Evaluation of the chemical, electronic and optoelectronic properties of γ-CuCl thin films and their fabrication on Si substrates

Abstract

CuCl is a I–VII semiconductor material with a direct band gap of ~3.4 eV. It exhibits a zincblende structure (γ-phase) at low temperatures, up to ~680 K. Unlike GaN, ZnO and related materials, CuCl has a relatively low lattice mismatch with Si (<0.4%) and a large excitonic binding energy (~190 meV). This suggests the possibility of the fabrication of excitonic-based blue/UV optoelectronic devices on Si with relatively low threading dislocation densities. In this study, CuCl has been deposited and examined as a candidate material for the fabrication of these devices. X-ray diffraction (XRD) measurements confirmed that the deposited films were preferentially oriented in the (1 1 1) plane. Room temperature photoluminescence measurements reveal a strong Z3 free exciton peak (3.232 eV). Both steady state dc and ac impedance spectroscopy experiments suggested that the deposited CuCl is a mixed ionic–electronic semiconductor material. An electronic conductivity of the order of 2.3 × 10−7 S cm−1 was deduced to be in coexistence with Cu+ ionic conductivity using irreversible electrodes (Au), while a total conductivity of the order of 6.5 × 10−7 S cm−1 was obtained using reversible electrodes (Cu) at room temperature. Further to this, we have identified some of the challenges in fabricating an optoelectronic device based on a CuCl/Si hybrid platform and propose some possible solutions.