ZnO metal-semiconductor-metal ultraviolet sensors with various contact electrodes

ZnO epitaxial films were grown on sapphire (0 0 0 1) substrates by using RF plasma-assisted molecular beam epitaxy. Metal-semiconductor-metal (MSM) sensors with Ag, Pd and Ni contact electrodes were then fabricated. It was found that barrier height at Ag/ZnO, Pd/ZnO and Ni/ZnO interfaces were 0.736, 0.701 and 0.613 eV, respectively. With an incident wavelength of 370 nm and I V applied bias, the maximum responsivity of the Ag/ZnO/Ag, Pd/ZnO/Pd and Ni/ZnO/Ni MSM sensors were respectively 0.066, 0.051 and 0.09A/W, which corresponds to quantum efficiency of 17.3%, 11.4% and 23.8%. For a given bandwidth of lOO Hz and I V applied bias, the noise equivalent power of the fabricated sensors with Ag, Pd and Ni electrodes were estimated to be 6.8 x 10(-13), 1.13 x 10(-12) and 6.4 x 10(-12) W, corresponding to the normalized detectivity (D) of 1.04 x 10(12), 6.25 x 10(11) and 1. 1 x 10(11) cm Hz(0.5)W(-1). (c) 2006 Elsevier B.V. All rights reserved.