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

Abstract

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 τ 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 6×10−13 W and 1.18×1012 cm Hz0.5/W, respectively.