding layer along a first direction to form a plurality of periodically arranged columnar PC structures.

[0127] This will be further described in conjunction with Figures 11 - 12 Process 800.

[0128] Figures 9 - 10 A schematic diagram showing an example of a process for forming hole-type PC structures according to some embodiments of the present invention. This process may be similar to the process of forming Figure 3 the semiconductor laser 330 in

[0129] As Figure 9 shown in

[0130] At (A), a substrate 910 is provided. In some embodiments, the substrate may be GaAs. As an example, the substrate 910 may include an N-type substrate.

[0131] At (B), a reflective layer 920 is formed on the substrate 910. In some embodiments, the reflective layer 920 may include a DBR or a metal reflective layer, etc. In some embodiments using a DBR, the DBR may be AlGaAs and may be composed of periodically arranged materials with high Al content and low Al content. As an example, the reflective layer 920 may include an N-type DBR.

[0132] At (D), an active region stack structure 940 is formed on the first cladding layer 930, and the active region stack structure 940 includes one or more active regions. In some embodiments, the active region stack structure 940 may include a plurality of active regions and one or more tunneling junctions arranged alternately in a first direction, wherein each tunneling junction connects adjacent active regions. As an example, the active region may include QW or MQWs.

[0133] At (E), a semiconductor material layer 950 is formed on the active region stack structure 940.

[0134] At (F), the semiconductor material layer 950 is etched to form a series of openings 955 in the first direction.

[0135] At (G), a second cladding layer 960 is grown on the semiconductor material layer 950 by epitaxial regrowth, thereby forming a PC hole structure 958. As an example, the second cladding layer 960 may be made of AlGaAs. As an example, the second cladding layer 960 may include a P-type cladding layer.

[0136] Go to Figure 10 , and the process continues. At (H), a contact layer 970 is formed on the second cladding layer 960. As an example, the contact layer 970 may include a P-type contact layer.

[0137] At (I), an electrode 980 is formed on one side of the substrate 910, and an electrode 990 is formed on the side of the contact layer 970 opposite to the electrode 980.

[0138] Although Figures 9 - 10 the process of forming Figure 3 the semiconductor laser 330 or a similar semiconductor laser in Figure 9 has been described, those skilled in the art can understand that the semiconductor lasers 310, 350 or similar semiconductor lasers in Figure 3 can be adaptively formed by, for example, omitting the step of forming the reflective layer 920 shown at (B) in Figure 9 , and the semiconductor lasers 370 or similar semiconductor lasers in Figure 3 can be adaptively formed by, for example, adjusting the execution order of the step of forming the reflective layer 920 shown at (B) in

[0139] Figures 11 - 12 FIG. shows a schematic diagram of an example process for forming a hole-type PC structure according to an embodiment of the present invention. This process may be similar to the process of forming Figure 4 the semiconductor laser 430 in

[0140] As Figure 11As shown in [Figure 0], at (A), a substrate 1110 is provided. In some embodiments, the substrate may be made of GaAs. As an example, the substrate 1110 may include an N-type substrate.

[0141] At (B), a reflective layer 1120 is formed on the substrate 1110. In some embodiments, the reflective layer 1120 may include a DBR or a metal reflective layer. In some embodiments using a DBR, the DBR may be made of AlGaAs and is composed of a periodic arrangement of materials with high Al content and low Al content. As an example, the reflective layer 1120 may include an N-type DBR.

[0142] At (C), a first cladding layer 1130 is formed on the reflective layer 1120. As an example, the first cladding layer 1130 may be made of AlGaAs. As an example, the first cladding layer 1130 may include an N-type cladding layer.

[0143] At (D), an active region stack structure 1140 is formed on the first cladding layer 1130, and the active region stack structure 1140 includes one or more active regions. In some embodiments, the active region stack structure 1140 may include a plurality of active regions and one or more tunneling junctions arranged alternately in a first direction, wherein each tunneling junction connects adjacent active regions. As an example, the active region may include a QW or MQWs.

[0144] At (E), a second cladding layer 1150 is formed on the active region stack structure 1140.

[0145] At (F), the second cladding layer 1150 is at least partially etched along the first direction to form a plurality of periodically arranged pillar structures 1158. Through this step, the second cladding layer 1150 includes an upper portion having a plurality of periodically arranged pillar structures 1158 and includes a lower portion.

[0146] Go to Figure 12 , the process continues. At (G), a transparent electrode layer 1160 is formed on the second cladding layer 1150.

[0147] At (H), an electrode 1170 is formed on one side of the substrate 1110, and an electrode 1180 is formed on the side of the transparent electrode layer 1160 opposite to the electrode 1170.

[0148] Although Figures 11 - 12 the process of forming Figure 4 the semiconductor laser 430 or a similar semiconductor laser in [Figure X] is described, those skilled in the art can understand that, for example, by omitting Figure 11 the step of forming the reflective layer 1120 shown at (B) in [Figure X], the semiconductor lasers 410, 450 or similar semiconductor lasers in Figure 4 [Figure Y] can be adaptively formed.

[0149] A semiconductor laser formed by a method according to an embodiment of the present invention, as a PCSEL, improves the shape of an output light spot and reduces packaging and testing costs compared to an EEL, and optimizes the divergence angle of the output light spot compared to a VCSEL. In addition, as a multi-junction PCSEL, it further increases the peak power compared to a conventional PCSEL including a single active region, and increases the PCE under high-power operating conditions.

Claims

1. A semiconductor laser, comprising: a substrate; and an epitaxial structure grown on the substrate along a first direction, the epitaxial structure comprising: an active region stack structure including a plurality of active regions stacked along the first direction; a photonic crystal structure located on a side away from the substrate relative to the active region stack structure along the first direction, wherein the laser generated by the semiconductor laser exits along the first direction from the substrate or from a side away from the substrate.

2. The semiconductor laser according to claim 1, wherein the active region stack structure includes a plurality of active regions and one or more tunneling junctions alternately arranged along the first direction, wherein each tunneling junction connects adjacent active regions.

3. The semiconductor laser according to claim 2, wherein the epitaxial structure is configured such that the optical field intensity of the excited mode of the semiconductor laser reaches a minimum value at the one or more tunneling junctions and reaches a maximum value at each active region.

4. The semiconductor laser according to claim 3, wherein the epitaxial structure is further configured such that the optical field intensity of the excited mode of the semiconductor laser reaches 70% or more of the maximum optical field intensity at the photonic crystal structure.

5. The semiconductor laser according to claim 3 or 4, wherein the semiconductor laser is configured to emit in a single mode.

6. The semiconductor laser according to claim 2, wherein the tunneling junction includes two first portions adjacent to the active regions on both sides connected thereto and a second portion between the two first portions, wherein the materials of the two first portions have a first refractive index, the material of the second portion has a second refractive index, and the first refractive index is different from the second refractive index.

7. The semiconductor laser according to claim 1, wherein the epitaxial structure includes a semiconductor material layer grown on a side away from the substrate of the active region stack structure along the first direction, the epitaxial structure further includes: a cladding layer grown on the semiconductor material layer on a side away from the substrate along the first direction, the photonic crystal structure includes: a hole structure formed by etching the semiconductor material layer and forming the cladding layer on the semiconductor material layer.

8. The semiconductor laser according to claim 1, wherein the photonic crystal structure includes a column structure, and the epitaxial structure further includes: a cladding layer grown on the active region stack structure on a side away from the substrate along the first direction, wherein the column structure is formed by at least partially etching the cladding layer along the first direction.

9. The semiconductor laser according to claim 1, wherein the epitaxial structure further includes: a reflective layer formed on a side of the active region stack structure facing away from the laser output.

10. A method of forming a semiconductor laser, comprising: providing a substrate; and growing an epitaxial structure on the substrate along a first direction, wherein growing the epitaxial structure includes: A growth active region stack structure, the active region stack structure including a plurality of active regions stacked along the first direction; and forming a photonic crystal structure along the first direction on a side of the active region stack structure away from the substrate; wherein, laser light generated by the semiconductor laser exits along the first direction from the substrate or from a side away from the substrate.

11. The method according to claim 10, wherein growing the active region stack structure includes: growing a plurality of active regions and one or more tunneling junctions arranged alternately along the first direction, wherein each tunneling junction connects adjacent active regions.

12. The method according to claim 11, wherein the epitaxial structure is configured such that the optical field intensity of the excited mode of the semiconductor laser reaches a minimum value at the one or more tunneling junctions and reaches a maximum value at each active region.

13. The method according to claim 12, wherein the epitaxial structure is further configured such that the optical field intensity of the excited mode of the semiconductor laser reaches 70% or more of the maximum optical field intensity at the photonic crystal structure.

14. The method according to claim 12 or 13, wherein the semiconductor laser is configured to emit in a single mode.

15. The method according to claim 11, wherein the tunneling junction includes two first portions adjacent to the active regions on the two connected sides and a second portion between the two first portions, wherein the materials of the two first portions have a first refractive index, the material of the second portion has a second refractive index, and the first refractive index is different from the second refractive index.

16. The method according to claim 10, wherein forming the photonic crystal structure includes: forming a semiconductor material layer along the first direction on a side of the active region stack structure away from the substrate; etching the semiconductor material layer; by epitaxial regrowth, growing a cladding layer along the first direction on a side of the semiconductor material layer away from the substrate.

17. The method according to claim 10, wherein forming the photonic crystal structure includes: growing a cladding layer along the first direction on a side of the active region stack structure away from the substrate; and etching at least a part of the cladding layer along the first direction.

18. The method according to claim 10, wherein growing the epitaxial structure further includes: forming a reflective layer on a side of the active region stack structure facing away from the laser output.

Images