Structure, optical absorption and electrical conductivity of amorphous AsSeGe thin films

Detailed studies on thickness dependence, 100-400 nm, of the optical, elect rical, and structural properties have been carried out on AsSeGe thin film samples prepared by thermal evaporation technique. The optical transmission and reflection spectra of these films were measured in the range of 200-11 00 nm. The mechanism of the optical absorption follows the rule of forbidde n non-direct transition. The band gap E-g, determined from plots of both (a lphah nu ()1/3) and (epsilon")(1/3) versus h nu, was found to increase with film thickness. Real and imaginary parts of the dielectric constant are de termined and it showed apparently little change with film thickness. Activa ted electrical conduction and some of the Mott parameters also showed a dec rease in the density of localized states around the Fermi level with an inc rease in thickness. The results are discussed in terms of the structure of As30Se60Ge10 films by extended X-ray diffraction and in terms of structure factor F(q) and radial distribution function J(r). The J(r) function predic ts the average coordination numbers for three different atoms. Their distan ces to the first coordination sphere have been determined in As30Se60Ge10. (C) 2001 Elsevier Science Ltd. All rights reserved.