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 0.78eV, respectively. With an incident wavelength of 370nm and 1V 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 0.13A/W, respectively. From transient response measurement, it was found that time constant τ of the fabricated photodetectors was 22ms. For a given bandwidth of 100Hz and 1V applied bias, we found that noise equivalent power and corresponding detectivity D* were 6×10^-13 W and 1.18×10¹² cm Hz^0.5/W, respectively.