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

We compare the performance characteristics of Al 0.05 Ga 0.95 N 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 × 10 5 and a significant increase in the responsivity of UV-APDs grown on a free-standing GaN substrate are observed. We believe that the high crystalline quality of Al 0.05 Ga 0.95 N 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.