Response of ultra-low dislocation density GaN photodetectors in the near- and vacuum-ultraviolet

The spectral response of metal-semiconductor-metal (MSM) and Schottky barrier photodiodes have been studied in the near- and vacuum ultraviolet (VUV). Devices were fabricated on micro-epitaxial lateral overgrowth GaN layers, which presented dislocation densities as low as $7×107 cm−2.$ Experimental results indicate that the surface properties become critical for the optical response at short wavelengths. Schottky barrier photodiodes showed a lower VUV sensitivity than MSMs as a result of the radiation absorption in the semitransparent Au top-layer. However, Schottky photodiodes yielded a better time stability operating in photovoltaic mode. For photon energies above 10.5 eV, the quantum efficiency of the MSM photodiodes was enhanced as a consequence of the different nature of light-semiconductor interactions, which provoke a decrease of the absorption coefficient and the generation of multiple electron-hole pairs for each impinging photon. The ionization energy for GaN has been also estimated.