A vcseL epitaxial structure and a manufacturing method thereof, and a vcseL chip

Abstract

The application provides a VCSEL epitaxial structure and a manufacturing method thereof and a VCSEL chip. x The VCSEL epitaxial structure comprises an N-type DBR reflection layer, a resonant cavity layer and a P-type DBR reflection layer which are stacked on a substrate, the resonant cavity layer comprises an active region, the P-type DBR reflection layer comprises a first DBR stacked structure and a first AlGaAs transition layer, the first DBR stacked structure comprises Al y GaAs layers which are alternately stacked, and the first AlGaAs transition layer is arranged between the Al x GaAs layers and Al y GaAs layers, the doping concentration of the P-type DBR reflection layer gradually increases along a first direction, and the thickness of the first AlGaAs transition layer decreases with the increase of the doping concentration of the P-type DBR reflection layer, so that the series resistance is reduced and the absolute reflectivity is improved.

Description

Technical Field

[0001] This invention relates to the field of light-emitting diode technology, and more specifically, to a VCSEL epitaxial structure and its fabrication method, and a VCSEL chip. Background Technology

[0002] VCSEL (Vertical-Cavity Surface-Emitting Laser) chips are widely used in optical communication, optical interconnection, and optical storage due to their advantages such as small size, circular output spot, single longitudinal mode output, low threshold current, low price, and easy integration into large-area arrays.

[0003] Distributed Bragg reflective (DBR) is a reflective structure comprising an adjustable multilayer structure of two optical materials. The most common type is the quarter-wavelength reflector, where the thickness of each layer corresponds to a quarter of the wavelength. In vertical-cavity surface-emitting lasers (VCSELs), the resonant cavity is not based on a cleaved surface but rather on a monolithically grown multilayer dielectric film to form a semiconductor Bragg reflector. This achieves reflectivity exceeding 99%, avoiding the performance degradation caused by mechanical damage, surface oxidation, and contamination in the cleaved cavity of edge-emitting lasers. In avalanche photodetectors, a front-illuminated chip structure combined with a Bragg reflector can replace the conventional back-illuminated chip structure.

[0004] To achieve high reflectivity, the two materials constituting the DBR need to have a large refractive index difference, resulting in a large bandgap difference. This leads to high series resistance in the DBR, causing unnecessary power loss. Interface barrier peaks impede carrier flow, also contributing to high series resistance. The large effective hole mass and low carrier mobility of P-type doped DBRs, in particular, result in high series resistance, negatively impacting semiconductor device performance. To reduce series resistance, a gradient DBR structure with a transition layer is designed. This transition layer reduces series resistance by gradually decreasing barrier peaks and improving barrier shape.

[0005] However, in existing VCSEL chips, under the same logarithmic conditions, the series resistance of the gradient DBR structure with a transition layer is improved compared to the abrupt DBR structure without a transition layer, but the absolute reflectivity is lower than that of the abrupt DBR structure without a transition layer. Summary of the Invention

[0006] In view of this, the present invention provides a VCSEL epitaxial structure and its fabrication method, as well as a VCSEL chip, to solve the problems in existing VCSEL chips where, under the same logarithmic conditions, the series resistance of a gradient DBR structure with a transition layer is improved compared to a sudden DBR structure without a transition layer, but the absolute reflectivity is lower than that of a sudden DBR structure without a transition layer.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A VCSEL epitaxial structure, characterized in that it comprises:

[0009] Substrate;

[0010] An N-type DBR reflective layer, a resonant cavity layer, and a P-type DBR reflective layer are sequentially stacked on the substrate along a first direction. The resonant cavity layer includes an active region. The first direction is perpendicular to the substrate and extends from the substrate toward the P-type DBR reflective layer.

[0011] The P-type DBR reflective layer includes a first DBR stack structure and a first AlGaAs transition layer. The first DBR stack structure includes AlGaAs layers stacked alternately. x GaAs layer and Al y GaAs layer, the first AlGaAs transition layer is disposed on the Al x GaAs layer and the Al y Between GaAs layers, where x <y;

[0012] The doping concentration of the P-type DBR reflective layer increases sequentially along the first direction, and the thickness of the first AlGaAs transition layer decreases as the doping concentration of the P-type DBR reflective layer increases.

[0013] Preferably, the thickness of the first AlGaAs transition layer decreases linearly with the increase of the doping concentration of the P-type DBR reflective layer;

[0014] Alternatively, the thickness of the first AlGaAs transition layer decreases in a stepwise manner as the doping concentration of the P-type DBR reflective layer increases;

[0015] Alternatively, the thickness of the first AlGaAs transition layer decreases parabolically as the doping concentration of the P-type DBR reflective layer increases.

[0016] Preferably, the Al x GaAs layer, the Al y Both the GaAs layer and the first AlGaAs transition layer are p-type doped, and the doping concentration of the first AlGaAs transition layer is higher than that of the adjacent AlGaAs layer. xGaAs layer and the Al y Doping concentration of the GaAs layer.

[0017] Preferably, the thickness of the first AlGaAs transition layer ranges from 5 to 25 nm, including the endpoint values.

[0018] Preferably, the N-type DBR reflective layer includes a second DBR stack structure and a second AlGaAs transition layer, wherein the second DBR stack structure includes alternating layers of Al... a GaAs layer and Al b The GaAs layer, the second AlGaAs transition layer is disposed on the Al a GaAs layer and the Al b Between GaAs layers, where a <b。

[0019] Preferably, the doping concentration of the N-type DBR reflective layer increases sequentially in the opposite direction to the first direction, and the thickness of the second AlGaAs transition layer decreases as the doping concentration of the N-type DBR reflective layer increases.

[0020] Preferably, the Al a GaAs layer, the Al b Both the GaAs layer and the second AlGaAs transition layer are N-type doped, and the doping concentration of the second AlGaAs transition layer is higher than that of the adjacent AlGaAs layer. a GaAs layer and the Al b Doping concentration of the GaAs layer.

[0021] Preferably, in the first direction, the resonant cavity layer includes an N-type confinement layer, the active region, a P-type confinement layer, and an oxide layer stacked sequentially.

[0022] Preferably, the VCSEL epitaxial structure further includes:

[0023] A buffer layer located between the substrate and the N-type DBR reflective layer;

[0024] An ohmic contact layer located on the side of the P-type DBR reflective layer away from the resonant cavity layer.

[0025] This invention also provides a method for preparing a VCSEL epitaxial structure, the method comprising the following steps:

[0026] Provide a substrate;

[0027] Using an MOCVD device, an N-type DBR reflective layer, a resonant cavity layer, and a P-type DBR reflective layer are sequentially grown on the substrate via metal-organic chemical vapor deposition. The resonant cavity layer includes an active region.

[0028] The P-type DBR reflective layer includes a first DBR stack structure and a first AlGaAs transition layer. The first DBR stack structure includes AlGaAs layers stacked alternately. x GaAs layer and Al y GaAs layer, the first AlGaAs transition layer is disposed on the Al x GaAs layer and the Al y Between GaAs layers, where x <y;

[0029] The doping concentration of the P-type DBR reflective layer increases sequentially along the first direction, and the thickness of the first AlGaAs transition layer decreases as the doping concentration of the P-type DBR reflective layer increases.

[0030] A VCSEL chip, the VCSEL chip comprising the VCSEL epitaxial structure described in any of the preceding claims.

[0031] The above technical solution achieves the following results:

[0032] 1. The VCSEL epitaxial structure provided by the present invention includes a first DBR stack structure and a first AlGaAs transition layer by setting a P-type DBR reflective layer. The first DBR stack structure includes alternating layers of Al... x GaAs layer and Al y GaAs layer, the first AlGaAs transition layer is set on Al x GaAs layer and Al y Between GaAs layers, the doping concentration of the P-type DBR reflective layer increases sequentially along the first direction, and the thickness of the first AlGaAs transition layer decreases with increasing doping concentration of the P-type DBR reflective layer. That is, in the P-type DBR reflective layer, the Al content closer to the active region is increased. x GaAs layer and Al y The lower the doping concentration of the GaAs layer, the lower the absorption loss. A thicker first AlGaAs transition layer is used to lower the potential barrier, which can effectively reduce the series resistance. The further away from the active region the Al... x GaAs layer and Al y The GaAs layer is set with a high doping concentration to reduce series resistance, and a relatively thin first AlGaAs transition layer is used to improve absolute reflectivity. This setup reduces series resistance and improves absolute reflectivity at the same time.

[0033] 2. The method for fabricating the VCSEL epitaxial structure provided by this invention can effectively solve the problem that, under the same logarithmic conditions, the series resistance of the gradient DBR structure with a transition layer is improved compared to the abrupt DBR structure without a transition layer, but the absolute reflectivity is lower than that of the abrupt DBR structure without a transition layer.

[0034] 3. The VCSEL chip provided by the present invention, by using the aforementioned VCSEL epitaxial structure, can effectively solve the problem that in existing VCSEL chips, under the same logarithmic condition, the series resistance of the gradient DBR structure with a transition layer is improved compared to the abrupt DBR structure without a transition layer, but the absolute reflectivity is lower than that of the abrupt DBR structure without a transition layer, thereby improving the luminous efficiency of the VCSEL chip. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the VCSEL epitaxial structure provided in an embodiment of the present invention;

[0037] Figure 2 for Figure 1 Schematic diagram of the P-type DBR reflective layer structure;

[0038] Figures 3.1 to 3.3 This is a schematic diagram illustrating the variation of the thickness of a VCSEL epitaxial structure with doping concentration according to another embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the N-type DBR reflective layer structure of the VCSEL epitaxial structure provided in another embodiment of the present invention;

[0040] Explanation of symbols in the diagram:

[0041] 1. Substrate; 2. Buffer layer; 3. N-type DBR reflective layer; 31. Second DBR stacked structure; 311. Al a GaAs layer; 312, Al b 32. GaAs layer; 4. Second AlGaAs transition layer; 5. Resonant cavity layer; 6. N-type confinement layer; 7. Active region; 8. P-type confinement layer; 9. Oxide layer; 10. P-type DBR reflective layer; 11. First DBR stacked structure; 12. Alx GaAs layer; 512, Al y 52. GaAs layer; 6. First AlGaAs transition layer; 7. Ohmic contact layer. Detailed Implementation

[0042] To make the content of this invention clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0044] Secondly, this application provides a detailed description in conjunction with schematic diagrams. When detailing the embodiments of this application, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of this application. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0045] An embodiment of the present invention provides a VCSEL epitaxial structure, such as... Figures 1 to 2 As shown, it includes:

[0046] Substrate 1;

[0047] An N-type DBR reflective layer 3, a resonant cavity layer 4, and a P-type DBR reflective layer 5 are sequentially stacked on a substrate 1 along a first direction. The resonant cavity layer 4 includes an active region 42, and the first direction is perpendicular to the substrate 1 and points from the substrate 1 to the P-type DBR reflective layer 5.

[0048] The P-type DBR reflective layer 5 includes a first DBR stack structure 51 and a first AlGaAs transition layer 52. The first DBR stack structure 51 includes AlGaAs layers stacked alternately. x GaAs layer 511 and Al y GaAs layer 512, first AlGaAs transition layer 52 is disposed on Al x GaAs layer 511 and Al y Between GaAs layers 512, where x <y;

[0049] The doping concentration of the P-type DBR reflective layer 5 increases sequentially along the first direction, and the thickness of the first AlGaAs transition layer 52 decreases as the doping concentration of the P-type DBR reflective layer 5 increases.

[0050] Specifically, in this VCSEL epitaxial structure, the substrate 1 can be made of GaAs; in the first DBR stacked structure 51, the optical thickness of each sublayer is one-quarter of the optical wavelength; the doping concentration of the P-type DBR reflective layer 5 can increase in a linear, stepwise, parabolic, or any other form known in the art.

[0051] Optionally, in this embodiment, the Al composition of the first AlGaAs transition layer 52 gradually increases from x to y or gradually decreases from y to x.

[0052] Optionally, in this embodiment, the thickness of the first AlGaAs transition layer 52 ranges from 5 to 25 nm, including the endpoint values.

[0053] Optionally, in this embodiment, Al x GaAs layer 511, Al y Both the GaAs layer 512 and the first AlGaAs transition layer 52 are p-type doped, and the doping concentration of the first AlGaAs transition layer 52 is higher than that of the adjacent AlGaAs layer. x GaAs layer 511 and Al y The doping concentration of GaAs layer 512.

[0054] Optionally, in another embodiment of this application, such as Figure 3.1 As shown, the thickness of the first AlGaAs transition layer 52 decreases linearly with the increase of the doping concentration of the P-type DBR reflective layer 5.

[0055] Or, such as Figure 3.2 As shown, the thickness of the first AlGaAs transition layer 52 decreases in a stepwise manner as the doping concentration of the P-type DBR reflective layer 5 increases.

[0056] Or, such as Figure 3.3 As shown, the thickness of the first AlGaAs transition layer 52 decreases parabolically as the doping concentration of the P-type DBR reflective layer 5 increases.

[0057] Optionally, in another embodiment of this application, such as Figure 4 As shown, the N-type DBR reflective layer 3 includes a second DBR stack structure 31 and a second AlGaAs transition layer 32. The second DBR stack structure 31 includes AlGaAs layers stacked alternately. a GaAs layer 311 and Al b GaAs layer 312, second AlGaAs transition layer 32 is disposed on Al aGaAs layer 311 and Al b Between GaAs layers 312, where a <b。

[0058] Specifically, in the second DBR stacked structure 31, the optical thickness of each sublayer is one-quarter of the optical wavelength.

[0059] Optionally, in this embodiment, the Al composition of the second AlGaAs transition layer 32 gradually increases from a to b or gradually decreases from b to a.

[0060] Optionally, in this embodiment, Al a GaAs layer 311, Al b Both the GaAs layer 312 and the second AlGaAs transition layer 32 are N-type doped, and the doping concentration of the second AlGaAs transition layer 32 is higher than that of the adjacent AlGaAs layer. a GaAs layer 311 and Al b The doping concentration of GaAs layer 312.

[0061] Optionally, in this embodiment, the doping concentration of the N-type DBR reflective layer 3 increases sequentially in the opposite direction to the first direction, while the thickness of the second AlGaAs transition layer 32 remains constant.

[0062] Specifically, the doping concentration of the N-type DBR reflective layer 3 can increase in a linear, stepwise, parabolic, or any other form known in the art.

[0063] Optionally, in another embodiment of this application, the doping concentration of the N-type DBR reflective layer 3 increases sequentially in the opposite direction to the first direction, and the thickness of the second AlGaAs transition layer 32 decreases as the doping concentration of the N-type DBR reflective layer 3 increases.

[0064] It should be noted that, in this embodiment, in the N-type DBR reflective layer, the Al is set closer to the active region. a GaAs layer and Al b The lower the doping concentration of the GaAs layer, the lower the absorption loss. A thicker second AlGaAs transition layer is used to lower the potential barrier, which can effectively reduce the series resistance. Furthermore, the further away from the active region the Al... a GaAs layer and Al b The GaAs layer is set with a high doping concentration to reduce series resistance, and a relatively thin second AlGaAs transition layer is used to improve absolute reflectivity. This setup reduces series resistance and improves absolute reflectivity at the same time.

[0065] Optionally, in this embodiment, the thickness of the second AlGaAs transition layer 32 ranges from 5 to 25 nm, including the endpoint values.

[0066] Optionally, in another embodiment of this application, reference is made to... Figure 3.1 As shown, the thickness of the second AlGaAs transition layer 32 decreases linearly with the increase of the doping concentration of the N-type DBR reflective layer 3.

[0067] Or, refer to Figure 3.2 As shown, the thickness of the second AlGaAs transition layer 32 decreases in a stepwise manner as the doping concentration of the N-type DBR reflective layer 3 increases.

[0068] Or, refer to Figure 3.3 As shown, the thickness of the second AlGaAs transition layer 32 decreases parabolically with the increase of the doping concentration of the N-type DBR reflective layer 3.

[0069] Optionally, in another embodiment of this application, reference is made to... Figure 1 As shown, in the first direction, the resonant cavity layer 4 includes an N-type confinement layer 41, an active region 42, a P-type confinement layer 43, and an oxide layer 44 stacked sequentially.

[0070] Optionally, in another embodiment of this application, reference is made to... Figure 1 As shown, the VCSEL epitaxial structure also includes:

[0071] Buffer layer 2 is located between substrate 1 and N-type DBR reflective layer 3.

[0072] Specifically, in this VCSEL epitaxial structure, the material of the buffer layer 2 can be GaAs.

[0073] The ohmic contact layer 6 is located on the side of the P-type DBR reflective layer 5 that is away from the resonant cavity layer 4.

[0074] This embodiment provides a method for fabricating a VCSEL epitaxial structure, used to create the aforementioned VCSEL epitaxial structure, referencing... Figures 1 to 2 As shown, the manufacturing method includes the following steps:

[0075] Provide a substrate 1;

[0076] Using an MOCVD device, an N-type DBR reflective layer 3, a resonant cavity layer 4, and a P-type DBR reflective layer 5 are sequentially grown on a substrate 1 via metal-organic chemical vapor deposition. The resonant cavity layer 4 includes an active region 42.

[0077] The P-type DBR reflective layer 5 includes a first DBR stack structure 51 and a first AlGaAs transition layer 52. The first DBR stack structure 51 includes AlGaAs layers stacked alternately. x GaAs layer 511 and Al y GaAs layer 512, first AlGaAs transition layer 52 is disposed on Al x GaAs layer 511 and Aly Between GaAs layers 512, where x <y;

[0078] The doping concentration of the P-type DBR reflective layer 5 increases sequentially along the first direction, and the thickness of the first AlGaAs transition layer 52 decreases as the doping concentration of the P-type DBR reflective layer 5 increases.

[0079] Specifically, in this VCSEL epitaxial structure, the substrate 1 can be made of GaAs; in the first DBR stacked structure 51, the optical thickness of each sublayer is one-quarter of the optical wavelength; the doping concentration of the P-type DBR reflective layer 5 can increase in a linear, stepwise, parabolic, or any other form known in the art.

[0080] Optionally, in this embodiment, the Al composition of the first AlGaAs transition layer 52 gradually increases from x to y or gradually decreases from y to x.

[0081] Optionally, in this embodiment, the thickness of the first AlGaAs transition layer 52 ranges from 5 to 25 nm, including the endpoint values.

[0082] Optionally, in this embodiment, Al x GaAs layer 511, Al y Both the GaAs layer 512 and the first AlGaAs transition layer 52 are p-type doped, and the doping concentration of the first AlGaAs transition layer 52 is higher than that of the adjacent AlGaAs layer. x GaAs layer 511 and Al y The doping concentration of GaAs layer 512.

[0083] Optionally, in another embodiment of this application, reference is made to... Figure 3.1 As shown, the thickness of the first AlGaAs transition layer 52 decreases linearly with the increase of the doping concentration of the P-type DBR reflective layer 5.

[0084] Or, refer to Figure 3.2 As shown, the thickness of the first AlGaAs transition layer 52 decreases in a stepwise manner as the doping concentration of the P-type DBR reflective layer 5 increases.

[0085] Or, refer to Figure 3.3 As shown, the thickness of the first AlGaAs transition layer 52 decreases parabolically as the doping concentration of the P-type DBR reflective layer 5 increases.

[0086] Optionally, in another embodiment of this application, reference is made to... Figure 4 As shown, the N-type DBR reflective layer 3 includes a second DBR stack structure 31 and a second AlGaAs transition layer 32. The second DBR stack structure 31 includes AlGaAs layers stacked alternately. aGaAs layer 311 and Al b GaAs layer 312, second AlGaAs transition layer 32 is disposed on Al a GaAs layer 311 and Al b Between GaAs layers 312, where a <b。

[0087] Specifically, in the second DBR stacked structure 31, the optical thickness of each sublayer is one-quarter of the optical wavelength.

[0088] Optionally, in this embodiment, the Al composition of the second AlGaAs transition layer 32 gradually increases from a to b or gradually decreases from b to a.

[0089] Optionally, in this embodiment, Al a GaAs layer 311, Al b Both the GaAs layer 312 and the second AlGaAs transition layer 32 are N-type doped, and the doping concentration of the second AlGaAs transition layer 32 is higher than that of the adjacent AlGaAs layer. a GaAs layer 311 and Al b The doping concentration of GaAs layer 312.

[0090] Optionally, in this embodiment, the doping concentration of the N-type DBR reflective layer 3 increases sequentially in the opposite direction to the first direction, while the thickness of the second AlGaAs transition layer 32 remains constant.

[0091] Specifically, the doping concentration of the N-type DBR reflective layer 3 can increase in a linear, stepwise, parabolic, or any other form known in the art.

[0092] Optionally, in another embodiment of this application, the doping concentration of the N-type DBR reflective layer 3 increases sequentially in the opposite direction to the first direction, and the thickness of the second AlGaAs transition layer 32 decreases as the doping concentration of the N-type DBR reflective layer 3 increases.

[0093] It should be noted that, in this embodiment, in the N-type DBR reflective layer, the Al is set closer to the active region. a GaAs layer and Al b The lower the doping concentration of the GaAs layer, the lower the absorption loss. A thicker second AlGaAs transition layer is used to lower the potential barrier, which can effectively reduce the series resistance. Furthermore, the further away from the active region the Al... a GaAs layer and Al b The GaAs layer is set with a high doping concentration to reduce series resistance, and a relatively thin second AlGaAs transition layer is used to improve absolute reflectivity. This setup reduces series resistance and improves absolute reflectivity at the same time.

[0094] Optionally, in this embodiment, the thickness of the second AlGaAs transition layer 32 ranges from 5 to 25 nm, including the endpoint values.

[0095] Optionally, in another embodiment of this application, reference is made to... Figure 3.1 As shown, the thickness of the second AlGaAs transition layer 32 decreases linearly with the increase of the doping concentration of the N-type DBR reflective layer 3.

[0096] Or, refer to Figure 3.2 As shown, the thickness of the second AlGaAs transition layer 32 decreases in a stepwise manner as the doping concentration of the N-type DBR reflective layer 3 increases.

[0097] Or, refer to Figure 3.3 As shown, the thickness of the second AlGaAs transition layer 32 decreases parabolically with the increase of the doping concentration of the N-type DBR reflective layer 3.

[0098] Optionally, in another embodiment of this application, reference is made to... Figure 1 As shown, in the growth direction, the resonant cavity layer 4 includes an N-type confinement layer 41, an active region 42, a P-type confinement layer 43, and an oxide layer 44 that are grown sequentially.

[0099] Optionally, in another embodiment of this application, reference is made to... Figure 1 As shown, the VCSEL epitaxial structure also includes:

[0100] Before growing the N-type DBR reflective layer 3, a buffer layer 2 is first grown, which is located between the substrate 1 and the N-type DBR reflective layer 3.

[0101] Specifically, in this VCSEL epitaxial structure, the material of the buffer layer 2 can be GaAs.

[0102] After the P-type DBR reflective layer 5 is grown, an ohmic contact layer 6 is grown on the P-type DBR reflective layer 5.

[0103] This embodiment provides a VCSEL chip, which includes any of the VCSEL epitaxial structures described above.

[0104] In summary, the above technical solution achieves the following results:

[0105] 1. The VCSEL epitaxial structure provided in this embodiment includes a first DBR stack structure and a first AlGaAs transition layer by setting a P-type DBR reflective layer. The first DBR stack structure includes alternating layers of Al... x GaAs layer and Al y GaAs layer, the first AlGaAs transition layer is set on Al x GaAs layer and Aly Between GaAs layers, the doping concentration of the P-type DBR reflective layer increases sequentially along the first direction, and the thickness of the first AlGaAs transition layer decreases with increasing doping concentration of the P-type DBR reflective layer. That is, in the P-type DBR reflective layer, the Al content closer to the active region is increased. x GaAs layer and Al y The lower the doping concentration of the GaAs layer, the lower the absorption loss. A thicker first AlGaAs transition layer is used to lower the potential barrier, which can effectively reduce the series resistance. The further away from the active region the Al... x GaAs layer and Al y The GaAs layer is set with a high doping concentration to reduce series resistance, and a relatively thin first AlGaAs transition layer is used to improve absolute reflectivity. This setup reduces series resistance and improves absolute reflectivity at the same time.

[0106] 2. The method for fabricating the VCSEL epitaxial structure provided in the embodiment can effectively solve the problem that, under the same logarithmic conditions, the series resistance of the gradient DBR structure with a transition layer is improved compared to the abrupt DBR structure without a transition layer, but the absolute reflectivity is lower than that of the abrupt DBR structure without a transition layer.

[0107] 3. The VCSEL chip provided in the embodiment, by using the aforementioned VCSEL epitaxial structure, can effectively solve the problem that in existing VCSEL chips, under the same logarithmic condition, the series resistance of the gradient DBR structure with a transition layer is improved compared to the abrupt DBR structure without a transition layer, but the absolute reflectivity is lower than that of the abrupt DBR structure without a transition layer, thereby improving the luminous efficiency of the VCSEL chip.

[0108] Those skilled in the art should understand that, in the disclosure of this invention, the terms "lateral", "longitudinal", "upper", "lower", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0109] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0110] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A VCSEL epitaxial structure, characterized in that, include: Substrate; An N-type DBR reflective layer, a resonant cavity layer, and a P-type DBR reflective layer are sequentially stacked on the substrate along a first direction. The resonant cavity layer includes an active region. The first direction is perpendicular to the substrate and extends from the substrate toward the P-type DBR reflective layer. The P-type DBR reflective layer includes a first DBR stack structure and a first AlGaAs transition layer. The first DBR stack structure includes AlGaAs layers stacked alternately. x GaAs layer and Al y GaAs layer, the first AlGaAs transition layer is disposed on the Al x GaAs layer and the Al y Between GaAs layers, where x <y; The doping concentration of the P-type DBR reflective layer increases sequentially along the first direction, and the thickness of the first AlGaAs transition layer decreases as the doping concentration of the P-type DBR reflective layer increases. Wherein, the Al x GaAs layer, the Al y Both the GaAs layer and the first AlGaAs transition layer are p-type doped, and the doping concentration of the first AlGaAs transition layer is higher than that of the adjacent AlGaAs layer. x GaAs layer and the Al y Doping concentration of the GaAs layer.

2. The VCSEL epitaxial structure according to claim 1, characterized in that: The thickness of the first AlGaAs transition layer decreases linearly with the increase of the doping concentration of the P-type DBR reflective layer; Alternatively, the thickness of the first AlGaAs transition layer decreases in a stepwise manner as the doping concentration of the P-type DBR reflective layer increases; Alternatively, the thickness of the first AlGaAs transition layer decreases parabolically as the doping concentration of the P-type DBR reflective layer increases.

3. The VCSEL epitaxial structure according to claim 1, characterized in that: The thickness of the first AlGaAs transition layer ranges from 5 to 25 nm, including the endpoint values.

4. The VCSEL epitaxial structure according to claim 1, characterized in that: The N-type DBR reflective layer includes a second DBR stack structure and a second AlGaAs transition layer. The second DBR stack structure includes alternating layers of Al... a GaAs layer and Al b The GaAs layer, the second AlGaAs transition layer is disposed on the Al a GaAs layer and the Al b Between GaAs layers, where a <b。 5. The VCSEL epitaxial structure according to claim 4, characterized in that: The doping concentration of the N-type DBR reflective layer increases sequentially in the opposite direction to the first direction, and the thickness of the second AlGaAs transition layer decreases as the doping concentration of the N-type DBR reflective layer increases.

6. The VCSEL epitaxial structure according to claim 4, characterized in that: The Al a GaAs layer, the Al b Both the GaAs layer and the second AlGaAs transition layer are N-type doped, and the doping concentration of the second AlGaAs transition layer is higher than that of the adjacent AlGaAs layer. a GaAs layer and the Al b Doping concentration of the GaAs layer.

7. The VCSEL epitaxial structure according to claim 1, characterized in that: In the first direction, the resonant cavity layer includes an N-type confinement layer, the active region, a P-type confinement layer, and an oxide layer stacked sequentially.

8. The VCSEL epitaxial structure according to claim 1, characterized in that: The VCSEL epitaxial structure also includes: A buffer layer located between the substrate and the N-type DBR reflective layer; An ohmic contact layer located on the side of the P-type DBR reflective layer away from the resonant cavity layer.

9. A method for fabricating a VCSEL epitaxial structure, characterized in that, The manufacturing method includes the following steps: Provide a substrate; Using an MOCVD equipment, an N-type DBR reflective layer, a resonant cavity layer, and a P-type DBR reflective layer are sequentially grown on the substrate along a first direction by metal-organic chemical vapor deposition. The resonant cavity layer includes an active region. The first direction is perpendicular to the substrate and points from the substrate to the P-type DBR reflective layer. The P-type DBR reflective layer includes a first DBR stack structure and a first AlGaAs transition layer. The first DBR stack structure includes AlGaAs layers stacked alternately. x GaAs layer and Al y GaAs layer, the first AlGaAs transition layer is disposed on the Al x GaAs layer and the Al y Between GaAs layers, where x <y; The doping concentration of the P-type DBR reflective layer increases sequentially along the first direction, and the thickness of the first AlGaAs transition layer decreases as the doping concentration of the P-type DBR reflective layer increases. Wherein, the Al x GaAs layer, the Al y Both the GaAs layer and the first AlGaAs transition layer are p-type doped, and the doping concentration of the first AlGaAs transition layer is higher than that of the adjacent AlGaAs layer. x GaAs layer and the Al y Doping concentration of the GaAs layer.

10. A VCSEL chip, characterized in that, The VCSEL chip includes the VCSEL epitaxial structure as described in any one of claims 1-8.

Images