Multiplication width dependent avalanche characteristics in GaN/4H-SiC heterojunction avalanche photodiodes

A Monte Carlo model using random ionization path lengths describing the carriers quantum transport in thin gallium nitride/silicon carbide (GaN/4H-SiC) heterojunction avalanche photodiodes (HAPDs) for ultraviolet detection is developed. This work simulated the multiplication gain and excess noise factor at multiplication width of w = 0.05 µm, 0.1 µm, 0.2 µm, 0.3 µm and 0.48 μm for both electron- and hole-initiated multiplication incorporating the dead space effect and hetero-interface effects on impact ionization coefficients and carrier feedback process at high electric field region. The carriers injected into the first layer undergo multiplication with material dependent electron and hole impact ionization coefficients α₁ and β₁. After traversing the first layer, the carriers enter the second layer based on their probability to cross the heterojunction. The carriers enter the second layer then undergoes the multiplication with α₂ and β₂ depending on material in second layer. The avalanche characteristics for different multiplication width ratio of GaN to 4H-SiC in multiplication region are investigated. Our work shows that the excess noise can be reduced by manipulating the multiplication width ratio of GaN to 4H-SiC in multiplication region. The hole-initiated 4H-SiC/GaN APDs with 0.9w 4H-SiC and 0.1w GaN demonstrates the lowest noise besides higher gain with lower applied voltage.