Preparation adn characterization of ZnSe:Al thin films

Thin films of ZnSe: Al were deposited on glass substrates by laser assisted evaporation. Parameters such as crystal structure, optical and electrical properties of the films have been investigated. X-ray diffraction shows that prepared films are polycrystalline with preferred ( 111) orientation and having a zinc blend cubic structure. The lattice constant has been evaluated for ZnSe, the value was found to be 0.56 nm, and the value does not show any appreciable change with the addition of aluminium. From optical measurement, it was found that optical band gap, Eg, decreases on adding Al. The value changes from 2.62 eV ( for ZnSe) to 1.85 eV with 3.0 wt % of Al in the film. Hall effect measurements showed that the films are all n-type and the carrier concentration increases with the increase of Al concentration in the film. DC electrical conductivity may be thermally activated with negligible activation energy only when the Al concentration is lower than 3 wt % at temperature up to 200degreesC, and the transport process may involve hopping of electrons in the localized states near the conduction band edge. However, at higher concentration of Al the process is dominated by usual transition of electrons to the mobility edge. Addition of Al up to 3 wt % does not only increase the electrical conductivity by a factor of 10(2) but also the carrier concentration by a factor of 10(3) which may bring about electron degeneracy at room temperature by dislodging the Fermi level.