Electrical conduction in ternary semiconductor Ga5Se20Te75 thin films

Abstract

Different thickness thin films of the ternary alloy Ga5Se20Te75 have been vacuum deposited on clean glass substrates held at room temperature at a very fast rate. The film resistance has been measured as a function of temperature during two cycles of heating and cooling. It has been found that the resistance-temperature (R-T) variation of the films during first heating and cooling is different, the R-T curve during heating lying above the R-T curve during cooling in the case of thinner films and below in the case of thicker films. There are two possible explanations for the difference in resistance variation during heating and cooling and between the thinner and thicker films. The first is due to the semiconducting nature of the material and the second is due to the removal of frozen-in defects and/or change in concentration depth profile. In addition to these, the phenomenon of self-annealing can also take place in thicker films. Log resistance vs reciprocal temperature plots are found to be linear, indicating activated conduction in the film material. It has also been found that resistance vs reciprocal thickness plot is near-linear as expected from the classical size effect theories. X-ray diffraction has established that the films are single phase. X-ray photoelectron spectroscopic (XPS) studies have revealed that the film surface is enriched with tellurium such as TeO2 [BE (3d5/2)=577 eV], in addition to the presence of selenium [BE (3d)=55.5 eV] and gallium in traces [BE (2p3/2)=1117 eV].