Experimental determination of electron and hole impact ionization coefficients in GaN avalanche photodiodes

In this study, we experimentally determined the impact ionization coefficients of GaN using p–i–n avalanche photodiodes with a hybrid mesa structure. Single-carrier-type initiation was achieved using two optical-window configurations based on the same hybrid-mesa p–i–n architecture, enabling p-side illumination for electron injection and n-side illumination for hole injection. The electron and hole impact ionization coefficients were obtained as α (E) = 2.22 × 106 exp(−1.64 × 107/E) cm−1 and β (E) = 1.58 × 105 exp(−3.29 × 106/E) cm−1, respectively, over the electric field range from 2.2 to 2.8 MV/cm. The results show that the impact ionization coefficient of holes is substantially greater than that of electrons (β/α > 10 at 2.5 MV/cm), indicating the advantage of hole-initiated avalanche multiplication for GaN-based avalanche photodiodes.