Multi-junction VCSEL laser and laser radar system

Abstract

The utility model belongs to the technical field of semiconductor lasers, and relates to a multi-junction VCSEL laser and a laser radar system.The multi-junction VCSEL laser comprises a substrate and an epitaxial unit, the epitaxial unit comprises a first reflecting mirror, a second reflecting mirror and a gain stacking structure comprising a plurality of gain unit bodies, and the first reflecting mirror grows on the top face 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 technical field of semiconductor lasers, in particular to a multi-junction VCSEL laser and a laser radar system. BACKGROUND

[0002] A vertical-cavity surface-emitting laser (VCSEL) is a kind of semiconductor laser, which forms a reflection cavity in the vertical direction of the substrate, emits laser light in the vertical direction, has low threshold current, circular light spot, high modulation bandwidth, single longitudinal mode oscillation, easy to realize high-density two-dimensional array, low manufacturing cost and many other advantages, and is widely used in many fields. For example, in the field of laser radar, multi-junction VCSEL is a key technology to obtain high power density. With the continuous development of intelligent driving technology and the continuous expansion of application scenarios, the accelerated layout of the city's automatic auxiliary navigation driving (Navigate on Autopilot, NOA) function, the laser radar in the field of automatic driving has higher standards of characteristics such as high power, low divergence angle and high modulation speed.

[0003] In the prior art, a multi-junction VCSEL laser can include two mirrors, and a reflection cavity is formed between the two mirrors. In order to improve the power, a tunnel junction is used in the reflection cavity to connect multiple active regions in series, but this will increase the equivalent cavity length of the reflection cavity, making it difficult to meet the requirements of divergence angle and modulation speed.

[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. CONTENT 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] To solve the above technical problem, the embodiments of the present application provide a multi-junction VCSEL laser, which adopts the following technical solution:

[0007] The multi-junction VCSEL laser includes a substrate and at least one epitaxial unit, and each epitaxial unit includes:

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

[0009] A second mirror is surrounded together with the first mirror to form a reflection cavity;

[0010] A gain stack structure is located in the reflection cavity and grown on the top of the second mirror; the gain stack structure comprises a plurality of gain units; the plurality of gain units are connected in series along the growth direction through a tunnel junction;

[0011] The first mirror comprises a first semiconductor layer and a first oxidation layer formed by partially oxidizing a second semiconductor layer, which are alternately epitaxially grown; the refractive index of the first semiconductor layer is greater than the refractive index of the first oxidation layer.

[0012] The second mirror comprises a third semiconductor layer and a second oxidation layer formed by at least partially oxidizing a fourth semiconductor layer, which are alternately epitaxially grown; the refractive index of the third semiconductor layer is greater than the refractive index of the second oxidation layer.

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

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

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

[0016] And / or, the alternating period between the third semiconductor layer and the second oxidation layer is 4 or 5.

[0017] In some embodiments of the present application, the thickness of the first semiconductor layer and the third semiconductor layer is the optical thickness of one quarter of the target wavelength;

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

[0019] The thickness of the fourth semiconductor layer is the optical thickness of one quarter of the target wavelength after the fourth semiconductor layer is oxidized to form the second oxidation 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 x=0~0.2; the second semiconductor layer and the fourth semiconductor layer are made of Al x Ga 1-x As semiconductor material, and 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 mirror, and an emission opening is formed.

[0022] In some embodiments of the present application, each of the gain units comprises an active layer and a current limiting layer stacked along a growth direction, a middle portion of the current limiting layer is formed with a current hole not oxidized, and a periphery of the current hole is a high-resistance region oxidized;

[0023] The first oxide layer, the second oxide layer, and the high-resistance region are simultaneously manufactured by simultaneously performing lateral oxidation on the first mirror, the second mirror, and the current limiting layer.

[0024] In some embodiments of the present application, a total thickness of the gain stack structure is an integer multiple of a half wave of a center wavelength of the target light wave;

[0025] The tunnel junction and the current limiting layer are located at a wave node of the target light wave in the reflection cavity;

[0026] And / or, each of the gain units further comprises a spacer bottom layer and a spacer top layer, a top surface of the spacer bottom layer is stacked with the active layer; a part of the spacer top layer is stacked on a top surface of the active layer, a part of the spacer top layer is stacked on a top surface of the current limiting layer, and the tunnel junction is stacked on the spacer top layer;

[0027] The second mirror is stacked on the spacer top layer of the gain stack structure, and the second mirror, the spacer top layer, and the positive electrode together enclose the light outlet.

[0028] In some embodiments of the present application, a bottom of the substrate is provided with a negative electrode;

[0029] The first oxide layer of the first mirror comprises an oxidized region and a non-oxidized region, the oxidized region and the non-oxidized region are arranged along a direction perpendicular to the growth direction, and the oxidized region covers the light outlet hole in the growth direction; the second mirror covers the current hole in the growth direction;

[0030] Current of the positive electrode flows to the negative electrode through the current hole and the non-oxidized region in sequence.

[0031] In some embodiments of the present application, at a periphery of the gain stack structure, the first mirror is formed with an oxidation groove in a direction away from the growth direction;

[0032] The multi-junction VCSEL laser further comprises an insulating layer formed on a top surface of the first mirror, a groove wall of the oxidation groove, a side wall, and a top surface of the gain stack structure;

[0033] The positive electrode is formed on an outer surface of the insulating layer.

[0034] In some embodiments of the present application, a plurality of epitaxial units are provided, and the plurality of epitaxial units are spaced apart from the top surface of the substrate;

[0035] The bottom of the substrate is provided with a negative electrode, and each epitaxial unit is provided with an independent positive electrode and is electrically connected to the positive electrode and the negative electrode.

[0036] To solve the above technical problems, the embodiments of the present application also provide a laser radar system, which adopts the technical scheme as follows: the laser radar system comprises the multi-junction VCSEL laser described above.

[0037] Compared with the prior art, the multi-junction VCSEL laser and the laser radar system provided by the embodiments of the present application have the following beneficial effects:

[0038] The multi-junction VCSEL laser comprises a first semiconductor layer and a first oxide layer formed by at least partial oxidation of a second semiconductor layer, and 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 composed of two kinds of semiconductor materials and oxide materials with different refractive indexes and a large refractive index difference. In this way, the penetration depth of the target light wave into the reflector can be reduced, the number of alternating periods between the semiconductor layers in the reflector can be reduced, a smaller equivalent cavity length can be achieved, the transmission bandwidth of the reflector can be improved, the modulation speed of the multi-junction VCSEL laser can be improved, and the divergence angle can be reduced, so that the requirements of high power, low divergence angle and high modulation speed can be met at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the schemes in the present application, the drawings required in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application or corresponding prior art, and other drawings can also be obtained by those skilled in the art without creative labor. Among them:

[0040] Figure 1 is a planar sectional view of the multi-junction VCSEL laser in the examples of the present application; the figure is also a schematic view of step S630 of the preparation method of the multi-junction VCSEL laser;

[0041] Figure 2 is a flowchart of the preparation method of the multi-junction VCSEL laser in the examples of the present application;

[0042] Figure 3 is another flowchart of the preparation method of the multi-junction VCSEL laser in the examples of the present application;

[0043] Figure 4is a flow chart of step S200 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0044] Figure 5 is a schematic diagram of step S100 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0045] Figure 6 is a schematic diagram of step S210, step S220 and step S230 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0046] Figure 7 is a schematic diagram of step S240, step S250 and step S260 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0047] Figure 8 is a schematic diagram of step S300 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0048] Figure 9 is a schematic diagram of step S410 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0049] Figure 10 is a schematic diagram of step S420 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0050] Figure 11 is a schematic diagram of step S430 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0051] Figure 12 is a schematic diagram of step S500 of the preparation method of the multi-junction VCSEL laser in the example of the present application;

[0052] Figure 13 is a schematic diagram of step S610 in the example of the present application;

[0053] Figure 14 is another schematic diagram of step S610 in the example of the present application;

[0054] Figure 15 is a schematic diagram of step S620 of the preparation method of the multi-junction VCSEL laser in the example of the present application.

[0055] The reference signs in the drawings are as follows:

[0056] 100, multi-junction VCSEL laser; 200, growth direction;

[0057] 1, substrate;

[0058] 2, epitaxial unit; 21, first mirror; 211, first semiconductor layer; 212, second semiconductor layer; 213, first oxide layer; 2131, oxide area; 2132, non-oxide area; 214, oxide groove;

[0059] 22, second mirror; 221, third semiconductor layer; 222, fourth semiconductor layer; 223, second oxide layer; 24, gain stack structure; 241, gain unit; 2411, active layer; 2412, current limiting layer; 24121, current hole; 24122, high resistance area; 2413, interval bottom layer; 2414, interval top layer; 24141, first sub-interval layer; 24142, second sub-interval layer; 242, tunnel junction;

[0060] 3, insulating layer; 4, positive electrode; 5, light outlet; 6, negative electrode. DETAILED DESCRIPTION

[0061] 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, for example, the terms "length", "width", "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like specify relative positions according to the orientations shown in the drawings and are merely used for convenience in describing specific embodiments, and are not intended to be limiting of the present application.

[0062] The terms "include", "has", "having" and any variations thereof in the specification and claims of the present application and the above description of the drawings are intended to cover the inclusion not the exclusion of any elements; the terms "first", "second", and the like in the specification and claims of the present application or the above description of the drawings are used to distinguish different objects, not to describe a particular order. The meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0063] In the specification and claims of the present application and the above description of the drawings, when an element is referred to as being "fixed to" or "attached to" or "disposed on" or "connected to" another element, it can be directly or indirectly on the other element. For example, when an element is referred to as being "connected to" another element, it can be directly or indirectly connected to the other element.

[0064] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0065] This application provides a multijunction VCSEL laser 100, which is applicable to products such as lidar and laser sensors, but is not listed here.

[0066] like Figure 1 As shown, the multi-junction VCSEL laser 100 includes a substrate 1 and at least one epitaxial unit 2. The substrate 1 is made of, but is not limited to, group 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 various semiconductor substrates 1, and the wavelength band (corresponding to the target light wave) can cover visible light, near-infrared, mid-infrared, etc.

[0067] In the embodiments of this application, such as Figure 1 As shown, each epitaxial unit 2 includes a first reflector 21, a second reflector 22, and a gain stack 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 reflecting cavity. The gain stack structure 24 is located in the reflecting cavity, with the second reflector 22 grown on top of it. Understandably, the gain stack structure 24 is formed between the first reflector 21 and the second reflector 22, and adjusts the beam gain within the reflecting cavity.

[0068] In the embodiments of this application, to improve the power of a single light-emitting point, the gain stack structure 24 includes a plurality of gain units 241, wherein the plurality of gain units 241 are connected in series along the growth direction 200 through tunnel junctions 242. In other words, the gain units 241 and tunnel junctions 242 are alternately stacked in the growth direction 200. Understandably, the number of tunnel junctions 242 is one less than the number of gain units 241, and to ensure high power, once the number of gain units 241 is determined, the total height relationship of the plurality of gain units 241 can be basically determined.

[0069] In order to ensure the modulation speed also meets the demand, and effectively increase the transmission bandwidth of the multi-junction VCSEL laser 100, the first mirror 21 comprises a first semiconductor layer 211 and a second semiconductor layer 212. In the first state, i.e. the preparation state of the first mirror 21, the first semiconductor layer 211 and the second semiconductor layer 212 are alternately epitaxially grown, and the second semiconductor layer 212 epitaxially grown is finally formed into a first oxidation layer 213 after being partially oxidized. In the second state, i.e. the use state of the first mirror 21, the first semiconductor layer 211 and the first oxidation layer 213 are alternately stacked to form the first mirror 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 oxidation layer 213.

[0070] Optionally, in order to achieve a reflectivity of the first mirror 21 exceeding 99.9%, the ratio of the refractive index of the first semiconductor layer 211 to the refractive index of the first oxidation layer 213 can be greater than 1.5. In this way, in the case of achieving a certain reflectivity, the larger refractive index difference can improve the reflection intensity of the first mirror 21, thereby reducing the penetration depth of the target light wave into the first mirror 21, facilitating the reduction of the number of alternating periods of the first semiconductor layer 211 and the second semiconductor layer 212, and facilitating the realization of a smaller equivalent cavity length, so as to improve the transmission bandwidth of the first mirror 21, and further improve the modulation speed of the multi-junction VCSEL laser 100.

[0071] Exemplarily, the thickness of the first semiconductor layer 211 is an optical thickness of one fourth of the target wavelength, and the thickness of the second semiconductor layer 212 is an optical thickness of one fourth of the target wavelength after the second semiconductor layer 212 is oxidized to form the first oxidation layer 213. In order to avoid the problem of lattice matching with the substrate 1, the materials of the first semiconductor layer 211 and the second semiconductor layer 212 are selected flexibly, which is conducive to realizing 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=0~0.2 in the first semiconductor layer 211, and x=0.98~1 in the second semiconductor layer 212, and the substrate 1 is made of GaAs material.

[0072] Further exemplarily, the Al x Ga 1-x As semiconductor material in the first semiconductor layer 211 is x=0~0.2, and the refractive index is about 3.6; correspondingly, the Al x Ga 1-xAs the x = 1 of the semiconductor material of the second semiconductor layer 212, the material of the first oxide layer 213 formed after the oxidation of the semiconductor material of the second semiconductor layer 212 is Al2O3, and the refractive index of the material is about 1.6. Therefore, the refractive index difference of the first mirror 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 the first semiconductor layer 211 and the first oxide layer 213 is 4 or 5, and the reflectivity of the first mirror 21 is more than 99.9%.

[0073] Similarly, on the basis of ensuring that the power meets the demand, in order to ensure that the modulation speed also meets the demand, and to effectively increase the transmission bandwidth of the multi-junction VCSEL laser 100, the second mirror 22 includes a third semiconductor layer 221 and a fourth semiconductor layer 222. In the first state, that is, the preparation state of the second mirror 22, the third semiconductor layer 221 and the fourth semiconductor layer 222 are alternately epitaxially grown, and the fourth semiconductor layer 222 epitaxially grown is at least partially oxidized to form a second oxide layer 223. In the second state, that is, in the use state of the second mirror 22, the third semiconductor layer 221 and the fourth semiconductor layer 222 are alternately stacked to form the second mirror 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.

[0074] Alternatively, in order to realize the reflectivity of the second mirror 22 more than 99.9%, the ratio of the refractive index of the third semiconductor layer 221 to the refractive index of the second oxide layer 223 can be greater than 1.5. In this way, in the case of realizing a certain reflectivity (for example, a reflectivity greater than 99.9%), a larger refractive index difference can increase the reflection intensity of the second mirror 22, thereby reducing the penetration depth of the target light wave into the second mirror 22, which is beneficial to reducing the number of alternating periods of the third semiconductor layer 221 and the fourth semiconductor layer 222, and is beneficial to realizing a smaller equivalent cavity length, so as to improve the transmission bandwidth of the second mirror 22, and further improve the modulation speed of the multi-junction VCSEL laser 100.

[0075] 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 considering the lattice matching problem with the substrate 1, the materials of the third semiconductor layer 221 and the fourth semiconductor layer 222 are selected flexibly, which is beneficial to realizing a higher refractive index difference. The third semiconductor layer 221 and the fourth semiconductor layer 222 are both made of Al x Ga 1-xAs semiconductor material, x = 0 ~ 0.2 in the third semiconductor layer 221, x = 0.98 ~ 1 in the fourth semiconductor layer 222, and the substrate 1 is made of GaAs material.

[0076] Further, the Al x Ga 1-x As semiconductor material, x = 0 ~ 0.2, and the refractive index is about 3.6; correspondingly, the Al x Ga 1-x 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, and the refractive index is about 1.6, so the refractive index difference of the second mirror 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), so that the alternating period between the third semiconductor layer 221 and the second oxide layer 223 is 4 or 5, which can realize the reflectivity of the second mirror 22 exceeding 99.9%.

[0077] Obviously, compared with the refractive index difference of about 0.5 of the conventional VCSEL laser (for example, the semiconductor material made of GaA base and the substrate 1 lattice matched), theoretically, more than 99.9% reflectivity requires 35 periods, and it is also possible that the mirror is doped with impurities, or compared with the refractive index difference of about 0.8 of the two high and low oxide materials of the mirror made of oxide dielectric film, theoretically, more than 99.9% reflectivity requires 10 periods, or on the basis of the oxide cutoff film, a high-reflectivity metal film layer is evaporated, and theoretically, more than 99.9% reflectivity requires 5~6 periods, the mirror (such as the first mirror 21 and / or the second mirror 22) of the present application is formed by using a semiconductor material based on a semiconductor material, part of which is oxidized to form an oxide layer, which can not only be used as the first mirror 21 located at the bottom, but also as the second mirror 22 located at the top, and the refractive index difference between the semiconductor material in the mirror and the oxidized material formed by oxidizing part of the semiconductor material is greater than 1.5, for example, close to 2, and theoretically, more than 99.9% reflectivity requires only 4 or 5 periods, which can greatly reduce the penetration depth of light in the mirror, and is beneficial to effectively improve the transmission bandwidth of the multi-junction VCSEL laser 100.

[0078] In summary, compared with the prior art, the multi-junction VCSEL laser 100 has at least the following beneficial effects:

[0079] The multi-junction VCSEL laser 100 is formed by the first semiconductor layer 211 and the first oxide layer 213 formed by at least partial oxidation of the second semiconductor layer 212, and the third semiconductor layer 221 and the second oxide layer 223 formed by at least partial oxidation of the fourth semiconductor layer 222, so that the first reflector 21 and the second reflector 22 are both formed by the combination of semiconductor materials and oxide materials with different refractive indexes and large refractive index difference, so as to reduce the penetration depth of the target light wave into the reflector, reduce the number of alternating periods between the semiconductor layers in the reflector, realize a smaller equivalent cavity length, improve the transmission bandwidth of the reflector, realize a high modulation speed of the multi-junction VCSEL laser 100, and reduce the divergence angle, and simultaneously meet the requirements of high power, low divergence angle and high modulation speed.

[0080] In order for those skilled in the art to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below in combination with the drawings.

[0081] In some embodiments of the present application, as shown in Figure 1 In order to realize the function of outputting laser of the multi-junction VCSEL laser 100 and make the overall structure more compact, a positive electrode 4 is arranged on the top surface of the gain layer stack structure 24 at the periphery of 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 layer 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 layer stack structure 24, and the light outlet 5 can be jointly surrounded by the second reflector 22, the top surface of the gain layer stack structure 24 and the positive electrode 4. Among them, the gain layer stack structure 24 can emit laser through the light outlet 5 after being electrified.

[0082] In some embodiments of the present application, as shown in Figure 1 Each gain unit body 241 of the gain layer stack structure 24 includes an active layer 2411 and a current limiting layer 2412 arranged in a stacking manner along the growth direction 200, so as to limit the current path in the reflection cavity and facilitate the emission of laser. The middle part of the current limiting layer 2412 is formed with a current hole 24121 which is not oxidized, and the periphery of the current hole 24121 is a high resistance area 24122 which is oxidized. 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. Alternatively, the current limiting layer 2412 is located above the active layer 2411. In addition, in order to improve the efficiency and modulation speed, the current hole 24121 can be located directly below the light outlet 5, the area of the current limiting layer 2412 which is not formed with the current hole 24121 is the high resistance area 24122, and the current hole 24121 is covered by the second reflector 22 in the growth direction 200.

[0083] To simplify the fabrication 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 fabricated by lateral oxidation of the first reflector 21, the second reflector 22, and the current-limiting layer 2412. Understandably, after forming the second semiconductor layer 212, the fourth semiconductor layer 222, and the current-limiting layer 2412, and after forming a current hole 24121 in the current-limiting layer 2412, lateral oxidation of the first reflector 21, the second reflector 22, and the current-limiting layer 2412 can be performed simultaneously to oxidize the second semiconductor layer 212 into the first oxide layer 213, the fourth semiconductor layer 222 into the second oxide layer 223, and the region of the current-limiting layer 2412 without the current hole 24121 into the high-resistance region 24122.

[0084] For example, the sidewalls of the first reflector 21 and the second reflector 22 can be exposed by an etching process, and the Al of the second semiconductor layer 212 can be oxidized by water vapor in a high-temperature oxidation furnace. x Ga 1-x As semiconductor materials are oxidized to Al2O3, since this process is a conventional process for manufacturing VCSELs by oxidizing and limiting the aperture, the oxidation of the mirror and the current limiting layer 2412 can be combined into one oxidation process by reasonably designing the relevant parameters of the VCSEL laser. This simplifies the epitaxial growth and fabrication process of the multi-junction VCSEL laser 100 and improves the compatibility and reliability of the multi-junction VCSEL laser 100.

[0085] It should be noted that the active layer 2411 is mainly used to generate the optical gain required for laser light, including but not limited to a multi-quantum-well structure. The high-resistivity region 24122 of the current-confining layer 2412 is mainly used to form electrical isolation for the non-injected current region, thereby limiting the current path. The high-resistivity region 24122 can be formed by lateral oxidation of semiconductor materials containing high aluminum content as described above, or it can also be formed by ion implantation.

[0086] In some embodiments of this application, such as Figure 1 As shown, to satisfy the standing wave condition, the total thickness H of the gain stack structure 24 is an integer multiple of half the center wavelength of the target light wave. Specifically, to reduce absorption loss, the tunnel junction 242 and the current confinement layer 2412 are located at the nodes of the target light wave within the reflection cavity.

[0087] In some embodiments of this application, such as Figure 1As shown, for the convenience of adjusting the equivalent cavity length of the reflection cavity, each gain unit further comprises a spacer bottom layer 2413 and a spacer top layer 2414, and the top surface of the spacer bottom layer 2413 is laminated with the active layer 2411. A part (corresponding to the first sub-spacer layer 24141) of the spacer top layer 2414 is laminated on the top surface of the active layer 2411, and a part (corresponding to the second sub-spacer layer 24142) of the spacer top layer 2414 is laminated on the top surface of the current limiting layer 2412 and laminated with the tunnel junction 242. The second mirror 22 is laminated on the spacer top layer 2414 of the gain lamination structure 24, and together with the positive electrode 4 and the spacer top layer 2414 to form the light outlet 5. Understandably, the spacer bottom layer 2413 and the spacer top layer 2414 are respectively located on the lower side and the upper side of the active layer 2411.

[0088] Exemplarily, the spacer bottom layer 2413 of the gain unit close to the first mirror 21 is epitaxially grown on the top surface of the first mirror 21, and the top surface of the spacer bottom layer 2413 is sequentially laminated with the active layer 2411, the first sub-spacer layer 24141, the current limiting layer 2412, the second sub-spacer layer 24142 and the tunnel junction 242.

[0089] In some embodiments of the present application, as shown in Figure 1 As shown, for the electrical connection of the multi-junction VCSEL laser 100, the bottom of the substrate 1 is provided with a negative electrode 6, and the first oxide layer 213 of the first mirror 21 in the second state comprises an oxidation area 2131 and a non-oxidation area 2132, wherein the oxidation area 2131 and the non-oxidation area 2132 are arranged along a direction perpendicular to the growth direction 200 (specifically, the width direction of the first mirror 21), and the oxidation area 2131 covers the light hole in the growth direction 200. The second mirror 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 area 2132 in turn.

[0090] In some embodiments of the present application, as shown in Figure 1 As shown, for the convenience of realizing the oxidation of the second semiconductor layer 212 in the first mirror 21, the first mirror 21 is formed with an oxidation groove 214 in a direction away from the growth direction 200 at the periphery of the gain lamination structure 24. That is, the first mirror 21 is recessed with the oxidation groove 214 to expose the sidewall of the first mirror 21.

[0091] In addition, in order to prevent current leakage and ensure electrical isolation of the non-current injection area, the top surface of the uppermost spacer top layer 2414 in the gain lamination structure 24 is current injected, as shown in Figure 1As shown, the multi-junction VCSEL laser 100 further comprises an insulating layer 3, wherein the insulating layer 3 is formed on the top surface of the first mirror 21, the groove wall of the oxidation groove 214, the side wall and the top surface of the gain layer stack structure 24. The positive electrode 4 is formed on the outer surface of the insulating layer 3.

[0092] In some embodiments of the present application, the bottom of the substrate 1 is provided with a negative electrode 6. Correspondingly, a plurality of epitaxial units 2 can be provided, and the plurality of epitaxial units 2 are spaced apart on the top surface of the substrate 1. Among them, 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. Understandably, by independently setting the positive electrode 4 on each epitaxial unit 2, and making each epitaxial unit 2 share the same negative electrode 6 on the substrate 1, the lighting of a specific epitaxial unit 2 can be realized, which is conducive to realizing the addressable function of the laser radar, and is suitable for use in high-performance laser radar systems based on addressable multi-junction VCSEL lasers 100.

[0093] 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. By designing the connection mode of the positive electrode 4 and the negative electrode 6, a single-point, linear-array, and specific-area independent addressable scanning working mode of the out-of-plane electrode can be realized to meet the technical requirements required by the current laser radar ranging. The specific connection mode of the positive electrode 4 and the negative electrode 6 can be determined according to actual needs, which will not be described here.

[0094] Based on the above multi-junction VCSEL laser 100, the embodiments of the present application further provide a laser radar system (not shown in the figure), wherein the laser radar system comprises the above multi-junction VCSEL laser 100.

[0095] In summary, compared with the prior art, the laser radar system has at least the following beneficial effects: by adopting the above multi-junction VCSEL laser 100, the laser radar system has the characteristics of high power, low divergence angle and high modulation speed, which is conducive to realizing the automatic auxiliary navigation driving function in the field of automatic driving.

[0096] The embodiments of the present application further provide a multi-junction VCSEL laser 100, which is exemplarily shown as Figure 1 The multi-junction VCSEL laser 100 comprises a substrate 1 and an epitaxial unit 2, and the epitaxial unit 2 is electrically connected to a positive electrode 4 and a negative electrode 6. The epitaxial unit 2 comprises a first mirror 21, a second mirror 22 and a gain layer stack structure 24, and the second mirror 22 and the first mirror 21 jointly form a reflection cavity (not shown in the figure) therebetween. The gain layer stack structure 24 is located in the reflection cavity and has the second mirror 22 grown on the top. Understandably, the gain layer stack structure 24 is formed between the first mirror 21 and the second mirror 22 to adjust the light beam in the reflection cavity.

[0097] In order to ensure the modulation speed also meets the demand, and effectively increase the transmission bandwidth of the multi-junction VCSEL laser 100, the first mirror 21 comprises a first semiconductor layer 211 and a first oxide layer 213 formed after the second semiconductor layer 212 is partially oxidized, 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 mirror 22 comprises a third semiconductor layer 221 and a second oxide layer 223 formed after the fourth semiconductor layer 222 is at least partially oxidized, and the refractive index of the third semiconductor layer 221 is greater than the refractive index of the second oxide layer 223.

[0098] In addition, as shown in Figure 2 , the gain stack structure 24 is formed with an output port 5. The gain stack structure 24 comprises a plurality of gain unit bodies 241, which are connected in series along the growth direction 200 through tunnel junctions 242. Each gain unit body 241 comprises a stack of an active layer 2411 and a current limiting layer 2412, wherein the middle part of the current limiting layer 2412 is formed with a current hole 24121 which is not oxidized, and the periphery of the current hole 24121 is a high resistance area 24122 which is oxidized.

[0099] Understandably, the multi-junction VCSEL laser 100 is formed by combining the first mirror 21 and the second mirror 22 with two semiconductor materials and oxide materials having different refractive indices and large refractive index differences, so as to reduce the penetration depth of the target light wave into the mirror, reduce the number of alternating periods between the semiconductor layers in the mirror, realize a smaller equivalent cavity length, improve the transmission bandwidth of the mirror, and realize high modulation speed and small divergence angle of the multi-junction VCSEL laser 100, which can meet the requirements of high power, low divergence angle and high modulation speed at the same time.

[0100] It should be noted that some details of the multi-junction VCSEL laser 100 can be the same as the above multi-junction VCSEL laser 100, which will not be described here.

[0101] In the embodiments of the present application, for the multi-junction VCSEL laser 100, as shown in Figure 3 and Figure 5 , the preparation method of the multi-junction VCSEL laser 100 comprises the following steps:

[0102] Step S100: using an epitaxial growth process to alternately epitaxially grow the first semiconductor layer 211 and the second semiconductor layer 212 of the first mirror 21 on the top surface of the substrate 1 (see Figure 4 ).

[0103] 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 periods of the first semiconductor layer 211 and the second semiconductor layer 212 alternately epitaxially grown is 3 or 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 epitaxially grown from AlxGa1-xAs semiconductor material, x = 0 ~ 0.2 in the first semiconductor layer 211 and x = 0.98 ~ 1 in the second semiconductor layer 212. x Ga 1-x As semiconductor material.

[0104] It should be noted that the first semiconductor layer 211 can be made of semiconductor material with high aluminum component, and the second semiconductor layer 212 can be made of semiconductor material with low aluminum component. The epitaxial growth process 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 GaAs, InP, GaSb, GaN and other III-V semiconductor materials. It should also be noted that the first reflector 21 can be in a symmetrical structure, and the material epitaxially grown on the substrate 1 is usually the same as the material forming the top surface of the first reflector 21.

[0105] Step S200: alternately epitaxially growing the gain unit 241 and the tunnel junction 242 on the top surface of the first reflector 21 using an epitaxial growth process to preliminarily form the gain layer stack structure 24. The tunnel junction 242 is located on the side of the gain unit 241 away from the first reflector 21. Understandably, to improve the power, the gain layer stack structure 24 includes a plurality of gain units 241, and a tunnel junction 242 is epitaxially grown between two adjacent gain units 241 to realize series connection between them.

[0106] In step S200, to meet the standing wave condition of the tunnel junction 242 and the current limiting layer 2412 in the gain layer stack structure 24, the total thickness H of the gain layer stack structure 24 is an integer multiple of half the center wavelength of the target light wave.

[0107] It should be noted that the epitaxial growth order of the active layer 2411 and the current limiting layer 2412 and the like in the gain unit 241 epitaxially grown in step S200 is not particularly limited and can be determined according to actual needs.

[0108] Exemplarily, in the step of epitaxially growing the gain unit 241 in step S200, the active layer 2411 and the current limiting layer 2412 are epitaxially grown in the order of the active layer 2411, the current limiting layer 2412, and the active layer 2411. Figure 6 andFigure 7 As shown, the specific steps of epitaxially growing gain unit 241 include:

[0109] Step S210: An epitaxial layer 2413 is grown on the top surface of the epitaxially grown first reflector 21. In this step, the material of the spacer layer 2413 should be as lattice-matched as possible with that of the substrate 1.

[0110] Step S220: An active layer 2411 is epitaxially grown on the top surface of the epitaxially grown spacer layer 2413. In step S220, the active layer 2411 may be a multi-quantum-well structure so that the emission band of the active layer 2411 can be adjusted to cover the target light wave by adjusting the thickness or composition of the wells.

[0111] Step S230: A first sub-spacer layer 24141 is epitaxially grown 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, a current limiting layer 2412 is epitaxially grown on the first sub-spacer layer 24141. In step S230, the current limiting layer 2412 may be made of Al with a high aluminum content. x Ga 1-x As semiconductor material. In order to effectively reduce absorption loss, in this step, a current-limiting layer 2412 is grown at the node of the target light wave in the reflecting cavity.

[0112] Step S240: A second sub-spacer layer 24142 is epitaxially grown on the top surface of the epitaxially grown current-limiting layer 2412 to form a gain unit cell 241 layer by layer (see...). Figure 7 ).

[0113] Among them, such as Figure 7 As shown, the aforementioned top layer 2414 includes a first sub-spacer layer 24141 and a second sub-spacer layer 24142. Exemplarily, a single gain unit 241 may include a 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, which are epitaxially grown sequentially, wherein the current limiting layer 2412 is located between the first sub-spacer layer 24141 and the second sub-spacer layer 24142 of the top layer 2414. That is, in step S200, steps S210, S220, S230, and S240 can be executed sequentially. Of course, in other examples, steps S210, S220, S230, and S240 may also adopt other suitable orders, which will not be elaborated here.

[0114] Understandably, after step S240 in step S200, as Figure 8 As shown, step S200 further includes the following steps:

[0115] Step S250: epitaxially growing a tunnel junction 242 on the top surface of the epitaxially grown second sub-separation layer 24142. In the step of epitaxially growing the tunnel junction 242 in step S250, to effectively reduce the absorption loss, the tunnel junction 242 is grown at the node of the target light wave in the reflection cavity.

[0116] Step S260: repeating the above steps S210-S250 on the top surface of the epitaxially grown tunnel junction 242.

[0117] In step S260, the number of repetitions of the above steps S210-S250 is one less than the total number of junctions of the multi-junction VCSEL laser 100. In addition, the number of tunnel junctions 242 formed in step S200 is also one less than the total number of junctions of the multi-junction VCSEL laser 100.

[0118] Step S300: alternately epitaxially growing a third semiconductor layer 221 and a fourth semiconductor layer 222 of the second mirror 22 on the top surface of the gain layer stack 24 using an epitaxial growth process.

[0119] In step S300, the third semiconductor layer 221 and the fourth semiconductor layer 222 of the second mirror 22 are alternately epitaxially grown, as shown in FIG. 3B. Figure 9 to Figure 11 In step S300, the third semiconductor layer 221 and the fourth semiconductor layer 222 of the second mirror 22 are alternately epitaxially grown, as shown in FIG. 3B. x Ga 1-x As semiconductor material, x = 0-0.2 in the third semiconductor layer 221, and x = 0.98-1 in the fourth semiconductor layer 222.

[0120] 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 in step S300 includes but is not limited to metal-organic chemical vapor deposition (MOCVD).

[0121] Step S400: etching the second mirror 22, the gain layer stack 24 and the first mirror 21 epitaxially grown in sequence to expose the inner cavity contact layer of the gain layer stack 24, the sidewall of the gain layer stack 24 and form a current hole 24121, and expose the sidewall of the first mirror 21.

[0122] It is understandable that the step S400 is performed after the epitaxial growth of the multi-junction VCSEL sample is completed, i.e., after the steps S100, S200 and S300 are sequentially completed, and belongs to the preparation process.

[0123] Exemplarily, as shown in FIG. 4, the step S400 can specifically include the following steps. Figure 9

[0124] Step S410: performing a first etching treatment on the second mirror 22 in the multi-junction VCSEL sample to expose the inner cavity contact layer of the gain layer stack structure 24 (see FIG. 5). Figure 10

[0125] Exemplarily, the second mirror 22 is etched so that the width of the second mirror 22 is less than the width of the gain layer stack structure 24, so that the top surface of the gain layer stack structure 24 and the side surface of the second mirror 22 are exposed. The first etching treatment in this step includes, but is not limited to, glue coating, exposure and development, and the etching gas includes, but is not limited to, Cl2, BCl3 and Ar.

[0126] Step S420: performing a second etching treatment on the gain layer stack structure 24 in the multi-junction VCSEL sample to expose the side wall of the gain layer stack structure 24 and form the current hole 24121 (see FIG. 6). Figure 11

[0127] Exemplarily, after the step S410, the gain layer stack structure 24 is etched so that the width of the gain layer stack structure 24 is less than the width of the first mirror 21, so that the side wall of the gain layer stack structure 24 is exposed. For example, dry etching is performed by using an ICP etching device to expose the side wall of the gain layer stack structure 24. In addition, the current limiting layer 2412 in the gain layer stack structure 24 is also etched to form the current hole 24121 along the growth direction 200 in each current limiting layer 2412. The second etching treatment in this step includes, but is not limited to, glue coating, exposure and development, and the etching gas includes, but is not limited to, Cl2, BCl3 and Ar.

[0128] Step S430: after the step S420, performing a third etching treatment on the first mirror 21 in the multi-junction VCSEL sample to expose the side wall of the first mirror 21 (see FIG. 7). Figure 12

[0129] Exemplarily, the side wall of the first mirror 21 can be exposed by forming an oxidation groove 214 on the top surface of the first mirror 21. In addition, the third etching treatment in this step S430 includes, but is not limited to, glue coating, exposure and development, and the etching gas includes, but is not limited to, Cl2, BCl3 and Ar.

[0130] ​​​​Also exemplary, before the step of simultaneously performing lateral oxidation on the etched current limiting layer 2412, the first mirror 21 and the second mirror 22, namely before the following step S500, specifically corresponding to the third etching treatment in step S430 of step S400, namely the etching method of the first mirror 21 has the following two specific embodiments:

[0131] In the first specific embodiment, which belongs to the double-side oxidation method, on the periphery of the second mirror 22, with the center line of the first mirror 21 as the symmetric center, symmetrically etch two etching grooves (not shown in the figure) with a target pattern on the top surface of the first mirror 21, so that the exposed second semiconductor layer 212 of the first mirror 21 gradually diffuses from each etching groove to the symmetric center.

[0132] Exemplarily, etch an etching groove with a symmetric hole or fan-shaped pattern on the top surface of the first mirror 21 to expose the first mirror 21 through the etching groove, wherein the second semiconductor layer 212 in the first mirror 21 exposed through the etching groove can spread diffusively from the etching groove corresponding area to the center line of the first mirror 21 under the oxidation of high-temperature water vapor, so that the second semiconductor layer 212 in the first mirror 21 is at least partially oxidized into a first oxidation layer 213, and the first oxidation layer 213 includes an oxidation area 2131 and a non-oxidation area 2132, wherein the oxidation area 2131 of the first oxidation layer 213 needs to cover the light outlet 5, and the current can flow from the non-oxidation area 2132 to the negative electrode 6.

[0133] Alternatively, in the second specific embodiment, which belongs to the single-side oxidation method, on the periphery of the second mirror 22, etch an etching groove with a target pattern on one side of the top surface of the first mirror 21, so that the exposed second semiconductor layer 212 of the first mirror 21 gradually diffuses from the etching groove in one direction.

[0134] Exemplarily, etch an etching groove with a strip-shaped pattern on one side of the top surface of the first mirror 21 (corresponding to the oxidation groove 214) to expose the first mirror 21 through the etching groove, wherein the second semiconductor layer 212 in the first mirror 21 exposed through the etching groove can spread diffusively in one direction from the etching groove corresponding area under the oxidation of high-temperature water vapor, so that the second semiconductor layer 212 in the first mirror 21 is at least partially oxidized into a first oxidation layer 213, wherein the first oxidation layer 213 includes an oxidation area 2131 and a non-oxidation area 2132, and the oxidation area 2131 of the first oxidation layer 213 on one side needs to cover the light outlet 5, and the current can flow from the non-oxidation area 2132 on the other side to the negative electrode 6.

[0135] Step S500: Simultaneously perform lateral oxidation on the etched current confinement layer 2412, the first reflector 21, and the second reflector 22, so that the current confinement layer 2412 forms an unoxidized current hole 24121 and an oxidized high-resistance region 24122, each of the second semiconductor layers 212 of the first reflector 21 becomes a first oxide layer 213, and each of the fourth semiconductor layers 222 of the second reflector 22 is oxidized to a second oxide layer 223, to form a laser sample (see...). Figure 12 ).

[0136] Understandably, combining the oxidation of the first reflector 21, the second reflector 22, and the current confinement layer 2412 into a single oxidation process simplifies the epitaxial growth and fabrication process of the multi-junction VCSEL laser 100, thereby improving the compatibility and reliability of the multi-junction VCSEL laser 100.

[0137] For example, such as Figure 13 to Figure 15 As shown, after step S430, a wet nitrogen oxidation device can be used to perform lateral oxidation on the current limiting layer 2412, the first reflector 21, and the second reflector 22. The oxidation rate can be controlled by adjusting parameters such as oxidation temperature, water vapor temperature, pressure, and flow rate, and the lateral oxidation depth can be controlled by controlling the time. This forms an unoxidized current hole 24121 at the center of the current limiting layer 2412 and an oxidized high-resistance region 24122 around the current hole 24121. The current injected into the laser is restricted to only be able to conduct 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 that 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 in the second reflector 22 is much higher than that of the current limiting layer 2412. Therefore, when the aperture size of the current hole 24121 in the current limiting layer 2412 reaches the required design size, the fourth semiconductor layer 222 of the second reflector 22 has been completely oxidized into the second oxide layer 223, and the oxide region 2131 of the first oxide layer 213 of the first reflector 21 has long been able to cover the light outlet 5, so that both the first reflector 21 and the second reflector 22 are ultimately composed of semiconductor materials and oxide materials.

[0138] Also exemplarily, in step S500, the AlxGa1-xAs semiconductor material of the first semiconductor layer 211 has x = 0 ~ 0.2, and the refractive index thereof can be about 3.6; correspondingly, the AlxGa1-xAs semiconductor material of the second semiconductor layer 212 has x = 1, i.e., the semiconductor material of the second semiconductor layer 212 is AlAs, and the material of the first oxide layer 213 formed after oxidation of the second semiconductor layer 212 is Al2O3, and the refractive index thereof is about 1.6, so that the refractive index difference of the first mirror 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), and thus the alternating period between the first semiconductor layer 211 and the first oxide layer 213 is 4 or 5, and the reflectivity of the first mirror 21 can be more than 99.9%.

[0139] Similarly, the AlxGa1-xAs semiconductor material of the third semiconductor layer 221 has x = 0 ~ 0.2, and the refractive index thereof is about 3.6; correspondingly, the AlxGa1-xAs semiconductor material of the fourth semiconductor layer 222 has x = 1, i.e., the semiconductor material of the fourth semiconductor layer 222 is AlAs, and the material of the second oxide layer 223 formed after oxidation of the fourth semiconductor layer 222 is Al2O3, and the refractive index thereof is about 1.6, so that the refractive index difference of the second mirror 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), and thus the alternating period between the third semiconductor layer 221 and the second oxide layer 223 is 4 or 5, and the reflectivity of the second mirror 22 can be more than 99.9%.

[0140] Step S600: performing a preparation process on the laser sample to form the multi-junction VCSEL laser 100 in a second state. The step S600 is performed after the step of forming the laser sample in step S500.

[0141] In some embodiments of the present application, as shown in Figure 15 The step S600 includes the following steps:

[0142] Step S610: forming an insulating layer 3 on the outer surface of the gain layer stack 24 and the first mirror 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 layer stack 24 to form a current injection area.

[0143] Exemplarily, step S610 can employ a PECVD device to deposit a material including but not limited to SiO2 or Si3N4 on the surface of the laser sample formed in step S500 to form the insulating layer 3. In addition, the insulating layer 3 formed on the top surface of the gain layer stack 24 is etched at the periphery of the second mirror 22 to expose a part of the top surface of the gain layer stack 24, so that the non-current injection region is electrically isolated by the insulating layer 3, and the current injection region is formed on the exposed part of the top surface.

[0144] The thickness of the insulating layer 3 ranges from 300 nm to 500 nm. The insulating layer 3 can be dry etched by an RIE device to expose a part of the top surface of the gain layer stack 24. The etching gas for the insulating layer 3 formed by SiO2 or Si3N4 can include but is not limited to CF4 and O2.

[0145] 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 of the current injection region to form the light emitting port 5 surrounded by the positive electrode 4, the second mirror 22 and the gain layer stack 24, and form the positive electrode 4 (see Figure 1 ).

[0146] Exemplarily, after step S610, the laser sample can be subjected to photoetching, and after the steps of uniform coating, photoetching and developing, the positive electrode 4 pattern of the VCSEL is formed. Then, the first metal electrode layer is evaporated by electron beam evaporation, and the sample after evaporation is subjected to Lift-off stripping process in acetone solution to remove the electrode part unnecessary for the half-VCSEL light emitting port 5, and finally the positive electrode 4 is formed. The material forming the positive electrode 4 includes but is not limited to Ti, Pt and Au.

[0147] Step S630: forming a second metal electrode layer on the bottom of the substrate 1 to form the negative electrode 6 (see ​ ).

[0148] Exemplarily, after step S620, the substrate 1 in the laser sample can be thinned and polished, and then the second metal electrode layer is evaporated on the bottom surface of the substrate 1 by electron beam evaporation. The material forming the negative electrode 6 includes but is not limited to Au-Ge, Ni and Au.

[0149] After step S630 is completed, the whole preparation process flow of the multi-junction VCSEL laser 100 is completed.

[0150] In general, the multi-junction VCSEL laser 100 prepared by the preparation method of the multi-junction VCSEL laser 100 has high compatibility, high reliability, high power, low divergence angle and high modulation speed, and also facilitates the realization of the addressable function of the laser radar system.

[0151] The above descriptions are merely some embodiments of the present application, but are not intended to limit the present application. Various modifications and changes can be made by those skilled in the art to the present application without departing from the spirit and scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of claims of the present application.

Claims

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

2. The multi-junction VCSEL laser of claim 1, wherein, the ratio of the refractive index of the first semiconductor layers to that of the first oxide layers is greater than 1.5; and / or, the ratio of the refractive index of the third semiconductor layers to that of the second oxide layers is greater than 1.5; and / or, the alternating period between the first semiconductor layers and the first oxide layers is 4 or 5; and / or, the alternating period between the third semiconductor layers and the second oxide layers is 4 or 5.

3. The multi-junction VCSEL laser of claim 1, wherein, the thickness of the first semiconductor layers and the third semiconductor layers is a quarter of the optical thickness of the target wavelength; the thickness of the second semiconductor layers is a quarter of the optical thickness of the target wavelength after the second semiconductor layers are oxidized to form the first oxide layers; the thickness of the fourth semiconductor layers is a quarter of the optical thickness of the target wavelength after the fourth semiconductor layers are oxidized to form the second oxide layers; 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 x=0~0.2; the second semiconductor layer and the fourth semiconductor layer are made of Al x Ga 1-x As semiconductor material, and x=0.98~1.

4. The multi-junction VCSEL laser of claim 1, wherein, on the periphery of the second mirror, the top surface of the gain layer stack is provided with a positive electrode and forms a light outlet.

5. The multi-junction VCSEL laser of claim 4, wherein, each of the gain unit bodies comprises an active layer and a current limiting layer arranged in a stack along the growth direction, a middle part of the current limiting layer is formed with a current hole which is not oxidized, and the periphery of the current hole is a high-resistance area which is oxidized; the first oxide layers, the second oxide layers and the high-resistance areas are simultaneously formed by transverse oxidation of the first mirror, the second mirror and the current limiting layer.

6. The multi-junction VCSEL laser of claim 5, wherein, the total thickness of the gain layer stack is an integer multiple of a half wave of the target optical wave central wavelength; the tunnel junction and the current limiting layer are located at a wave node of the target optical wave in the reflection 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 provided with the active layer in a stack; a part of the spacer top layer is arranged on the top surface of the active layer in a stack, a part of the spacer top layer is arranged on the top surface of the current limiting layer and is provided with the tunnel junction in a stack; the second mirror is arranged on the spacer top layer of the gain layer stack and together with the positive electrode and the spacer top layer forms the light outlet.

7. The multi-junction VCSEL laser of claim 5, wherein, the bottom of the substrate is provided with a negative electrode. The first oxidation layer of the first reflector comprises an oxidation region and a non-oxidation region, the oxidation region and the non-oxidation region are arranged along a direction perpendicular to the growth direction, and the oxidation region covers the light outlet 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 region in sequence.

8. The multi-junction VCSEL laser of claim 4, wherein, On the periphery of the gain layer stack structure, the first reflector is formed with an oxidation groove in a direction away from the growth direction; The multi-junction VCSEL laser further comprises an insulating layer, which is formed on the top surface of the first reflector, the groove wall of the oxidation groove, the side wall and the top surface of the gain layer stack structure; The positive electrode is formed on the outer surface of the insulating layer.

9. The multi-junction VCSEL laser of claim 1, wherein, The epitaxial units are spaced apart on the top surface of the substrate; The bottom of the substrate is provided with a negative electrode; each epitaxial unit is provided with an independent positive electrode and is electrically connected to the positive electrode and the negative electrode.

10. A lidar system, comprising: The laser radar system comprises the multi-junction VCSEL laser according to any one of claims 1 to 9.

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