Bulk GaN vertical cavity epitaxial structure, light-emitting device and light output array

Abstract

The application discloses a Bulk GaN vertical resonant cavity epitaxial structure, a light-emitting device and a light output array for high-speed optical communication. The epitaxial structure comprises a gallium nitride substrate, a porous DBR reflection layer, an n-type epitaxial layer, an active light-emitting layer, a p-type epitaxial layer and a top reflection layer are sequentially formed on the gallium nitride substrate, the porous DBR reflection layer, the n-type epitaxial layer, the active light-emitting layer and the p-type epitaxial layer are all nitride epitaxial layers, and the porous DBR reflection layer and the top reflection layer are located opposite to each other to form an optical resonant cavity. Compared with the prior art, the application has extremely low dislocation density and extremely high crystal quality, can effectively reduce bottom light emission loss and improve the external quantum efficiency of the Bulk GaN vertical resonant cavity light-emitting device.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, specifically to a Bulk GaN vertical resonant cavity epitaxial structure for high-speed optical communication, a Bulk GaN vertical resonant cavity light-emitting device using the epitaxial structure, and an optical output array containing the Bulk GaN vertical resonant cavity light-emitting device. Background Technology

[0002] Artificial Intelligence (AI) is a branch of computer science that aims to study and develop theories, methods, technologies, and application systems for simulating, extending, and expanding human intelligence. Currently, we are experiencing a boom in AI. AI, especially large-scale models and generative AI, places extremely high demands on computing power and data transmission speed, requiring the processing of massive amounts of data, such as large models with trillions of parameters, and complex matrix operations. This typically necessitates the use of GPU clusters (such as NVIDIA H100 / H200) or TPUs (Tensor Processing Units) for large-scale parallel computing.

[0003] Currently, on-board data transmission in GPU clusters still relies on copper wire transmission technology. However, copper wire transmission is limited by the limited space on the board and heat dissipation efficiency, making it difficult for data transmission capacity to increase exponentially. In the long run, it can no longer meet the needs of artificial intelligence for large-scale and efficient data processing.

[0004] Optical communication technology is a communication method that uses light waves as the information carrier. It transmits optical signals through optical fibers, enabling high-speed, high-capacity, and long-distance information transmission. Currently, optical communication technology is mainly used in two major fields: information transmission and sensing and detection. Information transmission is the absolute core, supporting the digital operation of modern society. In the AI ​​era, optical communication is key to solving the "computing power transmission bottleneck." AI training requires the high-speed transmission of massive amounts of data from storage to computing (GPUs), and optical communication provides a high-speed channel far exceeding that of traditional electrical signals, serving as the underlying technology supporting computing power networks.

[0005] Optical communication technology light sources are mainly divided into two categories: lasers and light-emitting diodes (LEDs). Lasers have the characteristics of good directionality, good monochromaticity, and high brightness, making them the absolute mainstream in high-speed, long-distance transmission. However, in short-distance transmission, lasers have problems such as high cost, high power consumption, and high heat dissipation requirements compared to LEDs. From a technical and market perspective, micro LEDs are more suitable for short-distance (within 1 meter) high-speed optical communication applications.

[0006] Currently, the following problems still need to be solved before applying miniature light-emitting diodes to the field of optical communication: (1) Conventionally, epitaxial layers are grown on sapphire substrates and micro-light-emitting diodes are fabricated using chip technology. There is a strong polarization electric field (quantum confinement Stark effect, QCSE), which causes electrons and holes to "separate" at both ends in the quantum well, resulting in low recombination efficiency and slow response speed. (2) The micro light-emitting diodes grown on sapphire substrates have a large defect density (10^10~10^12 cm-2). The high defect density will introduce non-radiative recombination centers, reduce luminous efficiency and generate noise. (3) Bottom emitted light loss: The micro light-emitting diode emits light in a divergent manner. Some of the downward emitted light is absorbed or scattered after entering the substrate, which limits the external quantum efficiency.

[0007] Therefore, there is an urgent need for an epitaxial structure and a light-emitting device for high-speed optical communication that can solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a Bulk GaN vertical resonant cavity epitaxial structure, a Bulk GaN vertical resonant cavity light-emitting device, and a light output array for high-speed optical communication. These structures have extremely low dislocation density and extremely high crystal quality, and can effectively reduce bottom-emitted light loss and improve the external quantum efficiency of the Bulk GaN vertical resonant cavity light-emitting device.

[0009] To achieve the above objectives, the present invention provides a Bulk GaN vertical resonant cavity epitaxial structure for high-speed optical communication, comprising: a gallium nitride substrate, wherein a porous DBR reflective layer, an n-type epitaxial layer, an active light-emitting layer, a p-type epitaxial layer and a top reflective layer are sequentially formed on the gallium nitride substrate, wherein the porous DBR reflective layer, the n-type epitaxial layer, the active light-emitting layer and the p-type epitaxial layer are all nitride epitaxial layers, and the porous DBR reflective layer and the top reflective layer are positioned opposite each other to form an optical resonant cavity.

[0010] Preferably, the gallium nitride substrate is nonpolar or semipolar, which can eliminate or significantly weaken the polarization electric field, resulting in a higher overlap between electron and hole wave functions, thereby significantly shortening the carrier lifetime and improving the modulation bandwidth of the device.

[0011] Preferably, the top reflective layer is a grid metal layer, which comprises a first metal layer and a second metal layer deposited sequentially, and the porosity of the grid metal layer is 70–95%. The grid metal layer not only facilitates the passage of light of a preset wavelength through the openings in the grid metal layer, improving the directionality of the light, but also keeps the top reflective layer within a certain reflectivity range, facilitating the formation of a good optical resonant cavity with the porous DBR reflective layer.

[0012] The linewidth of the mesh metal layer is 0.3–5 μm, the thickness of the mesh metal layer is 50–1500 nm, the spacing between adjacent parallel mesh lines of the mesh metal layer is 3–30 µm, and the equivalent reflectivity is 10–60%.

[0013] Preferably, the porous DBR reflective layer comprises a cross-stacked dense layer and a porous layer, wherein the dense layer is a dense gallium nitride layer and the porous layer is a porous gallium nitride layer. This invention grows a porous DBR reflective layer of gallium nitride material on a gallium nitride substrate, exhibiting extremely low dislocation density and extremely high crystal quality. This results in a significant improvement in internal quantum efficiency (IQE) and a substantial extension of device lifetime.

[0014] Furthermore, the thickness of the monolayer dense gallium nitride layer is 30~300nm, the thickness of the monolayer porous gallium nitride layer is 30~300nm, the number of alternation periods of the porous DBR reflective layer is 6~40, and the porosity of the porous gallium nitride layer is 20–80%.

[0015] Furthermore, the dense gallium nitride layer is a lightly doped gallium nitride layer, and the porous gallium nitride layer is obtained by electrochemical treatment of the heavily doped gallium nitride layer; the doping concentration of the heavily doped gallium nitride layer is at least one order of magnitude higher than that of the lightly doped gallium nitride layer.

[0016] Specifically, the doping concentration of the lightly doped gallium nitride layer is 1×10^17–5×10^18 cm⁻¹ - ³; The doping concentration of the heavily doped gallium nitride layer before electrochemical treatment is 1×10^19–5×10^20 cm⁻¹ - ³.

[0017] The active light-emitting layer is a single quantum well or a double quantum well. The light emission of a micro LED originates from the recombination of electrons in the conduction band and holes in the valence band. Since the energy band itself has a certain width (energy range), the energy difference (i.e., photon energy) during electron-hole recombination is not a fixed value but fluctuates within a range. This leads to natural spectral broadening and low light purity. In contrast, the active light-emitting layer of this invention, being a single quantum well or a double quantum well, can reduce carrier transport time, improve response speed, reduce spectral broadening, improve light purity, and reduce signal distortion during transmission.

[0018] The present invention also provides a Bulk GaN vertical resonant cavity light-emitting device, including an epitaxial structure, electrodes, and a microlens formed on the epitaxial structure, wherein the epitaxial structure is a Bulk GaN vertical resonant cavity epitaxial structure for high-speed optical communication as described above.

[0019] The present invention also provides an optical output array, including a carrier plate and a plurality of light-emitting devices arranged in an array on the carrier plate, wherein the light-emitting devices are Bulk GaN vertical resonant cavity light-emitting devices as described above.

[0020] Compared with existing technologies, on the one hand, the Bulk GaN vertical resonant cavity epitaxial structure of this invention adds a porous DBR reflective layer and a top reflective layer. The porous DBR reflective layer and the top reflective layer form an optical resonant cavity, which can reflect the emitted light towards the substrate to the target light emission direction, reduce the bottom emitted light loss, and improve the external quantum efficiency of the Bulk GaN vertical resonant cavity light-emitting device. On the other hand, this invention grows a porous DBR reflective layer, an n-type epitaxial layer, an active light-emitting layer, and a p-type epitaxial layer on a gallium nitride substrate. Since the gallium nitride substrate, the porous DBR reflective layer, the n-type epitaxial layer, the active light-emitting layer, and the p-type epitaxial layer all adopt a group III nitride material system, the lattice constants and thermal expansion coefficients of each structural layer in the epitaxial structure are very close, effectively reducing lattice mismatch and thermal stress at the interface, thereby reducing defect density, improving device performance and reliability, and significantly improving internal quantum efficiency (IQE) and device lifetime. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the extensional structure of the present invention.

[0022] Figure 2 This is a cross-sectional schematic diagram of the porous DBR reflective layer in the epitaxial structure of the present invention.

[0023] Figure 3 This is a schematic diagram of the structure of a Bulk GaN vertical resonant cavity light-emitting device in one embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram of the structure of a Bulk GaN vertical resonant cavity light-emitting device in another embodiment of the present invention.

[0025] Figure 5 This is a schematic diagram of the optical output array in this invention.

[0026] Figure 6 This is a structural diagram of the mesh metal layer in another embodiment of the present invention.

[0027] Figure label: 1-Gallium nitride substrate; 2-Porous DBR reflective layer; 2a-Dense gallium nitride layer; 2b-Porous gallium nitride layer; 3-Buffer layer; 4-First epitaxial layer; 5-Active light-emitting layer; 6-Second epitaxial layer; 7-Top reflective layer; 8-First electrode; 9-Microlens; 11-Passivation layer; 12-Transparent dielectric layer; 13-Second electrode; 14-External electrode. Detailed Implementation

[0028] To illustrate the technical content, structural features, objectives, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0029] refer to Figure 1 The present invention discloses a Bulk GaN vertical resonant cavity epitaxial structure for high-speed optical communication, including a gallium nitride substrate 1, on which a porous DBR reflective layer 2, an n-type epitaxial layer 4, an active light-emitting layer 5, a p-type epitaxial layer 6 and a top reflective layer 7 are sequentially formed. The porous DBR reflective layer 2 and the top reflective layer 7 are positioned opposite each other to form an optical resonant cavity.

[0030] In this design, a porous DBR reflective layer 2 is grown on a gallium nitride substrate 1, a buffer layer 3 is grown on the porous DBR reflective layer 2, and an n-type epitaxial layer 4, an active light-emitting layer 5, and a p-type epitaxial layer 6 are sequentially grown on the buffer layer 3. The buffer layer 3 can be an AlN layer or a GaN layer.

[0031] Among them, the n-type epitaxial layer 4 can be an n-type gallium nitride layer or an n-type AlGaN layer. The p-type epitaxial layer 6 can be a p-type gallium nitride layer or a p-type AlGaN layer.

[0032] Preferably, the gallium nitride substrate 1 is nonpolar or semipolar. Traditional GaN devices are grown on polar (c-plane) substrates, resulting in a strong polarization electric field (quantum confinement Stark effect, QCSE). This causes electrons and holes to "separate" at opposite ends of the quantum well, leading to low recombination efficiency and slow response speed. Compared to existing technologies, this invention uses a semipolar or nonpolar gallium nitride substrate, which can eliminate or significantly weaken the polarization electric field, resulting in a higher overlap of electron and hole wave functions, thereby significantly shortening carrier lifetime and increasing the device's modulation bandwidth (GHz level).

[0033] refer to Figure 2 In this embodiment, the porous DBR reflective layer 2 includes a dense layer and a porous layer that are stacked in a cross-shaped manner. The dense layer is a dense gallium nitride layer 2a, and the porous layer is a porous gallium nitride layer 2b.

[0034] The thickness of the single-layer dense gallium nitride layer 2a is 30~300nm, the thickness of the single-layer porous gallium nitride layer 2b is 30~300nm, the number of alternating periods of the porous DBR reflective layer 2 is 6~40, and the porosity of the porous gallium nitride layer 2b is 20–80%.

[0035] In this embodiment, the dense gallium nitride layer 2a is a lightly doped gallium nitride layer, and the porous gallium nitride layer 2b is obtained by electrochemical treatment of a heavily doped gallium nitride layer; the doping concentration of the heavily doped gallium nitride layer is at least one order of magnitude higher than that of the lightly doped gallium nitride layer. Specifically, the doping concentration of the lightly doped gallium nitride layer is 1×10^17–5×10^18 cm^2. - ³; The doping concentration of the heavily doped gallium nitride layer before electrochemical treatment is 1×10^19–5×10^20 cm⁻¹ - ³.

[0036] In this invention, the porous DBR reflective layer 2 is formed by alternating epitaxial growth of lightly doped gallium nitride layers and heavily doped gallium nitride layers, and then obtained by electrochemical treatment.

[0037] Specifically, lightly doped gallium nitride (GaN) layers and heavily doped GaN layers are first stacked alternately on a gallium nitride substrate 1. During electrochemical treatment of the heavily doped GaN layer, the dopant elements are preferentially displaced to form pores. Therefore, the lightly doped GaN layer serves as a dense GaN layer 2a, and the heavily doped GaN layer, after electrochemical treatment, serves as a porous GaN layer 2b. In this embodiment, both the lightly and heavily doped GaN layers generally use Si as the dopant element, with a Si doping concentration of 1×10^17–5×10^18 cm⁻¹ in the lightly doped GaN layer. - ³, the Si heavy doping concentration in the heavily doped gallium nitride layer is 1×10^19–5×10^20 cm⁻¹ - ³. The thickness of the single-layer dense gallium nitride layer 2a or the porous gallium nitride layer 2b is 30–300 nm, with an alternation period of 6–40. The optical thickness (physical thickness × refractive index) of each lightly doped gallium nitride layer and the heavily doped gallium nitride layer is typically designed to be one-quarter of the target wavelength. When light is reflected at the interface, the optical path difference is exactly an integer multiple of half the wavelength, resulting in mutual reinforcement of the reflected light.

[0038] The active light-emitting layer 5 is a single quantum well or a double quantum well. In this invention, the active light-emitting layer 5 includes N pairs of quantum wells, where N≤2, and preferably a single quantum well (SQW) or a double quantum well (DQW). Multiple quantum well (MQW) structures can lead to uneven carrier distribution between different wells, causing band fluctuations and spectral broadening. Using a single quantum well (SQW) or a very small number of quantum wells can reduce carrier transport time, improve response speed, reduce spectral broadening, improve light purity, and reduce signal distortion during transmission.

[0039] To further explain, a single quantum well (SQW) consists of a first GaN barrier layer, an InGaN well layer, and a second GaN barrier layer formed sequentially; a double quantum well (DQW) consists of a first GaN barrier layer, a first InGaN well layer, a second GaN barrier layer, a second InGaN well layer, and a third GaN barrier layer formed sequentially.

[0040] In this embodiment, the top reflective layer 7 is a mesh metal layer with an opening ratio of 70-95%. The mesh metal layer can also adjust the light emission angle, reduce the light emission range, and improve the directionality of the light.

[0041] The holes in the top reflective layer 7 (mesh metal layer) can be square. (See reference) Figure 6 The holes in the top reflective layer 7 (mesh metal layer) can also be rhomboid. Alternatively, the holes in the top reflective layer 7 (mesh metal layer) can be regular hexagons, pentagons, octagons, etc. The linewidth of the mesh metal layer in the top reflective layer 7 is 0.3–5 μm, the thickness of the reflective metal layer is 50–1500 nm, and the equivalent reflectivity is 10–60%. The top reflective layer 7 of this invention provides a preset equivalent reflectivity and cavity mirror phase modulation in the 460–470 nm or 535–540 nm wavelength band. The mesh metal layer of this invention is formed by a lift-off process or an electroplating process. The first metal layer is nickel (Ni), and the second metal layer is gold (Au).

[0042] The present invention also discloses a Bulk GaN vertical resonant cavity light-emitting device 100, including an epitaxial structure, an electrode electrically connected to the epitaxial structure, and a microlens 9 formed on the top reflective layer 7 in the epitaxial structure.

[0043] Specifically, the electrode includes a first electrode formed on the back side of the gallium nitride substrate 1 or connected to the n-type epitaxial layer, and a second electrode formed above the p-type epitaxial layer and connected to the p-type epitaxial layer.

[0044] refer to Figure 3 When the top reflective layer 7 is a mesh metal layer, it is directly used as the second electrode. Of course, there are other variations; see reference [link to reference]. Figure 4 An independent second electrode 13 is formed on the P-type epitaxial layer, and an external electrode 14 is formed on the top reflective layer 7. The second electrode 13 and the external electrode 14 are then electrically connected through the top reflective layer 7, or through other electrical connection structures. When the top reflective layer 7 is electrically connected to the second electrode, or when the top reflective layer 7 is directly used as the second electrode, the top reflective layer 7 can perform current spreading. (Reference) Figure 4 In this embodiment, a passivation layer 11 is covered on the P-type epitaxial layer, and a transparent dielectric layer 12 is formed on the passivation layer 11. The second electrode 13 passes through the passivation layer 11 and the transparent dielectric layer 12 and is connected to the p-type epitaxial layer 6. A top reflective layer 7 is formed on the transparent dielectric layer 12 and is electrically connected to the second electrode 13. The top reflective layer 7 can be directly electrically connected to the second electrode 13 or can be electrically connected to the second electrode 13 through a metal interconnect structure.

[0045] refer to Figure 5 The present invention also discloses a light output array, including multiple Bulk GaN vertical cavity light-emitting devices 100 as described above. These Bulk GaN vertical cavity light-emitting devices 100 are arranged in a matrix at a certain spacing on a carrier plate 200. The matrix shape can be rectangular, honeycomb (regular hexagon / octagonal), or circular. The spacing between adjacent Bulk GaN vertical cavity light-emitting devices 100 is 10-80 μm. In Example 1, the Bulk GaN vertical cavity epitaxial structure is suitable for blue light emission in the 460–470 nm wavelength band of GaN material systems. The specific parameters for the top reflective layer 7 and the porous DBR reflective layer 2 are set as follows: linewidth of the top reflective layer 7 is 0.5–2.5 µm; spacing between adjacent parallel grid lines of the top reflective layer 7 is 3–12 µm; porosity is 85–95%; and thickness is 100–600 nm. The thickness of the monolayer dense gallium nitride layer 2a is 30–300 nm, and the thickness of the monolayer porous gallium nitride layer 2b is also 30–300 nm. The number of alternation periods in the porous DBR reflective layer 2 is 10–28; the porosity of the porous gallium nitride layer 2b is 40–75%. Both lightly doped and heavily doped gallium nitride layers generally use Si as a dopant element, with a light Si doping concentration of 1 × 10^17–5 × 10^18 cm⁻¹. - ³, Si heavy doping concentration is 1×10^19–5×10^20 cm⁻¹ - ³. The spacing between adjacent Bulk GaN vertical resonant cavity light-emitting devices is 10-40 μm.

[0046] In Example 2, the Bulk GaN vertical resonant cavity epitaxial structure is suitable for light emission in the 535–540 nm green light band of the GaN material system. The specific parameters for the top reflective layer 7 and the porous DBR reflective layer 2 are set as follows: linewidth of the top reflective layer 7: 0.5–4 µm; spacing between adjacent parallel grid lines of the top reflective layer 7: 5–25 µm; porosity: 75–93%; thickness: 100–1000 nm. The thickness of the monolayer dense gallium nitride layer 2a is 30–300 nm, the thickness of the monolayer porous gallium nitride layer 2b is 30–300 nm, the alternation period number of the porous DBR reflective layer 2 is 12–35, and the porosity of the porous gallium nitride layer 2b is 30–70%. The lightly doped gallium nitride layer and the heavily doped gallium nitride layer generally use Si doping element, with a light Si doping concentration of 1×10^17–5×10^18 cm⁻¹. - ³, Si heavy doping concentration is 1×10^19–5×10^20 cm⁻¹ - ³. The spacing between adjacent Bulk GaN vertical resonant cavity light-emitting devices is 20-80 μm.

[0047] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the scope of the present invention are still within the scope of the present invention.

Claims

1. A Bulk GaN vertical resonant cavity epitaxial structure for high-speed optical communication, characterized in that, include: A gallium nitride substrate, wherein a porous DBR reflective layer, an n-type epitaxial layer, an active light-emitting layer, a p-type epitaxial layer and a top reflective layer are sequentially formed on the gallium nitride substrate. The porous DBR reflective layer, the n-type epitaxial layer, the active light-emitting layer and the p-type epitaxial layer are all nitride epitaxial layers. The porous DBR reflective layer and the top reflective layer are positioned opposite each other to form an optical resonant cavity.

2. The Bulk GaN vertical resonant cavity epitaxial structure according to claim 1, characterized in that: The gallium nitride substrate is nonpolar or semipolar.

3. The Bulk GaN vertical resonant cavity epitaxial structure according to claim 1, characterized in that: The top reflective layer is a mesh metal layer, which includes a first metal layer and a second metal layer deposited sequentially, and the porosity of the mesh metal layer is 70–95%.

4. The Bulk GaN vertical resonant cavity epitaxial structure according to claim 3, characterized in that: The linewidth of the mesh metal layer is 0.3–5 μm, the thickness of the mesh metal layer is 50–1500 nm, the spacing between adjacent parallel mesh lines of the mesh metal layer is 3–30 µm, and the equivalent reflectivity is 10–60%.

5. The Bulk GaN vertical resonant cavity epitaxial structure according to claim 1, characterized in that: The porous DBR reflective layer comprises a cross-stacked dense layer and a porous layer, wherein the dense layer is a dense gallium nitride layer and the porous layer is a porous gallium nitride layer.

6. The Bulk GaN vertical resonant cavity epitaxial structure according to claim 5, characterized in that, The thickness of the single-layer dense gallium nitride layer is 30~300nm, the thickness of the single-layer porous gallium nitride layer is 30~300nm, the number of alternation periods of the porous DBR reflective layer is 6~40, and the porosity of the porous gallium nitride layer is 20–80%.

7. The Bulk GaN vertical resonant cavity epitaxial structure according to claim 5, characterized in that, The dense gallium nitride layer is a lightly doped gallium nitride layer, and the porous gallium nitride layer is obtained by electrochemical treatment of a heavily doped gallium nitride layer; the doping concentration of the heavily doped gallium nitride layer is at least one order of magnitude higher than that of the lightly doped gallium nitride layer.

8. The Bulk GaN vertical resonant cavity epitaxial structure according to claim 7, characterized in that, The dense gallium nitride layer is a lightly doped gallium nitride layer with a doping concentration of 1×10^17–5×10^18 cm⁻¹. - ³; The porous gallium nitride layer is obtained by electrochemical treatment of a heavily doped gallium nitride layer. The doping concentration of the heavily doped gallium nitride layer before electrochemical treatment is 1×10^19–5×10^20 cm⁻¹ - ³.

9. The Bulk GaN vertical resonant cavity epitaxial structure according to claim 1, characterized in that: The active light-emitting layer is a single quantum well or a double quantum well.

10. A Bulk GaN vertical resonant cavity light-emitting device, characterized in that: It includes an epitaxial structure, electrodes, and a microlens formed above the top reflective layer in the epitaxial structure, wherein the epitaxial structure is a Bulk GaN vertical resonant cavity epitaxial structure for high-speed optical communication as described in any one of claims 1-9.

11. An optical output array, characterized in that: It includes a carrier plate and a plurality of light-emitting devices arranged in an array on the carrier plate, wherein the light-emitting devices are Bulk GaN vertical resonant cavity light-emitting devices as described in claim 10.

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