Effect of impurities on the thermoelectric power of amorphous germanium

Abstract

Large and anomalous changes in the thermoelectric power of amorphous (a-) Ge films have been observed on doping with impurities of Al, Fe and Sb. Depending on the concentration, Al and Sb impurities contribute a negative thermoelectric power below 300°K. and a positive thermoelectric power above 300°K. The effect of Fe is very small below 1 at. %. The thermoelectric power attains high temperature-independent positive values for large (> 1 at. %) concentrations of Al. The observed effects of the impurities cannot be understood in terms of the conventional crystalline semiconductor concepts. A band structure model for a-Ge has been proposed to qualitatively understand the changes in the sign and magnitude of the thermoelectric power with temperature.