Improved performance of AlGaN solar-blind avalanche photodiodes with dual multiplication layers

A back-illuminated separate absorption and multiplication (SAM) solar-blind ultraviolet (UV) avalanche photodiode (APD) with a low-Al-content p-graded AlxGa1-xN layer and a high/low-Al-content heterogeneous dual multiplication region is designed. An n-type insertion layer is inserted between the high/low-Al-content heterostructure dual multiplication region to adjust the polarization electric field between the dual multiplication layers. The AlGaN APD with dual multiplication layers exhibits a high hole ionization coefficient due to the existence of the low-Al-content Al0.3Ga0.7 N layer in the high/low-Al-content heterostructure multiplication region. Furthermore, the polarization effect between the high/low-Al-content AlGaN dual multiplication layers can make the polarization electric field in the dual multiplication layers consistent with the direction of the applied electric field, and the polarization doping effect of the p-type graded AlxGa1-xN layer also helps to reduce the breakdown voltage of the designed APD. The calculation results show that the avalanche multiplication gain and breakdown voltage of the AlGaN solar-blind UV APD with dual multiplication layers is 9.4 x 10(3) and 96.9 V, respectively. It is demonstrated that the gain of the designed APD with dual multiplication layers is 222% higher than that of the conventional APD, and the breakdown voltage is also reduced.