Epitaxial structure and preparation method thereof, and vcsel chip

Abstract

The application relates to an epitaxial structure and a preparation method thereof and a VCSEL chip, comprising: a first Bragg reflection layer and a second Bragg reflection layer which are arranged in a stack, and an active layer, wherein the first Bragg reflection layer and the second Bragg reflection layer have different conductive types; the active layer is located between the first Bragg reflection layer and the second Bragg reflection layer, and the active layer comprises a plurality of barrier layers and well layers which are alternately stacked, each well layer and two barrier layers adjacent to the well layer form a quantum well, and the components and / or thicknesses of the well layers and the barrier layers are designed so that the state density of each quantum well formed at a preset energy level is substantially the same. The epitaxial structure and the preparation method thereof and the VCSEL chip make the carriers of the quantum wells uniformly distributed, thereby significantly improving the radiation recombination efficiency and the light field uniformity of the laser device.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor lasers, in particular to an epitaxial structure, a preparation method thereof and a VCSEL chip. BACKGROUND

[0002] Vertical cavity surface emitting laser (VCSEL) has many excellent characteristics, such as high resolution, low power consumption, easy integration, high reliability, etc., so it is favored in short distance optical communication, laser printing, 3D sensing and other scenes.

[0003] The active layer of the multi-quantum well often has the problem of uneven distribution of carriers in the quantum well, which causes the carriers to escape from the quantum well, seriously affecting the light-emitting recombination efficiency of the carriers. Furthermore, from the perspective of energy conversion, the unevenly distributed carriers cannot efficiently interact with photons in the effective area of the quantum well, and thus the energy of most carriers cannot be fully converted into light energy, but is dissipated in the form of heat energy, which not only reduces the light-emitting efficiency of the laser, but also may cause local overheating of the device, thereby affecting the stability and life of the device.

[0004] In the prior art, the main means to suppress electron overflow in the quantum well is to increase the electron blocking layer, but increasing the electron blocking layer will increase the overall film thickness of the device, not only increasing the manufacturing process difficulty, but also directly leading to the increase of the overall resistance of the device, reducing the photoelectric conversion efficiency of the device and increasing the heat dissipation difficulty of the device.

[0005] Therefore, how to realize the uniform distribution of carriers in the active layer of the laser has become a technical problem that needs to be solved by those skilled in the art. SUMMARY

[0006] Therefore, it is necessary to provide an epitaxial structure, a preparation method thereof and a VCSEL chip to solve the problem of uneven distribution of carriers in the quantum well in the prior art.

[0007] To achieve the above-mentioned purpose, on one hand, the present application provides an epitaxial structure, comprising:

[0008] The first Bragg reflection layer and the second Bragg reflection layer are stacked, wherein the first Bragg reflection layer and the second Bragg reflection layer have different conductive types;

[0009] The active layer is located between the first Bragg reflection layer and the second Bragg reflection layer, and the active layer comprises a plurality of alternately stacked well layers and barrier layers, each well layer and two barrier layers adjacent thereto constitute a quantum well, and the composition and / or thickness of the well layer and the barrier layer are designed to make the state density formed by each quantum well at a preset energy level substantially the same.

[0010] In one of the embodiments, the preset energy level is a ground state energy level.

[0011] In one of the embodiments, along a stacking direction of the epitaxial structure, a well width of each of the quantum wells gradually changes according to a first variation trend; and / or,

[0012] A well depth of each of the quantum wells gradually changes according to a second variation trend, one of the first variation trend and the second variation trend is a decreasing variation trend, and the other is an increasing variation trend.

[0013] In one of the embodiments, a physical thickness of the well layer of each of the quantum wells gradually changes according to the first variation trend.

[0014] In one of the embodiments, a band gap width of each of the well layers of the active layer gradually changes according to the first variation trend, and / or a band gap width of each of the barrier layers of the active layer gradually changes according to the second variation trend.

[0015] In one of the embodiments, the well layer includes a first element, the barrier layer includes a second element, a composition of the first element in each of the well layers of the active layer gradually changes according to the second variation trend; and / or

[0016] A composition of the second element in each of the barrier layers of the active layer gradually changes according to the second variation trend.

[0017] In one of the embodiments, the composition of the second element of each of the barrier layers of the active layer changes linearly.

[0018] In one of the embodiments, the first Bragg reflection layer is of N-type, the second Bragg reflection layer is of P-type, the first variation trend is a decreasing variation trend, and the second variation trend is an increasing variation trend.

[0019] In one of the embodiments, in the quantum well closest to the first Bragg reflection layer, a band gap width of the barrier layer closest to the first Bragg reflection layer is greater than a band gap width of the adjacent barrier layer farthest from the first Bragg reflection layer, and the band gap width of the barrier layer closest to the first Bragg reflection layer is not greater than a band gap width of the barrier layer closest to the second Bragg reflection layer.

[0020] The application further provides a preparation method of an epitaxial structure, comprising:

[0021] providing a substrate, epitaxially growing a first Bragg reflection layer on the substrate;

[0022] a first Bragg reflection layer is formed on the substrate, the first Bragg reflection layer having a first conductivity type;

[0023] a second Bragg reflection layer is formed on the active layer, the first Bragg reflection layer and the second Bragg reflection layer having different conductivity types.

[0024] In one embodiment, the active layer is formed on the first Bragg reflection layer, including:

[0025] the well layers and the barrier layers are alternately formed on the first Bragg reflection layer, and in the epitaxial growth direction, a well width of each of the quantum wells gradually changes according to a first change trend, and / or,

[0026] a well depth of each of the quantum wells gradually changes according to a second change trend, one of the first change trend and the second change trend is a decreasing change trend, and the other is an increasing change trend.

[0027] In one embodiment, the well width of each of the quantum wells gradually changes according to the first change trend, including:

[0028] a growth time of the well layer of each of the quantum wells gradually changes according to the first change trend, so that a physical thickness of the well layer of each of the quantum wells gradually changes according to the first change trend.

[0029] In one embodiment, the well depth of each of the quantum wells gradually changes according to the second change trend, including:

[0030] a band gap width of each of the well layers of the active layer gradually changes according to a first change trend, and / or, a band gap width of each of the barrier layers of the active layer gradually changes according to a second change trend.

[0031] In one embodiment, the well layer includes a first element, the barrier layer includes a second element, the band gap width of each of the well layers of the active layer gradually changes according to the first change trend, including:

[0032] a flow rate of a first gas source generating the first element in each of the well layers gradually changes according to the second change trend, so that a composition of the first element in each of the well layers of the active layer gradually changes according to the second change trend;

[0033] The control of the band gap width of each of the barrier layers of the active layer gradually changes according to a second change trend, comprising:

[0034] The flow rate of the second gas source for regulating the generation of the second element in each of the barrier layers gradually changes according to the second change trend, so that the composition of the second element in each of the barrier layers of the active layer gradually changes according to the second change trend.

[0035] The application also provides a VCSEL chip comprising the epitaxial structure according to any one of the above embodiments.

[0036] In one embodiment, the VCSEL chip further comprises a photoelectric confinement layer located on the side of the second Bragg reflection layer close to the active layer, and the photoelectric confinement layer is configured to define the light-emitting area of the VCSEL chip.

[0037] In one embodiment, the VCSEL chip further comprises a first electrode and a second electrode, the first electrode is an N-type electrode for connecting the negative electrode of an external circuit, and the second electrode is a P-type electrode for connecting the positive electrode of an external circuit.

[0038] The epitaxial structure, the preparation method thereof, and the VCSEL chip, by arranging the active layer between the first Bragg reflection layer and the second Bragg reflection layer with opposite conductive types, and by arranging the active layer to comprise a plurality of alternating well layers and barrier layers, each well layer and the adjacent barrier layer forming a quantum well, the active layer comprising a plurality of quantum wells, and by designing the composition and / or thickness of the well layers and the barrier layers to make the state density of each quantum well formed at a preset energy level substantially the same, ensures the uniform distribution of injected carriers among the quantum wells, effectively avoids the non-radiative recombination loss caused by the aggregation of carriers in local quantum wells, thereby significantly improves the radiation recombination efficiency and light field uniformity of the device. Meanwhile, the epitaxial structure is conducive to enhancing the interaction between carriers and photons in the active layer, improving the photoelectric conversion efficiency of the laser, and is conducive to the high-power and high-efficiency application of the vertical cavity surface emitting laser device. In some embodiments, by arranging the energy band height of the barrier layer close to the first Bragg reflection layer in the quantum well closest to the first Bragg reflection layer to be higher than that of the adjacent barrier layer away from the first Bragg reflection layer, and by arranging the energy band height of the barrier layer close to the first Bragg reflection layer to be not higher than that of the barrier layer closest to the second Bragg reflection layer, the smooth injection of carriers is ensured, the injection efficiency of carriers is improved, the confinement ability of quantum wells to carriers is improved, and the leakage or escape of carriers is effectively suppressed. Meanwhile, the barrier layer close to the first Bragg reflection layer in the quantum well closest to the first Bragg reflection layer can also act as an electron injection barrier to effectively suppress the backflow of carriers. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the accompanying drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0040] Figure 1 A cross-sectional structure schematic diagram of an epitaxial structure provided in an embodiment;

[0041] Figure 2 A band structure schematic diagram of an epitaxial structure provided in an embodiment;

[0042] Figure 3 A flow chart of a preparation method of an epitaxial structure provided in an embodiment;

[0043] Figure 4 A cross-sectional structure schematic diagram of a substrate in a preparation method of an epitaxial structure provided in an embodiment;

[0044] Figure 5 A cross-sectional structure schematic diagram after forming a first Bragg reflection layer in a preparation method of an epitaxial structure provided in an embodiment;

[0045] Figure 6 A cross-sectional structure schematic diagram after forming an active layer in a preparation method of an epitaxial structure provided in an embodiment;

[0046] Figure 7 A cross-sectional structure schematic diagram of a VCSEL chip provided in an embodiment.

[0047] Explanation of reference signs:

[0048] 1-first Bragg reflection layer, 2-second Bragg reflection layer, 3-active layer, 31-well layer, 32-barrier layer, 33-quantum well, 4-substrate, 5-optoelectronic confinement layer, 6-first electrode, 7-second electrode. DETAILED DESCRIPTION

[0049] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the related drawings. The embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0051] It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or connected to the other element or layer or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. It will also be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section; for example, a first doped type could be termed a second doped type; and similarly, a second doped type could be termed a first doped type; a first doped type and a second doped type are different doped types, for example, a first doped type can be P-type and a second doped type can be N-type, or a first doped type can be N-type and a second doped type can be P-type.

[0052] Spatially relative terms, such as "beneath", "below", "lower", "under", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and / or operation in addition to the orientations depicted in the figures. For example, if a device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" or "over" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can also be oriented in the other direction, and the spatially relative terms used herein are intended to encompass such additional orientations. It is to be understood that the spatially relative terms used herein, including up, down, top, bottom, front, back, leading, trailing, left, right, over, under, above, below, under, lower, upper, and the like, are intended for the device's use in the particular orientation as shown in the figures. It will be appreciated that the spatially relative terms are intended to encompass different orientations of the device in use and / or operation in addition to the orientations depicted in the figures. For example, if a device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" or "over" the other elements or features. Therefore, the exemplary term "below" can encompass both an orientation of above and below. The device can also be oriented in the other direction, and the spatially relative terms used herein are intended to encompass such additional orientations.

[0053] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including", or the like, as used herein, specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Also, in the present specification, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0054] Referring to Figures 1 to 2 (wherein, Figure 2 In the energy band diagram shown in the upper part as the conduction band bottom and in the lower part as the valence band top, the application provides an epitaxial structure, comprising: a first Bragg reflection layer 1, an active layer 3 and a second Bragg reflection layer 2 arranged in a stack, wherein the first Bragg reflection layer 1 and the second Bragg reflection layer 2 have different conductivity types; the active layer 3 is located between the first Bragg reflection layer 1 and the second Bragg reflection layer 2, and the active layer 3 comprises a plurality of alternately stacked well layers 31 and barrier layers 32, each well layer 31 and the two barrier layers adjacent thereto form a quantum well 33, and the composition and / or thickness of the well layer 31 and the barrier layer 32 are designed so that the state density of each quantum well 33 formed at a preset energy level is substantially the same.

[0055] It should be noted that the substantially the same here is because in the actual epitaxial growth and device operation process, the factors affecting the state density have certain complexity and uncontrollability. For example, in the actual epitaxial process, due to the composition, temperature fluctuation or slight difference in growth rate, the strain state or energy band of different quantum wells 33 is slightly different, which affects the density distribution of carriers at the energy level; the setting of the multi-layer well layer 31 and the barrier layer 32 in the active layer 3 inevitably exists a sub-nanometer thickness fluctuation and an interface mixed layer, which further causes a slight difference between the actual well depth and well width of each quantum well 33 and the ideal state, thereby causing a slight deviation in the electron and hole wave function distribution and the energy state density of different quantum wells 33; in the device working process, especially under high power density conditions, there may be an electric field or thermal field gradient at the position of each quantum well 33, which will affect the energy band structure and carrier distribution, and further cause a slight difference in the dynamic state density; and the application is to optimize the design of the thickness and composition to ensure that the effective state density distribution of each quantum well 33 is at the same level within the process error range near the preset energy level, which is sufficient to meet the key performance requirements such as consistent light emission and consistent gain of the laser under the working wavelength. Further, the "substantially the same" reflects the engineering optimization strategy of the epitaxial structure under the actual realizable conditions, rather than the theoretical ideal state, which not only guarantees the performance, but also has practical manufacturability, and embodies the technical feasibility and industrial adaptability of the application.

[0056] In the above example, by arranging the active layer 3 between the first Bragg reflection layer 1 and the second Bragg reflection layer 2 with opposite conductive types, and the active layer 3 is composed of a plurality of alternating well layers 31 and barrier layers 32, each well layer 31 and the two adjacent barrier layers 32 constitute a quantum well 33, and the energy levels of the plurality of quantum wells 33 are consistent, which ensures the uniform distribution of injected carriers among the quantum wells 33, effectively avoids the non-radiative recombination loss caused by the aggregation of carriers in the local quantum well 33, thereby significantly improving the radiation recombination efficiency and light field uniformity of the device. At the same time, the above epitaxial structure is beneficial to enhancing the interaction of carriers and photons in the active layer 3, improving the photoelectric conversion efficiency of the laser, and is beneficial to the high-power and high-efficiency application of the vertical cavity surface emitting laser device.

[0057] In an embodiment, the epitaxial structure further includes a substrate 4 for serving as the growth basis of other structure layers in the epitaxial structure. Therefore, the substrate 4 has good lattice matching with other structure layers grown thereon in the epitaxial structure, so as to suppress the generation of dislocations and improve the material quality. In order to meet the light emission performance of the laser, the substrate 4 also has high light transmittance. The material of the substrate 4 includes gallium arsenide, indium phosphide, sapphire, silicon carbide, and silicon, so as to adapt to the growth of the epitaxial structure of lasers of different systems. In the present embodiment, the material of the substrate 4 is gallium arsenide. It should be noted that the size of the epitaxial structure can be selected according to actual conditions without limitation under the condition of meeting the performance of the epitaxial structure.

[0058] In an embodiment, the first Bragg reflection layer 1 and the second Bragg reflection layer 2 with opposite conductive types and located at opposite sides of the active layer 3 are formed in the epitaxial structure, so as to construct the optical resonant cavity of the laser, and the photons are confined in the active layer 3 by Bragg interference, so as to realize resonance enhanced light emission.

[0059] In the laser, the first Bragg reflection layer 1 and the second Bragg reflection layer 2 can be designed to serve as the electron injection layer and the hole injection layer respectively by doping, and become part of the electrical injection path. It should be noted that the main function of the first Bragg reflection layer 1 and the second Bragg reflection layer 2 is the optical mirror surface, and in order to achieve good electrical injection characteristics, the doping, thickness, material selection and structure optimization need to be considered to avoid affecting the performance of the first Bragg reflection layer 1 and the second Bragg reflection layer 2. For example, the concentration of elements in the first Bragg reflection layer 1 and the second Bragg reflection layer 2 can be designed to be gradient, so as to ensure high reflectivity while reducing the series resistance of the device and optimizing the electrical injection efficiency.

[0060] The first Bragg reflection layer 1 is located above the substrate 4, and comprises a plurality of layers of high and low refractive index materials, such as GaAs, AlGaAs, InGaAsP, InP, GaN, AlGaN, etc., which are alternately grown, and each layer of material has a thickness satisfying the Bragg condition, i.e., the ratio of the wavelength to four times the refractive index, and the first Bragg reflection layer 1 has a high lattice matching degree with the active layer 3 to ensure high quantum efficiency of the device, and the first Bragg reflection layer 1 also has high reflectivity, which can confine photons in the active layer 3 by Bragg interference, in addition, the first Bragg reflection layer 1 has an N-type conductivity, and has a relatively low energy band barrier, which is beneficial to electron injection.

[0061] The second Bragg reflection layer 2 is located on the side of the active layer 3 away from the substrate 4, and also comprises a plurality of layers of high and low refractive index materials, such as GaAs, AlGaAs, InGaAsP, InP, GaN, AlGaN, etc., which are alternately grown, and each layer of material has a thickness satisfying the Bragg condition, i.e., the ratio of the wavelength to four times the refractive index, to ensure high quantum efficiency of the device, and the second Bragg reflection layer 2 also has high reflectivity, which can confine photons in the active layer 3 by Bragg interference, in addition, the second Bragg reflection layer 2 has a P-type conductivity, and has a relatively high energy band barrier, which is beneficial to hole injection.

[0062] In one embodiment, the active layer 3 is located between the first Bragg reflection layer 1 and the second Bragg reflection layer 2, and the active layer 3 is composed of a plurality of well layers 31 and barrier layers 32 alternately grown, each well layer 31 and two adjacent barrier layers 32 form a quantum well 33, and the active layer 3 includes a plurality of quantum wells 33, since the band gap of the well layer 31 is lower than that of the barrier layer 32, in a semiconductor heterojunction, when two materials with different band gaps are in contact, the energy band will bend to match the Fermi level, wherein the material with a narrow band gap, such as the well layer 31, has a lower conduction band bottom and a higher valence band top, and the overall energy band is “concave”, and the material with a wide band gap, such as the barrier layer 32, has a higher conduction band bottom and a lower valence band top, and the overall energy band is “convex”, and thus the well layer 31 and the two adjacent barrier layers 32 form a potential well (similar to an “well-shaped” structure) in the active layer 3, which is called a quantum well 33.

[0063] In one embodiment, the well width of each quantum well 33 gradually changes according to a first change trend, and / or the well depth of each quantum well 33 gradually changes according to a second change trend, one of the first change trend and the second change trend is a decreasing change trend, and the other is an increasing change trend. That is, by adjusting the well width and / or the well depth, the energy levels of the phase-cascaded quantum wells 33 can be aligned, and the state density formed at the energy levels is substantially the same.

[0064] In one embodiment, the physical thickness of each well layer 31 of the active layer 3 gradually changes according to a first change trend, the physical thickness of each well layer 31 represents the actual well width of the quantum well 33, the narrower the well, the higher the quantized energy level, and the larger the energy level spacing, therefore, by adjusting the physical thickness of each well layer 31, the well width of the corresponding quantum well 33 can be adjusted. Exemplarily, the physical thickness of the well layer 31 is 5-30 nm; the physical thickness of the barrier layer 32 is 10-40 nm, and the physical thickness of the barrier layer 32 in each quantum well 33 is greater than the physical thickness of the well layer 31, that is, the physical thicknesses of the well layer 31 and the barrier layer 32 are both in the order of nanometers, which ensures the effect of the quantum well 33, and the thick enough barrier layer 32 also avoids the tunneling of carriers between the quantum wells 33.

[0065] In one embodiment, the band gap of each well layer 31 of the active layer 3 gradually changes according to a first change trend, and / or the band gap of each barrier layer 32 of the active layer 3 gradually changes according to a second change trend. The well depth of the quantum well 33 is mainly related to the band gaps of the barrier layer 32 and the well layer 31 that constitute the corresponding quantum well 33, the narrower the band gap of the well layer 31, that is, the lower the “bottom” of the quantum well 33, and the wider the band gap of the barrier layer 32, that is, the higher the “wall” of the quantum well 33, therefore, by adjusting the narrower band gap of the well layer 31, and / or the wider band gap of the barrier layer 32, the deeper well depth of the quantum well 33 can be achieved.

[0066] Further, the well layer 31 includes a first element, the barrier layer 32 includes a second element, the composition of the first element in each well layer 31 of the active layer 3 gradually changes according to a second change trend, and / or the composition of the second element in each barrier layer 32 of the active layer 3 gradually changes according to a second change trend. The band gaps of the well layer 31 and the barrier layer 32 are mainly achieved by adjusting the composition of the elements in the well layer 31 and the barrier layer 32.

[0067] Exemplarily, the well layer 31 is In x Ga 1-x As, the first element is an In element, wherein x represents the composition of the In element, 0≤x≤0.4; specifically, when the content of the In element increases, the band gap of the well layer 31 becomes narrower, that is, the “bottom” energy is lowered, and the bound state energy level is lowered; the barrier layer 32 includes Aly Ga 1-y As, the second element is Al element, y represents the component of Al element, 0≤y≤0.4; wherein, when the component of Al element increases, the band gap of the barrier layer 32 becomes higher, the "well wall" height is improved, the binding capacity of the carrier is improved, therefore, by controlling the component of Al element in the barrier layer 32 and the change of In element in the well layer 31, the quantum confinement effect in the quantum well 33 can be further regulated, so that the energy levels of each quantum well 33 remain consistent.

[0068] In the embodiment, the first Bragg reflection layer 1 is of N type, the second Bragg reflection layer 2 is of P type, the first change trend is a decreasing change trend, and the second change trend is an increasing change trend. Therefore, according to the above change trend, the well width of the quantum well 33 is regulated by adjusting the physical thickness of the well layer 31, and the well depth of the quantum well 33 is regulated by adjusting the components of the first element and the second element, so as to form a quantum well 33 with precise depth and width control, to accurately regulate the energy levels of each quantum well 33 to be aligned, and the state density formed at the energy level is basically the same, to realize the uniform distribution of carriers, improve the carrier light emission recombination efficiency, realize the inhibition of carrier overflow, and improve the retention of carriers in the quantum well; and improve the photoelectric conversion efficiency of carriers and photons in the region with high light field intensity.

[0069] Exemplarily, the preset energy level is a ground state energy level (M=1 energy level), that is, the energy level position corresponding to the first subband of the electron and the first subband of the hole. By reasonably regulating the component ratio and thickness parameters of each well layer 31 and its adjacent barrier layer 32, all quantum wells 33 have basically the same electron and hole state density at the ground state energy level, so as to realize the high alignment of the energy levels between the electron ground state and the hole ground state, facilitate the formation of excitons, maximize the spatial wave function overlap of the electron and the hole, enhance the radiation recombination probability, improve the optical gain and light emission intensity of the device, and at the same time, inhibit the non-radiative recombination path; and ensure the consistency and synchronization of each quantum well 33 in the multi-quantum well structure for laser output. It should be noted that although the above structure takes alignment as the preferred implementation manner, the present application is not limited to the configuration of the ground state energy level. For some special application scenarios, such as the need to realize multi-wavelength emission, enhance the high-order excited state recombination efficiency, or regulate the gain spectrum width, the energy level alignment of high-order excited states (such as the first excited state and the second excited state) can also be further introduced in the design. At this time, by further fine regulation of the quantum well layer structure parameters, the quantum well 33 can form a consistent state density distribution at one or more non-ground state energy levels, so as to realize a specific functional target, which will not be described here.

[0070] In one embodiment, the composition of the second element of each barrier layer 32 of the active layer 3 varies linearly. That is, each barrier layer 32 exhibits a band tilt structure, the higher end of which achieves effective inhibition of electron overflow, improving the carrier retention rate in the active layer 3, and the lower end of which helps to reduce the electron injection barrier, improving the injection efficiency. Therefore, the band tilt guides the carrier flow path, allowing the carriers to be more evenly distributed among the multiple quantum wells 33, reducing excessive recombination in a single quantum well, improving overall light-emitting efficiency, and effectively reducing the collision and non-radiative recombination of high-energy electrons among the multiple quantum wells 33. The composition in each barrier layer 32 can also remain unchanged or exhibit other trends, and is not limited to the above linear variation, while meeting the performance of the subsequently formed device.

[0071] In one embodiment, in order to inhibit electron backflow at the electron injection end, i.e., the side close to the first Bragg reflection layer 1, the band gap of the barrier layer 32 closest to the first Bragg reflection layer 1 in the quantum well 33 closest to the first Bragg reflection layer 1 is greater than that of the adjacent barrier layer 32 away from the first Bragg reflection layer 1, and the band gap of the barrier layer 32 closest to the first Bragg reflection layer 1 is not greater than that of the barrier layer 32 closest to the second Bragg reflection layer 2. While ensuring the injection efficiency of electrons, the barrier layer 32 closest to the first Bragg reflection layer 1 can also act as an electron barrier to effectively inhibit electron backflow.

[0072] Further, it should be noted that the band gap of each barrier layer 32 in the active layer 3 is less than that of the first Bragg reflection layer 1 and the second Bragg reflection layer 2, so as to effectively inhibit the carriers in the active layer 3, thereby maximizing the quantum efficiency of the device and ensuring the light-emitting intensity and photoelectric conversion efficiency.

[0073] The number of quantum wells 33 is not less than 3, so as to satisfy the synergistic optimization of carrier transport, optical gain, and thermal management, while ensuring the working efficiency of the device, the device life, heat control, and high-frequency response capability are also taken into account.

[0074] Referring to Figure 3 In one embodiment, the application also provides a preparation method of an epitaxial structure, comprising the following steps:

[0075] Step S1: providing a substrate 4, and epitaxially growing a first Bragg reflection layer 1 on the substrate 4;

[0076] Step S2: epitaxially growing an active layer 3 on the first Bragg reflection layer 1, the active layer 3 comprising a plurality of alternately stacked well layers 31 and barrier layers 32, each well layer 31 and the two barrier layers 32 adjacent thereto forming a quantum well 33, the composition and / or thickness of the well layer 31 and the barrier layer 32 being designed such that the state density formed at a predetermined energy level in each quantum well 33 is substantially the same.

[0077] Step S3: epitaxially growing a second Bragg reflection layer 2 on the active layer 3.

[0078] In the above example, the preparation method of the epitaxial structure realizes the preparation of the active layer 3 with the multiple quantum wells 33 having the energy level alignment and the first Bragg reflection layer 1 and the second Bragg reflection layer 2, and is suitable for the application of high-performance optical devices such as vertical cavity surface emitting lasers.

[0079] Specifically, referring to Figures 4 to 5 , step S1 is performed to provide a substrate 4 and epitaxially grow the first Bragg reflection layer 1 on the substrate 4.

[0080] In one embodiment, before epitaxially growing the first Bragg reflection layer 1 on the substrate 4, the method further comprises:

[0081] The substrate 4 is pretreated. Illustratively, the pretreatment of the substrate 4 includes cleaning by a solvent and drying by a gas to remove contaminants and ensure the quality of subsequent epitaxial growth.

[0082] In one embodiment, epitaxially growing the first Bragg reflection layer 1 on the substrate 4 comprises:

[0083] Materials with high and low refractive indexes are alternately grown on the substrate 4 to obtain the first Bragg reflection layer 1. The method of alternately growing the materials with high and low refractive indexes on the substrate 4 includes metal organic chemical vapor deposition or other suitable methods.

[0084] Specifically, referring to Figure 6 , step S2 is performed to epitaxially grow the active layer 3 on the first Bragg reflection layer 1, the active layer 3 comprising a plurality of alternately stacked well layers 31 and barrier layers 32, each well layer 31 and two adjacent barrier layers 32 thereof constituting a quantum well 33, the components and / or thicknesses of the well layers 31 and the barrier layers 32 being designed to make the state densities of each quantum well 33 formed at a preset energy level substantially the same.

[0085] In one embodiment, epitaxially growing the active layer 3 on the first Bragg reflection layer 1 comprises:

[0086] The barrier layers 32 and the well layers 31 are alternately grown on the substrate 4, and in the epitaxial growth direction, the well width of each quantum well is controlled to gradually change according to a first change trend, and / or the well depth of each quantum well 33 is controlled to gradually change according to a second change trend, one of the first change trend and the second change trend being a decreasing change trend and the other being an increasing change trend. The method of growing the barrier layers 32 and the well layers 31 on the substrate 4 includes a metal organic chemical vapor deposition process or other suitable methods.

[0087] Further, the well width of each quantum well 33 is gradually changed according to a first change trend, including:

[0088] The growth time of the well layer 31 of each quantum well 33 is gradually changed according to a first change trend, so that the physical thickness of the well layer 31 of each quantum well 33 is gradually changed according to the first change trend.

[0089] Further, the well width of each quantum well 33 is gradually changed according to a first change trend, including:

[0090] The band gap width of each well layer of the active layer 3 is gradually changed according to a first change trend, and / or the band gap width of each barrier layer 32 of the active layer 3 is gradually changed according to a second change trend.

[0091] Further, the well layer 31 includes a first element, the barrier layer 32 includes a second element, the band gap width of each well layer 31 of the active layer 3 is gradually changed according to a first change trend, including:

[0092] The flow rate of the first gas source generating the first element in each well layer 31 is gradually changed according to a second change trend, so that the composition of the first element in each well layer 31 of the active layer 3 is gradually changed according to the second change trend;

[0093] The band gap width of each barrier layer 32 of the active layer 3 is gradually changed according to a second change trend, including:

[0094] The flow rate of the second gas source generating the second element in each barrier layer 32 is gradually changed according to a second change trend, so that the composition of the second element in each barrier layer of the active layer 3 is gradually changed according to the second change trend.

[0095] Specifically, the first gas source and the second gas source are respectively used as precursors for generating the first element and the second element, the first gas source includes TMIn, and the second gas source includes TMAl.

[0096] In addition, the flow rate of the second gas source of each barrier layer 32 is linearly changed, so that the composition of the second element of each barrier layer 32 of the active layer 3 is linearly changed.

[0097] In addition, during the epitaxial growth of the active layer 3, the temperature uniformity needs to be ensured to prevent composition mismatch.

[0098] Specifically, referring to Figure 1 , step S3 is performed to epitaxially grow the second Bragg reflection layer 2 on the active layer 3.

[0099] In one embodiment, the second Bragg reflection layer 2 is epitaxially grown on the active layer 3, including:

[0100] The second Bragg reflection layer 2 is formed on the active layer 3 by alternately growing high and low refractive index materials using a metal organic chemical vapor deposition process. In this embodiment, the second Bragg reflection layer 2 is formed on the photoelectric confinement layer 5.

[0101] For the specific structure and related description in the example of the preparation method of the epitaxial structure, reference can be made to the related content in the embodiment of the epitaxial structure, which will not be described herein again.

[0102] Please refer to Figure 7 In another embodiment, the application further provides a VCSEL chip comprising the epitaxial structure according to any one of the above embodiments.

[0103] In one embodiment, the VCSEL chip further comprises a photoelectric confinement layer 5 located on the side of the second Bragg reflection layer 2 close to the active layer 3, and the photoelectric confinement layer 5 is configured to define the light-emitting area of the VCSEL chip. The photoelectric confinement layer 5 is obtained by selectively oxidizing one or more material layers in the second Bragg reflection layer 2 close to the active layer 3 through wet oxidation, and the unoxidized part serves as the light-emitting area of the VCSEL chip. For example, when the material of the second Bragg reflection layer 2 is AlGaAs, the material of the photoelectric confinement layer 5 is Al2O3. The photoelectric confinement layer 5 can achieve triple constraint of current, carrier and photon, so that the current only passes through the unoxidized part of the second Bragg reflection layer 2, the threshold current is reduced, the strong light field constraint is achieved through the difference in reflectivity between the unoxidized part of the second Bragg reflection layer 2 and the photoelectric confinement layer 5, and the potential barrier is formed by the photoelectric confinement layer 5 to block the lateral diffusion of holes, thereby improving the quantum efficiency.

[0104] In one embodiment, the VCSEL chip further comprises a first electrode 6 and a second electrode 7, the first electrode 6 is an N-type electrode for connecting the negative electrode of an external circuit, and the second electrode 7 is a P-type electrode for connecting the positive electrode of the external circuit.

[0105] For example, when the first electrode 6 and the second electrode 7 are located on the two sides of the active layer 3, the first electrode 6 is located on the surface of the substrate 4 away from the active layer 3, and the second electrode 7 is located on the surface of the second Bragg reflection layer 2 away from the active layer 3. The material of the first electrode 6 includes gold, nickel, cadmium or other suitable conductive materials; and the material of the second electrode 7 includes gold, platinum, titanium or other suitable conductive materials.

[0106] In the working process, the current flows from the second electrode 7, sequentially passes through the second Bragg reflection layer 2, the active layer 3 and the first Bragg reflection layer 1, and then flows out from the first electrode 6 to form a complete current path.

[0107] The shapes of the first electrode 6 and the second electrode 7 can be selected according to actual conditions. For example, the second electrode 7 can be designed as a ring shape to define a light path channel while improving the uniformity of current transmission and improving the performance of the chip.

[0108] It should be noted that the VCSEL chip includes the epitaxial structure described above, and specifically, the epitaxial structure can be applied to the preparation of the VCSEL chip, and through cooperation with subsequent processing processes (such as etching, photoelectric restriction layer formation, electrode deposition, cavity surface treatment, etc.), a VCSEL chip with high gain, high stability, low threshold, and good temperature control characteristics can be prepared.

[0109] The above-mentioned VCSEL chip has wide application prospects in high-end optoelectronic application scenarios such as communication, sensing, laser radar (LiDAR), and face recognition.

[0110] It should be understood that, although Figure 3 The steps in the flowchart of the method can be executed in the order indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, Figure 3 At least some of the steps in the method can include multiple steps or stages, which are not necessarily executed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be alternately or alternately executed with other steps or steps or stages in other steps.

[0111] In the description of the present specification, the description referring to the terms "some embodiments", "other embodiments", "ideal embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example.

[0112] The technical features of the above-described embodiments can be combined in any manner. In order to make the description concise, not all possible combinations of the technical features of the above-described embodiments are described, but as long as the combination of the technical features does not exist Contradiction, it should be considered as the scope of the present specification.

[0113] The above embodiments only express several implementation ways of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation to the patent scope of the application. It should be pointed out that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. An epitaxial structure, characterized by, The application relates to a semiconductor structure and a method for manufacturing the same. The semiconductor structure comprises: a first Bragg reflection layer and a second Bragg reflection layer which are arranged in a stack, wherein the first Bragg reflection layer and the second Bragg reflection layer have different conductive types; and an active layer which is located between the first Bragg reflection layer and the second Bragg reflection layer, wherein the active layer comprises a plurality of alternately stacked well layers and barrier layers, each well layer and two barrier layers adjacent to the well layer form a quantum well, the well width of each quantum well gradually changes according to a first change trend along the stacking direction of the epitaxial structure, the well depth of each quantum well gradually changes according to a second change trend, one of the first change trend and the second change trend is a decreasing change trend, and the other is an increasing change trend, the band gap width of each well layer of the active layer gradually changes according to the first change trend, the band gap width of each barrier layer of the active layer gradually changes according to the second change trend, the composition and thickness of the well layers and the barrier layers are designed so that the state density of each quantum well formed at a preset energy level is substantially the same, and the band gap width of the barrier layer closest to the first Bragg reflection layer is greater than the band gap width of the barrier layer farthest from the first Bragg reflection layer, and the band gap width of the barrier layer closest to the first Bragg reflection layer is not greater than the band gap width of the barrier layer closest to the second Bragg reflection layer. The preset energy level is a ground state energy level.

2. The epitaxial structure of claim 1, wherein The physical thickness of the well layer of each quantum well gradually changes according to the first change trend.

3. The epitaxial structure of claim 1, wherein The well layer comprises a first element, the barrier layer comprises a second element, the composition of the first element in each well layer of the active layer gradually changes according to the second change trend.

4. The epitaxial structure of claim 1, wherein, The composition of the second element in each barrier layer of the active layer gradually changes according to the second change trend. The composition of the second element in each barrier layer of the active layer changes linearly.

5. The epitaxial structure of claim 4, wherein, The conductive type of the first Bragg reflection layer is N type, the conductive type of the second Bragg reflection layer is P type, the first change trend is a decreasing change trend, and the second change trend is an increasing change trend.

6. The epitaxial structure of claim 1, wherein, The method comprises the following steps: providing a substrate, epitaxially growing a first Bragg reflection layer on the substrate; epitaxially growing an active layer on the first Bragg reflection layer, wherein the active layer comprises a plurality of alternately stacked barrier layers and well layers, each well layer and two barrier layers adjacent to the well layer form a quantum well, the well width of each quantum well gradually changes according to a first change trend along the stacking direction of the epitaxial structure, the well depth of each quantum well gradually changes according to a second change trend, one of the first change trend and the second change trend is a decreasing change trend, and the other is an increasing change trend; the band gap width of each well layer of the active layer gradually changes according to the first change trend, the band gap width of each barrier layer of the active layer gradually changes according to the second change trend, and the composition and thickness of the well layers and the barrier layers are designed so that the state density of each quantum well formed at a preset energy level is substantially the same.

7. A method of producing an epitaxial structure, characterized by, ​ ​ ​ ​ epitaxially growing a second Bragg reflection layer on the active layer, wherein the first Bragg reflection layer and the second Bragg reflection layer have different conductive types; in the quantum well closest to the first Bragg reflection layer, a band gap width of the barrier layer closest to the first Bragg reflection layer is greater than a band gap width of the adjacent barrier layer away from the first Bragg reflection layer, and the band gap width of the barrier layer closest to the first Bragg reflection layer is not greater than a band gap width of the barrier layer closest to the second Bragg reflection layer.

8. The method of claim 7, wherein the epitaxial structure is prepared by a method comprising: The active layer epitaxially grown on the first Bragg reflection layer comprises: alternately growing the barrier layer and the well layer on the first Bragg reflection layer, and controlling a well width of each quantum well to gradually change according to a first change trend in an epitaxial growth direction; controlling a well depth of each quantum well to gradually change according to a second change trend, one of the first change trend and the second change trend is a decreasing change trend, and the other is an increasing change trend.

9. The method of claim 8, wherein the epitaxial structure is prepared by a method comprising: The controlling of the well width of each quantum well to gradually change according to the first change trend comprises: controlling a growth time of the well layer of each quantum well to gradually change according to the first change trend, so that a physical thickness of the well layer of each quantum well gradually changes according to the first change trend.

10. The method of claim 8, wherein the epitaxial structure is prepared by a method comprising: The controlling of the well depth of each quantum well to gradually change according to the second change trend comprises: controlling a band gap width of each well layer of the active layer to gradually change according to a first change trend, and controlling a band gap width of each barrier layer of the active layer to gradually change according to a second change trend.

11. The method of claim 10, wherein the epitaxial structure is prepared by a method comprising: The well layer comprises a first element, and the barrier layer comprises a second element, the controlling of the band gap width of each well layer of the active layer to gradually change according to the first change trend comprises: controlling a flow of a first gas source generating the first element in each well layer to gradually change according to the second change trend, so that a component of the first element in each well layer of the active layer gradually changes according to the second change trend; The controlling of the band gap width of each barrier layer of the active layer to gradually change according to the second change trend comprises: controlling a flow of a second gas source generating the second element in each barrier layer to gradually change according to the second change trend, so that a component of the second element in each barrier layer of the active layer gradually changes according to the second change trend.

12. A VCSEL chip comprising the epitaxial structure according to any one of claims 1-6.

13. The VCSEL chip of claim 12, wherein, The VCSEL chip further comprises a photoelectric confinement layer, the photoelectric confinement layer is located on a side of the second Bragg reflection layer close to the active layer, and the photoelectric confinement layer is configured to define a light-emitting area of the VCSEL chip.

14. The VCSEL chip according to claim 12, further comprising a first electrode and a second electrode, the first electrode is an N-type electrode, used for connecting a negative electrode of an external circuit, and the second electrode is a P-type electrode, used for connecting a positive electrode of the external circuit.

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