Comparison of AlGaN p-i-n ultraviolet avalanche photodiodes grown on free-standing GaN and sapphire substrates

We compare the performance characteristics of Al0.05Ga0.95N UV avalanche photodiodes (APDs) grown on different substrates. UV-APDs grown on a free-standing GaN substrate show lower dark-current densities for all fabricated mesa sizes than similar UV-APDs grown on a GaN/sapphire template. In addition, a stable avalanche gain higher than 5 x 10(5) and a significant increase in the responsivity of UV-APDs grown on a freestanding GaN substrate are observed. We believe that the high crystalline quality of Al0.05Ga0.95N UV-APDs grown on a free-standing GaN substrate with low dislocation density is responsible for the observed low leakage currents, high performance characteirstics, and reliability of the devices. (C) 2015 The Japan Society of Applied Physics