Ultraviolet laser structure

Abstract

The invention provides an ultraviolet laser structure, and relates to the field of lasers. The laser structure comprises a substrate, a buffer layer and a lower limiting layer which are sequentially stacked from bottom to top, a lower waveguide layer, an active region, an upper waveguide layer, an alloy insertion layer and an upper limiting layer are sequentially laminated on one part of the surface of the lower limiting layer from bottom to top, and an n-side contact electrode is laminated on the other part of the surface of the lower limiting layer; a hole injection layer, a p-side contact layer and a p-side contact electrode are sequentially stacked on the upper limiting layer from bottom to top; the average forbidden bandwidth of the alloy insertion layer is larger than the average forbidden bandwidth of the upper waveguide layer and smaller than the average forbidden bandwidth of the upper limiting layer. Through the ultraviolet laser structure, electron leakage is effectively inhibited, hole injection efficiency is improved, and the performance of the laser is improved.

Description

Technical Field

[0001] This invention relates to the field of lasers, and more specifically to an ultraviolet laser structure. Background Technology

[0002] Ultraviolet lasers, with their unique photon energy and wavelength characteristics, have become a core technological support for scientific research, environmental monitoring, and other fields. Early ultraviolet laser sources mainly relied on gas discharge excimer lasers and solid-state frequency-doubled lasers. However, these devices have many inherent defects. Solid-state frequency-doubled lasers are limited by the conversion efficiency of nonlinear optical crystals, the beam quality of the output laser is easily affected by temperature fluctuations, and the wavelength tuning range is narrow, making it difficult to meet the needs of diverse application scenarios.

[0003] The advent of group III nitride semiconductor ultraviolet lasers has provided a new direction for addressing the aforementioned pain points. Compared to traditional ultraviolet laser sources, they offer significant advantages such as compact size, precise wavelength control, high beam quality, fast modulation response, and no harmful emissions, making them a core development direction for next-generation ultraviolet laser devices. Among them, GaN-based blue-green lasers have achieved industrialization breakthroughs, reaching mature technical indicators in terms of threshold current reduction, output power improvement, and long-term reliability optimization, and are widely used in consumer electronics, display lighting, and other fields.

[0004] However, as laser wavelengths extend into shorter wavelength regions, the development of AlGaN-based ultraviolet lasers (especially in the UV-B and UV-C bands) has encountered a bottleneck. The realization of room-temperature electrically pumped continuous laser emission has become increasingly difficult, and the core performance indicators are significantly different from industrialization requirements. The root cause of this predicament lies in the dual technical barriers faced by short-wavelength ultraviolet lasers: firstly, at the material epitaxy level, as the Al content increases, the lattice mismatch of AlGaN materials intensifies, and high-density dislocations, cracks, and other crystal defects are easily generated during epitaxy, significantly reducing the crystal quality and optical performance of the material; secondly, at the device fabrication and carrier transport level, p-type doping of high-Al-content AlGaN materials is extremely difficult. Due to factors such as the high activation energy of Mg acceptors and hydrogen impurity compensation, hole concentration and mobility are difficult to increase, resulting in low hole injection efficiency; at the same time, the effective mass of electrons is small and their mobility is high, making it easy for them to leak into the p-type region by overcoming the potential barrier structure of traditional devices, causing a significant decrease in the electron-hole recombination efficiency in the active region.

[0005] In existing technologies, researchers have attempted to improve performance by optimizing quantum well structures, adjusting p-type doping processes, and adding electron blocking layers, but with limited success. For example, simply thickening the electron blocking layer can suppress electron leakage to some extent, but it increases the potential barrier for hole injection, further exacerbating the problem of carrier distribution imbalance; increasing the p-type doping concentration easily leads to internal stress concentration in the material, intensifying the generation of crystal defects. Data shows that the internal quantum efficiency of AlGaN-based ultraviolet lasers in the UV-B and UV-C bands is generally below 20%, far lower than that of blue lasers (>75%) and near-ultraviolet lasers in the UV-A band (>60%). Low internal quantum efficiency directly leads to excessively high threshold current and insufficient output power, becoming a core bottleneck restricting their industrial application, and urgently requires new device structure solutions to overcome this challenge. Summary of the Invention

[0006] In view of this, this application proposes an ultraviolet laser structure. By introducing an alloy intercalation layer between the upper waveguide layer and the upper confinement layer, electron leakage is reduced and carrier injection efficiency is improved, thereby increasing the internal quantum efficiency and achieving higher laser performance.

[0007] This application proposes an ultraviolet laser structure, comprising a substrate, a buffer layer, and a lower confinement layer stacked sequentially from bottom to top; a portion of the surface of the lower confinement layer is stacked sequentially from bottom to top with a lower waveguide layer, an active region, an upper waveguide layer, an alloy insertion layer, and an upper confinement layer, and another portion of the surface of the lower confinement layer is stacked with an n-side contact electrode; the upper confinement layer is stacked sequentially from bottom to top with a hole injection layer, a p-side contact layer, and a p-side contact electrode; wherein, the average bandgap of the alloy insertion layer is greater than the average bandgap of the upper waveguide layer and less than the average bandgap of the upper confinement layer.

[0008] In this embodiment, the lower limiting layer has a convex center and concave ends, and the convex portion is stacked with a lower waveguide layer.

[0009] In this embodiment, the upper limiting layer has a raised middle section and recessed ends, and the raised portion is stacked with a cavity injection layer.

[0010] In this embodiment, the coverage areas of the lower waveguide layer, active region, upper waveguide layer, alloy insertion layer and upper confinement layer stacked from bottom to top decrease or remain unchanged in sequence.

[0011] In this embodiment, the material of the alloy insertion layer includes B. a Al b In c Ga 1-a-b-c N, where 0≤a≤1, 0≤b≤1, 0≤c≤1.

[0012] In this embodiment, the thickness of the alloy insertion layer is less than or equal to 10 nm.

[0013] In this embodiment, the active region includes 1 to 10 cycles of quantum well structures, and each cycle of the quantum well structure includes a quantum well layer and a quantum barrier layer.

[0014] The thickness of the quantum well layer is 1nm~8nm, and the thickness of the quantum barrier layer is 2nm~20nm.

[0015] In this embodiment, the thickness of the upper confinement layer is 0.01 μm to 1.0 μm, and the upper confinement layer is undoped or weakly p-type doped.

[0016] In this embodiment, the lower confinement layer is designed with n-type doping, the dopant is Si, and the doping concentration of Si is uniformly distributed or gradient-variable from bottom to top.

[0017] In this embodiment, the p-side contact layer surface is also provided with multiple pairs of etched trenches extending downward into the hole injection layer.

[0018] This application proposes an ultraviolet laser structure that, after using an intercalation layer with optimized thickness and composition, has the following beneficial effects:

[0019] (1) Effectively suppressing electron leakage, the alloy insertion layer can improve the electron blocking barrier, which can significantly reduce the proportion of electron current leakage on the p side from 78% to 26%, reduce electron overflow to the upper confinement layer, and reduce carrier ineffective loss.

[0020] (2) Improve hole injection efficiency. The alloy insertion layer can reduce the hole injection barrier, enhance the hole transport capability to the quantum well, increase the average hole concentration in the quantum well by 15%, and optimize the electron-hole distribution balance in the active region.

[0021] (3) Improve the core performance of the device. By optimizing the confinement and transport of charge carriers, the quantum efficiency of the laser is significantly improved, thereby effectively reducing the threshold current of the device and increasing the output power. This breaks through the technical bottleneck of high threshold current and room temperature electric pumped continuous lasing in UV-B and UV-C band ultraviolet lasers. Attached Figure Description

[0022] The embodiments of this application are described below with reference to the accompanying drawings, in which:

[0023] Figure 1 A schematic cross-sectional view of an ultraviolet laser structure according to an embodiment of this application is shown.

[0024] Figure 2a This illustration schematically shows a comparison of hole concentration distribution near the active region according to an embodiment of this application;

[0025] Figure 2b The diagram illustrates a comparison of electron leakage near the active region according to an embodiment of this application.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1-Substrate; 2-Buffer layer; 3-Lower confinement layer; 4-Lower waveguide layer; 5-Active region; 6-Upper waveguide layer; 7-Alloy insertion layer; 8-Upper confinement layer; 9-Hole injection layer; 10-P-side contact layer; 11-P-side contact electrode; 12-N-side contact electrode. Detailed Implementation

[0028] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0030] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0031] Secondly, this application provides a detailed description in conjunction with schematic diagrams. When detailing the embodiments of this application, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of this application. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0032] Figure 1 A schematic cross-sectional view of an ultraviolet laser structure according to an embodiment of this application is shown.

[0033] As shown in the figure, an ultraviolet laser structure according to an embodiment of this application includes a substrate 1, a buffer layer 2, and a lower confinement layer 3 stacked sequentially from bottom to top; a portion of the surface of the lower confinement layer 3 is stacked sequentially from bottom to top with a lower waveguide layer 4, an active region 5, an upper waveguide layer 6, an alloy insertion layer 7, and an upper confinement layer 8, and another portion of the surface of the lower confinement layer 3 is stacked with an n-side contact electrode 12; the upper confinement layer 8 is stacked sequentially from bottom to top with a hole injection layer 9, a p-side contact layer 10, and a p-side contact electrode 11.

[0034] Substrate 1 serves as the physical substrate for the entire ultraviolet laser and can be made of materials such as sapphire, silicon carbide, or aluminum nitride. The main functions of substrate 1 include: firstly, providing a smooth growth interface for subsequent epitaxial layers to ensure the crystallinity consistency of the layered structure; secondly, achieving efficient heat dissipation by rapidly dissipating the Joule heat generated during active region emission, preventing performance degradation due to localized overheating; and thirdly, some parts of substrate 1 (such as silicon carbide or silicon) can function as conductive pathways, assisting in optimizing the current distribution of the device.

[0035] Because of the difference in lattice constant and thermal expansion coefficient between substrate 1 and the upper group III nitride epitaxial layer (lower confinement layer 3), direct epitaxy is prone to defects such as high-density dislocations and cracks. Therefore, a buffer layer 2 is added between substrate 1 and lower confinement layer 3.

[0036] Specifically, the buffer layer 2 uses group III nitride materials such as InN, GaN, and AlGaN. Through the composite structure design of low-temperature nucleation and high-temperature annealing, the lattice constant can be gradually transitioned, the interfacial lattice mismatch stress can be reduced, and the crystal defects of subsequent functional layers can be significantly reduced, laying the material foundation for low-loss transport of charge carriers.

[0037] In this embodiment, the average bandgap of the alloy insertion layer 7 is greater than the average bandgap of the upper waveguide layer 6, but less than the bandgap of the upper confinement layer 8.

[0038] In the embodiments of this disclosure, when electrons are transported upward from the active region 5, they first pass through the upper waveguide layer 6 and then come into contact with the alloy insertion layer 7. Since the bandgap of the alloy insertion layer 7 is larger than that of the upper waveguide layer 6, an electron blocking barrier is formed. The energy of the electrons is difficult to cross this barrier, and they cannot continue to diffuse upward to the upper confinement layer 8. This avoids the ineffective leakage of electrons into the p-type region, locks more electrons near the active region 5, and ensures the effective retention of electrons.

[0039] Furthermore, when holes are transported from the p-side through the hole injection layer 9 to the active region 5, they need to pass through the upper confinement layer 8 and the upper waveguide layer 6. The upper confinement layer 8 has a relatively large bandgap, which will form a certain hole injection barrier; while the bandgap of the alloy insertion layer 7 is smaller than that of the upper confinement layer 8, which can reduce the overall hole injection barrier without affecting electron blocking, allowing holes to pass through the alloy insertion layer 7 and the upper waveguide layer 6 more smoothly into the active region 5, thereby improving the hole injection efficiency.

[0040] Meanwhile, with the synergistic assistance of the upper confinement layer 8 and the hole injection layer 9, the upper confinement layer 8 continues the optical field confinement function of the lower confinement layer, and further confines the optical field through its low refractive index characteristics.

[0041] In this embodiment, the hole injection layer 9 is a p-type doped group III nitride, which can generate three-dimensional hole gas through polarization effect, providing a stable hole source for the active region and ensuring a continuous supply of holes.

[0042] In the embodiments of this application, the lower confinement layer 3 is designed with n-type doping, the dopant is Si, and the doping concentration of Si is uniformly distributed or gradient-varying from bottom to top.

[0043] For example, the lower confinement layer 3 is an n-type Si-doped group III nitride material. Si doping provides sufficient free electrons, supplying an electron source for electron-hole recombination in the active region. Furthermore, the uniform or gradient distribution of the doping concentration allows for flexible control of the electron transport rate. Simultaneously, the low refractive index and high bandgap of the Si-doped group III nitride material create initial confinement of carriers and the optical field. Compared to the lower waveguide layer 4, the lower confinement layer 3 has a lower refractive index, allowing the optical field to be confined within the upper / lower waveguide layers and the active region 5 through total internal reflection. Its high bandgap also forms a potential barrier, preventing electrons in the active region 5 from diffusing downwards, thus achieving initial regional locking of electrons.

[0044] For example, the refractive indices of the lower waveguide layer 4 and the upper waveguide layer 6 are between those of the upper / lower confinement layers and the active region, and their band gaps are smaller than those of the corresponding confinement layers. This forms a refractive index gradient structure of confinement layer (low refractive index) - waveguide layer (medium refractive index) - active region (high refractive index). According to the principle of total internal reflection in optical waveguides, after the laser is generated in the active region 5, it will undergo total internal reflection at the interface between the upper / lower waveguide layers and the upper / lower confinement layers, thus being confined within the core region formed by the upper / lower waveguide layers and the active region 5. This prevents the light field from escaping to the outside of the device, significantly improving the utilization efficiency of the light field. At the same time, the weakly doped or undoped design of the waveguide layer can reduce the absorption loss of free carriers on light, ensuring the laser's output efficiency.

[0045] In this embodiment, the lower limiting layer 3 has a raised middle section and recessed ends, and the raised section is stacked with the lower waveguide layer 4.

[0046] For example, the raised region can physically constrain the lower waveguide layer 4 and the upper active region 5, reducing the lateral diffusion loss of charge carriers and allowing electrons to be transported more concentratedly to the active region. The recessed region provides a suitable mounting space for the n-side contact electrode 12, avoiding short circuits or performance interference caused by the n-side contact electrode 12 contacting the upper / lower waveguide layers, active region 5, and other functional layers.

[0047] In this embodiment, the upper limiting layer 8 has a raised middle section and recessed ends, and the raised portion is stacked with a hole injection layer 9.

[0048] The upper confinement layer 8 has a raised center and recessed ends, which can further compress the activity range of charge carriers and optical field, and increase the concentration of optical field in active region 5. The raised area can guide the directional transport of holes to active region 5, reducing the ineffective dissipation of holes in non-functional regions. At the same time, the recessed area can reduce the contact area between the upper confinement layer 8 and the surrounding structure, reduce the parasitic capacitance at the interface, and improve the modulation response speed of the device.

[0049] In this embodiment, the coverage areas of the lower waveguide layer 4, active region 5, upper waveguide layer 6, alloy insertion layer 7 and upper confinement layer 8, which are stacked sequentially from bottom to top, decrease or remain unchanged.

[0050] In this embodiment, the material of the alloy insertion layer 7 includes B. a Al b In c Ga 1-a-b-c N, where 0≤a≤1, 0≤b≤1, 0≤c≤1.

[0051] For example, by adjusting the composition of Ba, Al, In, and Ga, the bandgap and barrier height of the alloy insertion layer can be flexibly controlled to meet the device requirements of different short-wave ultraviolet bands such as UV-B and UV-C. Simultaneously, this material system exhibits higher lattice matching with group III nitride waveguide layers and confinement layers, reducing interlayer interface defects and lowering carrier recombination losses. The wide range of tunable composition provides ample parameter space for subsequent optimization of carrier confinement or transport performance.

[0052] In this embodiment, the thickness of the alloy insertion layer 7 is less than or equal to 10 nm.

[0053] For example, the thickness of the alloy intercalation layer 7 is less than or equal to 10 nm, which can ensure the modulation effect of the electron blocking barrier and hole injection barrier while avoiding additional optical absorption loss due to excessive layer thickness, thus ensuring the light transmission performance of the device. At the same time, the ultrathin layer design can reduce the lattice defect density of the alloy intercalation layer, improve the flatness of the interlayer interface, and reduce the interfacial scattering probability of charge carriers. Compared with thick layer structures, the ultrathin alloy intercalation layer is more likely to achieve uniform distribution of components, ensuring the stability and consistency of the barrier effect.

[0054] In this embodiment, the active region 5 includes 1 to 10 periods of quantum well structure, each period of which includes a quantum well layer and a quantum barrier layer; wherein the thickness of the quantum well layer is 1 nm to 8 nm, and the thickness of the quantum barrier layer is 2 nm to 20 nm.

[0055] The active region is the core of the laser generation device, employing a quantum well / quantum barrier structure with 1-10 cycles. The quantum well layer has a thickness of 1 nm to 8 nm, and its bandgap is smaller than that of the quantum barrier layer, thus forming a quantum confinement potential well for electrons and holes. When electrons and holes are transported to the quantum well, they are confined to a low-dimensional space within the well, significantly increasing the radiative recombination probability of electrons and holes. By adjusting the Al composition of the quantum well layer, its bandgap can be precisely controlled, thereby achieving laser output in different short-wavelength ultraviolet bands such as UV-B and UV-C.

[0056] In this embodiment, the thickness of the upper confinement layer 8 is 0.01 μm to 1.0 μm, and the upper confinement layer 8 is undoped or weakly p-type doped.

[0057] For example, a thickness of 0.01 μm to 1.0 μm can achieve carrier and optical field confinement while avoiding the accumulation of optical losses and increased epitaxial processing difficulty caused by excessive layer thickness. Undoped or weakly p-type doped designs can significantly reduce free carrier absorption losses in this layer, ensuring laser emission efficiency. Simultaneously, weakly p-type doping can help improve hole transport capacity and enhance hole injection into the active region without introducing excessive losses.

[0058] In this embodiment, the lower confinement layer 3 is designed with n-type doping, the dopant is Si, and the doping concentration of Si is uniformly distributed or gradient-variable from bottom to top.

[0059] For example, the Si-doped n-type lower confinement layer 3 can provide sufficient electron carriers, ensuring the electron supply in the active region and providing a basis for electron-hole recombination; uniform doping can ensure the stability of electron transport, while gradient doping can control the electron transport rate as needed, adapting to devices with different performance requirements; clear definition of dopant and distribution mode can improve the conductivity consistency of the lower confinement layer, reduce the series resistance of the device, and reduce Joule heat loss.

[0060] In this embodiment, a ridge waveguide structure can also be fabricated on the surface of the p-side contact layer 10, that is, etched trenches extending downward into the hole injection layer 9 are formed on both sides.

[0061] For example, extending the trench to the hole injection layer (9) can construct a directional transport channel for holes, reduce the accumulation and dissipation of holes in the p-side contact layer, and at the same time enhance the in-plane confinement capability of the light field, increase the light confinement factor, and reduce the lasing threshold of the laser.

[0062] Figure 2a This illustration schematically shows a comparison of hole concentration distribution near the active region according to an embodiment of this application; Figure 2b The diagram illustrates a comparison of electron leakage near the active region according to an embodiment of this application.

[0063] Figure 2a and Figure 2b The hole concentration distribution and electron leakage near the active region 5 were compared between a conventional ultraviolet laser and an ultraviolet laser with an alloy insert layer 7 having optimized thickness and composition.

[0064] As can be seen, the average hole concentration in the quantum well of the laser with the alloy insertion layer 7 is increased by 15%, and the proportion of electron current leaking from the p side is reduced from 78% to 26%. This is attributed to the enhanced potential barrier of the alloy insertion layer, which effectively prevents electrons from leaking to the p side; at the same time, it enhances hole transport into the quantum well, resulting in an increased hole concentration within the quantum well.

[0065] As can be seen, by introducing the alloy insertion layer 7, this application effectively solves the problems of insufficient hole injection and severe electron leakage in the prior art, thereby improving the internal quantum efficiency of the ultraviolet laser and achieving better device performance.

[0066] Those skilled in the art will understand that the features described in the various embodiments of this disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments of this disclosure can be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0067] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. An ultraviolet laser structure, characterized in that, It includes a substrate (1), a buffer layer (2) and a lower confinement layer (3) stacked sequentially from bottom to top; A portion of the surface of the lower confinement layer (3) is stacked from bottom to top with a lower waveguide layer (4), an active region (5), an upper waveguide layer (6), an alloy insertion layer (7), and an upper confinement layer (8), and another portion of the surface of the lower confinement layer (3) is stacked with an n-side contact electrode (12). The upper limiting layer (8) is stacked from bottom to top with a hole injection layer (9), a p-side contact layer (10) and a p-side contact electrode (11); The average bandgap of the alloy insertion layer (7) is greater than the average bandgap of the upper waveguide layer (6) and less than the bandgap of the upper confinement layer (8).

2. The ultraviolet laser structure according to claim 1, characterized in that, The lower limiting layer (3) has a raised middle section and recessed ends, and the raised section is stacked with the lower waveguide layer (4).

3. The ultraviolet laser structure according to claim 1, characterized in that, The upper limiting layer (8) has a raised middle section and recessed ends, and the raised section is stacked with the hole injection layer (9).

4. The ultraviolet laser structure according to claim 1, characterized in that, The coverage areas of the lower waveguide layer (4), the active region (5), the upper waveguide layer (6), the alloy insertion layer (7), and the upper confinement layer (8) stacked from bottom to top decrease or remain unchanged in sequence.

5. The ultraviolet laser structure according to claim 1, characterized in that, The material of the alloy insert layer (7) includes B. a Al b In c Ga 1-a-b-c N, where 0≤a≤1, 0≤b≤1, 0≤c≤1.

6. The ultraviolet laser structure according to claim 1, characterized in that, The thickness of the alloy insertion layer (7) is less than or equal to 10 nm.

7. The ultraviolet laser structure according to claim 1, characterized in that, The active region (5) includes 1 to 10 cycles of quantum well structures, each cycle of which includes a quantum well layer and a quantum barrier layer. The thickness of the quantum well layer is 1 nm to 8 nm, and the thickness of the quantum barrier layer is 2 nm to 20 nm.

8. The ultraviolet laser structure according to claim 1, characterized in that, The thickness of the upper confinement layer (8) is 0.01 μm to 1.0 μm, and the upper confinement layer (8) is undoped or weakly p-type doped.

9. The ultraviolet laser structure according to claim 1, characterized in that, The lower confinement layer (3) is an n-type doped design, the dopant is Si, and the doping concentration of Si is uniformly distributed or gradient-variable from bottom to top.

10. The ultraviolet laser structure according to claim 1, characterized in that, The p-side contact layer (10) also has etching grooves on both sides of its surface that extend downward into the hole injection layer (9).

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