Defect control in room temperature deposited cadmium sulfide thin films by pulsed laser deposition

The control of defects in cadmium sulfide thin films and its impact on the resulting CdS optical and electrical characteristics are studied. Sulfur vacancies and cadmium interstitial concentrations in the CdS films are controlled using the ambient pressure during pulsed laser deposition. CdS film resistivities ranging from 10^{- 1} to 10⁴ ω-cm are achieved. Hall Effect measurements show that the carrier concentration ranges from 10¹⁹ to 10¹³ cm^{- 3} and is responsible for the observed resistivity variation. Hall mobility varies from 2 to 12 cm ²/V-s for the same pressure regime. Although the energy bandgap remains unaffected (~ 2.42 eV), the optical transmittance is reduced due to the increase of defects in the CdS films. Rutherford back scattering spectroscopy shows the dependence of the CdS films stoichiometry with deposition pressure. The presence of CdS defects is attributed to more energetic species reaching the substrate, inducing surface damage in the CdS films during pulsed laser deposition.