Optoelectronic characterization of Au/Ni/n-AlGaN photodiodes after annealing at different temperatures

Abstract The optoelectronic characteristics of Ni/Au Schottky photodiodes based on Al 0.35 Ga 0.65 N were investigated. The transmission of the Ni (50 A)/Au (50 A) layer was determined by evaporating it on a quartz substrate. As evaporated, the transmission coefficient in the 200–350 nm wavelength range was found to be 43 to 48%. Annealing at temperatures of up to 400 °C did not influence the transmission coefficient. After annealing at 500 °C, the transmission coefficient increased from 50 to 68% over the 200–350 nm range. The reverse bias current was optimised in terms of annealing temperature and was found to be as low as 1.94×10 −13  A after annealing at 400 °C for a 0.6 mm diameter contact. The Schottky barrier heights increased with annealing temperature reaching as high as 1.46 and 1.89 eV for I – V and C – V measurements, respectively. The quantum efficiency was measured to be 20.5% and the responsivity reached its peak of 0.046 A/W at 275 nm. The cut-off wavelength was 292 nm.