Fine Control of the Electric Field Distribution in the Heterostructure Multiplication Region of AlGaN Avalanche Photodiodes

To enhance avalanche ionization, we designed a new separate absorption and multiplication AlGaN solar-blind avalanche photodiode (APD) by replacing the conventional AlGaN homogeneous multiplication region with a high/low Al content AlGaN heterostructure layer. The calculated results showed that the improved APD with the Al0.3Ga0.7N/Al0.45Ga0.55N heterogeneous multiplication region exhibits 51% higher gain than that of the conventional APD, benefiting from the six times higher hole ionization coefficient of Al0.3Ga0.7N, compared to that of Al0.45Ga0.55N. Furthermore, we inserted an intermediate n-type AlGaN charge layer into the heterogeneous multiplication region to obtain superior performance by finely controlling the electric field distribution. The dependence of breakdown voltage and multiplication gain on the Al content, doping concentration, and thickness of the charge layer is studied in detail to get the optimal structure. Meanwhile, the solar-blind characteristic is also taken into account when optimizing the APD structure.