High‐gain Zn1–xMgx O‐based ultraviolet photodetectors on Al2O3 and LiGaO2substrates. Issue 1 (2nd December 2014) - Olson, Christopher S.
Abstract We report the fabrication and characterization of highly responsive ZnMgO‐based ultraviolet (UV) photodetectors in the metal–semiconductor–metal (MSM) configuration for solar‐blind/visible‐blind optoelectronic application. MSM devices were fabricated from wurtzite Zn1–xMgx O/ZnO (x ∼ 0.44) thin‐film heterostructures grown on sapphire (α‐Al2O3) substrates and w‐Zn1–xMgx O (x ∼ 0.08), grown on nearly lattice‐matched lithium gallate (LiGaO2) substrates, both by radio‐frequency plasma‐assisted molecular beam epitaxy (PAMBE). Thin film properties were studied by AFM, XRD, and optical transmission spectra, while MSM device performance was analyzed by spectral photoresponse and current–voltage techniques. Under biased conditions, α‐Al2O3 grown devices exhibit peak responsivity of ∼7.6 A/W at 280 nm while LiGaO2 grown samples demonstrate peak performance of ∼119.3 A/W, albeit in the UV‐A regime (∼324 nm). High photoconductive gains (76, 525) and spectral rejection ratios (∼103, ∼104) were obtained for devices grown on α‐Al2O3 and LiGaO2, respectively. Exemplary device performance was ascribed to high material quality and in the case of lattice‐matched LiGaO2 films, decreased photocarrier trapping probability, presumably due to low‐density of dislocation defects. To the best of our knowledge, these results represent the highest performing ZnO‐based photodetectors on LiGaO2 yet fabricated, and demonstrate both the feasibility and substantial enhancement of photodetector device performance via growth on lattice‐matched substrates. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)