AlGaN solar-blind ultraviolet avalanche photodiodes with a p-graded AlxGa1-xN layer and high/low Al-content AlGaN multiplication layer

We design a back-illuminated p–i–n–i–n separate absorption and multiplication (SAM) AlGaN solar-blind avalanche photodiode (APD) with a low Al-content p-graded AlxGa1-xN layer and a high/low Al-content AlGaN multiplication layer. Simultaneously, an III-nitride AlN/Al0.64Ga0.36 N distributed Bragg reflector (DBR) structure is inserted to improve the solar-blind photoresponse for the designed APD. The simulation results show that the designed APD exhibits enhanced optoelectronic characteristics compared to the conventional APD, which is attributed to the higher holes impact ionization coefficient and generated polarization electric field in the same direction as the applied bias field of the designed APD. The designed APD exhibits significant enhanced avalanche gain and reduced avalanche breakdown voltage compared with the conventional APD.