Current-enhanced side-injected gallium nitride-based VCSELs

Abstract

This invention discloses a side-injected gallium nitride-based VCSEL with enhanced current spread, comprising a side-injection structure including a current aperture layer, a current confinement layer, and an ohmic contact metal layer. The current aperture layer is disposed on the surface of a P-type layer and includes at least a first sublayer and a second sublayer. The second sublayer is adjacent to the P-type layer, and the first sublayer is disposed on the side of the second sublayer facing away from the P-type layer. The resistivity of the second sublayer is higher than that of the first sublayer. The current aperture layer has a boss structure, which includes at least the first sublayer and defines a groove. The ohmic contact metal layer forms an ohmic contact only with the sidewall of the boss structure. During operation, current is injected from the ohmic contact metal layer, enters the first sublayer in the current aperture through the sidewall of the boss structure, and due to the higher resistivity of the second sublayer, the current is forced to preferentially spread laterally in the first sublayer, achieving uniform distribution, and then continues into the active region, thus achieving enhanced current spread.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more specifically to a current-spreading enhanced side-injected gallium nitride-based VCSEL. Background Technology

[0002] Gallium nitride-based vertical cavity surface emitting lasers (VCSELs) have broad application prospects in many fields such as visible light communication, laser display, and optical storage due to their advantages such as single-mode operation in visible light, low threshold current, circular spot, and easy realization of two-dimensional arrays.

[0003] like Figure 1 , 2 As shown, existing gallium nitride-based VCSELs mainly employ a dual-dielectric DBR structure or a dielectric / semiconductor hybrid DBR structure. However, the dielectric DBR is an insulating material and lacks conductivity. Furthermore, its lateral dimensions must be larger than the current-limiting aperture to ensure optical integrity. This prevents direct current injection into the active region via the DBR, necessitating the fabrication of an additional current injection layer. Currently, the primary approach is to fabricate in-cavity contact electrodes within the resonant cavity. The most common method is to deposit a layer of indium tin oxide (ITO) transparent conductive film, thus balancing current transport and photon transmittance. However, ITO-based in-cavity current injection structures present inherent performance contradictions. Specifically, achieving a balance between light absorption and resistivity with ITO is challenging: increasing the ITO thickness to reduce resistivity leads to light absorption loss, resulting in increased mode loss and threshold current; while thinning the ITO to increase transmittance reduces mode loss but introduces problems such as increased operating voltage, higher power consumption, and decreased efficiency.

[0004] To address the current injection problem, our research group previously filed a patent (application number: 202610461672.5) proposing a gallium nitride-based vertical-cavity surface-emitting laser with a lateral current injection structure, as shown in the following figure. Figure 3As shown, this scheme achieves lateral current injection from the sidewalls by setting specific current aperture layers and current confinement layers, and utilizing a metal layer that forms ohmic contact with the sidewalls of the protrusions in the current aperture layer. This eliminates the need for an additional conductive layer in the optical resonant path, fundamentally avoiding the additional optical absorption and scattering losses caused by ITO in traditional schemes. However, this scheme still has the following drawbacks: after current is injected from the sidewalls, its lateral expansion distance within the current aperture layer is limited, resulting in current concentration at the edge of the current aperture, while the current density in the central region of the current aperture is relatively low, affecting device performance. Simultaneously, current concentration at the edge of the current aperture can lead to localized overheating, accelerating device aging and even burnout, severely impacting device reliability and lifespan. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the above-mentioned technologies by providing a side-injected gallium nitride-based VCSEL with enhanced current spreading, so as to solve the problems of device performance degradation, heat accumulation, and difficulty in application to large-aperture devices caused by insufficient lateral current spreading in the existing side-injected gallium nitride-based vertical cavity surface emission lasers.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A current-spreading enhanced laterally injected gallium nitride-based VCSEL includes a stacked P-side Bragg mirror, a lateral current injection structure, a gallium nitride-based epitaxial layer, and an N-side Bragg mirror. The lateral current injection structure includes a current aperture layer, a current confinement layer, and an ohmic contact metal layer. The current aperture layer is disposed on the surface of the P-type layer in the gallium nitride-based epitaxial layer and forms an electrical connection with the P-type layer. The current aperture layer includes at least a first sublayer and a second sublayer stacked and electrically connected in a vertical direction; wherein the second sublayer is disposed adjacent to the P-type layer, and the first sublayer is disposed on the side of the second sublayer facing away from the P-type layer; the resistivity of the second sublayer is higher than that of the first sublayer. The current aperture layer has a boss structure, the boss structure includes at least a first sub-layer and the first sub-layer does not extend beyond the boundary of the boss structure, thereby defining a groove on the surface of the P-type layer or the current aperture layer; the top surface of the boss structure is in contact with the P-side Bragg mirror. The current limiting layer is disposed on the surface of the groove and contacts the sidewall of the boss structure. The surface of the current limiting layer is closer to the bottom surface of the boss structure than the top surface of the boss structure. The ohmic contact metal layer covers the surface of the current limiting layer and is electrically insulated from the current limiting layer; the ohmic contact metal layer only forms ohmic contact with the sidewall of the boss structure.

[0007] The current-spreading enhanced lateral injection gallium nitride-based VCSEL provided by this invention, during operation, has its driving current injected from the ohmic contact metal layer. Since the ohmic contact metal layer and the current-limiting layer are electrically insulated from each other, the current cannot directly pass through the current-limiting layer in the vertical direction. Instead, it enters the current aperture layer via the sidewalls of the protrusion structure forming an ohmic contact with the ohmic contact metal layer. Because the resistivity of the second sub-layer is greater than that of the first sub-layer, the resistance of the current propagation along the center path and edge path of the current aperture is similar. Therefore, the current spreads sufficiently laterally in the first sub-layer and continues to pass through the current aperture layer and the P-type layer into the active region, thereby achieving enhanced lateral injection current spread. Compared with the original lateral current injection structure, this invention allows for sufficient lateral current spread within the first sub-layer, significantly improving current spread uniformity, effectively suppressing edge current concentration, improving heat accumulation, and enhancing device performance. It overcomes the bottleneck of limited current spread distance in the original structure and can be applied to gallium nitride-based VCSELs with larger apertures.

[0008] As an alternative scheme for the side-implanted gallium nitride-based VCSEL of the present invention, the current aperture layer is a p-type doped gallium nitride-based material; the bottom surface of the boss structure is circular with a diameter of 0.1μm~20μm and the height of the boss structure is 20nm~2μm.

[0009] As an alternative scheme for the side-implanted gallium nitride-based VCSEL of the present invention, the thickness of the second sublayer is 5nm~200nm.

[0010] As an alternative to the side-implanted gallium nitride-based VCSEL of the present invention, the resistivity of the second sublayer is 2 to 100 times that of the first sublayer.

[0011] As an alternative embodiment of the side-implanted gallium nitride-based VCSEL of the present invention, the first sublayer is a p-type doped gallium nitride-based material with a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 20 cm -3 .

[0012] As an alternative to the side-implanted gallium nitride-based VCSEL of the present invention, the second sublayer is a p-type doped gallium nitride-based monolayer structure with a doping concentration lower than that of the first sublayer.

[0013] As an alternative embodiment of the side-implanted gallium nitride-based VCSEL of the present invention, the second sub-layer is a p-type doped gallium nitride-based stacked structure, consisting of alternating stacked high-resistivity gallium nitride-based material layers and low-resistivity gallium nitride-based material layers, wherein the resistivity of the high-resistivity gallium nitride-based material layer is higher than that of the low-resistivity gallium nitride-based material layer and the first sub-layer; the boss structure includes the second sub-layer, and all low-resistivity gallium nitride-based material layers in the second sub-layer do not exceed the boundary of the boss structure and do not contact the ohmic contact metal layer.

[0014] As a preferred option among the above-mentioned alternatives, the doping concentration of the high-resistivity gallium nitride-based material layer is lower than that of the low-resistivity gallium nitride-based material layer and the first sublayer.

[0015] As an alternative embodiment of the side-implanted gallium nitride-based VCSEL of the present invention, the first sublayer is Mg-doped In. X Ga 1-X N, 0.05≤X≤0.15; the second sublayer is Mg-doped Al Y Ga 1-Y N, 0.1 ≤ Y ≤ 0.4; or the second sublayer is Mg-doped GaN / In Z Ga 1-Z N-stacked structure, 0.05≤Z≤0.15.

[0016] As an alternative embodiment of the side-implanted gallium nitride-based VCSEL of the present invention, the material of the current confinement layer is an oxide dielectric material or a nitride semiconductor material, and the refractive index of the current confinement layer is lower than that of the current aperture layer; the material of the ohmic contact metal layer is selected from one or more of Cr / Au, Cr / Pt / Au, and Ni / Au; the absolute value of the height difference between the surface of the ohmic contact metal layer away from the current confinement layer and the top surface of the boss structure is not greater than 10 nm.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, some of which will become clear as the description proceeds, and others will be learned by practicing the invention. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic cross-sectional view of a gallium nitride-based vertical cavity surface-emitting laser with a dual-dielectric DBR structure in the prior art.

[0020] Figure 2 This is a schematic cross-sectional view of a gallium nitride-based vertical cavity surface-emitting laser with a dielectric / semiconductor hybrid DBR structure in the prior art.

[0021] Figure 3 This is a cross-sectional schematic diagram of a gallium nitride-based vertical cavity surface-emitting laser with a lateral current injection structure, as described in patent application number 202610461672.5.

[0022] Figure 4 This is a schematic cross-sectional view of the current-spreading enhanced side-implanted gallium nitride-based VCSEL in Embodiment 1 of this application.

[0023] Figure 5 This is a cross-sectional schematic diagram of the P-type layer and the lateral current injection structure in Embodiment 2 of this application.

[0024] Figure 6 This is a cross-sectional schematic diagram of the P-type layer and the lateral current injection structure in Embodiments 3 and 4 of this application.

[0025] Figure 7 This is a schematic cross-sectional view of the current-spreading enhanced side-implanted gallium nitride-based VCSEL in Embodiment 5 of this application.

[0026] In the figure: 1-substrate, 2-bonding metal layer, 3-P-side Bragg mirror, 4-ohmic contact metal layer, 5-current confinement layer, 6-current aperture layer, 7-P-type layer, 8-P-type AlGaN electron blocking layer, 9-multiple quantum well active region, 10-N-type layer, 11-N electrode, 12-N-side Bragg mirror, 13-gallium nitride-based epitaxial layer, 14-lateral current injection structure, 15-GaN substrate; 601-first sublayer, 602-second sublayer, 610-boob structure (dashed box). Detailed Implementation

[0027] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the technical solutions of this invention will be described in more detail below with reference to the embodiments and accompanying drawings. It should be noted that the accompanying drawings of this invention are all simplified and not precisely to scale, and are only used to facilitate the explanation of this invention. Obviously, the following embodiments are only some embodiments of this invention, not all embodiments. All other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0028] In vertical-cavity surface-emitting lasers (VCSELs) with lateral current injection structures, the current is injected into the resonant cavity through a laterally positioned ohmic contact metal layer, solving the current injection problem caused by the non-conductivity of the dielectric dielectric barrier (DBR). However, after the current is injected from the sidewall of the boss, its lateral propagation distance within the current aperture layer is limited, leading to current concentration at the edge of the current aperture region, which affects device performance. This current concentration at the current aperture edge causes localized overheating, accelerating device aging and even burnout. Research has revealed that the main reason for this uneven current propagation is that the vertical resistance of the P-type layer closer to the active region is insufficient compared to the lateral resistance of the current aperture layer. The current mainly propagates along the low-resistance path at the edge of the current aperture, resulting in poor lateral current propagation within the current aperture.

[0029] To address the aforementioned issues, this application proposes a side-injected gallium nitride-based VCSEL with enhanced current spread, comprising a stacked P-side Bragg mirror 3, a side current injection structure 14, a gallium nitride-based epitaxial layer 13, and an N-side Bragg mirror 12. The side current injection structure 14 includes a current aperture layer 6, a current confinement layer 5, and an ohmic contact metal layer 4. The current aperture layer 6 is disposed on the surface of the P-type layer 7 in the gallium nitride-based epitaxial layer 13 and forms an electrical connection with the P-type layer 7. The current aperture layer 6 includes at least a first sublayer 601 and a second sublayer 602 stacked and electrically connected in a vertical direction; wherein the second sublayer 602 is disposed adjacent to the P-type layer 7, and the first sublayer 601 is disposed on the side of the second sublayer 602 away from the P-type layer 7; the resistivity of the second sublayer 602 is higher than that of the first sublayer 601. The current aperture layer 6 has a boss structure 610, which includes at least a first sub-layer 601 and the first sub-layer 601 does not extend beyond the boundary of the boss structure 610, thereby defining a groove on the surface of the P-type layer 7 or the current aperture layer 6; the top surface of the boss structure 610 is in contact with the P-side Bragg reflector 3. The current limiting layer 5 is disposed on the surface of the groove and contacts the side wall of the boss structure 610. The surface of the current limiting layer 5 is closer to the bottom surface of the boss structure 610 than the top surface of the boss structure 610. The ohmic contact metal layer 4 covers the surface of the current limiting layer 5 and is electrically insulated from the current limiting layer 5. The ohmic contact metal layer 4 forms an ohmic contact only with the sidewall of the boss structure 610. It should be noted that when the ohmic contact metal layer is in contact with only the sidewall of the first sub-layer, the current in the ohmic contact metal layer enters the first sub-layer entirely through the sidewall of the boss structure. When the ohmic contact metal layer is in contact with the sidewalls of both the first and second sub-layers simultaneously, a portion of the current in the ohmic contact metal layer directly enters the second sub-layer through the sidewall of the boss structure, while the remaining current enters the first sub-layer through the sidewall of the boss structure.

[0030] In some implementations, the ohmic contact metal layer does not contact the second sublayer. It should be noted that the absence of contact between the ohmic contact metal layer and the second sublayer allows the current to flow entirely into the first sublayer via the sidewall of the boss structure that forms the ohmic contact with the ohmic contact metal layer.

[0031] In some embodiments, the current aperture layer 6 is a p-type doped gallium nitride-based material; the bottom surface of the boss structure is circular with a diameter of 0.1 μm to 20 μm, and the height of the boss structure is 20 nm to 2 μm. It should be noted that the lateral current injection structure uses a boss structure as the current aperture. The diameter of the boss structure is selected based on the study of the relationship between the current aperture size and device performance: a larger aperture (e.g., greater than 10 μm) helps to improve output power and differential efficiency, but requires strong current spread. The current aperture layer of this invention can ensure current spread and uniform injection; a smaller aperture (e.g., less than 5 μm) is beneficial for achieving single transverse mode operation and significantly reducing the threshold current. The diameter can be selected according to the specific application scenario. Meanwhile, the height of the boss affects the ohmic contact resistance and the confinement effect of the lateral optical field. On the one hand, the larger the boss height, the larger the contact area between the ohmic contact metal layer and the boss sidewall, and the smaller the ohmic contact resistance, which is beneficial for reducing the device series resistance and operating voltage. At the same time, the thickness of the first sublayer is limited by the boss height, and the thicker the first sublayer, the better the current spread. To make the first sublayer thicker, the boss should be as high as possible. However, when the height is too large (e.g., close to 2μm), the sidewall area increases significantly, and the improvement in contact resistance tends to saturate. At the same time, although an excessively high boss will enhance the confinement of the lateral optical field, it is easy to excite higher-order lateral modes, which will destroy the stability of the base lateral mode and increase the difficulty of the etching process. On the other hand, when the boss height is too small (e.g., close to 20nm), the sidewall area is insufficient, the ohmic contact resistance increases, leading to increased Joule heating and decreased efficiency. At the same time, too small a height will weaken the ability to confine the lateral optical field, and some of the optical field will leak into the current confinement layer area around the boss, increasing lateral optical loss and increasing the threshold gain. Therefore, the height of the boss must be optimized based on the device aperture size, operating mode (single-mode or multi-mode), and contact resistance requirements.

[0032] In some implementations, the thickness of the second sublayer is 5 nm to 200 nm. It should be noted that the thickness of the second sublayer cannot be too thin (less than 5 nm), because if it is too thin, the charge carriers will tunnel directly through the layer, thus causing the second sublayer to lose its function of forcing the lateral expansion of the current; at the same time, it cannot be too thick (greater than 200 nm), to prevent excessive series resistance from causing a significant increase in the device operating voltage, and to avoid lattice relaxation or cracks during the epitaxial growth of thick high-resistivity materials, which would affect the epitaxial quality and device reliability.

[0033] In some embodiments, the resistivity of the second sublayer 602 is 2 to 100 times that of the first sublayer 601. It should be noted that the resistivity of the second sublayer is only higher than that of the first sublayer. If the resistivity of the second sublayer is too high compared to the first sublayer, the series resistance of the device will be too large, easily leading to heat accumulation, which is detrimental to the stable and reliable operation of the device. If the resistivity of the second sublayer is close to that of the first sublayer, the current cannot achieve a good lateral spread effect in the first sublayer. Therefore, ensuring that the resistivity relationship between the second and first sublayers is within the above-mentioned range can satisfy the requirement for more uniform current spread while avoiding excessive series resistance. The preferred resistivity ratio is related to the current aperture size. Given other parameters, a larger current aperture requires a higher current spread, and this ratio needs to be increased accordingly.

[0034] In some embodiments, the first sublayer 601 is a p-type doped gallium nitride-based material with a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 20 cm -3 It should be noted that controlling the doping concentration within the above range can result in a lower resistivity of the first sublayer, which can effectively reduce the resistive loss of hole lateral transport and thus improve the uniformity of current spread.

[0035] In some embodiments, the second sublayer 602 is a p-type doped gallium nitride-based monolayer structure, and the doping concentration is lower than that of the first sublayer 601. It should be noted that the lower doping concentration of the second sublayer compared to the first sublayer is to ensure that the resistivity of the second sublayer is higher than that of the first sublayer.

[0036] In some embodiments, the second sub-layer 602 is a p-type doped gallium nitride-based stacked structure, composed of alternating layers of high-resistivity gallium nitride-based material and low-resistivity gallium nitride-based material, wherein the resistivity of the high-resistivity gallium nitride-based material layer is higher than that of the low-resistivity gallium nitride-based material layer and the first sub-layer 601; the boss structure 610 includes the second sub-layer 602, and all low-resistivity gallium nitride-based material layers in the second sub-layer 602 do not exceed the boundary of the boss structure 610 and do not contact the ohmic contact metal layer 4. It should be noted that the alternating high and low resistivity gallium nitride-based stacked structure, while having the same function as the single-layer structure, also allows current to spread in each low-resistivity layer of the stacked structure, further promoting uniform current distribution. To prevent current from spreading outside the current aperture, all low-resistivity layers in the second sublayer are limited to not exceeding the boundary of the boss structure; to prevent almost all current from being directly injected from the ohmic contact metal layer into the low-resistivity layers in the second sublayer, thus affecting the current spreading effect, all low-resistivity layers in the second sublayer are limited to not contacting the ohmic contact metal layer.

[0037] In some embodiments, the doping concentration of the high-resistivity gallium nitride-based material layer is lower than that of the low-resistivity gallium nitride-based material layer and the first sublayer 601. It should be noted that the resistivity relationship is defined by limiting the doping concentration relationship to ensure the current spreading effect in the first sublayer.

[0038] In some implementations, the first sublayer is Mg-doped In. X Ga 1-X N, 0.05≤X≤0.15; the second sublayer is Mg-doped Al Y Ga 1-Y N, 0.1 ≤ Y ≤ 0.4; or the second sublayer is Mg-doped GaN / In Z Ga 1-Z For the N-layer stacked structure, 0.05 ≤ Z ≤ 0.15. It should be noted that choosing InGaN material with a narrower bandgap and a higher valence band top energy for the first sublayer can significantly reduce the ionization energy of acceptor impurities, increasing the activation rate of Mg dopant by more than an order of magnitude, thereby achieving lower resistivity. Simultaneously, controlling the In composition between 5% and 15% not only benefits the reduction in bandgap but also avoids phase separation or increased defect density due to excessive composition. When the second sublayer is a monolayer structure, AlGaN material is used, with the Al composition controlled between 0.1 and 0.4%, utilizing its wider bandgap to further improve the vertical resistivity. When the second sublayer is a stacked structure, a GaN / InGaN stacked structure is used, with the In composition range set the same as the first sublayer. This stacked structure is chosen because the narrow bandgap InGaN well layer effectively reduces the valence band barrier, the interface polarization between the two is weak, which can reduce the device operating voltage, and the material lattice matching is good, simplifying epitaxial growth.

[0039] In some embodiments, the current-confining layer 5 is made of an oxide dielectric material or a nitride semiconductor material, and its refractive index is lower than that of the current aperture layer 6. The ohmic contact metal layer 4 is made of one or more of Cr / Au, Cr / Pt / Au, and Ni / Au. It should be noted that the material of the current-confining layer is preferably one of SiO2, Al2O3, or AlN, all of which have good electrical insulation properties, thereby preventing current from being injected into the active region through the grooves provided in the current aperture layer. Furthermore, the refractive index of the current-confining layer is lower than that of the current aperture layer, making the effective refractive index of the resonant cavity in the boss structure region greater than that in the resonant cavity in the current-confining layer region, forming a fiber-like structure that confines lateral light leakage and reduces lateral light loss. It should also be noted that the material of the ohmic contact metal layer readily forms ohmic contacts with p-type doped gallium nitride-based materials and exhibits good adhesion.

[0040] In some embodiments, the absolute value of the height difference between the surface of the ohmic contact metal layer 4 away from the current limiting layer 5 and the top surface of the boss structure 610 is no greater than 10 nm. It should be noted that the relative height between the ohmic contact metal layer and the top surface of the boss structure affects the sidewall ohmic contact area. When the height difference is negative (i.e., the surface of the ohmic contact metal layer away from the current limiting layer is lower than the top surface of the boss structure), the larger the absolute value of the height difference, the smaller the sidewall ohmic contact area. Since the sidewall ohmic contact area directly affects the contact resistance, a decrease in the sidewall ohmic contact area will lead to an increase in the device's series resistance. Conversely, when the height difference is positive (i.e., the surface of the ohmic contact metal layer away from the current limiting layer is higher than the top surface of the boss structure), the sidewall ohmic contact area is a fixed value. Further increasing the thickness of the ohmic contact metal layer not only fails to improve contact performance but also results in material waste. Therefore, the relative height between the ohmic contact metal layer and the top surface of the boss structure should be reasonably adjusted to ensure good electrical performance while avoiding unnecessary resource consumption. The sidewall ohmic contact area is maximized when the surface of the ohmic contact metal layer away from the current limiting layer is flush with the top surface of the boss structure.

[0041] In some embodiments, the P-side Bragg reflector 3 is formed by periodically alternating stacks of oxide dielectric materials; the N-side Bragg reflector 12 is formed by periodically alternating stacks of oxide dielectric materials or nitride semiconductor materials; the coverage area of ​​the P-side Bragg reflector 3 is not less than the top surface of the boss structure 610; the coverage area of ​​the N-side Bragg reflector 12 is not less than the vertical projection area of ​​the boss structure 610 on the surface of the N-type layer 10 in the gallium nitride-based epitaxial layer 13. It should be noted that, limited by gallium nitride epitaxial technology, the P-side and N-side Bragg reflectors generally use oxide dielectric materials such as Nb2O5 / SiO2, TiO2 / SiO2, and HfO2 / SiO2. Specifically, to enhance the accuracy of cavity length control, the N-side Bragg reflector can also use nitride semiconductor materials such as GaN / AlN or GaN / AlInN, which are homoepitaxially grown from GaN. To reduce light leakage, the P-side Bragg reflector at least covers the surface of the protrusion in the current aperture layer; the N-side Bragg reflector at least covers the vertical projection area of ​​the protrusion structure 610 on the surface of the N-type layer 10. Furthermore, the periodically alternating stacked materials of oxide dielectric and nitride semiconductor materials exhibit no absorption in the visible light range.

[0042] The following are some embodiments of this application, and the embodiments of the present invention will further describe the technical solution of the present invention in detail. Example 1

[0043] This embodiment provides a current-spreading enhanced side-implanted gallium nitride-based VCSEL, with the specific structure as follows: Figure 4As shown, the structure includes a substrate 1 at the bottom and, sequentially stacked on the substrate 1, a bonding metal layer 2, a P-side Bragg mirror 3, an ohmic contact metal layer 4, a current confinement layer 5, a current aperture layer 6, a P-type layer 7, a P-type AlGaN electron blocking layer 8, a multi-quantum-well active region 9, an N-type layer 10, an N-electrode 11, and an N-side Bragg mirror 12. The ohmic contact metal layer 4, the current confinement layer 5, and the current aperture layer 6 constitute a lateral current injection structure 14.

[0044] Specifically, the current aperture layer 6 consists of a first sub-layer 601 and a second sub-layer 602 stacked vertically and electrically connected. The second sub-layer 602 is disposed on the lower surface of the P-type layer 7 and completely covers the P-type layer 7, while the first sub-layer 601 is disposed on the lower surface of the second sub-layer 602 and partially covers the second sub-layer 602. The first sub-layer 601 forms a boss structure 610, and the second sub-layer 602 forms a groove. A current limiting layer 5 is disposed on the surface of the groove, and the thickness of the current limiting layer 5 is less than the thickness of the first sub-layer 601. An ohmic contact metal layer 4 covers the lower surface of the current limiting layer 5 and contacts the sidewall of the boss structure 610 (first sub-layer 601), and the lower surface of the ohmic contact metal layer 4 is flush with the top surface of the boss structure 610.

[0045] The first sublayer 601 is Mg-doped In. X Ga 1-X Material N, X=0.1, Mg doping concentration is 5×10⁻⁶ 19 cm -3 The first sublayer 601 has a thickness of 500 nm. The first sublayer 601 forms a cylindrical boss structure 610, with a base diameter of 1 μm and a height of 500 nm. The second sublayer 602 is Mg-doped Al. Y Ga 1-Y N, Y=0.2, Mg doping concentration is 4×10 19 cm -3 The conductivity of the second sublayer 602 is approximately 10 times that of the first sublayer 601, and the thickness of the second sublayer 602 is 30 nm. The current-limiting layer 5 is made of AlN and has a thickness of 30 nm. The ohmic contact metal layer 4 is made of Cr / Au metal and forms ohmic contacts only with the sidewalls of the boss structure 610.

[0046] In this embodiment, substrate 1 is a metal substrate, and bonding metal layer 2 is used to bond substrate 1 and P-side Bragg reflector 3, and provide a current path. Both P-side Bragg reflector 3 and N-side Bragg reflector 12 are composed of alternately stacked high-refractive-index and low-refractive-index oxide dielectric materials, with a material combination of Nb₂O₅ / SiO₂. To achieve laser emission along the direction perpendicular to substrate 1 towards N-side Bragg reflector 12, the reflectivity of both P-side Bragg reflector 3 and N-side Bragg reflector 12 is greater than 99%, with the reflectivity of P-side Bragg reflector 3 being higher than that of N-side Bragg reflector 12. To reduce light leakage, P-side Bragg reflector 3 at least covers the surface of boss structure 610; N-side Bragg reflector 12 at least covers the vertical projection area of ​​boss structure 610 on the surface of N-type layer 10. The material of N-electrode 11 is Cr / Au.

[0047] In this embodiment, the bottom diameter of the boss structure 610 is 1 μm, which not only precisely defines the light-emitting volume of the active region but also significantly improves the current injection density, facilitating low threshold current and fundamental transverse mode operation. Combined with the current expansion structure of this invention, it ensures that the current fully covers the entire aperture area, avoiding current concentration at the edges. The boss height is 500 nm, providing sufficient vertical space for the first sublayer, which is beneficial for the current to be fully expanded in the first sublayer before being vertically injected into the active region. The ohmic contact metal layer 4 is made of Cr / Au metal, which easily forms ohmic contact with the sidewall of the boss structure 610 and has good adhesion. The current confinement layer 5 is made of AlN material with a thickness of 30 nm, which can achieve good electrical insulation and has a lower reflectivity than the first sublayer 601, thus reducing transverse light loss.

[0048] When the current-spreading enhanced lateral injection gallium nitride-based VCSEL provided in this embodiment is working, the current is injected from the ohmic contact metal layer 4. In the vertical direction, it is blocked by the electrically insulating current limiting layer 5 and then conducts laterally. The current is injected into the first sub-layer 601 through the ohmic contact ring formed by the ohmic contact metal layer 4 and the sidewall of the boss structure 610 (i.e., the first sub-layer 601). Since the second sub-layer 602 has relatively high longitudinal resistance, the current injected into the first sub-layer 601 is more likely to spread laterally in this layer, making the current distribution in the current aperture more uniform, and finally injecting into the multi-quantum well active region 9 and emitting light in a concentrated manner. Example 2

[0049] This embodiment provides another current-spreading enhanced side-injected gallium nitride-based VCSEL. Compared to Embodiment 1, the main difference is that the boss structure consists of the entire first sublayer and a portion of the second sublayer, and the materials and thicknesses of the first and second sublayers differ from those in Embodiment 1. Additionally, the boss diameter increases from 1 μm to 3 μm, and the height increases from 500 nm to 1.05 μm. The ohmic contact metal layer partially contacts the second sublayer. The P-type layer and side-injection structure are as follows: Figure 5 As shown, it includes an ohmic contact metal layer 4, a current confinement layer 5, a current aperture layer 6, and a P-type layer 7 stacked sequentially. The ohmic contact metal layer 4, the current confinement layer 5, and the current aperture layer 6 form a lateral current injection structure 14.

[0050] Specifically, the current aperture layer 6 consists of a first sublayer 601 and a second sublayer 602 stacked vertically and electrically connected. The second sublayer 602 is disposed on the lower surface of the P-type layer 7 and completely covers the P-type layer 7. The first sublayer 601 is disposed on the lower surface of the second sublayer 602 and maintains the same morphology as the second sublayer 602. The entire first sublayer 601 and a portion of the second sublayer 602 form a boss structure 610, and the area of ​​the second sublayer 602 not covered by the boss structure 610 forms a groove. A current limiting layer 5 is disposed on the surface of the groove, and the thickness of the current limiting layer 5 is less than the thickness of the portion of the second sublayer 602 that forms the boss structure 610. An ohmic contact metal layer 4 covers the lower surface of the current limiting layer 5 and contacts the sidewall of the boss structure 610 (the first sublayer 601 and a portion of the second sublayer 602), and the lower surface of the ohmic contact metal layer 4 is flush with the top surface of the boss structure 610.

[0051] The first sublayer 601 is a Mg-doped AlInGaN material with an Al composition of 0.01, an In composition of 0.1, and a Mg doping concentration of 5 × 10⁻⁶. 19 cm -3 The first sublayer 601 has a thickness of 1 μm. The second sublayer 602 is Mg-doped GaN with a Mg doping concentration of 2 × 10⁻⁶. 19 cm -3 The resistivity of the second sublayer 602 is approximately 15 times that of the first sublayer 601. The thickness of the second sublayer 602 is 50 nm, of which 40 nm of thickness forms a cylindrical boss structure 610 with the entire first sublayer 601, and the remaining 10 nm of thickness of the second sublayer 602 forms a groove. The bottom diameter of the boss structure 610 is 3 μm, and the height of the boss structure 610 is 1.05 μm.

[0052] In this embodiment, the bottom diameter of the boss structure 610 is 3μm, balancing threshold current and output power. Combined with the current spreading structure of this invention, it ensures that the current fully covers the entire 3μm aperture area. The boss height is 1.05μm, providing sufficient vertical space for the first sub-layer, which facilitates the full lateral spreading of the current in the first sub-layer before vertical injection into the active region. Simultaneously, the higher boss also increases the ohmic contact area of ​​the sidewalls, helping to reduce contact resistance. The current limiting layer 5 is made of 30nm thick AlN material, achieving good electrical insulation and having a lower reflectivity than the second sub-layer 602, thus reducing lateral light loss.

[0053] In this embodiment, both the P-side Bragg reflector 3 and the N-side Bragg reflector 12 are composed of alternating stacked high-refractive-index and low-refractive-index oxide dielectric materials, with the material combination being TiO2 / SiO2.

[0054] The selection of other materials and dimensions in this embodiment are the same as in Embodiment 1. Example 3

[0055] This embodiment provides another current-spreading enhanced side-injected gallium nitride-based VCSEL. Compared to Embodiment 1, the main difference is that the boss structure consists of the entire first sublayer and the entire second sublayer, and the materials and thicknesses of the first and second sublayers are different from those in Embodiment 1. The second sublayer is a GaN / InGaN stacked structure. Simultaneously, the boss diameter increases from 1 μm to 5 μm, the height increases from 500 nm to 1.55 μm, and the current-confining layer thickness increases from 30 nm to 50 nm. The P-type layer and the side-injection structure are as follows... Figure 6 As shown, it includes an ohmic contact metal layer 4, a current confinement layer 5, a current aperture layer 6, and a P-type layer 7 stacked sequentially. The ohmic contact metal layer 4, the current confinement layer 5, and the current aperture layer 6 form a lateral current injection structure 14.

[0056] Specifically, the current aperture layer 6 consists of a first sub-layer 601 and a second sub-layer 602 stacked vertically and electrically connected. The second sub-layer 602 is disposed on the lower surface of the P-type layer 7 and partially covers the P-type layer 7, while the first sub-layer 601 is disposed on the lower surface of the second sub-layer 602 and completely covers the second sub-layer 602. The first sub-layer 601 and the second sub-layer 602 together form a boss structure 610, and the area of ​​the P-type layer 7 not covered by the boss structure 610 forms a groove. A current limiting layer 5 is disposed on the surface of the groove, and the thickness of the current limiting layer 5 is greater than the thickness of the second sub-layer 602 and less than the height of the boss structure 610. An ohmic contact metal layer 4 covers the lower surface of the current limiting layer 5 and contacts the sidewall of the boss structure 610 (first sub-layer 601), and the lower surface of the ohmic contact metal layer 4 is flush with the top surface of the boss structure 610.

[0057] The first sublayer 601 is Mg-doped In. X Ga 1-X Material N, X=0.1, Mg doping concentration is 1×10⁻⁶ 20 The first sublayer 601 has a thickness of 1.5 μm. The second sublayer 602 is a 5-period GaN / InGaN stacked structure with an In composition of 0.1. The first layer is GaN and the last layer is InGaN. The total thickness of the second sublayer 602 is 40 nm, and the GaN doping concentration is 5 × 10⁻⁶. 19 cm -3The resistivity is approximately 20 times that of the first sublayer 601, the single-layer thickness is 5 nm, and the InGaN doping concentration is 1 × 10⁻⁶. 20 cm -3 The thickness of each sublayer is 3 nm. The first sublayer 601 and the second sublayer 602 are cylindrical with a bottom diameter of 5 μm. The height of the boss structure 610 formed by the first sublayer 601 and the stacked second sublayer 602 is 1.55 μm. The current limiting layer 5 is made of AlN and has a thickness of 30 nm. The ohmic contact metal layer 4 is made of Cr / Au metal and forms ohmic contacts only with the sidewalls of the boss structure 610.

[0058] In this embodiment, the bottom diameter of the boss structure 610 is 5 μm. This size is close to the critical bottleneck of the current spread distance of the lateral current injection structure. However, thanks to the better current spread effect of the present invention, the current can spread laterally sufficiently within the low-resistivity layer, covering the entire 5 μm aperture area, effectively suppressing edge current concentration and keeping the gain distribution of the active region uniform. Therefore, this size can still achieve low threshold current and basic transverse mode operation, while significantly improving the output power of the device, breaking through the limitations of lateral current injection structures in large aperture applications. The boss height is 1.5 μm, providing more vertical space for the first sublayer, which is beneficial for the current to spread laterally over a long distance in the first sublayer before being vertically injected into the active region. In addition, the higher boss further increases the ohmic contact area of ​​the sidewall, effectively reducing contact resistance and improving the thermal characteristics and reliability of the device. The current limiting layer 5 is a 50 nm thick SiO2 material, which can achieve good electrical insulation and has a lower reflectivity than the first sublayer 601 and the second sublayer 602, thus reducing lateral light loss.

[0059] In this embodiment, both the P-side Bragg reflector 3 and the N-side Bragg reflector 12 are composed of alternating stacked high-refractive-index and low-refractive-index oxide media materials, with the material combination being Ta2O5 / SiO2.

[0060] The selection of other materials and dimensions in this embodiment are the same as in Embodiment 1. Example 4

[0061] This embodiment provides another current-spreading enhanced side-injected gallium nitride-based VCSEL. The main difference from Embodiment 3 is that the second sublayer is a low-doped GaN / high-doped GaN stacked structure. The P-type layer and side current injection structure are also as described above. Figure 6 As shown.

[0062] The second sublayer 602 is a 5-period low-doped GaN / high-doped GaN stacked structure, with the first layer being low-doped GaN and the last layer being high-doped GaN. The total thickness of the second sublayer 602 is 40 nm, and the doping concentration of the low-doped GaN is 5 × 10⁻⁶.19 cm -3 The resistivity is approximately 20 times that of the first sublayer 601, and the single-layer thickness is 5 nm; the doping concentration of the highly doped GaN is 1 × 10⁻⁶. 20 cm -3 The thickness of a single layer is 3nm.

[0063] The selection of other materials and dimensions in this embodiment are the same as in Embodiment 3. Example 5

[0064] This embodiment provides another current-spreading enhanced side-implanted gallium nitride-based VCSEL. Compared to Embodiment 1, the main difference is that this embodiment is a hybrid DBR structure VCSEL, and the boss structure is composed of the entire first sublayer and a portion of the second sublayer. The boss height is increased from 500nm to 505nm. The specific structure is as follows: Figure 7 As shown, the structure includes a GaN substrate 16 below and, sequentially stacked on the GaN substrate 15, an N-side Bragg mirror 12, an N-type layer 10, a multi-quantum-well active region 9, a P-type AlGaN electron blocking layer 8, a P-type layer 7, a current aperture layer 6, a current confinement layer 5, an ohmic contact metal layer 4, and a P-side Bragg mirror 3. An N-electrode 11 is also provided on the N-type layer 10. The ohmic contact metal layer 4, the current confinement layer 5, and the current aperture layer 6 constitute a lateral current injection structure 14.

[0065] Specifically, the current aperture layer 6 consists of a first sub-layer 601 and a second sub-layer 602 stacked vertically and electrically connected. The second sub-layer 602 is disposed on the upper surface of the P-type layer 7 and completely covers the P-type layer 7. The first sub-layer 601 is disposed on the upper surface of the second sub-layer 602 and maintains the same morphology as the second sub-layer 602. The entire first sub-layer 601 and a portion of the second sub-layer 602 form a boss structure 610, and the area of ​​the second sub-layer 602 not covered by the boss structure 610 forms a groove. A current limiting layer 5 is disposed on the surface of the groove, and the thickness of the current limiting layer 5 is greater than the thickness of the portion of the second sub-layer 602 that forms the boss structure 610 and less than the height of the boss structure 610. An ohmic contact metal layer 4 covers the upper surface of the current limiting layer 5 and contacts the sidewall of the boss structure 610 (first sub-layer 601), and the upper surface of the ohmic contact metal layer 4 is flush with the top surface of the boss structure 610.

[0066] In this structure, the 5nm thick portion of the second sublayer 602, together with the entire first sublayer 601, forms a cylindrical boss structure 610, while the remaining 25nm thick portion of the second sublayer 602 forms a groove. The height of the boss structure 610 is 505nm.

[0067] In this embodiment, the P-side Bragg mirror 3 is composed of alternating stacks of high-refractive-index and low-refractive-index oxide dielectric materials, with a material combination of HfO2 / SiO2. The N-side Bragg mirror 12 is a nitride semiconductor DBR homoepitaxially grown on a GaN substrate 15, with a material of AlN / GaN.

[0068] The selection of other materials and dimensions in this embodiment are the same as in Embodiment 1.

[0069] The embodiments of this disclosure have now been described in detail with reference to the accompanying drawings.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A current-spreading enhanced laterally injected gallium nitride-based VCSEL, comprising a stacked P-side Bragg mirror, a lateral current injection structure, a gallium nitride-based epitaxial layer, and an N-side Bragg mirror, wherein the lateral current injection structure comprises: Current aperture layer, current confinement layer, and ohmic contact metal layer; The current aperture layer is disposed on the surface of the P-type layer in the gallium nitride-based epitaxial layer, and forms an electrical connection with the P-type layer; characterized in that: The current aperture layer includes at least a first sub-layer and a second sub-layer stacked and electrically connected in a vertical direction; wherein the second sub-layer is disposed adjacent to the P-type layer, and the first sub-layer is disposed on the side of the second sub-layer facing away from the P-type layer; the resistivity of the second sub-layer is higher than that of the first sub-layer. The current aperture layer has a boss structure, the boss structure includes at least the first sub-layer and the first sub-layer does not extend beyond the boundary of the boss structure, thereby defining a groove on the surface of the P-type layer or the current aperture layer; the top surface of the boss structure is in contact with the P-side Bragg mirror. The current limiting layer is disposed on the surface of the groove and contacts the sidewall of the boss structure. The surface of the current limiting layer is closer to the bottom surface of the boss structure than the top surface of the boss structure. The ohmic contact metal layer covers the surface of the current limiting layer and is electrically insulated from the current limiting layer; the ohmic contact metal layer forms an ohmic contact only with the sidewall of the boss structure.

2. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 1, characterized in that: The current aperture layer is a p-type doped gallium nitride-based material; the bottom surface of the boss structure is circular with a diameter of 0.1 μm to 20 μm, and the height of the boss structure is 20 nm to 2 μm.

3. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 1, characterized in that: The thickness of the second sublayer is 5nm~200nm.

4. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 1, characterized in that: The resistivity of the second sublayer is 2 to 100 times that of the first sublayer.

5. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 1, characterized in that: The first sublayer is a p-type doped gallium nitride-based material with a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 20 cm -3 .

6. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 1, characterized in that: The second sublayer is a p-type doped gallium nitride-based monolayer structure with a lower doping concentration than the first sublayer.

7. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 1, characterized in that: The second sub-layer is a p-type doped gallium nitride-based stacked structure, consisting of alternating stacked high-resistivity gallium nitride-based material layers and low-resistivity gallium nitride-based material layers, wherein the resistivity of the high-resistivity gallium nitride-based material layer is higher than that of the low-resistivity gallium nitride-based material layer and the first sub-layer; the boss structure includes the second sub-layer, and all low-resistivity gallium nitride-based material layers in the second sub-layer do not exceed the boundary of the boss structure and do not contact the ohmic contact metal layer.

8. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 7, characterized in that: The doping concentration of the high resistivity gallium nitride-based material layer is lower than that of the low resistivity gallium nitride-based material layer and the first sublayer.

9. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 1, characterized in that: The first sublayer is Mg-doped In X Ga 1-X N, 0.05≤X≤0.15; the second sublayer is Mg-doped Al Y Ga 1-Y N, 0.1 ≤ Y ≤ 0.4; or the second sublayer is Mg-doped GaN / In Z Ga 1-Z N-stacked structure, 0.05≤Z≤0.

15.

10. The current-spreading enhanced side-implanted gallium nitride-based VCSEL according to claim 1, characterized in that: The current limiting layer is made of an oxide dielectric material or a nitride semiconductor material, and the refractive index of the current limiting layer is lower than that of the current aperture layer; the ohmic contact metal layer is made of one or more of Cr / Au, Cr / Pt / Au, and Ni / Au; the absolute value of the height difference between the surface of the ohmic contact metal layer away from the current limiting layer and the top surface of the boss structure is not greater than 10 nm.

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