Epitaxial structure of avalanche photodetector

Abstract

The invention provides an avalanche photodetector epitaxial structure which comprises a substrate, a buffer layer, an absorption layer, a transition layer, a charge control layer, a diffusion stop layer, a cap layer and an ohmic contact layer which are sequentially stacked, and the diffusion stop layer is an intrinsic InP epitaxial layer. According to the invention, by inserting the diffusion stop layer with a proper thickness, two layers of P-type doped regions with different concentrations and depths and sharp edges can be formed under the same diffusion condition. On the premise of ensuring that the target is achieved, the technological process is simplified.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to an epitaxial structure for an avalanche photodetector. Background Technology

[0002] Avalanche photodiodes (APDs) exhibit significant technological advantages and broad application potential due to their superior photoelectric conversion efficiency under low-light conditions. Specifically, in long-distance optical communication systems, APDs can efficiently detect weak light signals, ensuring high-speed and stable data transmission, thereby significantly improving the overall system performance. In LiDAR applications, their high sensitivity and fast response characteristics enable accurate detection and ranging of distant targets, making them widely used in autonomous driving, 3D mapping, and remote sensing. In spectral analysis, APDs can effectively detect low-intensity spectral signals, providing a high signal-to-noise ratio detection method for chemical sensing, environmental monitoring, and substance identification. Furthermore, in biomedical imaging, the high gain and low noise characteristics of APDs allow imaging systems to maintain high spatial resolution and detection sensitivity even under extremely low light conditions, providing crucial image support for precision medicine and clinical diagnosis. Therefore, APDs hold an irreplaceable position in multiple high-tech fields such as optical communication, LiDAR, spectral detection, and bioimaging.

[0003] In the fabrication of APDs, the formation of the p-type region is crucial, and zinc (Zn) diffusion is a key process for achieving doping in this region. Zn is chosen as the p-type dopant primarily because, as a group II element, it provides stable acceptor properties in group III-V compound semiconductors (such as InGaAs / InP) and exhibits good diffusion controllability and process compatibility. By precisely controlling the diffusion temperature, time, and atmosphere, Zn atoms can be localized and doped to a fixed depth in the active region of the device, thereby precisely controlling the junction depth, steepness, and doping concentration distribution of the pn junction. The quality of this diffusion directly determines the avalanche breakdown voltage, dark current level, noise figure, and gain uniformity of the APD, making it a core manufacturing step for achieving high responsivity and low leakage current devices. In contrast, other doping methods such as ion implantation easily cause lattice damage, and defects are difficult to completely eliminate after annealing. Zn diffusion, however, can form a high-quality p-type region under relatively low damage conditions, which is beneficial for improving device reliability and yield. Therefore, the Zn diffusion process requires extremely high process consistency and controllability, and its optimization level directly affects the final performance and mass production stability of the APD.

[0004] Currently, Zn exhibits a high diffusion coefficient in InP materials, causing secondary diffusion to extend beyond the junction depth established by primary diffusion. This poses a significant challenge to the precise control of the final junction depth and doping profile. Furthermore, this process requires two independent photolithography steps, significantly increasing process complexity and manufacturing costs, thus becoming a major factor restricting the development and cost control of APD products. Summary of the Invention

[0005] In view of this, the present invention provides an epitaxial structure for an avalanche photodetector. By improving the epitaxial structure, the problem of difficult control of Zn diffusion depth is solved, and precise control of P-type doping depth is achieved, thereby reducing the development cost of APD process and improving yield and stability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The present invention provides an epitaxial structure for an avalanche photodetector, comprising a substrate, a buffer layer, an absorption layer, a transition layer, a charge control layer, a diffusion stop layer, a cap layer, and an ohmic contact layer stacked sequentially, wherein the diffusion stop layer is an intrinsic InP epitaxial layer.

[0007] Preferably, the thickness of the diffusion stopping layer is 50-200 nm.

[0008] Preferably, in the intrinsic InP epitaxial layer, the effective supply of phosphorus source is 6 times that of indium source.

[0009] Preferably, the substrate comprises a 2, 3, 4, or 6-inch N-type Si-doped InP substrate with a doping concentration of 1e17-2e18 cm⁻¹. -3 .

[0010] Preferably, the buffer layer is an N-type Si-doped InP epitaxial layer, and the Si doping concentration is 1e18-3e18 cm⁻¹. -3 ; and / or, The thickness of the buffer layer is 100-1000 nm.

[0011] Preferably, the absorption layer comprises an intrinsic InGaAs epitaxial layer; and / or, The thickness of the absorption layer is 1000-4000 nm; and / or, The lattice mismatch of the absorption layer is ≤ ±500ppm.

[0012] Preferably, the transition layer comprises an intrinsic InGaAsP epitaxial layer; and / or, The transition layer comprises a single-component monolayer InGaAsP, a graded-component InGaAsP, or a multilayer gradient-component InGaAsP; and / or The components of the transition layer include In 0.853 Ga0.147 As 0.31 P 0.69 ; and / or, The wavelength of the transition layer is 1050-1550nm.

[0013] Preferably, the charge control layer is an N-type Si-doped InP epitaxial layer with a doping concentration of 5e16-5e17 cm⁻¹. -3 ; and / or, The thickness of the charge control layer is 100-200 nm.

[0014] Preferably, the cap layer is an intrinsic InP epitaxial layer or an N-type Si-doped InP epitaxial layer. When the cap layer is an N-type Si-doped InP epitaxial layer, the doping concentration is 1e15-1e16 cm⁻¹. -3 ; and / or, The thickness of the cap layer is 2000nm-4000nm.

[0015] Preferably, the ohmic contact layer is an intrinsic InGaAsP epitaxial layer; and / or, The ohmic contact layer comprises In 0.724 Ga 0.276 As 0.588 P 0.412 ; and / or, The thickness of the ohmic contact layer is 50-200 nm; and / or, The ohmic contact layer emits light at a wavelength of 1100-1200 nm.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention adds a high-P vacancy defect InP epitaxial layer (diffusion stopping layer) at the target diffusion depth. According to the Zn diffusion interstitial-substitution mechanism, Zn atoms exist in InP in two forms: interstitial donors and substituted acceptors. These two forms can transform depending on the number of point defects in InP. Generally, the main defect in n-type or intrinsic InP is a group III vacancy, i.e., an In vacancy. The presence of In vacancy leads to a faster diffusion rate but a lower concentration of interstitial donor Zn. i m+ Substitute acceptor Zn with slower diffusion rate but higher concentration s - Transformation. P vacancies, however, can cause some interstitial acceptors to convert to neutral compounds like V. p ZnV pThe transformation involves another part: the conversion to a substitute acceptor. This manifests as a decrease in diffusion rate and an increase in concentration. Based on this, by inserting an InP epitaxial layer (diffusion stop layer) of appropriate thickness with high P-vacancy site defects, two P-type doped regions with different concentrations and depths and sharp edges can be formed under the same diffusion conditions. This simplifies the process flow while ensuring the target is achieved. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the epitaxial structure of an avalanche photodetector provided in an embodiment of the present invention.

[0018] Figure reference numerals: avalanche photodetector epitaxial structure 100, substrate 1, buffer layer 2, absorption layer 3, transition layer 4, charge control layer 5, diffusion stop layer 6, cap layer 7, ohmic contact layer 8. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0020] Avalanche photodiodes (APDs) exhibit significant technological advantages and broad application potential due to their superior photoelectric conversion efficiency under low-light conditions. Specifically, in long-distance optical communication systems, APDs can efficiently detect weak light signals, ensuring high-speed and stable data transmission, thereby significantly improving the overall system performance. In LiDAR applications, their high sensitivity and fast response characteristics enable accurate detection and ranging of distant targets, making them widely used in autonomous driving, 3D mapping, and remote sensing. In spectral analysis, APDs can effectively detect low-intensity spectral signals, providing a high signal-to-noise ratio detection method for chemical sensing, environmental monitoring, and substance identification. Furthermore, in biomedical imaging, the high gain and low noise characteristics of APDs allow imaging systems to maintain high spatial resolution and detection sensitivity even under extremely low light conditions, providing crucial image support for precision medicine and clinical diagnosis. Therefore, APDs hold an irreplaceable position in multiple high-tech fields such as optical communication, LiDAR, spectral detection, and bioimaging.

[0021] In the fabrication of APDs, the formation of the p-type region is crucial, and zinc (Zn) diffusion is a key process for achieving doping in this region. Zn is chosen as the p-type dopant primarily because, as a group II element, it provides stable acceptor properties in group III-V compound semiconductors (such as InGaAs / InP) and exhibits good diffusion controllability and process compatibility. By precisely controlling the diffusion temperature, time, and atmosphere, Zn atoms can be localized and doped to a fixed depth in the active region of the device, thereby precisely controlling the junction depth, steepness, and doping concentration distribution of the pn junction. The quality of this diffusion directly determines the avalanche breakdown voltage, dark current level, noise figure, and gain uniformity of the APD, making it a core manufacturing step for achieving high responsivity and low leakage current devices. In contrast, other doping methods such as ion implantation easily cause lattice damage, and defects are difficult to completely eliminate after annealing. Zn diffusion, however, can form a high-quality p-type region under relatively low damage conditions, which is beneficial for improving device reliability and yield. Therefore, the Zn diffusion process requires extremely high process consistency and controllability, and its optimization level directly affects the final performance and mass production stability of the APD.

[0022] Currently, Zn exhibits a high diffusion coefficient in InP materials, causing secondary diffusion to extend beyond the junction depth established by primary diffusion. This poses a significant challenge to the precise control of the final junction depth and doping profile. Furthermore, this process requires two independent photolithography steps, significantly increasing process complexity and manufacturing costs, thus becoming a major factor restricting the development and cost control of APD products.

[0023] To solve the above technical problems, combined with Figure 1 The present invention provides an avalanche photodetector epitaxial structure 100, comprising a substrate 1, a buffer layer 2, an absorption layer 3, a transition layer 4, a charge control layer 5, a diffusion stop layer 6, a cap layer 7, and an ohmic contact layer 8 stacked sequentially, wherein the diffusion stop layer 6 is an intrinsic InP epitaxial layer.

[0024] In the above technical solution, the present invention does not specifically limit the specific materials and preparation steps of the substrate 1, buffer layer 2, absorption layer 3, transition layer 4, charge control layer 5, cap layer 7, and ohmic contact layer 8, as long as the technical effects required by this application can be achieved. The substrate 1 is used to provide a bottom electrode and a lattice matching platform. The buffer layer 2 is used to smooth the surface, shield defects in the substrate 1, and improve the epitaxial quality. The absorption layer 3 is used to complete the generation of photogenerated carriers. The transition layer 4 functions to alleviate the valence band step between InGaAs and InP, reduce the hole injection barrier and interface recombination, and improve carrier transport and bandgap alignment. The charge control layer 5 precisely sets the electric field ratio between the absorption region and the multiplication region through built-in charge, so that the InP multiplication region obtains a high electric field (avalanche only occurs in InP), while suppressing the tunneling current and avalanche triggering in the InGaAs absorption region. The cap layer 7 is used to protect the underlying structure, serve as a diffusion entry window, and help form a stable junction morphology. The ohmic contact layer 8 is used to achieve a metal / semiconductor ohmic contact with low contact resistance; the metal system can be Ti / Pt / Au or Ni / AuZn / Au, etc. This layer can also be used as a p-electrode lead-out layer before and after diffusion.

[0025] In particular, this invention adds a high-P vacancy defect InP epitaxial layer (diffusion stopping layer 6) at the target diffusion depth by setting a diffusion stopping layer 6. According to the Zn diffusion interstitial-substitution mechanism, Zn atoms exist in InP in two forms: interstitial donors and substitution acceptors. These two forms can transform depending on the number of point defects in InP. Generally, the main defect in n-type or intrinsic InP is a group III vacancy, i.e., an In vacancy. The presence of In vacancy leads to a faster diffusion rate but a lower concentration of interstitial donor Zn. i m+ Substitute acceptor Zn with slower diffusion rate but higher concentration s - Transformation. P vacancies, however, can cause some interstitial acceptors to convert to neutral compounds like V. p ZnV p The transformation involves another part: the conversion to a substitute acceptor. This manifests as a decrease in diffusion rate and an increase in concentration. Based on this, by inserting an InP epitaxial layer with a suitable thickness and high P-vacancy site defects (diffusion stop layer 6), two P-type doped regions with different concentrations and depths and sharp edges can be formed under the same diffusion conditions. This simplifies the process flow while ensuring the target is achieved.

[0026] Furthermore, the thickness of the diffusion stop layer 6 is 50-200 nm. The thickness range of 50-200 nm achieves the optimal comprehensive effect under the multi-dimensional trade-off of diffusion physics, device electric field, process fluctuations and metal contact: it can provide sufficient P-site vacancy density to achieve self-limitation of Zn diffusion and sharpening of the doping front, while avoiding adverse effects on the multiplication region, electrical performance and process compatibility, ensuring that a double-layer P-type doped region with steep edges and distinct depths and stable device parameters can be obtained in one diffusion.

[0027] Furthermore, in the intrinsic InP epitaxial layer, the effective supply of phosphorus source is 6 times that of indium source. Setting the effective V / III ratio of the intrinsic InP diffusion stop layer 6 to approximately 6 represents the optimal engineering balance between "obtaining sufficient P-site vacancies to control Zn diffusion" and "maintaining excellent crystal quality and surface morphology": it achieves the desired defect engineering goals while ensuring process window width and device consistency.

[0028] In some embodiments, the substrate 1 comprises a 2, 3, 4, or 6-inch N-type Si-doped InP substrate with a doping concentration of 1e17-2e18 cm⁻¹. -3 .

[0029] In some embodiments, the buffer layer 2 is an N-type Si-doped InP epitaxial layer, and the Si doping concentration is 1e18-3e18 cm⁻¹. -3 .

[0030] In some embodiments, the thickness of the buffer layer 2 is 100-1000 nm.

[0031] In some embodiments, the absorption layer 3 includes an intrinsic InGaAs epitaxial layer; further, the thickness of the absorption layer 3 is 1000-4000 nm; and further, the lattice mismatch of the absorption layer 3 is ≤ ±500 ppm.

[0032] In some embodiments, the transition layer 4 includes an intrinsic InGaAsP epitaxial layer. Further, the transition layer 4 includes a single-component monolayer InGaAsP, a graded-component InGaAsP, or a multilayer gradient-component InGaAsP. Further, the composition of the transition layer 4 includes In... 0.853 Ga 0.147 As 0.31 P 0.69 The wavelength of the transition layer 4 is 1050-1550nm.

[0033] In some embodiments, the charge control layer 5 is an N-type Si-doped InP epitaxial layer with a doping concentration of 5e16-5e17 cm⁻¹. -3 .

[0034] Furthermore, the thickness of the charge control layer 5 is 100-200 nm.

[0035] In some embodiments, the cap layer 7 is an intrinsic InP epitaxial layer or an N-type Si-doped InP epitaxial layer. When the cap layer 7 is an N-type Si-doped InP epitaxial layer, the doping concentration is 1e15-1e16 cm⁻¹. -3 Furthermore, the thickness of the cap layer 7 is 2000nm-4000nm.

[0036] In some embodiments, the ohmic contact layer 8 is an intrinsic InGaAsP epitaxial layer; further, the composition of the ohmic contact layer 8 includes In. 0.724 Ga 0.276 As 0.588 P 0.412 Furthermore, the thickness of the ohmic contact layer 8 is 50-200 nm, and the emission wavelength of the ohmic contact layer 8 is 1100-1200 nm.

[0037] In some embodiments, the method for fabricating the epitaxial structure 100 of the avalanche photodetector includes the following steps: 1) On an InP substrate, a 100 nm n-InP buffer layer 2, a 2 μm intrinsic In0.53GaAs absorber layer 3, a 30 nm intrinsic InGaAsP transition layer 4, and a 100 nm n-type doped InP charge control layer 5 are grown sequentially. The process conditions used are conventional metal-organic chemical vapor deposition (MOCVD) epitaxial processes.

[0038] 2) Growth of a high-P vacancy site defect diffusion stop layer 6, growth temperature 550-650℃, V / III ratio 6, thickness 200nm.

[0039] 3) Grow an intrinsic or N-type doped InP cap layer, preferably N-type doped InP, with a doping concentration of 1e15cm. -3 Thickness 3μm.

[0040] 4) Grow an InGaAsP ohmic contact layer 8 with a thickness of 200 nm and an emission wavelength of 1200 nm.

[0041] Once all the above steps are completed, the epitaxial structure growth is finished.

[0042] The doping concentration of the n-type doped InP buffer layer 2 is 3e18cm. -3 The n-type doped InP charge control layer 5 has a doping concentration of 1e17cm. -3 .

[0043] Unless otherwise specified, all raw materials used in this invention are existing substances that can be purchased directly from the market.

[0044] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An epitaxial structure for an avalanche photodetector, characterized in that, It includes a substrate, a buffer layer, an absorption layer, a transition layer, a charge control layer, a diffusion stop layer, a cap layer, and an ohmic contact layer stacked in sequence, wherein the diffusion stop layer is an intrinsic InP epitaxial layer.

2. The epitaxial structure of the avalanche photodetector according to claim 1, characterized in that, The thickness of the diffusion stopping layer is 50-200 nm.

3. The epitaxial structure of the avalanche photodetector according to claim 2, characterized in that, In the intrinsic InP epitaxial layer, the effective supply of phosphorus source is 6 times that of indium source.

4. The epitaxial structure of the avalanche photodetector according to claim 1, characterized in that, The substrates include 2, 3, 4, and 6-inch N-type Si-doped InP substrates with a doping concentration of 1e17-2e18 cm⁻¹. -3 .

5. The epitaxial structure of the avalanche photodetector according to claim 1, characterized in that, The buffer layer is an N-type Si-doped InP epitaxial layer with a Si doping concentration of 1e18-3e18 cm⁻¹. -3 ; and / or, The thickness of the buffer layer is 100-1000 nm.

6. The epitaxial structure of the avalanche photodetector according to claim 1, characterized in that, The absorption layer includes an intrinsic InGaAs epitaxial layer; and / or, The thickness of the absorption layer is 1000-4000 nm; and / or, The lattice mismatch of the absorption layer is ≤ ±500ppm.

7. The epitaxial structure of the avalanche photodetector according to claim 1, characterized in that, The transition layer includes an intrinsic InGaAsP epitaxial layer; and / or, The transition layer comprises a single-component monolayer InGaAsP, a graded-component InGaAsP, or a multilayer gradient-component InGaAsP; and / or... The components of the transition layer include In 0.853 Ga 0.147 As 0.31 P 0.69 ; and / or, The wavelength of the transition layer is 1050-1550nm.

8. The epitaxial structure of the avalanche photodetector according to claim 1, characterized in that, The charge control layer is an N-type Si-doped InP epitaxial layer with a doping concentration of 5e16-5e17 cm⁻¹. -3 ; and / or, The thickness of the charge control layer is 100-200 nm.

9. The epitaxial structure of the avalanche photodetector according to claim 1, characterized in that, The cap layer is an intrinsic InP epitaxial layer or an N-type Si-doped InP epitaxial layer. When the cap layer is an N-type Si-doped InP epitaxial layer, the doping concentration is 1e15-1e16 cm⁻¹. -3 ; and / or, The thickness of the cap layer is 2000nm-4000nm.

10. The epitaxial structure of the avalanche photodetector according to claim 1, characterized in that, The ohmic contact layer is an intrinsic InGaAsP epitaxial layer; and / or... The ohmic contact layer comprises In 0.724 Ga 0.276 As 0.588 P 0.412 ; and / or, The thickness of the ohmic contact layer is 50-200 nm; and / or, The ohmic contact layer emits light at a wavelength of 1100-1200 nm.

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