Epitaxial structure for avalanche photodetector

Abstract

The application 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. By inserting the diffusion stop layer with a proper thickness, two P-type doped regions with different concentrations and depths and sharp edges can be formed under the same diffusion condition. The process flow is simplified under the premise of ensuring that the target is reached.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductors, and particularly relates to an avalanche photodetector epitaxial structure. BACKGROUND

[0002] The avalanche photodiode (APD) has a significant technical advantage and wide application potential due to its excellent photoelectric conversion efficiency under low illumination conditions. Specifically, in a long-distance optical communication system, the APD can efficiently detect weak optical signals, ensuring high-speed and stable data transmission, thereby significantly improving the overall performance of the system. In laser radar (LiDAR) applications, its high sensitivity and fast response characteristics enable it to achieve accurate detection and ranging of distant targets, and is widely used in autonomous driving, three-dimensional mapping, and remote sensing detection. In terms of spectral analysis, the APD can effectively detect low-intensity spectral signals, providing a high signal-to-noise ratio detection method for chemical sensing, environmental monitoring, and material identification. In addition, in biomedical imaging, the high gain and low noise characteristics of the APD enable the imaging system to maintain high spatial resolution and detection sensitivity under extremely low light conditions, providing key image support for precision medicine and clinical diagnosis. As can be seen, the APD has an irreplaceable position in the fields of optical communication, laser radar, spectral detection, and biomedical imaging.

[0003] In the preparation process of the APD, the formation of the p-type region is crucial, and zinc (Zn) diffusion is a key process for realizing the doping of this region. Zn is chosen as the p-type dopant mainly because it can provide stable acceptor characteristics in III-V compound semiconductors (such as InGaAs / InP) as a group II element, and has good diffusion controllability and process compatibility. By precisely controlling the diffusion temperature, time, and atmosphere environment, localized and deep doping of Zn atoms into the active region of the device can be achieved, thereby precisely controlling the junction depth, steepness, and doping concentration distribution of the p-n junction. The diffusion quality directly determines the avalanche breakdown voltage, dark current level, noise coefficient, and gain uniformity of the APD, and is a core manufacturing link for realizing high responsivity and low leakage current devices. In contrast, other doping methods such as ion implantation can easily cause lattice damage, and defects are difficult to completely eliminate after annealing, while Zn diffusion can form high-quality p-type regions under lower damage conditions, which is beneficial to improving the reliability and yield of the device. Therefore, the Zn diffusion process needs to have very high process consistency and controllability, and the optimization degree is directly related to the final performance and production stability of the APD.

[0004] At present, Zn has a high diffusion coefficient in InP material, resulting in that secondary diffusion further extends on the basis of the junction depth formed by primary diffusion, so that the accurate control of the final junction depth and doping profile faces severe challenges. In addition, the process must rely on two independent photolithography steps, which significantly increases the process complexity and manufacturing cost, thereby becoming an important factor restricting the development and cost control of APD products. SUMMARY

[0005] In view of this, the present application provides an avalanche photodetector epitaxial structure, which solves the problem of difficult control of Zn diffusion depth by improving the epitaxial structure, realizes accurate control of P-type doping depth, reduces the development cost of APD process, and improves the yield and stability.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] The present application 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, wherein the diffusion stop layer is an intrinsic InP epitaxial layer.

[0008] Preferably, the thickness of the diffusion stop layer is 50-200nm.

[0009] Preferably, in the intrinsic InP epitaxial layer, the effective supply amount of phosphorus source is 6 times that of indium source.

[0010] Preferably, the substrate comprises a 2, 3, 4, 6-inch N-type Si-doped InP substrate, and the doping concentration is 1e17-2e18cm -3 .

[0011] Preferably, the buffer layer is an N-type Si-doped InP epitaxial layer, and the doping concentration of Si is 1e18-3e18cm -3 ; and / or,

[0012] The thickness of the buffer layer is 100-1000nm.

[0013] Preferably, the absorption layer comprises an intrinsic InGaAs epitaxial layer; and / or,

[0014] The thickness of the absorption layer is 1000-4000nm; and / or,

[0015] The lattice mismatch degree of the absorption layer is ≤±500ppm.

[0016] Preferably, the transition layer comprises an intrinsic InGaAsP epitaxial layer; and / or,

[0017] The transition layer comprises a single-component single-layer InGaAsP, a gradually-changing-component InGaAsP or a multi-layer gradient-component InGaAsP; and / or,

[0018] The component of the transition layer comprises In 0.853 Ga 0.147 As 0.31 P 0.69 ; and / or,

[0019] The wavelength of the transition layer is 1050-1550nm.

[0020] Preferably, the charge control layer is an N-type Si-doped InP epitaxial layer, and the doping concentration is 5e16-5e17cm -3 ; and / or,

[0021] The thickness of the charge control layer is 100-200nm.

[0022] Preferably, the cap layer is an intrinsic InP epitaxial layer or an N-type Si-doped InP epitaxial layer, and when the cap layer is an N-type Si-doped InP epitaxial layer, the doping concentration is 1e15-1e16cm -3 ; and / or,

[0023] The thickness of the cap layer is 2000nm-4000nm.

[0024] Preferably, the ohmic contact layer is an intrinsic InGaAsP epitaxial layer; and / or,

[0025] The component of the ohmic contact layer comprises In 0.724 Ga 0.276 As 0.588 P 0.412 ; and / or,

[0026] The thickness of the ohmic contact layer is 50-200nm; and / or,

[0027] The light-emitting wavelength of the ohmic contact layer is 1100-1200nm.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] The present application adds an InP epitaxial layer with high P-vacancy point defects (diffusion stop layer) at the target diffusion depth of the InP epitaxial layer. According to the Zn diffusion interstitial-substitution mechanism, Zn atoms exist in InP in the form of interstitial donors and substitutional acceptors. The two forms are converted due to the number of point defects in InP. Generally, the main defect in n-type or intrinsic InP is group III vacancies, i.e. In vacancies. The existence of In vacancies leads to interstitial donors Zn im+ The substitutional acceptor Zn s - The conversion. While P-vacancies will cause part of the interstitial acceptors to neutralize into V p ZnV p The conversion, another part of the conversion into substitutional acceptors. Namely, the phenomenon of reduced diffusion rate and increased concentration. On this basis, by inserting a high P-vacancy point defect InP epitaxial layer (diffusion stop layer) of appropriate thickness, two P-type doped regions with different concentrations and depths and sharp edges can be formed under the same diffusion conditions. On the premise of ensuring the target, simplify the process flow. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The structure diagram of the avalanche photodetector epitaxial structure provided by an embodiment of the present application.

[0031] The reference signs: 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 DESCRIPTION

[0032] The present application will be further described in conjunction with specific embodiments to make those skilled in the art more clearly understand the present application.

[0033] The avalanche photodiode (APD) has significant technical advantages and wide application potential due to its excellent photoelectric conversion efficiency under low illumination conditions. Specifically, in long-distance optical communication systems, APD can efficiently detect weak optical signals, ensuring high-speed and stable data transmission, thereby significantly improving the overall system performance. In laser radar (LiDAR) applications, its high sensitivity and fast response characteristics enable it to achieve accurate detection and ranging of long-distance targets, and is widely used in autonomous driving, three-dimensional mapping and remote sensing detection fields. In terms of spectral analysis, APD can effectively detect low-intensity spectral signals, providing high signal-to-noise ratio detection means for chemical sensing, environmental monitoring and material identification. In addition, in biomedical imaging, the high gain and low noise characteristics of APD enable the imaging system to maintain high spatial resolution and detection sensitivity under extremely low light conditions, providing key image support for precision medicine and clinical diagnosis. As can be seen, APD has an irreplaceable position in the fields of optical communication, laser radar, spectral detection and biomedical imaging.

[0034] In the preparation process of APD, the formation of p-type region is crucial, and zinc (Zn) diffusion is the key process to realize the doping of the region. Zn is selected as the p-type dopant mainly because it can provide stable acceptor characteristics as a group II element in III-V compound semiconductors (such as InGaAs / InP) and has good diffusion controllability and process compatibility. By precisely controlling the diffusion temperature, time and atmosphere environment, localized and depth-doped Zn atoms can be realized in the active region of the device, so as to accurately control the junction depth, steepness and doping concentration distribution of the p-n junction. The diffusion quality directly determines the avalanche breakdown voltage, dark current level, noise coefficient and gain uniformity of the APD, and is the core manufacturing link to realize high responsivity and low leakage current devices. In comparison, other doping methods such as ion implantation are prone to cause lattice damage, and defects are difficult to completely eliminate after annealing, while Zn diffusion can form high-quality p-type regions under lower damage conditions, which is conducive to improving the reliability and yield of the device. Therefore, the Zn diffusion process needs to have very high process consistency and controllability, and the optimization degree is directly related to the final performance and production stability of the APD.

[0035] At present, Zn has a high diffusion coefficient in InP material, which leads to secondary diffusion that further extends on the basis of the junction depth formed by primary diffusion, making it challenging to accurately control the final junction depth and doping profile. In addition, the process must rely on two independent photolithography steps, significantly increasing the process complexity and manufacturing cost, thus becoming an important factor restricting the development and cost control of APD products.

[0036] To solve the above technical problems, in combination with Figure 1 The present application 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, which are sequentially stacked. The diffusion stop layer 6 is an intrinsic InP epitaxial layer.

[0037] In the above technical solution, the present application does not specifically limit the specific preparation materials and specific preparation steps of the substrate 1, the buffer layer 2, the absorption layer 3, the transition layer 4, the charge control layer 5, the cap layer 7 and the ohmic contact layer 8, as long as the technical effects required by the present 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 flatten the surface, shield the defects of the substrate 1 and improve the epitaxial quality. The absorption layer 3 is used to complete the generation of photo-generated carriers. The function of the transition layer 4 is to relieve the valence band step between InGaAs and InP, reduce the hole injection barrier and interface recombination, and improve the carrier transport and band gap alignment. The charge control layer 5 precisely sets the electric field ratio of the absorption region and the multiplication region through the built-in charge, so that the InP multiplication region obtains a high electric field (only avalanche occurs in InP), while the tunneling current and avalanche triggering of the InGaAs absorption region are inhibited. The cap layer 7 is used to protect the lower structure, as a diffusion window and help to form a stable junction morphology. The ohmic contact layer 8 is used to realize the metal / semiconductor ohmic contact with low contact resistance; the metal system can adopt 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.

[0038] In particular, by setting the diffusion stop layer 6, a high P-vacancy point defect InP epitaxial layer (diffusion stop layer 6) is added at the target diffusion depth of the InP epitaxial layer. According to the Zn diffusion interstitial-substitution mechanism, Zn atoms exist in the form of interstitial donors and substitutional acceptors in InP. These two forms will be converted due to the number of point defects in InP. Generally speaking, the main defect in n-type or intrinsic InP is group III vacancies, i.e. In vacancies. The existence of In vacancies will cause the interstitial donor Zn i m+ to convert into the substitutional acceptor Zn s - . The P-vacancy will cause part of the interstitial acceptor to convert into the neutral compound V p ZnV p , and the other part to convert into the substitutional acceptor. That is, it is embodied in the phenomenon of reduced diffusion rate and increased concentration. On this basis, by inserting a high P-vacancy point defect InP epitaxial layer (diffusion stop layer 6) with a suitable thickness, two P-type doped regions with different concentrations and depths and sharp edges can be formed under the same diffusion conditions. On the premise of ensuring the target, the process flow is simplified.

[0039] Further, the thickness of the diffusion stop layer 6 is 50-200 nm. The thickness range of 50-200 nm achieves the optimal comprehensive effect in the multi-dimensional trade-off of diffusion physics, device electric field, process fluctuation and metal contact: it can provide sufficient P-site vacancy surface density to achieve Zn diffusion self-limiting and sharpening of the doping front, avoid adverse effects on the multiplication region, electrical performance and process compatibility, and ensure that a steep edge, clear deep and shallow double-layer P-type doped region and stable device parameters can be obtained by one diffusion.

[0040] Further, in the intrinsic InP epitaxial layer, the effective supply amount 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 about 6 is the engineering optimum between “obtaining sufficient P-site vacancies to regulate Zn diffusion” and “maintaining excellent crystal quality and surface morphology”: it achieves the required defect engineering target, and ensures the process window width and device consistency.

[0041] In some embodiments, the substrate 1 includes a 2, 3, 4, 6-inch N-type Si-doped InP substrate, with a doping concentration of 1e17-2e18cm -3 .

[0042] In some embodiments, the buffer layer 2 is an N-type Si-doped InP epitaxial layer, with a Si doping concentration of 1e18-3e18cm -3 .

[0043] In some embodiments, the thickness of the buffer layer 2 is 100-1000 nm.

[0044] 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, further, the lattice mismatch degree of the absorption layer 3 is ≤±500 ppm.

[0045] In some embodiments, the transition layer 4 includes an intrinsic InGaAsP epitaxial layer, further, the transition layer 4 includes a single-component single-layer InGaAsP, a gradually changing component InGaAsP or a multi-layer gradient component InGaAsP, further, the component of the transition layer 4 includes In 0.853 Ga 0.147 As 0.31 P 0.69 , and the wavelength of the transition layer 4 is 1050-1550 nm.

[0046] In some embodiments, the charge control layer 5 is an N-type Si-doped InP epitaxial layer, with a doping concentration of 5e16-5e17cm -3 .

[0047] Further, the thickness of the charge control layer 5 is 100-200 nm.

[0048] In some embodiments, the cap layer 7 is an intrinsic InP epitaxial layer or an N-type Si-doped InP epitaxial layer, and when the cap layer 7 is an N-type Si-doped InP epitaxial layer, the doping concentration is 1e15-1e16 cm -3 Further, the thickness of the cap layer 7 is 2000-4000 nm.

[0049] In some embodiments, the ohmic contact layer 8 is an intrinsic InGaAsP epitaxial layer, and further, the composition of the ohmic contact layer 8 includes In 0.724 Ga 0.276 As 0.588 P 0.412 Further, the thickness of the ohmic contact layer 8 is 50-200 nm, and further, the light emission wavelength of the ohmic contact layer 8 is 1100-1200 nm.

[0050] In some embodiments, the method for preparing the avalanche photodetector epitaxial structure 100 includes the following steps:

[0051] 1) On an InP substrate, sequentially grow an n-InP buffer layer 2 of 100 nm, an intrinsic In0.53GaAs absorption layer 3 of 2 μm, an intrinsic InGaAsP transition layer 4 of 30 nm, and an n-type doped InP charge control layer 5 of 100 nm. The process conditions used are metal organic chemical vapor deposition (MOCVD) conventional epitaxial process.

[0052] 2) Grow a high-P-vacancy site defect diffusion stop layer 6, the growth temperature is 550-650℃, the V / III ratio is 6, and the thickness is 200 nm.

[0053] 3) Grow an intrinsic or N-type doped InP cap layer, preferably N-type doped InP, the doping concentration is 1e15 cm -3 , and the thickness is 3 μm.

[0054] 4) Grow an InGaAsP ohmic contact layer 8, the thickness is 200 nm, and the light emission wavelength is 1200 nm.

[0055] After the above steps are all completed, the epitaxial structure growth is completed.

[0056] The doping concentration of the n-type doped InP buffer layer 2 is 3e18 cm -3 , and the doping concentration of the n-type doped InP charge control layer 5 is 1e17 cm -3 .

[0057] In the present application, the specific raw materials not mentioned are already existing substances, which can be directly purchased from the market.

[0058] The above merely preferred embodiments of the present application and are not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An avalanche photodetector epitaxial structure, comprising: The substrate, the buffer layer, the absorbing layer, the transition layer, the charge control layer, the diffusion stopping layer, the cap layer and the ohmic contact layer are sequentially stacked, the diffusion stopping layer is an intrinsic InP epitaxial layer; The thickness of the diffusion stopping layer is 50-200nm; In the intrinsic InP epitaxial layer, the effective supply amount of phosphorus source is 6 times of the indium source; The ohmic contact layer is an intrinsic InGaAsP epitaxial layer; The composition of the ohmic contact layer includes In 0.724 Ga 0.276 As 0.588 P 0.412 ; The thickness of the ohmic contact layer is 50-200nm; The light emitting wavelength of the ohmic contact layer is 1100-1200nm.

2. The avalanche photodetector epitaxial structure of claim 1, wherein, The substrate comprises 2, 3, 4, 6 inch N-type Si-doped InP substrate, the doping concentration is 1e17-2e18cm -3 .

3. The avalanche photodetector epitaxial structure of claim 1, wherein, The buffer layer is an N-type Si-doped InP epitaxial layer, the doping concentration of Si is 1e18-3e18cm -3 ; and / or, The thickness of the buffer layer is 100-1000nm.

4. The avalanche photodetector epitaxial structure of claim 1, wherein, The absorbing layer comprises an intrinsic InGaAs epitaxial layer; and / or, The thickness of the absorbing layer is 1000-4000nm; and / or, The lattice mismatch degree of the absorbing layer is ≤±500ppm.

5. The avalanche photodetector epitaxial structure of claim 1, wherein, The transition layer comprises an intrinsic InGaAsP epitaxial layer; and / or, The transition layer comprises a single-component single-layer InGaAsP, a gradually-changing-component InGaAsP or a multi-layer gradient-component InGaAsP; and / or, The composition of the transition layer includes In 0.853 Ga 0.147 As 0.31 P 0.69 ; and / or, The wavelength of the transition layer is 1050-1550nm.

6. The avalanche photodetector epitaxial structure of claim 1, wherein, The charge control layer is an N-type Si-doped InP epitaxial layer, with a doping concentration of 5e16-5e17cm -3 ; and / or, The thickness of the charge control layer is 100-200nm.

7. The avalanche photodetector epitaxial structure of claim 1, wherein, 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 1e15-1e16cm -3 ; and / or, The thickness of the cap layer is 2000nm-4000nm.

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