GaN Schottky Metal–Semiconductor–Metal UV Photodetectors on Si(111) Grown by Ammonia-MBE

For the development of GaN-based ultraviolet (UV) photodetectors, a simple epilayer structure consisting of GaN (600 nm)/AlN (200 nm) was grown on 100-mm Si substrate using ammonia-molecular beam epitaxy growth technique. The epilayers were crack-free and showed good surface and optical quality. Metal-semiconductor-metal (MSM) interdigitated Schottky-based contacts, fabricated using Ni/Au metallic layers, showed a low dark current of 0.43 nA at 15 V. The analysis of dark current as a function of applied bias revealed that the major current conduction mechanism was through thermionic emission over a Schottky barrier of 0.902 eV. Moreover, the Schottky barrier was found to reduce with the bias, which has been attributed to the image force reduction in the devices. The MSM devices exhibited a peak responsivity of 0.183 A/W at an incident wavelength of 362 nm with a UV/visible rejection ratio of 170. The peak responsivity corresponds to external quantum efficiency of ~70%. The devices also showed good linearity and almost flat responsivity with input power for the applied bias beyond 7 V.