An Improved Design for Solar-Blind AlGaN Avalanche Photodiodes

To enhance the impact ionization coefficient of holes, we proposed an improved solar-blind AlGaN avalanche photodiode (APD) structure by using a low-Al-composition AlGaN multiplication layer and a filter based on periodic photonic crystal together with a composition graded interlayer between separate absorption and multiplication regions. The simulation results show that the improved APD presents a lower breakdown voltage and dark current, and a higher optical gain when compared to its conventional counterpart. Further, we found that the composition graded interlayer can modify profitably energy-band profile of heterostructure interfaces besides adjusting the electric field distribution, which is beneficial to the injection of holes from the absorption region to multiplication region. Therefore, we optimized the doping concentration and thickness of the interlayer, and analyzed the effects of these parameters on the APD performances.