Conductive ZnS:Zn thin films grown by molecular beam deposition

Thin films of ZnS, with varying concentrations of Zn, have been grown onto p−-Si using the molecular beam deposition method. By increasing the Zn content, a rise in the conductivity is seen and a peak is achieved. With too much Zn, however, the conductivity reduces quickly. The most conducting film forms an ohmic contact with the p−-Si substrate. Calculation of the Fermi energy in this device shows that the Fermi level lies at 0.11 eV below the conduction band. The less conducting material is found to form a pseudoSchottky barrier at the p−-Si interface. The conduction process is thought to occur due to an excess of S vacancies (donor sites) compared to Zn vacancies (acceptor sites). The addition of Zn seems to reduce the effect of autocompensation, usually a hindrance in the fabrication of conducting ZnS films.