Orthorhombic undoped k-Ga2O3 epitaxial thin films for sensitive, fast, and stable direct X-ray detectors

Photoelectronic properties of orthorhombic undoped k-Ga2O3 epitaxial thin films, grown on sapphire substrates by metal-organic vapour phase epitaxy, were evaluated under X-ray irradiation (CuKa line, 8.05 keV) for the first time. Photoresponse linearity at low dose-rates (varying in the 10-200 uGy s-1 range), and excellent detection sensitivity (up to 342.3 uC Gy-1 cm-3), were demonstrated even at very low applied electric fields (down to 0.001 V um-1). Photocurrent rise time was evaluated to be <0.5 s, and signal stability was assessed for exposure times up to 2 h, highlighting no degradation of the performance. These encouraging results, mostly due to the extremely low dark current measured (in the pA range), suggest that orthorhombic undoped k-Ga2O3 is a promising material for the fabrication of sensitive and stable large-area X-ray detectors with minimum power consumption.