The effect of high-temperature heat treatment on the electrical power factor and morphology of silicon germanium-gallium phosphide alloys

Abstract

The results of an experimental investigation into the effect of high-temperature heat treatment on the electrical resistivity and Seebeck coefficient of silicon germanium-gallium phosphide alloys and the accompanying changes in morphology are reported. The specimens were heat treated for different periods of time and quenched or allowed to cool slowly in air. Their morphology was investigated using scanning electron microscopy and electron spectroscopy for chemical analysis. The electrical resistivity and Seebeck coefficient were measured as a function of temperature from room temperature to about 800 K. Substantial changes in the electrical properties and in morphology were observed after 15 min and 4-h periods of heat treatment, respectively. A less significant decrease in electrical resistivity accompanied further heat treatment. However, the Seebeck coefficient remained almost constant which resulted in an increase in the electrical power factor. Prior to heat treatment, the alloy consisted of host matrix and a silicon-rich black phase. Heat treatment was accompanied by the appearance of a white phase which was rich in germanium and gallium phosphide. Although in general it was not possible to correlate the changes in electrical properties with the morphology. The highest power factor obtained in this investigation corresponded to a morphology which consisted of the host matrix and a significant proportion of white phase.