A1(x)Ga(1-x)N ultraviolet avalanche photodiodes grown on GaN substrates
AlxGa1-xN(x = 0.05) ultraviolet (UV) avalanche photodiodes grown on a GaN substrate are reported. The epitaxial structure was grown by metal-organic chemical vapor deposition on a free-standing bulk GaN substrate having low dislocation density. The growth conditions for AlxGa1-xN epitaxial layers on GaN substrates were optimized to achieve improved crystalline and structural quality. With UV illumination at lambda similar to 250 nm, devices with mesa diameters of similar to 30 mu m achieve stable maximum optical gains of similar to 50 at a reverse bias voltage of similar to 87 V.