An improved design for AlGaN solar-blind avalanche photodiodes with enhanced avalanche ionization

To enhance the avalanche ionization, we designed a new separate absorption and multiplication AlGaN solar-blind avalanche photodiode (APD) by using a high/low-Al-content AlGaN heterostructure as the multiplication region instead of the conventional AlGaN homogeneous layer. The calculated results show that the designed APD with Al_0.3Ga_0.7N/Al_0.45Ga_0.55N heterostructure multiplication region exhibits a 60% higher gain than the conventional APD and a smaller avalanche breakdown voltage due to the use of the low-Al-content Al_0.3Ga_0.7N which has about a six times higher hole ionization coefficient than the high-Al-content Al_0.45Ga_0.55N. Meanwhile, the designed APD still remains a good solar-blind characteristic by introducing a quarter-wave AlGaN/AlN distributed Bragg reflectors structure at the bottom of the device.