Study On Gan - Based P-i-n Ultraviolet Detector

Band-gap semiconductors such as GaN and its ternary alloys AlGaN have wide band gap, excellent thermal stability and chemical inertness. These characteristics make it an ideal choice for uses in the field of opto-electronic devices, particularly ultra-violet(UV) photodetectors. Photodetectors operating in the wavelength range of 240～280nm, referred to as the solar-blind region, can be uesed for applications such as missile plume detection, flame detection, and secure-from-earth inter-satellite communications, which attracts intense interest in many countries in recent years.This dissertation topic focuses on the design, fabrication, and characterization of a solar-blind GaN-based p-i-n back-illuminated photodetector with a high temperature AlN template. The major topic focuses on the MOCVD growth of high temperature AlN template layer, the p-type doping of GaN and the fabracation of ohmic contacts to p-GaN.Experiment investigation demonstrates that atomically flat AlN epilayers can be obtained at a low V/III flow ratio without nitridation on the sapphire substrate at 1200℃. High quality n-doped AlGaN layers with high Al content(>0.4) were obtained using the as-grown atomically flat AlN layers. Mg-gradual-δ-doping p-type GaN epilayers are grown on HT-AlN/sapphire, the hole concentration above 5.0×1017cm-3. Analysis of the measurement's results demonstrates that the Mg-gradual-δ-doping process and HT-AlN/sapphire template improve the crystal quality of p-type GaN epilayers and enhace the p-type performace. At the same time, the p-type ohmic contact was investigated with rapid thermal annealing and circuit transmission line model measurement. High quality p-type ohmic contact with specific contact resistance 5.14×10-5Ω·cm2 is obtained by 600℃150 second rapid thermal annealing.A solar-blind GaN-based p-i-n back-illuminated photodetector was fabricated based on the high quality HT-AlN template, p-type GaN layer and p-type ohmic contact. Measurement on the current-voltage and spectral responsivity is carried out, results show that the photodetector is indeed work on solar-blind model with a peak responsivity of 0.0864A/W at 275nm with a 1.5V reverse bias.