Photoinduced interdiffusion in nanolayered Se/As2S3 films:: Optical and x-ray photoelectron spectroscopic studies

Photoinduced interdiffusion was observed with above band gap light in nanolayered Se/As2S3 films. It is discussed in terms of the optical parameters such as band gap, Urbach edge (E-e) [F. Urbach, Phys. Rev. 92, 1324 (1953)], and B-1/2 (Tauc's parameter) [J. Tauc , Phys. Status Solidi 15, 627 (1966)]. Experimental data of B-1/2 and E-e for as-prepared samples do not show clear correlation implied by the Mott-Davis model [N. F. Mott and E. A. Davis, Electronic Process in Non-crystalline Materials (Clarendon, Oxford 1979), p. 287]. It is also shown that the optical parameters can be changed with a change in the Se sublayer thickness. Variations of these optical parameters as a function of modulation period and photoinduced interdiffusion were discussed in terms of the quantum confinement effect and changes in the valence and conduction bands. We proposed a model to explain the mechanism of Se diffusion in As2S3, which suggests that diffusion takes place through the wrong bonds. X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical alternations in the bonding. The proposed model was supported by the XPS data. (C) 2006 American Institute of Physics.