Combinatorial study of the structural, optical, and electrical properties of low temperature deposited Cd1-xZnxTe (0 ≤ x ≤ 1) thin films by MOCVD

Abstract

Polycrystalline Cd1-xZnxTe thin films prepared by a combinatorial MOCVD process were characterised for their structural, optical, and electrical properties. Films became smoother with smaller grains displaying higher sub-bandgap transmittance with increasing x. The X-ray diffraction pattern indicated (111) texture for all films, with increasing compositional inhomogeneity for ternary compositions. Room-temperature optical transmittance and micro-photoluminescence (PL) spectra were analysed to determine the dependence of composition with the bandgap. The non-linear variation of the bandgap with composition was fitted, giving around 0.7 and 0.3 band bowing parameters from optical and PL spectra, respectively. Raman scattering experiments showed that ZnTe-like LO mode varies linearly for x > 0.2. However, Te-related modes (due to surface migration of tellurium) emerge along with the smearing out of parent Raman modes with increasing excitation power. Temporal behaviour of Te modes with excitation power indicated formation of tensile stress due to laser heating. The film resistance increased up to 4 orders of magnitude, corroborating with the semiconductor grain size trend, with increasing Zn concentration. Post-growth annealing of the films in a hydrogen environment above 430 °C decreased the inhomogeneity in ternary alloys, making these films more appealing, for example, for photovoltaic applications.