Investigation of back-illuminated AlGaN avalanche photodiodes with p-type graded AlxGa1-xN layer

The AlGaN avalanche photodiodes (APDs) with a p-type graded AlGaN layer has been designed to investigate the polarization doping effect on the performance of the AlGaN APDs. The calculated results show that the APD with p-type graded AlGaN layer exhibits lower avalanche breakdown voltage and increased maximum multiplication gain compared with the conventional structures. The improved performances of the designed APDs are due to the polarization-assisted enhancement of the ionization electric field at the point of maximum multiplication gain. The spectral responsivity and distribution of electric field for the specific APDs are investigated numerically to explain the superior performances.