Temperature-dependent phase transition of CuZnS thin films and its effects on morphological, optical and electrical properties

Abstract

Herein we report on the structural transitions of CuZnS (CZS) thin films with respect to annealing temperature, and its effects on their electrical and optical properties. The films were deposited by thermal evaporation technique from cubic CZS powders. The as-deposited CZS films are amorphous. However, raising the annealing temperature increase their crystallinity and phase transitions were induced between 200°C and 300°C. Phase transitions from covellite to chalcocite phases of Cu2-xS and/or cubic to hexagonal occurred. In addition, vibrational modes of CZS films observed by Raman spectroscopy revealed that the phase transitions might ensue a blue shift and that the S-S stretching peaks tend to have an asymmetric shape with reduction in intensity, which is associated with the defects induced by phase transition. Furthermore, the electrical properties of CZS films are influenced by grain size variations and phase transition defects in the lattice. Optical properties show that the amorphous film has higher absorption density than the crystalline films. On the other hand, annealing temperature increment amalgamated grains growth, and thus absorption density is increased from lower to higher temperature. The estimated band gap values varied between 1.6 eV and 2.3 eV. Temperature-induced coalescence of the smaller grains modified the morphology to flake shapes.