ZnO metal-semiconductor-metal ultraviolet photodetectors with Iridium contact electrodes

ZnO epitaxial films were grown on sapphire (0001) substrates by using rf plasma-assisted molecular beam epitaxy. Metal-semiconductor-metal (MSM) photodetectors with Iridium (Ir) electrodes were then fabricated. It was found that Schottky barrier heights at the non-annealed and 500-C-annealed Ir/ZnO interfaces were around 0.65 and 0.78-eV, respectively. With an incident wavelength of 370-nm and 1-V applied bias, it was found that the maximum responsivities for the Ir/ZnO/Ir MSM photodetectors with and without thermal annealing were 0.18 and 0.13-A/W, respectively. From transient response measurement, it was found that time constant - of the fabricated photodetectors was 22-ms. For a given bandwidth of 100-Hz and 1-V applied bias, we found that noise equivalent power and corresponding detectivity D- were 6-10.