Structural and optical properties of cadmium sulfide thin films modified by hydrogen annealing

This paper provides a systematic study of structural and optical properties of cadmium sulfide (CdS) films annealed under hydrogen (H2) in a wide range of temperatures (200–450°C) and times (3–120min). The aim is to present the properties of the CdS film as a function of hydrogen annealing conditions and to discuss the mechanism behind these changes. The stressed cubic lattice of as-deposited CdS film was relaxed by increasing the temperature and the time of H2 annealing. The surface porosity of CdS films revealed the highest temperature and duration applicable to H2 annealing. The dependence of the band gap as a function of annealing conditions is discussed. The origin of changed optical properties accompanying the shrinkage of the lattice is explained by the incorporation of the hydroxide group on the sulfur site in the CdS lattice during the deposition process and its decomposition after 300°C. A relationship between CdS properties and the decomposition process of Cd(OH)2 to water and CdO during annealing in H2 was established at different low, moderate and high temperatures of annealing.