Laser radar system, multi-junction VCSEL laser and preparation method of multi-junction VCSEL laser

Abstract

The invention belongs to the technical field of semiconductor lasers, and relates to a laser radar system, a multi-junction VCSEL laser and a preparation method thereof, the laser radar system comprises a substrate and an epitaxial unit, the epitaxial unit comprises a first reflector, a second reflector and a gain stacking structure comprising a plurality of gain unit bodies, and the first reflector grows on the top surface of the substrate; the second reflecting mirror and the first reflecting mirror jointly define a reflecting cavity; the gain stacking structure is located in the reflection cavity, and a second reflector grows on the top; the first reflecting mirror comprises a first semiconductor layer and a first oxide layer formed after partial oxidation of a second semiconductor layer which alternately grow in an epitaxial mode, and the second reflecting mirror comprises a third semiconductor layer and a second oxide layer formed after at least partial oxidation of a fourth semiconductor layer which alternately grow in an epitaxial mode. The refractive indexes of the first semiconductor layer and the third semiconductor layer are respectively greater than those of the first oxide layer and the second oxide layer. The application can meet the requirements of high power, low divergence angle and high modulation speed at the same time.

Description

Technical Field

[0001] The present application relates to the field of semiconductor laser technology, and in particular to a laser radar system, a multi-junction VCSEL laser and a method for manufacturing the same. Background Art

[0002] Vertical-Cavity Surface-Emitting Laser (VCSEL) is a semiconductor laser that forms a reflection cavity in the vertical direction of the substrate and emits laser in the vertical direction. It has many advantages such as low threshold current, circular spot, high modulation bandwidth, single longitudinal mode lasing, easy to achieve high-density two-dimensional array, low production cost, etc., and is widely used in many fields. Taking the field of LiDAR as an example, multi-junction VCSEL is a key technology to achieve high power density. With the continuous development of intelligent driving technology and the continuous expansion of application scenarios, the accelerated layout of automatic assisted navigation driving (Navigate on Autopilot, referred to as NOA) functions in cities, the LiDAR in the field of autonomous driving requires multi-junction VCSELs with higher standards such as high power, low divergence angle and high modulation speed.

[0003] In the prior art, a multi-junction VCSEL laser may include two reflectors, with a reflective cavity formed between the two reflectors. In order to increase the power, a tunnel junction is used in the reflective cavity to connect multiple groups of active areas in series. However, this will increase the equivalent cavity length of the reflective cavity, resulting in a divergence angle and modulation speed that are difficult to meet the requirements.

[0004] Therefore, there is an urgent need for a multi-junction VCSEL laser that meets the requirements of high power, low divergence angle and high modulation speed. Summary of the invention

[0005] The purpose of the embodiments of the present application is to solve the technical problem that the existing multi-junction VCSEL laser is difficult to meet the requirements of high power, low divergence angle and high modulation speed.

[0006] In order to solve the above technical problems, the embodiment of the present application provides a multi-junction VCSEL laser, which adopts the following technical solution:

[0007] The multi-junction VCSEL laser comprises a substrate and at least one epitaxial unit, each of the epitaxial units comprising:

[0008] A first reflector, grown on the top surface of the substrate by an epitaxial growth process;

[0009] A second reflector, which together with the first reflector forms a reflective cavity;

[0010] A gain stacked structure is located in the reflection cavity and has the second reflector grown on the top; the gain stacked structure includes a plurality of gain unit bodies; the plurality of gain unit bodies are connected in series along the growth direction through tunnel junctions;

[0011] The first reflector includes a first semiconductor layer that is alternately epitaxially grown and a first oxide layer that is formed by partial oxidation of the second semiconductor layer, and the refractive index of the first semiconductor layer is greater than the refractive index of the first oxide layer;

[0012] The second reflector includes a third semiconductor layer grown by alternate epitaxial growth and a second oxide layer formed by at least partial oxidation of the fourth semiconductor layer. The refractive index of the third semiconductor layer is greater than the refractive index of the second oxide layer.

[0013] In some embodiments of the present application, a ratio of a refractive index of the first semiconductor layer to a refractive index of the first oxide layer is greater than 1.5;

[0014] and / or, a ratio of a refractive index of the third semiconductor layer to a refractive index of the second oxide layer is greater than 1.5;

[0015] and / or, the alternating period between the first semiconductor layer and the first oxide layer is 4 or 5;

[0016] and / or, the alternating period between the third semiconductor layer and the second oxide layer is 4 or 5;

[0017] and / or, the thickness of the first semiconductor layer and the third semiconductor layer are both optical thicknesses of one quarter of the target wavelength;

[0018] The thickness of the second semiconductor layer is an optical thickness of one quarter of the target wavelength after the second semiconductor layer is oxidized to form the first oxide layer;

[0019] The thickness of the fourth semiconductor layer is an optical thickness of one quarter of the target wavelength after the fourth semiconductor layer is oxidized to form the second oxide layer;

[0020] The substrate is made of GaAs material; the first semiconductor layer and the third semiconductor layer are made of Al x Ga 1-x As semiconductor material, and its x=0-0.2; the second semiconductor layer and the fourth semiconductor layer are made of Al x Ga 1-x It is made of As semiconductor material, and its x=0.98~1.

[0021] In some embodiments of the present application, a positive electrode is provided on the top surface of the gain stack structure at the periphery of the second reflector, and a light outlet is formed;

[0022] And / or, the epitaxial unit is provided in plurality, and the plurality of epitaxial units are formed at intervals on the top surface of the substrate;

[0023] A negative electrode is provided at the bottom of the substrate; each of the epitaxial units is provided with an independent positive electrode and is electrically connected to the positive electrode and the negative electrode.

[0024] In some embodiments of the present application, each of the gain unit bodies includes an active layer and a current limiting layer stacked along a growth direction, a current hole that is not oxidized is formed in the middle portion of the current limiting layer, and the periphery of the current hole is an oxidized high resistance region;

[0025] The first oxide layer, the second oxide layer and the high resistance region are synchronously manufactured by simultaneously performing lateral oxidation on the first reflector, the second reflector and the current limiting layer.

[0026] In some embodiments of the present application, the total thickness of the gain stack structure is an integer multiple of half the central wavelength of the target light wave;

[0027] The tunnel junction and the current confinement layer are located at a node of the target light wave in the reflective cavity;

[0028] And / or, each of the gain units further comprises a spacer bottom layer and a spacer top layer, the top surface of the spacer bottom layer is stacked with the active layer; a portion of the spacer top layer is stacked on the top surface of the active layer, a portion of the spacer top layer is stacked on the top surface of the current limiting layer and is stacked with the tunnel junction;

[0029] The second reflector is stacked on the top spacing layer of the gain stack structure, and together with the positive electrode and the top spacing layer, forms the light outlet;

[0030] And / or, a negative electrode is provided at the bottom of the substrate;

[0031] The first oxide layer of the first reflector includes an oxide region and a non-oxide region, the oxide region and the non-oxide region are arranged in a direction perpendicular to the growth direction, and the oxide region covers the light exit hole in the growth direction; the second reflector covers the current hole in the growth direction;

[0032] The current of the positive electrode flows to the negative electrode through the current hole and the non-oxidation area in sequence.

[0033] In some embodiments of the present application, an oxidation groove is formed on the periphery of the gain stack structure along a direction away from the growth direction of the first reflector;

[0034] The multi-junction VCSEL laser further comprises an insulating layer, wherein the insulating layer is formed on a top surface of the first reflector, a groove wall of the oxidation groove, and a side wall and a top surface of the gain stack structure;

[0035] The positive electrode is formed on an outer surface of the insulating layer.

[0036] In order to solve the above technical problems, an embodiment of the present application further provides a laser radar system, which adopts the technical solution described below: the laser radar system includes the above-mentioned multi-junction VCSEL laser.

[0037] In order to solve the above technical problems, the embodiment of the present application further provides a method for preparing a multi-junction VCSEL laser, and the method for preparing a multi-junction VCSEL laser is applied to a multi-junction VCSEL laser;

[0038] The multi-junction VCSEL laser comprises a substrate and an epitaxial unit, wherein the epitaxial unit is electrically connected to a positive electrode and a negative electrode; the epitaxial unit comprises:

[0039] A first reflector includes a first semiconductor layer and a first oxide layer formed by partial oxidation of the second semiconductor layer, wherein the refractive index of the first semiconductor layer is greater than the refractive index of the first oxide layer;

[0040] a second reflector, which together with the first reflector forms a reflective cavity; the second reflector comprises a third semiconductor layer and a second oxide layer formed by at least partial oxidation of the fourth semiconductor layer, the refractive index of the third semiconductor layer being greater than the refractive index of the second oxide layer;

[0041] A gain stacked structure is formed with a light outlet; the gain stacked structure comprises a plurality of gain unit bodies, the plurality of gain unit bodies are connected in series along a growth direction through a tunnel junction; each of the gain unit bodies comprises a stacked active layer and a current limiting layer, a middle portion of the current limiting layer is formed with an unoxidized current hole, and the periphery of the current hole is an oxidized high resistance region;

[0042] The preparation method of the multi-junction VCSEL laser comprises:

[0043] Using an epitaxial growth process to alternately epitaxially grow the first semiconductor layer and the second semiconductor layer of the first reflector on the top surface of the substrate;

[0044] The gain unit body and the tunnel junction are alternately epitaxially grown on the top surface of the first reflector by using an epitaxial growth process to preliminarily form the gain stacked structure; wherein the tunnel junction is located on a side of the gain unit body away from the first reflector;

[0045] Using an epitaxial growth process to alternately epitaxially grow the third semiconductor layer and the fourth semiconductor layer of the second reflector on the top surface of the gain stack structure;

[0046] Sequentially etching the epitaxially grown second reflector, the gain stack structure and the first reflector to respectively expose the inner cavity contact layer of the gain stack structure, the side wall of the gain stack structure and form the current hole, and expose the side wall of the first reflector;

[0047] At the same time, the etched current limiting layer, the first reflector and the second reflector are laterally oxidized so that the current limiting layer forms the unoxidized current hole and the oxidized high resistance area, the second semiconductor layers of the first reflector become the first oxide layer, and the fourth semiconductor layers of the second reflector are oxidized to the second oxide layer to form a laser sample.

[0048] In some embodiments of the present application, after the step of forming the laser sample, the method for preparing the multi-junction VCSEL laser further includes:

[0049] forming an insulating layer on the outer surfaces of the gain stack structure and the first reflector of the laser sample to electrically isolate the non-current injection area, and etching the insulating layer on the top surface of the gain stack structure to form a current injection area;

[0050] Forming a first metal electrode layer on at least a portion of the insulating layer of the laser sample, and removing the first metal electrode layer in the current injection region, so that the positive electrode, the second reflector and the gain stack structure together enclose the light outlet and form the positive electrode;

[0051] forming a second metal electrode layer at the bottom of the substrate to form the negative electrode;

[0052] And / or, in the step of epitaxially growing the gain unit body, specifically comprising:

[0053] epitaxially growing a spacer bottom layer on the top surface of the epitaxially grown first reflecting mirror;

[0054] epitaxially growing an active layer on the top surface of the epitaxially grown spacer bottom layer;

[0055] Epitaxially growing a first sub-spacer layer on the top surface of the epitaxially grown active layer, and after the thickness of the first sub-spacer layer reaches a preset thickness, epitaxially growing a current limiting layer on the first sub-spacer layer;

[0056] Epitaxially growing a second sub-spacer layer on the top surface of the epitaxially grown current limiting layer to form the gain unit body by stacking layer by layer;

[0057] And / or, in the step of alternately epitaxially growing the first semiconductor layer and the second semiconductor layer of the first reflector, the number of alternating cycles of the alternate epitaxial growth is 3, 4, or 5, the thickness of the first semiconductor layer is an optical thickness of one quarter of the target wavelength; the thickness of the second semiconductor layer is an optical thickness of one quarter of the target wavelength after the second semiconductor layer is oxidized to form the first oxide layer; the first semiconductor layer and the second semiconductor layer are composed of Al x Ga 1-x As semiconductor material is epitaxially grown, wherein x in the first semiconductor layer is 0 to 0.2, and x in the second semiconductor layer is 0.98 to 1;

[0058] And / or, in the step of alternately epitaxially growing the third semiconductor layer and the fourth semiconductor layer of the second reflector, the number of alternating cycles of the alternate epitaxial growth is 3, 4 or 5, the thickness of the third semiconductor layer is an optical thickness of one quarter of the target wavelength; the thickness of the fourth semiconductor layer is an optical thickness of one quarter of the target wavelength after the fourth semiconductor layer is oxidized to form the second oxide layer; the third semiconductor layer and the fourth semiconductor layer are made of Al x Ga 1-x As semiconductor material is epitaxially grown, x in the third semiconductor layer is 0 to 0.2, and x in the fourth semiconductor layer is 0.98 to 1;

[0059] And / or, before the step of simultaneously performing lateral oxidation on the etched current limiting layer, the first reflector and the second reflector, the steps of the etching method of the first reflector include:

[0060] At the periphery of the second reflector, two symmetrical etching grooves with a target pattern are etched on the top surface of the first reflector with the center line of the first reflector as the center of symmetry, so that the exposed second semiconductor layer of the first reflector is gradually diffusely oxidized from each of the etching grooves toward the center of symmetry; or, at the periphery of the second reflector, etching grooves of a target pattern are etched on a single side of the top surface of the first reflector, so that the exposed second semiconductor layer of the first reflector is gradually diffusely oxidized from the etching grooves in one direction.

[0061] In some embodiments of the present application, the total thickness of the gain stack structure is an integer multiple of half the central wavelength of the target light wave;

[0062] In the step of epitaxially growing the tunnel junction, the tunnel junction is grown at a node of a target light wave in the reflective cavity;

[0063] In the step of epitaxially growing the current confinement layer, the current confinement layer is grown at a node of a target light wave in the reflection cavity.

[0064] Compared with the prior art, the laser radar system, multi-junction VCSEL laser and its preparation method provided in the embodiments of the present application mainly have the following advantages:

[0065] Beneficial effects:

[0066] The multi-junction VCSEL laser is formed by alternately epitaxially growing a first semiconductor layer and a first oxide layer formed by partial oxidation of a second semiconductor layer, and alternately epitaxially growing a third semiconductor layer and a second oxide layer formed by at least partial oxidation of a fourth semiconductor layer, so that the first reflector and the second reflector are both composited by two semiconductor materials and an oxide material with different refractive indices and a large refractive index difference, so as to reduce the penetration depth of the target light wave entering the reflector under the condition of achieving a specific reflectivity, reduce the number of alternating cycles between semiconductor layers in the reflector, and facilitate the realization of a smaller equivalent cavity length, so as to increase the transmission bandwidth of the reflector to achieve a high modulation speed of the multi-junction VCSEL laser, and reduce the divergence angle, and can simultaneously meet the requirements of high power, low divergence angle and high modulation speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the scheme in this application, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are some embodiments of this application or corresponding prior art. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0068] Figure 1 is a planar cross-sectional view of a multi-junction VCSEL laser in an example of the present application; the figure is also a schematic diagram of step S630 of the method for preparing a multi-junction VCSEL laser;

[0069] Figure 2 is a flow chart of a method for preparing a multi-junction VCSEL laser in an example of the present application;

[0070] Figure 3 is another flow chart of the method for preparing a multi-junction VCSEL laser in an example of the present application;

[0071] Figure 4 is a flow chart of step S200 of the method for preparing a multi-junction VCSEL laser in an example of the present application;

[0072] Figure 5 is a schematic diagram of step S100 of the method for preparing a multi-junction VCSEL laser in an example of the present application;

[0073] Figure 6 is a schematic diagram of step S210, step S220 and step S230 of the method for preparing a multi-junction VCSEL laser in an example of the present application;

[0074] Figure 7 is a schematic diagram of step S240, step S250 and step S260 of the method for preparing a multi-junction VCSEL laser in an example of the present application;

[0075] Figure 8 is a schematic diagram of step S300 of the method for preparing a multi-junction VCSEL laser in an example of the present application;

[0076] Fig. 9 is a schematic diagram of step S410 of the method for preparing a multi-junction VCSEL laser in the example of the present application;

[0077] Fig.10 is a schematic diagram of step S420 of the method for preparing a multi-junction VCSEL laser in the example of the present application;

[0078] Fig.11 is a schematic diagram of step S430 of the method for preparing a multi-junction VCSEL laser in the example of the present application;

[0079] Fig.12 is a schematic diagram of step S500 of the method for preparing a multi-junction VCSEL laser in an example of the present application;

[0080] Fig.13 This is a schematic diagram of step S610 in the example of this application;

[0081] Fig.14 is another schematic diagram of step S610 in the example of this application;

[0082] Fig.15 It is a schematic diagram of step S620 of the method for preparing a multi-junction VCSEL laser in the example of the present application.

[0083] The reference numerals in the accompanying drawings are as follows:

[0084] 100, multi-junction VCSEL laser; 200, growth direction;

[0085] 1. Substrate;

[0086] 2. epitaxial unit; 21. first reflector; 211. first semiconductor layer; 212. second semiconductor layer; 213. first oxide layer; 2131. oxide region; 2132. non-oxide region; 214. oxide groove;

[0087] 22, second reflector; 221, third semiconductor layer; 222, fourth semiconductor layer; 223, second oxide layer; 24, gain stack structure; 241, gain unit body; 2411, active layer; 2412, current limiting layer; 24121, current hole; 24122, high resistance region; 2413, spacer bottom layer; 2414, spacer top layer; 24141, first sub-spacer layer; 24142, second sub-spacer layer; 242, tunnel junction;

[0088] 3. Insulating layer; 4. Positive electrode; 5. Light outlet; 6. Negative electrode. DETAILED DESCRIPTION

[0089] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of this application; the terms used in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. For example, the directions or positions indicated by the terms "length", "width", "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the directions or positions shown in the drawings, which are only for the convenience of description and cannot be understood as limitations on the present technical solution.

[0090] The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions; the terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order. "Multiple" means two or more, unless otherwise clearly and specifically limited.

[0091] In the specification and claims of this application and the above-mentioned drawings, when an element is referred to as being "fixed to" or "mounted on" or "disposed on" or "connected to" another element, it may be directly or indirectly located on the other element. For example, when an element is referred to as being "connected to" another element, it may be directly or indirectly connected to the other element.

[0092] In addition, reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0093] The embodiment of the present application provides a multi-junction VCSEL laser 100, which includes but is not limited to being applicable to laser radars, and can also be applicable to products such as laser sensors, which are not listed one by one here.

[0094] like Figure 1 As shown, the multi-junction VCSEL laser 100 includes a substrate 1 and at least one epitaxial unit 2, wherein the substrate 1 includes but is not limited to being made of III-V semiconductor materials such as GaAs, InP, GaSb, and GaN. The specific material used can be determined according to actual needs and is not particularly limited here. In addition, the multi-junction VCSEL laser 100 can be applied to a variety of semiconductor substrates 1, and the wavelength band (corresponding to the target light wave) can cover visible light, near infrared, mid-infrared, etc.

[0095] In the embodiments of the present application, Figure 1 As shown, each epitaxial unit 2 includes a first reflector 21, a second reflector 22 and a gain stacked structure 24. The first reflector 21 is grown on the top surface of the substrate 1 through an epitaxial growth process. The second reflector 22 and the first reflector 21 together form a reflection cavity. The gain stacked structure 24 is located in the reflection cavity, and the second reflector 22 is grown on the top. It can be understood that the gain stacked structure 24 is formed between the first reflector 21 and the second reflector 22, and the gain and other adjustments are performed on the light beam in the reflection cavity.

[0096] In the embodiment of the present application, in order to increase the power of a single light emitting point, the gain stack structure 24 includes a plurality of gain unit bodies 241, wherein the plurality of gain unit bodies 241 are connected in series along the growth direction 200 through tunnel junctions 242. In other words, the gain unit bodies 241 and the tunnel junctions 242 are alternately stacked in the growth direction 200. It can be understood that the number of tunnel junctions 242 is one less than the number of gain unit bodies 241, and to ensure high power, once the number of gain unit bodies 241 is confirmed, the total height relationship of the plurality of gain unit bodies 241 can be basically determined.

[0097] On the basis of ensuring that the power meets the requirements, in order to ensure that the modulation speed also meets the requirements, so as to effectively increase the transmission bandwidth of the multi-junction VCSEL laser 100, the first reflector 21 includes a first semiconductor layer 211 and a second semiconductor layer 212, wherein in a first state, that is, in the preparation state of the first reflector 21, the first semiconductor layer 211 and the second semiconductor layer 212 are alternately epitaxially grown, and the epitaxially grown second semiconductor layer 212 is partially oxidized to eventually form a first oxide layer 213. In a second state, that is, in the use state of the first reflector 21, the first semiconductor layer 211 and the first oxide layer 213 are alternately stacked to jointly form the first reflector 21 in the second state (see Figure 1), and the refractive index of the first semiconductor layer 211 is greater than the refractive index of the first oxide layer 213.

[0098] Optionally, to achieve a reflectivity of the first reflector 21 exceeding 99.9%, the ratio of the refractive index of the first semiconductor layer 211 to the refractive index of the first oxide layer 213 may be greater than 1.5. In this way, when a specific reflectivity is achieved, a larger refractive index difference may increase the reflection intensity of the first reflector 21, thereby reducing the penetration depth of the target light wave into the first reflector 21, facilitating a reduction in the number of alternating cycles of the first semiconductor layer 211 and the second semiconductor layer 212, facilitating a smaller equivalent cavity length, thereby increasing the transmission bandwidth of the first reflector 21, and further increasing the modulation speed of the multi-junction VCSEL laser 100.

[0099] Exemplarily, the thickness of the first semiconductor layer 211 is an optical thickness of one quarter of the target wavelength, and the thickness of the second semiconductor layer 212 is an optical thickness of one quarter of the target wavelength after the second semiconductor layer 212 is oxidized to form the first oxide layer 213. In order to avoid the need to consider the lattice matching problem with the substrate 1, the material selection of the first semiconductor layer 211 and the second semiconductor layer 212 is flexible, which is conducive to achieving a higher refractive index difference. The first semiconductor layer 211 and the second semiconductor layer 212 are both made of Al x Ga 1-x As semiconductor material, x in the first semiconductor layer 211 is 0-0.2, x in the second semiconductor layer 212 is 0.98-1, and the substrate 1 is made of GaAs material.

[0100] For further example, the Al x Ga 1-x As semiconductor material has x=0-0.2, and its refractive index is about 3.6; correspondingly, Al x Ga 1-x The x of the As semiconductor material is 1, that is, the semiconductor material of the second semiconductor layer 212 is AlAs, and the material of the first oxide layer 213 formed after oxidation is Al2O3, and its refractive index is about 1.6. Therefore, the refractive index difference of the first reflector 21 composed of the first semiconductor layer 211 and the first oxide layer 213 is close to 2 (specifically 3.6 / 1.6=2.25). In this way, the alternating period of 4 or 5 between the first semiconductor layer 211 and the first oxide layer 213 can achieve a reflectivity of the first reflector 21 exceeding 99.9%.

[0101] Similarly, on the basis of ensuring that the power meets the requirements, in order to ensure that the modulation speed also meets the requirements, so as to effectively increase the transmission bandwidth of the multi-junction VCSEL laser 100, the second reflector 22 includes a third semiconductor layer 221 and a fourth semiconductor layer 222, wherein in the first state, that is, in the preparation state of the second reflector 22, the third semiconductor layer 221 and the fourth semiconductor layer 222 are alternately epitaxially grown, and the epitaxially grown fourth semiconductor layer 222 is at least partially oxidized to eventually form a second oxide layer 223. In the second state, that is, in the use state of the second reflector 22, the third semiconductor layer 221 and the fourth semiconductor layer 222 are alternately stacked to jointly form the second reflector 22 in the second state (see Figure 1 ), the refractive index of the third semiconductor layer 221 is greater than the refractive index of the second oxide layer 223.

[0102] Optionally, in order to achieve a reflectivity of the second reflector 22 exceeding 99.9%, the ratio of the refractive index of the third semiconductor layer 221 to the refractive index of the second oxide layer 223 may be greater than 1.5. In this way, when a specific reflectivity (e.g., a reflectivity greater than 99.9%) is achieved, a larger refractive index difference may increase the reflection intensity of the second reflector 22, thereby reducing the penetration depth of the target light wave into the second reflector 22, facilitating a reduction in the number of alternating cycles of the third semiconductor layer 221 and the fourth semiconductor layer 222, facilitating a smaller equivalent cavity length, thereby increasing the transmission bandwidth of the second reflector 22, and further increasing the modulation speed of the multi-junction VCSEL laser 100.

[0103] Exemplarily, the thickness of the third semiconductor layer 221 is an optical thickness of one quarter of the target wavelength, and the thickness of the fourth semiconductor layer 222 is an optical thickness of one quarter of the target wavelength after the fourth semiconductor layer 222 is oxidized to form the second oxide layer 223. In order to avoid the need to consider the lattice matching problem with the substrate 1, the material selection of the third semiconductor layer 221 and the fourth semiconductor layer 222 is flexible, which is conducive to achieving a higher refractive index difference. The third semiconductor layer 221 and the fourth semiconductor layer 222 are both made of Al x Ga 1-x As semiconductor material, x in the third semiconductor layer 221 is 0-0.2, x in the fourth semiconductor layer 222 is 0.98-1, and the substrate 1 is made of GaAs material.

[0104] For further example, the Al x Ga 1-x As semiconductor material has x=0-0.2, and its refractive index is about 3.6; correspondingly, Al x Ga 1-xFor As semiconductor material, x=1, that is, the semiconductor material of the fourth semiconductor layer 222 is AlAs, and the material of the second oxide layer 223 formed after oxidation is Al2O3, whose refractive index is about 1.6. Therefore, the refractive index difference of the second reflector 22 composed of the third semiconductor layer 221 and the second oxide layer 223 is close to 2 (specifically 3.6 / 1.6=2.25). In this way, 4 or 5 alternating periods between the third semiconductor layer 221 and the second oxide layer 223 can achieve a reflectivity of the second reflector 22 exceeding 99.9%.

[0105] Obviously, compared with the conventional VCSEL laser (for example, made of GaA-based semiconductor materials lattice-matched to substrate 1), the refractive index difference is about 0.5, and theoretically 35 cycles are required to achieve a reflectivity greater than 99.9%. It is also possible that the reflector is doped with impurities, or compared with the reflector made of an oxide dielectric film, the refractive index difference between the two high and low oxide materials is about 0.8, and theoretically 10 cycles are required to achieve a reflectivity greater than 99.9%. Or, a highly reflective metal film layer is evaporated on the basis of the oxide cut-off film, and theoretically 5 to 6 cycles are required to achieve a reflectivity greater than 99.9%. The reflector (such as the first reflector 21 and / or the second reflector 22) is a reflector based on a semiconductor material, a portion of which is formed by oxidation to form an oxide layer. It can be used not only as the first reflector 21 located at the bottom, but also as the second reflector 22 located at the top. The difference in refractive index between the semiconductor material in the reflector and the oxide material formed after partial oxidation of the semiconductor material is greater than 1.5, for example, close to 2. Theoretically, only 4 or 5 cycles are needed to achieve a reflectivity greater than 99.9%, which can greatly reduce the penetration depth of light in the reflector, thereby effectively improving the transmission bandwidth of the multi-junction VCSEL laser 100.

[0106] In summary, compared with the prior art, the multi-junction VCSEL laser 100 has at least the following beneficial effects:

[0107] The multi-junction VCSEL laser 100 comprises a first semiconductor layer 211 grown by alternating epitaxial growth and a first oxide layer 213 formed by partial oxidation of a second semiconductor layer 212, and a third semiconductor layer 221 grown by alternating epitaxial growth and a second oxide layer 223 formed by at least partial oxidation of a fourth semiconductor layer 222, so that the first reflector 21 and the second reflector 22 are both composited by two semiconductor materials and an oxide material having different refractive indices and a large refractive index difference, so as to reduce the penetration depth of the target light wave into the reflector under the condition of achieving a specific reflectivity, reduce the number of alternating cycles between semiconductor layers in the reflector, and facilitate the realization of a smaller equivalent cavity length, so as to increase the transmission bandwidth of the reflector to achieve a high modulation speed of the multi-junction VCSEL laser 100, and reduce the divergence angle, so as to meet the requirements of high power, low divergence angle and high modulation speed at the same time.

[0108] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0109] In some embodiments of the present application, Figure 1 As shown, in order to realize the function of the multi-junction VCSEL laser 100 to output laser light and make the overall structure more compact, a positive electrode 4 is provided on the top surface of the gain stack structure 24 outside the second reflector 22, and a light outlet 5 is formed. Exemplarily, the second reflector 22 is formed on the top surface of the gain stack structure 24. In the second state, that is, in the use state of the multi-junction VCSEL laser 100, the width of the second reflector 22 is smaller than the width of the gain stack structure 24, and the light outlet 5 can be surrounded by the second reflector 22, the top surface of the gain stack structure 24 and the positive electrode 4. After the gain stack structure 24 is powered on, laser light can be emitted through the light outlet 5.

[0110] In some embodiments of the present application, Figure 1 As shown, each gain unit body 241 of the gain stacked structure 24 includes an active layer 2411 and a current limiting layer 2412 stacked along the growth direction 200. In order to limit the current path in the reflection cavity to facilitate the laser emission, the middle part of the current limiting layer 2412 is formed with an unoxidized current hole 24121, and the periphery of the current hole 24121 is an oxidized high resistance area 24122. It should be noted that the stacking order of the active layer 2411 and the current limiting layer 2412 can be determined according to actual needs. Optionally, the current limiting layer 2412 is located above the active layer 2411. In addition, in order to improve efficiency and modulation speed, the current hole 24121 can be located directly below the light outlet 5, and the area in the current limiting layer 2412 where the current hole 24121 is not formed is the high resistance area 24122, and the current hole 24121 is covered by the second reflector 22 in the growth direction 200.

[0111] In order to simplify the preparation process of the multi-junction VCSEL laser 100, the first oxide layer 213, the second oxide layer 223 and the high resistance region 24122 are simultaneously manufactured by lateral oxidation of the first reflector 21, the second reflector 22 and the current limiting layer 2412. It can be understood that after the second semiconductor layer 212, the fourth semiconductor layer 222 and the current limiting layer 2412 are formed, and the current hole 24121 is formed in the current limiting layer 2412, the first reflector 21, the second reflector 22 and the current limiting layer 2412 can be lateral oxidized simultaneously, so that the second semiconductor layer 212 is oxidized into the first oxide layer 213, the fourth semiconductor layer 222 is oxidized into the second oxide layer 223, and the area of ​​the current limiting layer 2412 where the current hole 24121 is not formed is oxidized into the high resistance region 24122.

[0112] For example, the sidewalls of the first reflector 21 and the second reflector 22 can be exposed by an etching process, and the Al2O3 layer of the second semiconductor layer 212 can be oxidized by water vapor in a high-temperature oxidation furnace. x Ga 1-x As semiconductor material is oxidized to Al2O3. Since this process is a conventional process for manufacturing oxidation-limited aperture of VCSEL, the oxidation of the reflector and the oxidation of the current limiting layer 2412 can be combined into one oxidation process by reasonably designing relevant parameters of the VCSEL laser, which is beneficial to simplify the epitaxial growth and manufacturing process of the multi-junction VCSEL laser 100 and improve the compatibility and reliability of the multi-junction VCSEL laser 100.

[0113] It should be noted that the active layer 2411 is mainly used to generate the optical gain required for the laser, including but not limited to a multi-quantum well structure. The high resistance region 24122 of the current limiting layer 2412 is mainly used to form electrical isolation for the non-injected current region, and plays a role in limiting the current path. The high resistance region 24122 can be formed by lateral oxidation of the semiconductor material containing a high aluminum component as described above, or can also be formed by ion implantation.

[0114] In some embodiments of the present application, Figure 1 As shown, to meet the standing wave condition, the total thickness H of the gain stack structure 24 is an integer multiple of half the central wavelength of the target light wave. To reduce absorption loss, the tunnel junction 242 and the current confinement layer 2412 are located at the node of the target light wave in the reflection cavity.

[0115] In some embodiments of the present application, Figure 1As shown, in order to facilitate the adjustment of the equivalent cavity length of the reflective cavity, each gain unit also includes a spacing bottom layer 2413 and a spacing top layer 2414, and the top surface of the spacing bottom layer 2413 is stacked with an active layer 2411. A portion of the spacing top layer 2414 (corresponding to the first sub-spacing layer 24141) is stacked on the top surface of the active layer 2411, and a portion of the spacing top layer 2414 (corresponding to the second sub-spacing layer 24142) is stacked on the top surface of the current limiting layer 2412 and is stacked with a tunnel junction 242. The second reflector 22 is stacked on the spacing top layer 2414 of the gain stacking structure 24, and together with the positive electrode 4 and the spacing top layer 2414, forms a light outlet 5. It can be understood that the spacing bottom layer 2413 and the spacing top layer 2414 are respectively located on the lower side and the upper side of the active layer 2411.

[0116] Exemplarily, the spacer bottom layer 2413 of the gain unit near the first reflector 21 is epitaxially grown on the top surface of the first reflector 21, and the top surface of the spacer bottom layer 2413 is sequentially stacked with an active layer 2411, a first sub-spacer layer 24141, a current limiting layer 2412, a second sub-spacer layer 24142 and a tunnel junction 242.

[0117] In some embodiments of the present application, Figure 1 As shown, in order to realize the electrical connection of the multi-junction VCSEL laser 100, a negative electrode 6 is provided at the bottom of the substrate 1, and the first oxide layer 213 of the first reflector 21 in the second state includes an oxidation region 2131 and a non-oxidation region 2132, wherein the oxidation region 2131 and the non-oxidation region 2132 are arranged along a direction perpendicular to the growth direction 200 (specifically, the width direction of the first reflector 21), and the oxidation region 2131 covers the light exit hole in the growth direction 200. The second reflector 22 covers the current hole 24121 in the growth direction 200, and the current of the positive electrode 4 flows to the negative electrode 6 through the current hole 24121 and the non-oxidation region 2132 in sequence.

[0118] In some embodiments of the present application, Figure 1 As shown, in order to facilitate oxidation of the second semiconductor layer 212 in the first reflector 21, an oxidation groove 214 is formed on the periphery of the gain stack structure 24 in the first reflector 21 in a direction away from the growth direction 200. That is, the first reflector 21 is concavely provided with the oxidation groove 214 to expose the sidewall of the first reflector 21.

[0119] In addition, to prevent current leakage and ensure electrical isolation of the non-current injection area, current is injected into the top surface of the top spacing layer 2414 located at the top of the gain stack structure 24, such as Figure 1As shown, the multi-junction VCSEL laser 100 further includes an insulating layer 3, wherein the insulating layer 3 is formed on the top surface of the first reflector 21, the groove wall of the oxidation groove 214, and the side wall and top surface of the gain stack structure 24. The positive electrode 4 is formed on the outer surface of the insulating layer 3.

[0120] In some embodiments of the present application, a negative electrode 6 is provided at the bottom of the substrate 1. Correspondingly, a plurality of epitaxial units 2 may be provided, and a plurality of epitaxial units 2 are formed at intervals on the top surface of the substrate 1. Each epitaxial unit 2 is provided with an independent positive electrode 4, and is electrically connected to the positive electrode 4 and the negative electrode 6. It can be understood that by independently setting the positive electrode 4 on each epitaxial unit 2 and making each epitaxial unit 2 share the negative electrode 6 on the same substrate 1, it is possible to light up a specific epitaxial unit 2, so as to facilitate the addressable function of the laser radar, and is suitable for a high-performance laser radar system based on an addressable multi-junction VCSEL laser 100.

[0121] It should be noted that the multi-junction VCSEL laser 100 in the present application can be expanded into a multi-point array structure of any size, and by designing the connection method of the positive electrode 4 and the negative electrode 6, the single point, linear array, and specific area of ​​the electrodes on different surfaces can be independently addressed and scanned to meet the technical requirements of the current laser radar ranging. The specific connection method of the positive electrode 4 and the negative electrode 6 can be determined according to actual needs and will not be described in detail here.

[0122] Based on the above-mentioned multi-junction VCSEL laser 100 , an embodiment of the present application further provides a laser radar system (not shown), wherein the laser radar system includes the above-mentioned multi-junction VCSEL laser 100 .

[0123] In summary, compared with the prior art, the laser radar system has at least the following beneficial effects: the laser radar system adopts the above-mentioned multi-junction VCSEL laser 100, which has the characteristics of high power, low divergence angle and high modulation speed, which is conducive to realizing automatic assisted navigation driving functions in the field of autonomous driving.

[0124] The present application also provides a method for preparing a multi-junction VCSEL laser, and the method for preparing a multi-junction VCSEL laser is applied to a multi-junction VCSEL laser 100. Figure 1 As shown, the multi-junction VCSEL laser 100 includes a substrate 1 and an epitaxial unit 2, and the epitaxial unit 2 is electrically connected to the positive electrode 4 and the negative electrode 6. The epitaxial unit 2 includes a first reflector 21, a second reflector 22 and a gain stack structure 24, and the second reflector 22 and the first reflector 21 together form a reflection cavity (not shown). The gain stack structure 24 is located in the reflection cavity, and the second reflector 22 is grown on the top. It can be understood that the gain stack structure 24 is formed between the first reflector 21 and the second reflector 22, and the gain and other adjustments are made to the light beam in the reflection cavity.

[0125] On the basis of ensuring that the power meets the demand, in order to ensure that the modulation speed also meets the demand, so as to effectively increase the transmission bandwidth of the multi-junction VCSEL laser 100, the first reflector 21 includes a first semiconductor layer 211 and a first oxide layer 213 formed by partial oxidation of the second semiconductor layer 212, and the refractive index of the first semiconductor layer 211 is greater than the refractive index of the first oxide layer 213. Correspondingly, the second reflector 22 includes a third semiconductor layer 221 and a second oxide layer 223 formed by at least partial oxidation of the fourth semiconductor layer 222, and the refractive index of the third semiconductor layer 221 is greater than the refractive index of the second oxide layer 223.

[0126] In addition, if Figure 1 As shown, the gain stacked structure 24 is formed with a light outlet 5. The gain stacked structure 24 includes a plurality of gain unit bodies 241, and the plurality of gain unit bodies 241 are connected in series along the growth direction 200 through a tunnel junction 242. Each gain unit body 241 includes a stacked active layer 2411 and a current limiting layer 2412, wherein a non-oxidized current hole 24121 is formed in the middle portion of the current limiting layer 2412, and an oxidized high resistance region 24122 is formed around the current hole 24121.

[0127] It can be understood that the multi-junction VCSEL laser 100 is formed by making the first reflector 21 and the second reflector 22 both composited by two semiconductor materials and an oxide material with different refractive indices and a large refractive index difference, so as to reduce the penetration depth of the target light wave into the reflector under the condition of achieving a specific reflectivity, reduce the number of alternating cycles between the semiconductor layers in the reflector, and facilitate the realization of a smaller equivalent cavity length, so as to increase the transmission bandwidth of the reflector and realize a high modulation speed of the multi-junction VCSEL laser 100, and reduce the divergence angle, so as to meet the requirements of high power, low divergence angle and high modulation speed at the same time.

[0128] It should be noted that some details of the multi-junction VCSEL laser 100 may be the same as those of the multi-junction VCSEL laser 100 described above, and will not be described in detail herein.

[0129] In the embodiments of the present application, Figure 2 and Figure 3 As shown, the method for preparing a multi-junction VCSEL laser includes the following steps:

[0130] Step S100: epitaxially growing the first semiconductor layer 211 and the second semiconductor layer 212 of the first reflector 21 alternately on the top surface of the substrate 1 by using an epitaxial growth process (see Figure 5 ).

[0131] In the step of alternately epitaxially growing the first semiconductor layer 211 and the second semiconductor layer 212 of the first reflector 21 in step S100, the number of alternating cycles of the alternate epitaxial growth of the first semiconductor layer 211 and the second semiconductor layer 212 is 3, 4, or 5, and the thickness of the first semiconductor layer 211 is an optical thickness of one quarter of the target wavelength. Correspondingly, the thickness of the second semiconductor layer 212 is an optical thickness of one quarter of the target wavelength after the second semiconductor layer 212 is oxidized to form the first oxide layer 213. The first semiconductor layer 211 and the second semiconductor layer 212 are made of Al x Ga 1-x As semiconductor material is epitaxially grown, x in the first semiconductor layer 211 is 0-0.2, and x in the second semiconductor layer 212 is 0.98-1.

[0132] It should be noted that the first semiconductor layer 211 can be made of a semiconductor material with a high aluminum component, and the second semiconductor layer 212 can be made of a semiconductor material with a low aluminum component. The epitaxial growth process described in step S100 includes but is not limited to metal-organic chemical vapor deposition (MOCVD), and the substrate 1 can include but is not limited to being made of III-V semiconductor materials such as GaAs, InP, GaSb, and GaN. It should also be noted that the first reflector 21 can have a symmetrical structure, and the material epitaxially grown on the substrate 1 is usually the same material as the material forming the top surface of the first reflector 21.

[0133] Step S200: epitaxially grow the gain unit body 241 and the tunnel junction 242 alternately on the top surface of the first reflector 21 by using an epitaxial growth process to preliminarily form a gain stack structure 24. The tunnel junction 242 is located on the side of the gain unit body 241 away from the first reflector 21. It can be understood that in order to improve the power, the gain stack structure 24 includes a plurality of gain unit bodies 241, and a tunnel junction 242 is epitaxially grown between two adjacent gain unit bodies 241 to achieve a series connection between the two.

[0134] In step S200 , in order to satisfy the standing wave conditions of the tunnel junction 242 and the current confinement layer 2412 in the gain stack structure 24 , the total thickness H of the gain stack structure 24 is an integer multiple of half the central wavelength of the target light wave.

[0135] It should be noted that the epitaxial growth order of the active layer 2411 and the current confinement layer 2412 in the gain unit body 241 epitaxially grown in step S200 is not particularly limited and can be determined according to actual needs.

[0136] For example, in the step of epitaxially growing the gain unit body 241 in step S200, as shown in FIG. Figure 4 and Figure 6 As shown, the steps of epitaxially growing the gain unit body 241 specifically include:

[0137] Step S210: epitaxially grow a spacer bottom layer 2413 on the top surface of the epitaxially grown first reflector 21. In this step, the material of the spacer bottom layer 2413 needs to match the lattice of the substrate 1 as much as possible.

[0138] Step S220: epitaxially grow an active layer 2411 on the top surface of the epitaxially grown spacer bottom layer 2413. In step S220, the active layer 2411 may be a multi-quantum well structure, so that the light-emitting wavelength of the active layer 2411 can be adjusted to cover the target light wave by adjusting the thickness or composition of the well.

[0139] Step S230: epitaxially grow a first sub-spacer layer 24141 on the top surface of the epitaxially grown active layer 2411. After the thickness of the first sub-spacer layer 24141 reaches a preset thickness, epitaxially grow a current limiting layer 2412 on the first sub-spacer layer 24141. In step S230, the current limiting layer 2412 may be made of Al with a high aluminum component. x Ga 1-x To effectively reduce the absorption loss, in this step, the current limiting layer 2412 is grown at the node of the target light wave in the reflection cavity.

[0140] Step S240: epitaxially grow a second sub-spacer layer 24142 on the top surface of the epitaxially grown current limiting layer 2412 to form a gain unit body 241 by stacking layer by layer (see Figure 7 ).

[0141] Among them, Figure 7 As shown, the above-mentioned spacer top layer 2414 includes a first sub-spacer layer 24141 and a second sub-spacer layer 24142. Exemplarily, a single gain unit body 241 may include a spacer bottom layer 2413, an active layer 2411, a first sub-spacer layer 24141, a current limiting layer 2412 and a second sub-spacer layer 24142 that are epitaxially grown in sequence, wherein the current limiting layer 2412 is located between the first sub-spacer layer 24141 and the second sub-spacer layer 24142 of the spacer top layer 2414. That is, in step S200, step S210, step S220, step S230, and step S240 may be performed in sequence. Of course, in other examples, step S210, step S220, step S230, and step S240 may also be performed in other suitable orders, which will not be described in detail here.

[0142] Understandably, after step S240 of step S200, as Figure 7 As shown, step S200 also includes the following steps:

[0143] Step S250: epitaxially grow a tunnel junction 242 on the top surface of the epitaxially grown second sub-spacer layer 24142. In the step of epitaxially growing the tunnel junction 242 in step S250, the tunnel junction 242 is grown at the node of the target light wave in the reflection cavity to effectively reduce absorption loss.

[0144] Step S260 : repeating the above steps S210 to S250 on the top surface of the epitaxially grown tunnel junction 242 .

[0145] In step S260, the number of steps S210 to S250 is repeated once less than the total number of the multi-junction VCSEL laser 100. In addition, the number of tunnel junctions 242 formed in step S200 is also once less than the total number of the multi-junction VCSEL laser 100.

[0146] Step S300 : epitaxially growing the third semiconductor layer 221 and the fourth semiconductor layer 222 of the second reflector 22 alternately on the top surface of the gain stack structure 24 by using an epitaxial growth process.

[0147] Among them, Figure 8 As shown, in the step of alternately epitaxially growing the third semiconductor layer 221 and the fourth semiconductor layer 222 of the second reflector 22 in step S300, the number of alternating cycles of the alternate epitaxial growth of the third semiconductor layer 221 and the fourth semiconductor layer 222 is 3, 4, or 5, and the thickness of the third semiconductor layer 221 is an optical thickness of one quarter of the target wavelength. Correspondingly, the thickness of the fourth semiconductor layer 222 is an optical thickness of one quarter of the target wavelength after the fourth semiconductor layer 222 is oxidized to form the second oxide layer 223. The third semiconductor layer 221 and the fourth semiconductor layer 222 are made of Al x Ga 1-x As semiconductor material is epitaxially grown, x in the third semiconductor layer 221 is 0-0.2, and x in the fourth semiconductor layer 222 is 0.98-1.

[0148] It should be noted that the third semiconductor layer 221 can be made of a semiconductor material with a high aluminum component, and the fourth semiconductor layer 222 can be made of a semiconductor material with a low aluminum component. The epitaxial growth process described in step S300 includes but is not limited to metal-organic chemical vapor deposition (MOCVD).

[0149] Step S400: sequentially etching the epitaxially grown second reflector 22 , gain stack structure 24 and first reflector 21 to respectively expose the inner cavity contact layer of the gain stack structure 24 , the sidewall of the gain stack structure 24 and the current hole 24121 , and expose the sidewall of the first reflector 21 .

[0150] It can be understood that step S400 is performed after step S100, step S200 and step S300 are completed in sequence to form the epitaxial growth part of the multi-junction VCSEL, that is, after the multi-junction VCSEL sample is formed, and belongs to the preparation process link.

[0151] For example, Figures 9 to 11 As shown, step S400 may specifically include the following steps:

[0152] Step S410: Perform a first etching process on the second reflector 22 in the multi-junction VCSEL sample to expose the inner cavity contact layer of the gain stack structure 24 (see Fig. 9 ).

[0153] Exemplarily, the second reflector 22 is etched so that the width of the second reflector 22 is smaller than the width of the gain stack structure 24, so that the top surface of the gain stack structure 24 and the side surface of the second reflector 22 are exposed. The first etching process described in this step includes coating, exposure and development, and the etching gas includes but is not limited to Cl2, BCl3, and Ar.

[0154] Step S420: Perform a second etching process on the gain stack structure 24 in the multi-junction VCSEL sample to expose the sidewall of the gain stack structure 24 and form the current hole 24121 (see Fig.10 ).

[0155] Exemplarily, after step S410, the gain stack structure 24 is etched so that the width of the gain stack structure 24 is smaller than the width of the first reflector 21, so that the sidewalls of the gain stack structure 24 are exposed. For example, dry etching is performed by an ICP etching device to expose the sidewalls of the gain stack structure 24. In addition, the current limiting layer 2412 in the gain stack structure 24 is also etched to form current holes 24121 along the growth direction 200 in each current limiting layer 2412. The second etching process described in this step includes coating, exposure and development, and the etching gas includes but is not limited to Cl2, BCl3, and Ar.

[0156] Step S430: After step S420, the first reflector 21 in the multi-junction VCSEL sample is subjected to a third etching process to expose the sidewall of the first reflector 21 (see Fig.11 ).

[0157] Exemplarily, an oxidation groove 214 may be formed on the top surface of the first reflector 21 to expose the sidewall of the first reflector 21. In addition, the third etching process described in step S430 includes resist coating, exposure and development, and the etching gas includes but is not limited to Cl2, BCl3, and Ar.

[0158] Also exemplarily, before the step of simultaneously performing lateral oxidation on the etched current limiting layer 2412, the first reflector 21, and the second reflector 22, that is, before the following step S500, the third etching process corresponding to step S430 in step S400, that is, the etching method of the first reflector 21 has the following two specific implementations:

[0159] In the first specific embodiment, a double-sided oxidation method is used. On the periphery of the second reflector 22, two symmetrical etching grooves with a target pattern are etched on the top surface of the first reflector 21 with the center line of the first reflector 21 as the center of symmetry (not shown), so that the second semiconductor layer 212 of the exposed first reflector 21 is gradually diffusely oxidized from each etching groove to the center of symmetry.

[0160] Exemplarily, symmetrical holes or fan-shaped etching grooves are etched on the top surface of the first reflector 21 to expose the first reflector 21 through the etching grooves, wherein the second semiconductor layer 212 in the first reflector 21 exposed through the etching grooves can diffuse from the corresponding area of ​​the etching grooves to the center line of the first reflector 21 under the oxidation action of high-temperature water vapor, so that the second semiconductor layer 212 in the first reflector 21 is at least partially oxidized to form a first oxide layer 213, wherein the first oxide layer 213 includes an oxidation area 2131 and a non-oxidation area 2132, wherein the oxidation area 2131 of the first oxide layer 213 needs to be able to cover the light outlet 5, and the current can flow from the non-oxidation area 2132 to the negative electrode 6.

[0161] Alternatively, in a second specific embodiment, which is a unilateral oxidation method, an etching groove of a target pattern is etched on a single side of the top surface of the first reflector 21 at the periphery of the second reflector 22, so that the second semiconductor layer 212 of the exposed first reflector 21 is gradually diffusely oxidized from the etching groove in one direction.

[0162] Exemplarily, an etching groove (corresponding to the oxidation groove 214) with a strip shape or the like is etched on one side of the top surface of the first reflector 21 to expose the first reflector 21 through the etching groove, wherein the second semiconductor layer 212 in the first reflector 21 exposed through the etching groove can diffusely spread unidirectionally from the corresponding area of ​​the etching groove under the oxidation action of high-temperature water vapor, so that the second semiconductor layer 212 in the first reflector 21 is at least partially oxidized to form a first oxide layer 213, wherein the first oxide layer 213 includes an oxidation area 2131 and a non-oxidation area 2132, and the oxidation area 2131 of the first oxide layer 213 located on one side needs to be able to cover the light outlet 5, and the current can flow from the non-oxidation area 2132 located on the other side to the negative electrode 6.

[0163] Step S500: The etched current limiting layer 2412, the first reflector 21 and the second reflector 22 are lateral-oxidized at the same time, so that the current limiting layer 2412 forms an unoxidized current hole 24121 and an oxidized high resistance region 24122, each second semiconductor layer 212 of the first reflector 21 becomes a first oxide layer 213, and each fourth semiconductor layer 222 of the second reflector 22 is oxidized to a second oxide layer 223, so as to form a laser sample (see Fig.12 ).

[0164] It can be understood that combining the oxidation of the first reflector 21 , the oxidation of the second reflector 22 and the oxidation of the current limiting layer 2412 into one oxidation process is beneficial to simplifying the epitaxial growth and manufacturing process of the multi-junction VCSEL laser 100 , and can improve the compatibility and reliability of the multi-junction VCSEL laser 100 .

[0165] For example, Fig.12 As shown, after step S430, a wet nitrogen oxidation device can be used to perform transverse oxidation on the current limiting layer 2412, the first reflector 21 and the second reflector 22, so as to control the oxidation rate by adjusting parameters such as oxidation temperature, water vapor temperature, pressure, flow rate, and control the lateral oxidation depth by controlling time, so as to form an unoxidized current hole 24121 in the center of the current limiting layer 2412 and an oxidized high resistance area 24122 at the periphery of the current hole 24121, so as to limit the current injected into the laser through the current hole 24121 to be conducted only through the current hole 24121. Because the content of high aluminum components in the first reflector 21 and the second reflector 22 is higher than the content of high aluminum components in the current limiting layer 2412, the oxidation rate of the second semiconductor layer 212 in the first reflector 21 and the fourth semiconductor layer 222 of the second reflector 22 is much greater than the oxidation rate of the current limiting layer 2412. Therefore, when the aperture size of the current hole 24121 of the current limiting layer 2412 reaches the size required by the design, the fourth semiconductor layer 222 of the second reflector 22 has been completely oxidized into the second oxide layer 223, and the oxidation area 2131 of the first oxide layer 213 of the first reflector 21 can already cover the light outlet 5, so that the first reflector 21 and the second reflector 22 are finally both composite structures of semiconductor materials and oxide materials.

[0166] Also exemplarily, in step S500, x=0~0.2 of the AlxGa1-xAs semiconductor material of the first semiconductor layer 211, and its refractive index may be approximately 3.6; correspondingly, x=1 of the AlxGa1-xAs semiconductor material of the second semiconductor layer 212, that is, the semiconductor material of the second semiconductor layer 212 is AlAs, and the material of the first oxide layer 213 formed after oxidation is Al2O3, and its refractive index is approximately 1.6. Therefore, the refractive index difference of the first reflector 21 composed of the first semiconductor layer 211 and the first oxide layer 213 is close to 2 (specifically 3.6 / 1.6=2.25). In this way, 4 or 5 alternating periods between the first semiconductor layer 211 and the first oxide layer 213 can achieve a reflectivity of the first reflector 21 exceeding 99.9%.

[0167] Similarly, the AlxGa1-xAs semiconductor material of the third semiconductor layer 221 has x=0~0.2, and its refractive index is about 3.6; correspondingly, the AlxGa1-xAs semiconductor material of the fourth semiconductor layer 222 has x=1, that is, the semiconductor material of the fourth semiconductor layer 222 is AlAs, and the material of the second oxide layer 223 formed after oxidation is Al2O3, and its refractive index is about 1.6. Therefore, the refractive index difference of the second reflector 22 composed of the third semiconductor layer 221 and the second oxide layer 223 is close to 2 (specifically 3.6 / 1.6=2.25). In this way, 4 or 5 alternating periods between the third semiconductor layer 221 and the second oxide layer 223 can achieve a reflectivity of the second reflector 22 exceeding 99.9%.

[0168] Step S600: Perform a preparation process on the laser sample to form the multi-junction VCSEL laser 100 in the second state. The step S600 is located after the step of forming the laser sample in step S500.

[0169] In some embodiments of the present application, Figures 13 to 15 As shown, step S600 includes the following steps:

[0170] Step S610: forming an insulating layer 3 on the outer surfaces of the gain stack structure 24 and the first reflector 21 of the laser sample to electrically isolate the non-current injection area, and etching the insulating layer 3 on the top surface of the gain stack structure 24 to form a current injection area.

[0171] Exemplarily, step S610 may use PECVD equipment to deposit materials including but not limited to SiO2 or Si3N4 on the surface of the laser sample formed in step S500 to form an insulating layer 3. In addition, at the periphery of the second reflecting mirror 22, the insulating layer 3 formed on the top surface of the gain stack structure 24 is etched to expose a portion of the top surface of the gain stack structure 24, so that the non-current injection area is electrically isolated by the insulating layer 3, and a current injection area is formed on the exposed top surface portion.

[0172] The thickness of the insulating layer 3 is in the range of 300nm to 500nm. The insulating layer 3 may be dry-etched by RIE equipment to expose a portion of the top surface of the gain stack structure 24. The etching gas for the insulating layer 3 formed of SiO2 or Si3N4 material may include but is not limited to CF4 and O2.

[0173] Step S620: forming a first metal electrode layer on at least part of the insulating layer 3 of the laser sample, and removing the first metal electrode layer in the current injection region, so as to form a light outlet 5 by the positive electrode 4, the second reflector 22 and the gain stack structure 24, and forming the positive electrode 4 (see Fig.15 ).

[0174] For example, after step S610, the laser sample may be photolithographically processed, and after the steps of coating, photolithography, and development, the positive electrode 4 pattern of the VCSEL is formed, and then the first metal electrode layer is evaporated by electron beam evaporation, and then the sample after evaporation is subjected to a lift-off stripping process in an acetone solution to remove the electrode portion not needed by the half-VCSEL light outlet 5, and finally form the positive electrode 4. The materials forming the positive electrode 4 include but are not limited to Ti, Pt, and Au.

[0175] Step S630: forming a second metal electrode layer at the bottom of the substrate 1 to form a negative electrode 6 (see Figure 1 ).

[0176] Illustratively, after step S620, the substrate 1 in the laser sample may be thinned and polished, and then a second metal electrode layer may be deposited on the bottom surface of the substrate 1 by electron beam evaporation, wherein the material forming the negative electrode 6 includes but is not limited to Au-Ge, Ni, and Au.

[0177] After completing step S630 , the entire manufacturing process of the multi-junction VCSEL laser 100 is completed.

[0178] In general, the multi-junction VCSEL laser 100 prepared by the method for preparing the multi-junction VCSEL laser 100 has high compatibility, high reliability, high power, low divergence angle and high modulation speed, and also facilitates the addressability function of the laser radar system.

[0179] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A multi-junction VCSEL laser, characterized in that: The multi-junction VCSEL laser comprises a substrate and at least one epitaxial unit, each of the epitaxial units comprising: A first reflector, grown on the top surface of the substrate by an epitaxial growth process; A second reflector, which together with the first reflector forms a reflective cavity; A gain stacked structure is located in the reflection cavity and has the second reflector grown on the top; the gain stacked structure includes a plurality of gain unit bodies; the plurality of gain unit bodies are connected in series along the growth direction through tunnel junctions; The first reflector includes a first semiconductor layer that is alternately epitaxially grown and a first oxide layer that is formed by partial oxidation of the second semiconductor layer, and the refractive index of the first semiconductor layer is greater than the refractive index of the first oxide layer; The second reflector includes a third semiconductor layer grown by alternate epitaxial growth and a second oxide layer formed by at least partial oxidation of the fourth semiconductor layer. The refractive index of the third semiconductor layer is greater than the refractive index of the second oxide layer.

2. The multi-junction VCSEL laser according to claim 1, characterized in that: The ratio of the refractive index of the first semiconductor layer to the refractive index of the first oxide layer is greater than 1.5; and / or, a ratio of a refractive index of the third semiconductor layer to a refractive index of the second oxide layer is greater than 1.5; and / or, the alternating period between the first semiconductor layer and the first oxide layer is 4 or 5; and / or, the alternating period between the third semiconductor layer and the second oxide layer is 4 or 5; and / or, the thickness of the first semiconductor layer and the third semiconductor layer are both optical thicknesses of one quarter of the target wavelength; The thickness of the second semiconductor layer is an optical thickness of one quarter of the target wavelength after the second semiconductor layer is oxidized to form the first oxide layer; The thickness of the fourth semiconductor layer is an optical thickness of one quarter of the target wavelength after the fourth semiconductor layer is oxidized to form the second oxide layer; The substrate is made of GaAs material; the first semiconductor layer and the third semiconductor layer are made of Al x Ga 1-x As semiconductor material, and its x=0-0.2; the second semiconductor layer and the fourth semiconductor layer are made of Al x Ga 1-x It is made of As semiconductor material, and its x=0.98~1.

3. The multi-junction VCSEL laser according to claim 1, characterized in that: A positive electrode is provided on the top surface of the gain stack structure at the periphery of the second reflector, and a light outlet is formed; And / or, the epitaxial unit is provided in plurality, and the plurality of epitaxial units are formed at intervals on the top surface of the substrate; A negative electrode is provided at the bottom of the substrate; each of the epitaxial units is provided with an independent positive electrode and is electrically connected to the positive electrode and the negative electrode.

4. The multi-junction VCSEL laser according to claim 3, characterized in that: Each of the gain unit bodies comprises an active layer and a current limiting layer stacked along a growth direction, a non-oxidized current hole is formed in the middle of the current limiting layer, and the periphery of the current hole is an oxidized high resistance area; The first oxide layer, the second oxide layer and the high resistance region are synchronously manufactured by simultaneously performing lateral oxidation on the first reflector, the second reflector and the current limiting layer.

5. The multi-junction VCSEL laser according to claim 4, characterized in that: The total thickness of the gain stack structure is an integer multiple of half the central wavelength of the target light wave; The tunnel junction and the current confinement layer are located at a node of the target light wave in the reflective cavity; And / or, each of the gain units further comprises a spacer bottom layer and a spacer top layer, the top surface of the spacer bottom layer is stacked with the active layer; a portion of the spacer top layer is stacked on the top surface of the active layer, a portion of the spacer top layer is stacked on the top surface of the current limiting layer and is stacked with the tunnel junction; The second reflector is stacked on the top spacing layer of the gain stack structure, and together with the positive electrode and the top spacing layer, forms the light outlet; And / or, a negative electrode is provided at the bottom of the substrate; The first oxide layer of the first reflector includes an oxide region and a non-oxide region, the oxide region and the non-oxide region are arranged in a direction perpendicular to the growth direction, and the oxide region covers the light exit hole in the growth direction; the second reflector covers the current hole in the growth direction; The current of the positive electrode flows to the negative electrode through the current hole and the non-oxidation area in sequence.

6. The multi-junction VCSEL laser according to claim 3, characterized in that: The first reflector is provided with an oxidation groove in a direction away from the growth direction at the periphery of the gain stack structure; The multi-junction VCSEL laser further comprises an insulating layer, wherein the insulating layer is formed on a top surface of the first reflector, a groove wall of the oxidation groove, and a side wall and a top surface of the gain stack structure; The positive electrode is formed on an outer surface of the insulating layer.

7. A laser radar system, characterized in that: The laser radar system comprises the multi-junction VCSEL laser according to any one of claims 1 to 6.

8. A method for preparing a multi-junction VCSEL laser, wherein the method for preparing a multi-junction VCSEL laser is applied to a multi-junction VCSEL laser, characterized in that: The multi-junction VCSEL laser comprises a substrate and an epitaxial unit, wherein the epitaxial unit is electrically connected to a positive electrode and a negative electrode; The epitaxial unit comprises: A first reflector includes a first semiconductor layer and a first oxide layer formed by partial oxidation of the second semiconductor layer, wherein the refractive index of the first semiconductor layer is greater than the refractive index of the first oxide layer; a second reflector, which together with the first reflector forms a reflective cavity; the second reflector comprises a third semiconductor layer and a second oxide layer formed by at least partial oxidation of the fourth semiconductor layer, the refractive index of the third semiconductor layer being greater than the refractive index of the second oxide layer; A gain stacked structure is formed with a light outlet; the gain stacked structure comprises a plurality of gain unit bodies, the plurality of gain unit bodies are connected in series along a growth direction through a tunnel junction; each of the gain unit bodies comprises a stacked active layer and a current limiting layer, a middle portion of the current limiting layer is formed with an unoxidized current hole, and the periphery of the current hole is an oxidized high resistance region; The preparation method of the multi-junction VCSEL laser comprises: Using an epitaxial growth process to alternately epitaxially grow the first semiconductor layer and the second semiconductor layer of the first reflector on the top surface of the substrate; The gain unit body and the tunnel junction are alternately epitaxially grown on the top surface of the first reflector by using an epitaxial growth process to preliminarily form the gain stacked structure; wherein the tunnel junction is located on a side of the gain unit body away from the first reflector; Using an epitaxial growth process to alternately epitaxially grow the third semiconductor layer and the fourth semiconductor layer of the second reflector on the top surface of the gain stack structure; Sequentially etching the epitaxially grown second reflector, the gain stack structure and the first reflector to respectively expose the inner cavity contact layer of the gain stack structure, the side wall of the gain stack structure and form the current hole, and expose the side wall of the first reflector; At the same time, the etched current limiting layer, the first reflector and the second reflector are laterally oxidized so that the current limiting layer forms the unoxidized current hole and the oxidized high resistance area, the second semiconductor layers of the first reflector become the first oxide layer, and the fourth semiconductor layers of the second reflector are oxidized to the second oxide layer to form a laser sample.

9. The method for preparing a multi-junction VCSEL laser according to claim 8, characterized in that: After the step of forming the laser sample, the method for preparing the multi-junction VCSEL laser further comprises: forming an insulating layer on the outer surfaces of the gain stack structure and the first reflector of the laser sample to electrically isolate the non-current injection area, and etching the insulating layer on the top surface of the gain stack structure to form a current injection area; Forming a first metal electrode layer on at least a portion of the insulating layer of the laser sample, and removing the first metal electrode layer in the current injection region, so that the positive electrode, the second reflector and the gain stack structure together enclose the light outlet and form the positive electrode; forming a second metal electrode layer at the bottom of the substrate to form the negative electrode; And / or, in the step of epitaxially growing the gain unit body, specifically comprising: epitaxially growing a spacer bottom layer on the top surface of the epitaxially grown first reflecting mirror; epitaxially growing an active layer on the top surface of the epitaxially grown spacer bottom layer; Epitaxially growing a first sub-spacer layer on the top surface of the epitaxially grown active layer, and after the thickness of the first sub-spacer layer reaches a preset thickness, epitaxially growing a current limiting layer on the first sub-spacer layer; Epitaxially growing a second sub-spacer layer on the top surface of the epitaxially grown current limiting layer to form the gain unit body by stacking layer by layer; And / or, in the step of alternately epitaxially growing the first semiconductor layer and the second semiconductor layer of the first reflector, the number of alternating cycles of the alternate epitaxial growth is 3, 4, or 5, the thickness of the first semiconductor layer is an optical thickness of one quarter of the target wavelength; the thickness of the second semiconductor layer is an optical thickness of one quarter of the target wavelength after the second semiconductor layer is oxidized to form the first oxide layer; the first semiconductor layer and the second semiconductor layer are composed of Al x Ga 1-x As semiconductor material is epitaxially grown, wherein x in the first semiconductor layer is 0 to 0.2, and x in the second semiconductor layer is 0.98 to 1; And / or, in the step of alternately epitaxially growing the third semiconductor layer and the fourth semiconductor layer of the second reflector, the number of alternating cycles of the alternate epitaxial growth is 3, 4 or 5, the thickness of the third semiconductor layer is an optical thickness of one quarter of the target wavelength; the thickness of the fourth semiconductor layer is an optical thickness of one quarter of the target wavelength after the fourth semiconductor layer is oxidized to form the second oxide layer; the third semiconductor layer and the fourth semiconductor layer are made of Al x Ga 1-x As semiconductor material is epitaxially grown, x in the third semiconductor layer is 0 to 0.2, and x in the fourth semiconductor layer is 0.98 to 1; And / or, before the step of simultaneously performing lateral oxidation on the etched current limiting layer, the first reflector and the second reflector, the steps of the etching method of the first reflector include: At the periphery of the second reflector, two symmetrical etching grooves with a target pattern are etched on the top surface of the first reflector with the center line of the first reflector as the center of symmetry, so that the exposed second semiconductor layer of the first reflector is gradually diffusely oxidized from each of the etching grooves toward the center of symmetry; or, at the periphery of the second reflector, etching grooves of a target pattern are etched on a single side of the top surface of the first reflector, so that the exposed second semiconductor layer of the first reflector is gradually diffusely oxidized from the etching grooves in one direction.

10. The method for preparing a multi-junction VCSEL laser according to claim 9, characterized in that: The total thickness of the gain stack structure is an integer multiple of half the central wavelength of the target light wave; In the step of epitaxially growing the tunnel junction, the tunnel junction is grown at a node of a target light wave in the reflective cavity; In the step of epitaxially growing the current confinement layer, the current confinement layer is grown at a node of a target light wave in the reflection cavity.

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