Structural, chemical and electrical properties of CdS thin films fabricated by pulsed laser deposition using varying background gas pressure

The present study outlines the evolution of the composition, strain and electrical properties of cadmium sulfide (CdS) thin films deposited via pulsed laser deposition (PLD), under varied chamber pressure ranging from 0.13 to 13.33 Pa. The CdS thin films presented a hexagonal crystalline structure at the various deposition pressures as well as improved crystallinity at higher deposition pressures. The electrical resistivity of the resulting films ranged from 10(-1) to 10(7) Omega-cm for deposition pressures of 2.66 to 10.66 Pa. Such a change is closely related to stoichiometry variations in the CdS films, which comprise an excess of Cd compared to S. This change in chemical composition is accompanied by an increase in deposition rate, a decrease in electrical resistivity and grain size, and a broadening of the longitudinal optical (LO) Raman peak, which indicates structural disorder in the CdS films. This disorder is attributed to defects in the crystalline lattice that manifest as a cadmium excess and/or sulfur vacancy left by the evaporated material at low deposition pressures, due to the increased kinetic energy of depositing species during PLD and the desorption of sulfur.