Vertical cavity surface emitting laser and preparation method thereof

Abstract

The vertical cavity surface emitting laser specifically comprises a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer which are sequentially stacked, a current injection barrier layer is further stacked, and a current injection channel is formed in the current injection barrier layer; the second electrode contact part, the transparent conductive thin film and the heavily doped semiconductor material part are positioned on the upper surface side of the second conductive semiconductor layer; wherein in the stacking direction, the projection of the heavily doped semiconductor material part falls into the range of the projection of the current injection channel, and the projection of the second electrode contact part does not coincide with the projection of the current injection channel; one part of the transparent conductive film is conductively connected with the second electrode contact part, and the other part of the transparent conductive film is conductively connected with the second conductive semiconductor layer through the heavily doped semiconductor material part. In this way, control over current distribution is better achieved, and the light emitting divergence angle of the VCSEL is optimized.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a vertical cavity surface emitting laser and a preparation method thereof. Background Art

[0002] Vertical-Cavity Surface-Emitting Laser (VCSEL) is a semiconductor laser whose laser emission direction is perpendicular to the epitaxial plane. Different from general edge-emitting lasers, VCSEL has the advantages of small far-field divergence angle, easy fiber coupling, small threshold current, high bandwidth and high test efficiency.

[0003] However, in practical applications, the light divergence angle of the VCSEL chip has become a technical indicator that needs to be focused on, especially in application scenarios with strict requirements on beam quality, the control of the divergence angle is particularly critical. In order to optimize the divergence angle, some effective technical means have been explored in this field. For example, by adding an optical lens to the light-emitting surface of the VCSEL, the emitted light can be converged, thereby reducing the divergence angle; or, the epitaxial surface of the VCSEL is shallowly etched to further control the divergence angle by suppressing the light emission of the unetched area. However, improving the VCSEL chip only in the optical path is not enough to meet the optimization requirements of the divergence angle. In a typical VCSEL structure, in order to avoid the center of the light-emitting hole being blocked, the metal electrode can only be made in the outer ring of the light-emitting hole, so that the current can only be injected from the periphery of the light-emitting hole, resulting in the current density at the edge of the light-emitting hole being greater than the current density in the center of the light-emitting hole. The unevenness of the current distribution will aggravate the divergence of the light beam, further increasing the divergence angle, thereby affecting the beam quality and application effect of the VCSEL.

[0004] Therefore, how to further optimize the light divergence angle of VCSEL, especially to control the current distribution in structural design, has become an important issue to be solved in this field. Summary of the invention

[0005] In view of this, embodiments of the present application provide a vertical cavity surface emitting laser and a method for manufacturing the same in order to solve at least one problem existing in the background technology.

[0006] In a first aspect, an embodiment of the present application provides a vertical cavity surface emitting laser, comprising:

[0007] A first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer stacked in sequence. A current injection blocking layer is further stacked between the first conductive semiconductor layer and the active layer and / or between the second conductive semiconductor layer and the active layer. A current injection channel is formed in the current injection blocking layer. The second conductive semiconductor layer has an upper surface away from the current injection blocking layer;

[0008] A second electrode contact portion, a transparent conductive thin film, and a heavily doped semiconductor material portion located on the upper surface side of the second conductive semiconductor layer;

[0009] Wherein,

[0010] In the stacking direction, the projection of the heavily doped semiconductor material portion falls within the projection range of the current injection channel, and the projection of the second electrode contact portion does not coincide with the projection of the current injection channel;

[0011] A part of the transparent conductive thin film is electrically connected to the second electrode contact portion, and the other part is electrically connected to the second conductive semiconductor layer through the heavily doped semiconductor material portion.

[0012] Combined with the first aspect of the present application, in an alternative embodiment, the heavily doped semiconductor material portion is in direct contact with the upper surface of the second conductive semiconductor layer; the transparent conductive thin film covers the heavily doped semiconductor material portion and the second conductive semiconductor layer; the second electrode contact portion is located on the transparent conductive thin film.

[0013] Combined with the first aspect of the present application, in an alternative embodiment, in the stacking direction,

[0014] The projection center of the heavily doped semiconductor material portion coincides with the projection center of the current injection channel; and / or,

[0015] The projection of the heavily doped semiconductor material portion is circular or annular.

[0016] Combined with the first aspect of the present application, in an alternative embodiment, the material of the transparent conductive thin film includes ITO.

[0017] Combined with the first aspect of the present application, in an alternative embodiment, it further includes at least one transparent material layer stacked on the side of the transparent conductive thin film away from the second conductive semiconductor layer. The transparent conductive thin film satisfies:

[0018]

[0019] Where n0 is the refractive index of the transparent conductive thin film, d0 is the thickness of the transparent conductive thin film, n i is the refractive index of the i-th transparent material layer, di is the thickness of the i-th transparent material layer, where i is a positive integer, x is the total number of transparent material layers, k is a positive integer, and λ is the emission wavelength of the vertical cavity surface emitting laser.

[0020] In a second aspect, an embodiment of the present application provides a method for manufacturing a vertical cavity surface emitting laser, the method comprising:

[0021] providing a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer stacked in sequence, and a current injection blocking layer is further stacked between the first conductive semiconductor layer and the active layer and / or between the second conductive semiconductor layer and the active layer, and a current injection channel forming position is provided in the current injection blocking layer;

[0022] forming a second electrode contact portion, a transparent conductive thin film, and a heavily doped semiconductor material portion on the second conductive semiconductor layer; wherein, along the stacking direction, the projection of the heavily doped semiconductor material portion falls within the projection range of the current injection channel forming position, and the projection of the second electrode contact portion does not coincide with the projection of the current injection channel forming position; a part of the transparent conductive thin film is electrically connected to the second electrode contact portion, and the other part is electrically connected to the second conductive semiconductor layer through the heavily doped semiconductor material portion.

[0023] Combined with the second aspect of the present application, in an alternative embodiment, forming a second electrode contact portion, a transparent conductive thin film, and a heavily doped semiconductor material portion on the second conductive semiconductor layer includes:

[0024] forming a heavily doped semiconductor material layer directly contacting the second conductive semiconductor layer on the upper surface of the second conductive semiconductor layer;

[0025] performing a patterning process on the heavily doped semiconductor material layer to form the heavily doped semiconductor material portion;

[0026] forming the transparent conductive thin film covering the heavily doped semiconductor material portion and the second conductive semiconductor layer;

[0027] forming the second electrode contact portion on the transparent conductive thin film;

[0028] The method further includes:

[0029] forming a trench exposing the current injection blocking layer, oxidizing the current injection blocking layer through the trench, and an unoxidized portion at the center of the current injection blocking layer forms the current injection channel.

[0030] Combined with the second aspect of the present application, in an alternative embodiment, along the stacking direction,

[0031] The projection center of the heavily doped semiconductor material portion coincides with the projection center of the current injection channel; and / or,

[0032] The projection of the heavily doped semiconductor material portion is circular or annular.

[0033] Combined with the second aspect of the present application, in an alternative embodiment, the material of the transparent conductive thin film includes ITO.

[0034] Combined with the second aspect of the present application, in an alternative embodiment, the method further includes:

[0035] Forming at least one transparent material layer on the upper surface of the transparent conductive thin film;

[0036] The transparent conductive thin film satisfies:

[0037]

[0038] where n0 is the refractive index of the transparent conductive thin film, d0 is the thickness of the transparent conductive thin film, n i is the refractive index of the i-th transparent material layer, d i is the thickness of the i-th transparent material layer, i is a positive integer, x is the total number of transparent material layers, k is a positive integer, and λ is the emission wavelength of the vertical cavity surface emitting laser.

[0039] The vertical cavity surface emitting laser and its manufacturing method provided by the embodiments of the present application are configured by providing a second electrode contact portion, a transparent conductive thin film, and a heavily doped semiconductor material portion on the upper surface side of the second conductive semiconductor layer; wherein, along the stacking direction, the projection of the heavily doped semiconductor material portion falls within the projection range of the current injection channel, and the projection of the second electrode contact portion does not coincide with the projection of the current injection channel; a part of the transparent conductive thin film is electrically connected to the second electrode contact portion, and the other part is electrically connected to the second conductive semiconductor layer through the heavily doped semiconductor material portion; thus, after the current is injected through the second electrode contact portion, it flows through the transparent conductive thin film to the heavily doped semiconductor material portion, and then enters the second conductive semiconductor layer through the heavily doped semiconductor material portion. Since the projection of the heavily doped semiconductor material portion falls within the projection range of the current injection channel, the current can pass through the current injection channel more uniformly, thereby better controlling the current distribution and optimizing the light emission divergence angle of the VCSEL.

[0040] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Description of the Drawings

[0041] The accompanying drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0042] Figure 1 is a schematic cross-sectional structure diagram of a vertical cavity surface emitting laser in the related art;

[0043] Figure 2 is a schematic top view structure diagram of a vertical cavity surface emitting laser in the related art;

[0044] Figure 3 is a comparison diagram of light distribution curves under two different current density distributions;

[0045] Figure 4 is a schematic cross-sectional structure diagram of a vertical cavity surface emitting laser provided by an embodiment of the present application;

[0046] Figure 5 is a schematic flow chart of a preparation method of a vertical cavity surface emitting laser provided by an embodiment of the present application;

[0047] Figures 6 to 14 is a schematic cross-sectional structure diagram of a vertical cavity surface emitting laser during the preparation process provided by an embodiment of the present application;

[0048] Figure 15 is a schematic cross-sectional structure diagram of a vertical cavity surface emitting laser provided by a variant example of the present application;

[0049] Figure 16 is a schematic cross-sectional structure diagram of a vertical cavity surface emitting laser provided by another variant example of the present application. Detailed Embodiments

[0050] Hereinafter, the exemplary embodiments disclosed in the present application will be described in more detail with reference to the accompanying drawings. Although the exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the specific embodiments set forth herein. On the contrary, these embodiments are provided so that the present application can be more thoroughly understood and the scope of the present application disclosed can be completely conveyed to those skilled in the art.

[0051] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features well known to those skilled in the art are not described; that is, not all features of the actual embodiments are described here, and the well-known functions and structures are not described in detail.

[0052] In the drawings, for the sake of clarity, the dimensions of layers, regions, elements and their relative dimensions may be exaggerated. Throughout the drawings, like reference numerals denote like elements.

[0053] When an element or layer is referred to as being "on", "adjacent to", "connected to" or "coupled to" another element or layer, it can be directly on, adjacent to, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on", "directly adjacent to", "directly connected to" or "directly coupled to" another element or layer, there are no intervening elements or layers. Although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and / or portions, these elements, components, regions, layers and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or portion from another element, component, region, layer or portion. Thus, without departing from the teachings of the present application, the first element, component, region, layer or portion discussed below may be denoted as the second element, component, region, layer or portion. And when discussing the second element, component, region, layer or portion, it does not imply that a first element, component, region, layer or portion necessarily exists in the present application.

[0054] Spatial relationship terms such as "under", "below", "beneath", "underneath", "above", "over", etc. are used herein for convenience in describing the relationship of one element or feature shown in the figures to other elements or features. In addition to the orientation shown in the figures, the spatial relationship terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figures is flipped, then an element or feature described as "under" or "beneath" or "underneath" another element or feature will be oriented "over" the other element or feature. Thus, the exemplary terms "under" and "beneath" can include both an upper and a lower orientation. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatial descriptors used herein are to be interpreted accordingly.

[0055] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present application. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, specify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of the associated listed items.

[0056] To thoroughly understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. The preferred embodiments of this application are described in detail below. However, in addition to these detailed descriptions, this application may have other implementation manners.

[0057] Combined with Figure 1 and Figure 2 As shown, in a vertical cavity surface emitting laser, the metal electrode 170 is located on the outer ring of the light output hole. After the current flows into the second conductive semiconductor layer 140 through the electrode 170, it is blocked by the current injection barrier layer 130 and only enters the active layer 120 from the current injection channel 131 (the position of the light output hole) therein. Figure 2 In [reference], the flow direction of the current is indicated by arrowed lines. When flowing along the shortest movement path, the charge tends to enter the active layer 120 through the edge of the current injection channel 131 (i.e., the edge of the light output hole), resulting in a higher current density at the edge and a relatively lower current density in the center. And the regional light output energy is proportional to the current density in this region. Therefore, the light output energy is large at the edge and small in the center, which directly leads to a larger divergence angle.

[0058] Figure 3 FIG. [reference] is a comparison diagram of light distribution curves under two different current density distributions. It can be seen from the figure that when the central current density is large, the light output energy in the central region is greater, and at this time the light shape is more concentrated and the divergence angle is smaller; on the contrary, when the central current density is small, the light output energy in the central region is lower, and at this time the light shape is more dispersed and the divergence angle is larger.

[0059] Based on this, the embodiments of this application provide a vertical cavity surface emitting laser. Please refer to Figure 4, the vertical cavity surface emitting laser includes: a first conductive semiconductor layer 110, an active layer 120, and a second conductive semiconductor layer 140 stacked in sequence. A current injection blocking layer 130 is also stacked between the first conductive semiconductor layer 110 and the active layer 120 and / or between the second conductive semiconductor layer 140 and the active layer 120 (only the case where the current injection blocking layer 130 is located between the second conductive semiconductor layer 140 and the active layer 120 is shown in the figure). A current injection channel 131 is formed in the current injection blocking layer 130. The second conductive semiconductor layer 140 has an upper surface away from the current injection blocking layer 130. The vertical cavity surface emitting laser further includes: a second electrode contact portion 171, a transparent conductive thin film 160, and a heavily doped semiconductor material portion 150 located on the upper surface side of the second conductive semiconductor layer 140. Among them, in the stacking direction, the projection of the heavily doped semiconductor material portion 150 falls within the projection range of the current injection channel 131, and the projection of the second electrode contact portion 171 does not coincide with the projection of the current injection channel 131. A part of the transparent conductive thin film 160 is electrically connected to the second electrode contact portion 171, and the other part is electrically connected to the second conductive semiconductor layer 140 through the heavily doped semiconductor material portion 150.

[0060] Comparison Figure 1 and Figure 4 By referring to the direction of the arrowed lines in Figure 1 and Figure 4 , it can be understood that in the embodiments of the present application, although the projection of the second electrode contact portion 171 does not coincide with the projection of the current injection channel 131 (specifically, for example, it is located on the outer ring of the current injection channel 131 as in the related art), after the current is injected through the second electrode contact portion 171, it no longer enters the second conductive semiconductor layer 140 from the position where the second electrode contact portion 171 is located. Instead, it flows through the transparent conductive thin film 160 to the heavily doped semiconductor material portion 150, and then enters the second conductive semiconductor layer 140 through the heavily doped semiconductor material portion 150. Since the projection of the heavily doped semiconductor material portion 150 falls within the projection range of the current injection channel 131, the current can pass through the current injection channel 131 more uniformly. In this way, better control of the current distribution is achieved, thereby optimizing the light emission divergence angle of the VCSEL.

[0061] Among them, the first conductive semiconductor layer 110, the active layer 120, and the second conductive semiconductor layer 140 as a whole can be referred to as an epitaxial structure layer. In practical applications, the first conductivity type is specifically, for example, N-type, and the second conductivity type is specifically, for example, P-type. Thus, the first conductive semiconductor layer 110 is an N-type semiconductor layer, specifically, for example, an N-type DBR (Distributed Bragg Reflection) layer; the second conductive semiconductor layer 140 is a P-type semiconductor layer, specifically, for example, a P-type DBR layer. The active layer 120 can specifically be a quantum well structure, which is used to generate the optical gain required for forming laser light.

[0062] The epitaxial structure layer can be formed by epitaxial growth on a substrate; specifically, a substrate can also be included under the first conductive semiconductor layer 110. The material of the substrate can include group III-V semiconductor materials such as GaAs, InP, GaSb, etc., and is specifically selected according to the output wavelength.

[0063] The stacking direction of depositing each material layer on the substrate, which is also called the height direction of the device, or the direction perpendicular to the plane where the substrate and each material layer are located. For example, along the stacking direction, it can also be understood as along the direction perpendicular to the upper surface of the second conductive semiconductor layer 140; along the stacking direction, the projection of the heavily doped semiconductor material portion 150 falls within the projection range of the current injection channel 131, which can also be understood as the heavily doped semiconductor material portion 150 being located in the region directly above the current injection channel 131.

[0064] Combined Figures 12 to 13 As shown, the current injection barrier layer 130 can be formed by oxidizing the initially deposited material layer. The material of the current injection barrier layer 130 is usually a group III-V multi-compound with a high Al component, specifically, for example, Al z Ga 1-z As (0.9 < z ≤ 1). In the actual preparation process, a wet oxidation process can be used to make the part in contact with the oxidant on the outside react to form an insulating oxide (such as Al2O3). As the oxidation reaction continues, the current injection barrier layer 130 is gradually oxidized along the direction from the outer periphery to the center. Under the control of a certain reaction time, oxidation temperature, and oxidant flow rate, the finally prepared current injection barrier layer 130 includes an unoxidized part at the center position, that is, the current injection channel 131, and charges can pass through the current injection channel 131; the current injection barrier layer 130 also includes an oxidized part at the outer periphery position, that is, the oxide region 132, and charges will be blocked by this part when flowing.

[0065] Although the current injection barrier layer 130 is shown between the first conductive semiconductor layer 110 and the active layer 120 in each drawing; obviously, the current injection barrier layer 130 can also be between the second conductive semiconductor layer 140 and the active layer 120, and can also include both the part between the first conductive semiconductor layer 110 and the active layer 120 and the part between the second conductive semiconductor layer 140 and the active layer 120 (in some specific applications, it can also be considered that the current injection barrier layer 130 is within the active layer 120).

[0066] The heavily doped semiconductor material portion 150 can also be referred to as an ohmic contact portion, and can be specifically formed by processes well-known in the art, such as ion implantation. In order to reduce the contact resistance when electrically leading out the second conductive semiconductor layer 140, a heavily doped semiconductor material layer is often formed between the second conductive semiconductor layer 140 and the electrode. In the embodiments of the present application, the position and region of the heavy doping are adjusted such that, along the stacking direction, the projection of the heavily doped semiconductor material portion 150 falls within the projection range of the current injection channel 131. Thus, the region of the second conductive semiconductor layer 140 directly above the current injection channel 131 is used for external electrical connection. In an embodiment where the second conductive semiconductor layer 140 is a P-type semiconductor layer, the heavily doped semiconductor material portion 150 is specifically a P-type heavily doped semiconductor material portion (P++).

[0067] Please refer to Figure 4 , Figure 7 and Figure 8 , the heavily doped semiconductor material portion 150 can be located on the upper surface of the second conductive semiconductor layer 140. In the actual preparation process, a layer of heavily doped semiconductor material layer 1500 (or called Cap layer) can be first formed on the upper surface of the second conductive semiconductor layer 140, and then through patterning treatment, only the portion directly above the current injection channel 131 is retained, thereby forming the required heavily doped semiconductor material portion 150. The heavily doped semiconductor material portion 150 can be cylindrical. The material of the heavily doped semiconductor material portion 150 can be the same as the material of the second conductive semiconductor layer 140.

[0068] However, the heavily doped semiconductor material portion 150 being located on the upper surface side of the second conductive semiconductor layer 140 is not limited to this; as a variant, please refer to Figure 15 , the heavily doped semiconductor material portion 150 can also be located in the surface layer of the second conductive semiconductor layer 140, specifically formed by heavily doping a partial region on the upper surface side of the second conductive semiconductor layer 140.

[0069] The projection of the heavily doped semiconductor material portion 150 falling within the projection range of the current injection channel 131 includes both the case where the projection area of the heavily doped semiconductor material portion 150 is smaller than the projection area of the current injection channel 131, and does not exclude the case where the two projections overlap. Please refer to Figure 4 , considering that after current injection, in addition to injecting into the active layer 120 in the vertically downward direction, there will also be some lateral diffusion. Therefore, in order to further reduce the divergence angle, the projection of the heavily doped semiconductor material portion 150 falls within the projection range of the current injection channel 131, and the projection area of the heavily doped semiconductor material portion 150 is smaller than the projection area of the current injection channel 131.

[0070] Optionally, in the stacking direction, the projection center of the heavily doped semiconductor material portion 150 coincides with the projection center of the current injection channel 131; thereby making the current distribution more centrosymmetric with respect to the light-emitting aperture. However, it should be understood that the present application does not exclude the case where the projection centers of the heavily doped semiconductor material portion 150 and the current injection channel 131 do not coincide for other design considerations. Based on the improved concept proposed in the present application, by adjusting the position of the heavily doped semiconductor material portion 150, the current can be injected into the second conductive semiconductor layer 140 from a specific region, thereby improving the controllability of the current distribution.

[0071] Optionally, in the stacking direction, the projection of the heavily doped semiconductor material portion 150 is circular or annular. It can be understood that when the projection of the heavily doped semiconductor material portion 150 is circular, the charges flowing into the second conductive semiconductor layer 140 through the heavily doped semiconductor material portion 150 can be more evenly distributed, and the current is more likely to be concentrated in the central region. The current density at the center of the light-emitting aperture is greatly increased, and correspondingly, the current density at the edge of the light-emitting aperture is reduced, thereby effectively reducing the light-emitting divergence angle. In addition, in some applications, a larger divergence angle at the edge of the light-emitting aperture is required, then the projection shape of the heavily doped semiconductor material portion 150 can also be designed as an annular shape to meet the actual requirements.

[0072] As an optional specific implementation manner, in the stacking direction, the projection of the heavily doped semiconductor material portion 150 is circular, and the projection center of the heavily doped semiconductor material portion 150 coincides with the projection center of the current injection channel 131, and the projection area of the heavily doped semiconductor material portion 150 is smaller than the projection area of the current injection channel 131. In this way, the current density at the center of the light-emitting aperture is greatly increased, and the light-emitting divergence angle is reduced.

[0073] In some embodiments, the projection radius of the heavily doped semiconductor material portion 150 can be 70% or less of the projection radius of the current injection channel 131; further, it can be 50% or less.

[0074] Further, the projection of the second electrode contact portion 171 does not coincide with the projection of the current injection channel 131, thereby avoiding the second electrode contact portion 171 from blocking the light emission of the device. The projection of the second electrode contact portion 171 can surround the projection of the current injection channel 131 (which can be understood in combination with Figure 2 this); the projection center of the second electrode contact portion 171 can coincide with the projection center of the current injection channel 131. In practical applications, the second electrode contact portion 171 can include a metal stack structure, and specifically, the commonly used VCSEL P-side ohmic contact materials in the art, such as Ti / Pt / Au or other suitable metal materials, etc., are not specifically limited in the present application.

[0075] The material of the transparent conductive film 160 may include ITO (indium tin oxide). In addition, AZO (aluminum-doped zinc oxide) conductive film, nanosilver wire conductive film or other suitable transparent conductive film materials may also be used.

[0076] A part of the transparent conductive film 160 is electrically connected to the second electrode contact portion 171, and the other part is electrically connected to the second conductive semiconductor layer 140 through the heavily doped semiconductor material portion 150. Thus, the transparent conductive film 160 has a lateral span between directly above and laterally above the current injection channel 131. As an optional specific embodiment, the transparent conductive film 160 covers the upper surface of the second conductive semiconductor layer 140, while covering the upper surface and side walls of the heavily doped semiconductor material portion 150. Since there is no heavily doped portion in the area where the transparent conductive film 160 is in direct contact with the second conductive semiconductor layer 140, the contact between the two is a high-resistance contact; while in the area where the heavily doped semiconductor material portion 150 is located, that is, directly above the light-emitting hole, it is a low-resistance contact; therefore, after the current is injected through the second electrode contact portion 171, it spreads laterally through the transparent conductive film 160 (spreads in the plane where the transparent conductive film 160 is located), and finally can only flow into the second conductive semiconductor layer 140 through the area directly above the light-emitting hole with low-resistance contact, thereby making the current distribution more uniform and controllable, and the current density at the center of the light-emitting hole is greatly increased.

[0077] Optionally, the heavily doped semiconductor material portion 150 is in direct contact with the upper surface of the second conductive semiconductor layer 140; the transparent conductive film 160 covers the heavily doped semiconductor material portion 150 and the second conductive semiconductor layer 140; the second electrode contact portion 171 is located on the transparent conductive film 160. Thus, the device structure design is optimized and the manufacturing process is simple.

[0078] In addition, this application is not limited to this. Obviously, other arrangements can also be adopted to achieve the electrical connection between the heavily doped semiconductor material portion 150, the transparent conductive film 160 and the second electrode contact portion 171. For example, the side walls of the heavily doped semiconductor material portion 150 may not be covered by the transparent conductive film 160, but a transparent dielectric layer is formed on the upper surface of the second conductive semiconductor layer 140 except for the area where the heavily doped semiconductor material portion 150 is located, and the transparent conductive film 160 covers the heavily doped semiconductor material portion 150 and the transparent dielectric layer; another example is that the second electrode contact portion 171 may not be located on the transparent conductive film 160, but is partially embedded in the transparent conductive film 160.

[0079] Please continue to refer to Figure 4, the vertical cavity surface emitting laser further includes at least one transparent material layer laminated on the side of the transparent conductive thin film 160 away from the second conductive semiconductor layer 140 (please refer to the first transparent material layer 181 and the second transparent material layer 182 shown in the figure), and the transparent conductive thin film 160 satisfies:

[0080]

[0081] where n0 is the refractive index of the transparent conductive thin film 160, d0 is the thickness of the transparent conductive thin film 160, n i is the refractive index of the i-th transparent material layer, d i is the thickness of the i-th transparent material layer, i is a positive integer, x is the total number of transparent material layers, k is a positive integer, and λ is the emission wavelength of the vertical cavity surface emitting laser.

[0082] Thus, according to the thickness and refractive index of each transparent material layer laminated on the transparent conductive thin film 160, and combined with the refractive index of the transparent conductive thin film 160 itself, the thickness of the transparent conductive thin film 160 can be determined, and then the transparent conductive thin film 160 can be set according to the determined thickness to improve the transmittance, reduce light loss, and optimize the optical performance.

[0083] Specifically, taking the example that the transparent material layer includes and only includes the first transparent material layer 181 and the second transparent material layer 182, the refractive index of the first transparent material layer 181 is n1 and the thickness is d1, the refractive index of the second transparent material layer 182 is n2 and the thickness is d2, then the following is satisfied between the transparent conductive thin film 160 and each transparent material layer:

[0084]

[0085] That is to say, the transparent conductive thin film 160 satisfies:

[0086]

[0087] Thus, in the case of selecting the material of the transparent conductive thin film 160, according to the refractive index of the transparent conductive thin film 160, the thickness of the transparent conductive thin film 160 can be calculated.

[0088] Next, please refer to Figure 16 . On the basis of the foregoing embodiments, the vertical cavity surface emitting laser may further include an optical path converging element 200. The optical path converging element 200 is disposed on the light emitting surface side of the vertical cavity surface emitting laser. Specifically, for example, an optical lens is used to achieve the convergence of the emitted light. The technical solution provided by the present application can not only directly change the emitted light itself by changing the current density distribution; at the same time, it can also be used in combination with an optical path convergence scheme (such as adding a lens on the surface) to further reduce the divergence angle.

[0089] On this basis, an embodiment of the present application further provides a method for manufacturing a vertical cavity surface emitting laser. Please refer to Figure 5 , and the method includes:

[0090] Step S501: Provide a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer stacked in sequence. A current injection barrier layer is further stacked between the first conductive semiconductor layer and the active layer and / or between the second conductive semiconductor layer and the active layer. A current injection channel formation position is provided in the current injection barrier layer;

[0091] Step S502: Form a second electrode contact portion, a transparent conductive thin film, and a heavily doped semiconductor material portion on the second conductive semiconductor layer; wherein, in the stacking direction, the projection of the heavily doped semiconductor material portion falls within the projection range of the current injection channel formation position, and the projection of the second electrode contact portion does not coincide with the projection of the current injection channel formation position; a part of the transparent conductive thin film is conductively connected to the second electrode contact portion, and the other part is conductively connected to the second conductive semiconductor layer through the heavily doped semiconductor material portion.

[0092] In this way, after the current is injected through the second electrode contact portion, it flows through the transparent conductive thin film to the heavily doped semiconductor material portion, and then enters the second conductive semiconductor layer through the heavily doped semiconductor material portion. Since the projection of the heavily doped semiconductor material portion falls within the projection range of the current injection channel, the current can pass through the current injection channel more uniformly, thereby better realizing the control of the current distribution and optimizing the light emission divergence angle of the VCSEL.

[0093] Next, Figures 6 to 14 A further detailed description will be given to the vertical cavity surface emitting laser and its manufacturing method provided by the embodiment of the present application.

[0094] First, please refer to Figure 6 . Provide a first conductive semiconductor layer 110, an active layer 120, and a second conductive semiconductor layer 140 stacked in sequence. A current injection barrier layer 130 is further stacked between the first conductive semiconductor layer 110 and the active layer 120 and / or between the second conductive semiconductor layer 140 and the active layer 120 (only the case where the current injection barrier layer 130 is located between the second conductive semiconductor layer 140 and the active layer 120 is shown in the figure for example). A current injection channel formation position is provided in the current injection barrier layer 130.

[0095] The first conductive semiconductor layer 110, the active layer 120, and the second conductive semiconductor layer 140 can be formed by using the commonly used epitaxial growth process in the art. Specifically, although not clearly shown in the figure, in the actual manufacturing process, a substrate can be provided first, and then the above-mentioned epitaxial layers are epitaxially grown on the substrate in sequence.

[0096] The material of the substrate may include group III-V semiconductor materials such as GaAs, InP, GaSb, etc., and is specifically selected according to the output wavelength.

[0097] The first conductive semiconductor layer 110 may be an N-type semiconductor layer, specifically, for example, an N-type DBR layer; the second conductive semiconductor layer 140 may be a P-type semiconductor layer, specifically, for example, a P-type DBR layer.

[0098] The active layer 120 may specifically be a quantum well structure for generating the optical gain required to form a laser.

[0099] The material of the current injection blocking layer 130 is generally a group III-V multi-component compound with a high Al component, specifically, for example, Al z Ga 1-z As (0.9 < z ≤ 1).

[0100] Next, please refer to Figure 7 and Figure 8 . A heavily doped semiconductor material layer 1500 in direct contact with the second conductive semiconductor layer 140 is formed on the upper surface of the second conductive semiconductor layer 140; then, the heavily doped semiconductor material layer 1500 is patterned to form a heavily doped semiconductor material portion 150.

[0101] The heavily doped semiconductor material layer 1500 may be formed by a deposition process combined with an ion implantation process. The material of the heavily doped semiconductor material layer 1500 (heavily doped semiconductor material portion 150) may be the same as the material of the second conductive semiconductor layer 140. In an embodiment where the second conductive semiconductor layer 140 is a P-type semiconductor layer, the heavily doped semiconductor material portion 150 is specifically a P-type heavily doped semiconductor material portion (P++).

[0102] The patterning of the heavily doped semiconductor material layer 1500 may specifically be performed by a photolithography process. First, a photoresist layer is coated on the heavily doped semiconductor material layer 1500; then, the photoresist layer is patterned through steps such as exposure and development; then, the heavily doped semiconductor material layer 1500 is etched using the patterned photoresist layer as a mask. The etching process may specifically be performed by a dry etching process, and the present application does not make specific limitations in this regard; after the etching is completed, the remaining photoresist layer is removed to form the required heavily doped semiconductor material portion 150.

[0103] It should be noted that the present application is not limited to this. Please refer to Figure 15 , and the heavily doped semiconductor material portion 150 may also be located on the surface layer of the second conductive semiconductor layer 140, specifically formed by heavily doping a specific region on the upper surface side of the second conductive semiconductor layer 140.

[0104] Whether the patterned portion of the heavily doped semiconductor material layer 1500 is retained to form the heavily doped semiconductor material portion 150, or the heavily doped semiconductor material portion 150 is formed by heavily doping a specific region on the upper surface side of the second conductive semiconductor layer 140, the projection of the heavily doped semiconductor material portion 150 needs to fall within the projection range of the current injection channel 131 that will be formed in the subsequent process. The projected area of the heavily doped semiconductor material portion 150 is usually smaller than the projected area of the current injection channel 131, but the case where the projections of the two overlap is not excluded.

[0105] In some alternative embodiments, along the stacking direction, the projection center of the heavily doped semiconductor material portion 150 coincides with the projection center of the current injection channel 131; thus making the current distribution more centrosymmetric with respect to the light exit aperture. However, it should be understood that in this application, the case where the projection centers of the heavily doped semiconductor material portion 150 and the current injection channel 131 do not coincide is not excluded for other design considerations. Based on the improved concept proposed in this application, by adjusting the position of the heavily doped semiconductor material portion 150, the current can be injected into the second conductive semiconductor layer 140 from a specific region, thereby improving the controllability of the current distribution.

[0106] In some alternative embodiments, along the stacking direction, the projection of the heavily doped semiconductor material portion 150 is circular or annular. It can be understood that when the projection of the heavily doped semiconductor material portion 150 is circular (the heavily doped semiconductor material portion 150 is cylindrical as a whole), the charges flowing into the second conductive semiconductor layer 140 through the heavily doped semiconductor material portion 150 can be more evenly distributed, and the current is more likely to be concentrated in the central region, greatly increasing the current density at the center of the light exit aperture. Correspondingly, the current density at the edge of the light exit aperture decreases, thereby effectively reducing the light emission divergence angle. In addition, in some applications, a larger divergence angle at the edge of the light exit aperture is required, then the projection shape of the heavily doped semiconductor material portion 150 can also be designed as an annulus to meet the actual requirements.

[0107] As an alternative specific embodiment, along the stacking direction, the projection of the heavily doped semiconductor material portion 150 is circular, and the projection center of the heavily doped semiconductor material portion 150 coincides with the projection center of the current injection channel 131, and the projected area of the heavily doped semiconductor material portion 150 is smaller than the projected area of the current injection channel 131. In this way, the current density at the center of the light exit aperture is greatly increased, and the light emission divergence angle is reduced.

[0108] In some embodiments, the projection radius of the heavily doped semiconductor material portion 150 can be 70% or less of the projection radius of the current injection channel 131; further, it can be 50% or less.

[0109] In a specific application, those skilled in the art can adjust the position, shape, and size of the heavily doped semiconductor material portion 150 according to actual needs.

[0110] Next, please refer to Figure 9 to form a transparent conductive thin film 160 covering the heavily doped semiconductor material portion 150 and the second conductive semiconductor layer 140.

[0111] The transparent conductive thin film 160 can be formed by a deposition process. The material of the transparent conductive thin film 160 can include ITO (indium tin oxide). In addition, an AZO (aluminum-doped zinc oxide) conductive thin film, a nano silver wire conductive film, or other suitable transparent conductive thin film materials can also be used.

[0112] The thickness of the transparent conductive thin film 160 is greater than the thickness of the heavily doped semiconductor material portion 150, so that the heavily doped semiconductor material portion 150 is in direct contact with the upper surface and side walls of the heavily doped semiconductor material portion 150.

[0113] Next, please refer to Figure 10 to form a second electrode contact portion 171 on the transparent conductive thin film 160.

[0114] The second electrode contact portion 171 can be formed on the upper surface of the transparent conductive thin film 160 through photolithography, evaporation, and lift-off processes. In actual applications, the second electrode contact portion 171 can include a metal stack structure. Specifically, commonly used VCSEL P-side ohmic contact materials in the art, such as Ti / Pt / Au or other suitable metal materials, can be used. This application does not make specific limitations in this regard.

[0115] Through photolithography patterning, it is ensured that the projection of the second electrode contact portion 171 does not coincide with the projection of the current injection channel 131, thereby avoiding the second electrode contact portion 171 from blocking the light output of the device. The projection of the second electrode contact portion 171 can surround the projection of the current injection channel 131; the center of the projection of the second electrode contact portion 171 can coincide with the center of the projection of the current injection channel 131.

[0116] Next, please refer to Figure 11 to form a first transparent material layer 181 on the upper surface of the transparent conductive thin film 160. The first transparent material layer 181 specifically can cover the second electrode contact portion 171 and the transparent conductive thin film 160. The thickness of the first transparent material layer 181 can be greater than the thickness of the second electrode contact portion 171.

[0117] The first transparent material layer 181 can be formed by a deposition process. The material of the first transparent material layer 181 can be a transparent insulating material, specifically including SiN for example.

[0118] Next, please refer toFigure 12 Form a trench exposing the current injection barrier layer 130.

[0119] Specifically, a photoresist layer can be formed on the first transparent material layer 181, and then the photoresist layer is patterned through steps such as exposure and development; then, etching is performed using the patterned photoresist layer as a mask, and the etching depth exceeds the current injection barrier layer 130. The etching process can specifically be carried out using a dry etching process, and the present application does not make specific limitations on this. In this way, the formed trench penetrates through the first transparent material layer 181, the transparent conductive thin film 160, and the second conductive semiconductor layer 140, and can further penetrate through the current injection barrier layer 130, and even can extend into the first conductive semiconductor layer 110.

[0120] Next, please refer to Figure 13 Oxidize the current injection barrier layer 130 through the trench, and the unoxidized part at the center of the current injection barrier layer 130 forms a current injection channel 131.

[0121] Specifically, the current injection barrier layer 130 can be oxidized through a wet oxidation process, so that the part in contact with the oxidant on the outside reacts and is converted into an insulating oxide (such as Al2O3). As the oxidation reaction continues, the current injection barrier layer 130 is gradually oxidized along the direction from the outer periphery to the center. Under the control of a certain oxidation time, oxidation temperature, and oxidant flow rate, the finally prepared current injection barrier layer 130 includes an unoxidized part at the center position, that is, the current injection channel 131 (or conductive via), and charges can pass through the current injection channel 131; the current injection barrier layer 130 also includes an oxidized part at the outer periphery position, that is, the oxide region 132, and charges will be blocked by this part when flowing.

[0122] Furthermore, a second transparent material layer 182 is formed on the first transparent material layer 181.

[0123] The second transparent material layer 182 can specifically be formed by a deposition process. The material of the second transparent material layer 182 is a transparent insulating material, specifically including SiN for example. The second transparent material layer 182 not only covers the upper surface of the first transparent material layer 181, but can also further cover the side walls and the bottom wall of the trench.

[0124] It should be noted that although the formation of the first transparent material layer 181 and the second transparent material layer 182 is described in the embodiments of the present application, in specific applications, one transparent material layer or more than three transparent material layers can also be formed according to actual needs, and the present application does not make specific limitations on this.

[0125] At least one transparent material layer is formed on the upper surface of the transparent conductive thin film 160, and the transparent conductive thin film 160 satisfies:

[0126]

[0127] where n0 is the refractive index of the transparent conductive thin film 160, d0 is the thickness of the transparent conductive thin film 160, n i is the refractive index of the i-th transparent material layer, d i is the thickness of the i-th transparent material layer, i is a positive integer, x is the total number of transparent material layers, k is a positive integer, and λ is the emission wavelength of the vertical cavity surface emitting laser. Thus, according to the thickness and refractive index of each transparent material layer stacked on the transparent conductive thin film 160, and combined with the refractive index of the transparent conductive thin film 160 itself, the thickness of the transparent conductive thin film 160 can be determined, and then the transparent conductive thin film 160 can be set according to the determined thickness to improve the transmittance, reduce light loss and optimize the optical performance. The transparent conductive thin film 160 and each transparent material layer refer to all conductive or non-conductive transparent film layers on the light-emitting surface side of the VCSEL (specifically covering above the light-emitting hole).

[0128] Finally, please refer to Figure 14 . Perform subsequent process steps to complete the preparation of the VCSEL.

[0129] Specifically, an etching process can be performed to form a through hole exposing the second electrode contact portion 171; a conductive material is filled in the through hole to form an electrode path 172. Next, a wire bonding electrode 173 electrically connected to the electrode path 172 (specifically electrically connected through the electrode path 172 and the second electrode contact portion 171) is fabricated on the transparent material layer. The wire bonding electrode 173 is specifically the P-side electrode of the VCSEL. Next, the back surface of the device structure can be thinned to fabricate a back surface electrode 190. The back surface electrode 190 is specifically the N-side electrode of the VCSEL. Finally, the structure is diced into die. The above processes can all be completed by conventional VCSEL manufacturing processes and will not be elaborated here.

[0130] Understandably, compared with the method of converging the light-emitting optical path to improve the divergence angle, in this embodiment, a highly doped Cap layer (i.e., the heavily doped semiconductor material portion 150) in a specific area is retained on the surface of the epitaxial layer through an etching process, and a transparent conductive thin film 160 is grown on the surface of the light-emitting hole. The combination of the two enables current to be injected into the epitaxial layer only from the specific area where the highly doped Cap layer is retained (specifically, it first flows into the second conductive semiconductor layer 140), greatly increasing the current density in the specific area, thereby changing the divergence angle. Among them, the specific area can be an area that is aligned with the center of the light-emitting hole and smaller than the area of the light-emitting hole, or a non-centered area selected according to actual needs. According to the embodiments of the present application, the control of the current distribution can be realized, and the optimization of the specific required light-emitting divergence angle can be achieved.

[0131] In addition, the above method may further include: forming an optical path converging element 200 on the light-emitting surface side of the vertical cavity surface emitting laser. The optical path converging element 200 specifically adopts an optical lens, for example, to achieve the convergence of the emitted light. The technical solution provided by the present application can not only directly change the light emission itself by changing the current density distribution; at the same time, it can also be used in combination with an optical path converging solution (such as adding a lens on the surface) to further reduce the divergence angle.

[0132] It should be noted that the embodiments of the vertical cavity surface emitting laser provided by the present application and the embodiments of the preparation method of the vertical cavity surface emitting laser belong to the same concept; among the technical features in the technical solutions recorded in each embodiment, they can be arbitrarily combined without conflict. However, it should be further noted that for the vertical cavity surface emitting laser provided by the embodiments of the present application, the combination of its technical features can already solve the technical problems to be solved by the present application; therefore, the vertical cavity surface emitting laser provided by the embodiments of the present application may not be limited by the preparation method of the vertical cavity surface emitting laser provided by the embodiments of the present application, and any vertical cavity surface emitting laser prepared by a preparation method that can form the structure of the vertical cavity surface emitting laser provided by the embodiments of the present application is within the protection scope of the present application.

[0133] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners. Without departing from the scope of the present disclosure, various deformations and changes can also be made on the basis of the above embodiments. Similarly, the technical features of the above embodiments can also be arbitrarily combined to form other embodiments of the present application that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present application and do not limit the protection scope of the patent of the present application.

Claims

1. A vertical cavity surface emitting laser, characterized in that: include: A first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer are stacked in sequence, a current injection blocking layer is further stacked between the first conductive semiconductor layer and the active layer and / or between the second conductive semiconductor layer and the active layer, a current injection channel is formed in the current injection blocking layer, and the second conductive semiconductor layer has an upper surface away from the current injection blocking layer; A second electrode contact portion, a transparent conductive film and a heavily doped semiconductor material portion located on the upper surface side of the second conductive semiconductor layer; in, Along the stacking direction, the projection of the heavily doped semiconductor material portion falls within the range of the projection of the current injection channel, and the projection of the second electrode contact portion does not overlap with the projection of the current injection channel; A portion of the transparent conductive film is conductively connected to the second electrode contact portion, and another portion is conductively connected to the second conductive semiconductor layer through the heavily doped semiconductor material portion.

2. The vertical cavity surface emitting laser according to claim 1, characterized in that: The heavily doped semiconductor material portion is in direct contact with the upper surface of the second conductive semiconductor layer; the transparent conductive film covers the heavily doped semiconductor material portion and the second conductive semiconductor layer; and the second electrode contact portion is located on the transparent conductive film.

3. The vertical cavity surface emitting laser according to claim 1, characterized in that: Along the stacking direction, The projection center of the heavily doped semiconductor material portion coincides with the projection center of the current injection channel; and / or, The projection of the heavily doped semiconductor material portion is circular or ring-shaped.

4. The vertical cavity surface emitting laser according to claim 1, characterized in that: The material of the transparent conductive film includes ITO.

5. The vertical cavity surface emitting laser according to claim 1, characterized in that: It also includes at least one transparent material layer stacked on a side of the transparent conductive film away from the second conductive semiconductor layer, and the transparent conductive film meets the following requirements: Wherein, n0 is the refractive index of the transparent conductive film, d0 is the thickness of the transparent conductive film, n i is the refractive index of the i-th transparent material layer, d i is the thickness of the i-th transparent material layer, i is a positive integer, x is the total number of transparent material layers, k is a positive integer, and λ is the emission wavelength of the vertical cavity surface emitting laser.

6. A method for preparing a vertical cavity surface emitting laser, characterized in that: The method comprises: Providing a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer stacked in sequence, wherein a current injection blocking layer is stacked between the first conductive semiconductor layer and the active layer and / or between the second conductive semiconductor layer and the active layer, and a current injection channel forming position is provided in the current injection blocking layer; A second electrode contact portion, a transparent conductive film and a heavily doped semiconductor material portion are formed on the second conductive semiconductor layer; wherein, along the stacking direction, the projection of the heavily doped semiconductor material portion falls within the range of the projection of the current injection channel formation position, and the projection of the second electrode contact portion does not overlap with the projection of the current injection channel formation position; a portion of the transparent conductive film is conductively connected to the second electrode contact portion, and the other portion is conductively connected to the second conductive semiconductor layer through the heavily doped semiconductor material portion.

7. The method for preparing a vertical cavity surface emitting laser according to claim 6, characterized in that: Forming a second electrode contact portion, a transparent conductive film and a heavily doped semiconductor material portion on the second conductive semiconductor layer, comprising: forming a heavily doped semiconductor material layer on an upper surface of the second conductive semiconductor layer and in direct contact with the second conductive semiconductor layer; Performing patterning on the heavily doped semiconductor material layer to form the heavily doped semiconductor material portion; forming the transparent conductive film covering the heavily doped semiconductor material portion and the second conductive semiconductor layer; forming the second electrode contact portion on the transparent conductive film; The method further comprises: A groove is formed to expose the current injection blocking layer, and the current injection blocking layer is oxidized through the groove, so that the central unoxidized portion of the current injection blocking layer forms the current injection channel.

8. The method for preparing a vertical cavity surface emitting laser according to claim 6, characterized in that: Along the stacking direction, The projection center of the heavily doped semiconductor material portion coincides with the projection center of the current injection channel; and / or, The projection of the heavily doped semiconductor material portion is circular or ring-shaped.

9. The method for preparing a vertical cavity surface emitting laser according to claim 6, characterized in that: The material of the transparent conductive film includes ITO.

10. The method for preparing a vertical cavity surface emitting laser according to claim 6, characterized in that: The method further comprises: forming at least one transparent material layer on the upper surface of the transparent conductive film; The transparent conductive film meets the following requirements: Wherein, n0 is the refractive index of the transparent conductive film, d0 is the thickness of the transparent conductive film, n i is the refractive index of the i-th transparent material layer, d i is the thickness of the i-th transparent material layer, i is a positive integer, x is the total number of transparent material layers, k is a positive integer, and λ is the emission wavelength of the vertical cavity surface emitting laser.

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