Structural, electrical, and optical properties of thermally evaporated amorphous Ge_xTe_1-x films

Abstract

Electronmicroscopy, amorphous → crystalline transformation kinetics, electrical resistivity and its temperature and frequency dependence, thermoelectric power (TEP), and optical absorption have been studied in thermally evaporated amorphous Ge_xTe_1-x films. The addition of Te to Ge appears to decrease appreciably the density of voids and associated dangling bonds. Further, the addition of Te increases both the activation energy of conduction at all temperatures and the optical gap. The TEP is positive at all temperatures and varies as the inverse of temperature for large (x < 0.4) concentrations of Te. The various properties of amorphous Ge_xTe_1-x films are understandable in terms of changes in the void structure and formation of random bounds between Ge and Te atoms. The continuous change in the various physical properties with composition together with the structural data published in the literature suggest that amorphous Ge_xTe_1-x films are a random mixture of Ge and Te atoms. There is no clear evidence of the existence of any amorphous compound at any composition, particularly at the compositions Ge_0.5Te_0.5 and Ge_0.33Te_0.67.