| With the development of science and technology, there is a rapid development in ultraviolet (UV) detection. The technology of UV detection can be widely applied. It is playing an important role in military and civilian areas. In military applications, due to the presence of the atmosphere, the UV light which wavelength is shorter than290nm can be absorbed. Then there forms a solar-blind in the Earth’s surface. Due to the solar-blind characteristics, the technology of UV detection with good anti-jamming and privacy is of great significance in the military areas. In the civilian areas, the UV detection technology can be applied in the detection of flame, biomedical analysis, ozone monitoring, sun illumination monitoring, public reconnaissance. Metal-semiconductor-metal (MSM) photodiodes, p-i-n type photodiodes and Schottky type photodiodes are relatively common nitride detectors. The detection efficiency of these detectors is low and there is lack of gain. Those detectors cannot be widely used because the detection efficiency is low and there is less gain. GaN avalanche photodiode (APD) has a higher multiplication factor (up to105), but does not have the solar-blind characteristics. Therefore, the APD based on AlGaN materials with good solar-blind characteristics has more advantages.In this work, we have designed a separate absorption and multiplication (SAM) APD. This article focuses on the simulation and optimization of the structure, preparation and the study of spectral response.The main results are as follows:1.We focused on the optimization design of the n-type layer between the absorption region and the multiplication region and used SILVACO software to simulate the electric field distribution. We found that the doping concentration and thickness of the n-type layer played an important role in the electric field distribution of the entire device. When n1layer is too thin and the doping concentration is too low (eg, thickness of50nm, the doping concentration of2x1017/cm3), or when the nl layer is too thick and the doping concentration is too high (eg, thickness of100nm, the doping concentration of2x1019/cm3), the device electric field will degenerate into the electric field distribution of a pin APD. Then it will fail to reflect the advantages of the SAM structure. We also optimized and adjusted the structural parameters by simulating the current characteristics of the device, the avalanche multiplication factor and the spectral response curve. Analog display devices in the reverse voltage of100V avalanche breakdown with the multiplication factor of8000.2. In the manufacturing process, we optimized and improved the traditional preparation processes. First of all, we explored the optimal annealing conditions to reduce the resistance of the p-type ohmic contact. We found that the metal layer of Ni/Au (20nm/80nm) annealed in the air atmosphere of600℃for12min was more suitable, and the resistance is lowered by3orders of magnitude after annealing comparison. Then we reduced the etching damage by optimizing conditions of the ICP etching(60W of the etching power,20W of RF power). Meanwhile, we reduced the etching damage and surface defects by using hot KOH solution to steep the device for3min after etching. Further, a two-step mesa process was applied, which can effectively reduce the leakage current of the device and prevent the device from the early breakdown.3. Finally, we compare the spectral response curve of the AlGaN-based SAM structure APD and the traditional p-i-n structure APD. We found in the reverse voltage of60V, the responsivity of the SAM structure APD could reach to0.9A/W and the maximum quantum efficiency could reach to383%, higher than the traditional p-i-n structure APD under the same reverse voltage. So SAM structure is more conducive to prepare the AlGaN solar-blind UV APD. |
