Structural and transport properties of CdS films grown on Si substrates

Abstract

Epitaxial films of CdS have been grown on thermally cleaned single‐crystal Si substrates. The films were grown by electron‐beam evaporation of CdS powder in a UHV system. X‐ray Laue and transmission electron diffraction techniques have been used to examine the structure of the films. It has been found that epitaxial growth occurred on (111) substrates at a deposition temperature of approximately 340 °C. Polycrystalline films were obtained at temperatures below 300 °C on (111) substrates. Films grown on (100) substrates were polycrystalline over the range of deposition temperatures 100–390 °C. The electron transport properties of these films have been studied. The Hall mobility measurements of films grown on (111) substrates gave a value of 320 cm²(V sec)⁻¹ for the epitaxial films, decreasing to approximately 100 cm²(V sec)⁻¹ for polycrystalline films grown at 200 °C. For films grown on 〈100〉 substrates the Hall mobility ranged from 60 cm²(V sec)⁻¹ at 200 °C to approximately 90 cm²(V sec)⁻¹ at 340 °C. The electrical resistivity of the epitaxial films was 20 Ω cm and that of the polycrystalline films ranged from 10 to 300 Ω cm. Photoconductivity measurements of these films showed a relatively high trap density extending to greater than 1 eV above the valence band edge. A peak in the response at 800 nm is thought to be due to that of the Cd vacancies.