Obliquely deposited amorphous Ge films. II. Electrical properties

Abstract

Ac, dc, and high field conductivity and thermoelectric power are studied of normal and obliquely deposited a-Ge films. Basic processes of electronic conduction are qualitatively similar in normal and obliquely deposited films. Oblique deposition results in a decrease of electrical conductivity and density of localized states at the Fermi level and an increase in the activation energy (at and below room temperature) and thermoelectric power. Similar changes are produced on annealing and deposition at elevated temperatures; the magnitude of changes decreases with obliqueness. The high temperature activation energy value of 0.55 eV is independent of the sample history. Also, the low temperature (100 to 400 K) dc conductivity data in all cases fit Mott's variable range hopping relation. The ac conductivity data show an ω_s dependence and the value of s increases with increasing obliqueness. The field dependence of conductivity is nearly the same for normal and oblique incidence films. Considerable changes in the temperature variation of the thermoelectric power are observed with increasing obliqueness. As expected, obliquely deposited films also exhibit an electrical anisotropy which increases with increasing obliqueness. The observed changes in the various electrical properties are interpreted in terms of an asymmetric energy-band diagram.