Gallium Nitride PIN Avalanche Photodiode with Double-step Mesa Structure

Typical gallium nitride (GaN) PIN avalanche photodiodes (APDs) are fabricated using a beveled mesa structure due to the difficulty of the ion-implantation process for GaN. The bevel angle of mesa structure must be very small in order to suppress the localized electric field at the junction sidewall that limits the maximum APD gain. In this study, we proposed a double-step mesa structure that can suppress the high electric field at the junction sidewall while maximizing the electric field strength inside the active region under the avalanche bias condition.