Major role of intrinsic defects in optical and electrical properties adopting a highly defect-controlled photoconductivity in spin-coated α-MoO₃ thin films gained after UV illumination

Abstract

Spin-coated MoO3 thin films were subsequently subjected to later thermal treatment (LTT) at different temperatures. The x-ray diffraction (XRD) results corroborated that the produced films crystallise in their α-phase with layer structure featured by preferential orientations along the (0k0) planes, and it was also revealed that the thermal energy gained by the later heat treatment plays a major role in enhancing crystallinity enlarging crystallite size. The optical spectroscopic analysis showed that in the visible and near-infrared regions, the average transmission of the film samples remarkably increases with increasing the LTT temperature, whereas the films prepared at 625 °C exhibits an average optical transmission of 79.92%. The optical bandgaps of the film samples were calculated to be of comparable values to the bulk one of α-MoO3 when increasing the LTT temperature from 375 to 525 °C, but it was found to be little greater than the bulk value by further increase in the LTT temperature. The DC electrical results revealed that raising the LTT temperature significantly enhances the electrical resistivity of the film samples, chiefly over the low working-temperatures. These results ascertained the realization of more than one conduction mechanism with different activation energies for the same film, and ramarkable upswings in activation energies were observed by increasing the LTT temperature. The photoconductivity (PC) analysis indicated the occurrence of various trapping processes associated with different photoexcitation energies. The PC analysis also corroborated that the highly resistive thin films exhibit much greater sensitivity to UV illumination compared with the remaining films, whereas the film prepared at the LTT temperature 625 °C presents the higher illumination current at the steady state condition exceeding the dark current value by a factor of 66.01.