Influence of annealing on microstructure and optical properties of hot wall deposited PbxSn(1−x)S thin films

Abstract

PbxSn(1 − x)S (0.05 < x < 0.20) thin films with the thickness of 2 μm were deposited on glass substrates using hot wall vacuum deposition method at the vacuum pressure of 5 × 10−4 Pa, wall temperature of 600°С, substrate temperature of 300°С and subsequently annealed at 450 °C in vacuum at 5 × 10−4 Pa. The microstructure and optical properties of the as-deposited and annealed films were examined in relation to the film composition. The explanations of lattice parameter deviations from the bulk crystals for both as-deposited and annealed PbxSn(1 − x)S thin films are discussed. The PbxSn(1 − x)S thin films exhibit a preferred orientation around the [111] direction. The annealing decreases the film microstrain values and increases the grain size and the degree of preferred orientation. Thermal probe measurements showed the sulfur-deficient films to be p-type and the sulfur-rich films to be n-type. The PbxSn(1 − x)S films exhibit direct allowed transitions with energy band gap Eg(d) increasing with the increase of Pb mole fraction. The Eg(d) values for as-deposited films range from 0.95 to 0.98 eV and for annealed films they variy from 0.90 to 0.94 eV.