Al x Ga1- x N Ultraviolet Avalanche Photodiodes With Avalanche Gain Greater Than [Formula Omitted]

Ultraviolet (UV) avalanche photodiodes (APDs) based on Al x Ga1- x N wide-bandgap semiconductor alloys ([Formula Omitted]) are reported. The epitaxial structure was grown by metalorganic chemical vapor deposition on a GaN substrate having a low dislocation density. Step graded n-type Si-doped Al x Ga1- x N layers ([Formula Omitted] and 0.02) were introduced instead of a thick n-Al0.05Ga0.95N:Si layer to minimize strain-induced defects and crack formation, resulting in reduced leakage current densities of the devices with various circular mesa diameters. Under UV illumination at [Formula Omitted] nm, high avalanche gains greater than [Formula Omitted] were achieved at reverse biases of [Formula Omitted] V for the APDs with mesa diameters of 30-[Formula Omitted]. In addition, significantly increased spectral responsivities of devices having a 70-[Formula Omitted] mesa diameter was observed at reverse biases of [Formula Omitted] V, indicating the device approaches to avalanche multiplication.