OPTICAL AND ELECTRONIC-PROPERTIES OF BI-MODIFIED AMORPHOUS THIN-FILMSOF GE20TE80-XBIX

An investigation of the effect of addition of Bi impurities on the ele ctrical, optical and thermoelectric properties of vacuum evaporated am orphous thin films of Ge20Te80-xBix (x = 0, 0.19, 2.93 and 7.35) has b een carried out. The synthesized thin films were characterized by x-ra y diffraction and electron probe microanalysis. Analysis of the result s revealed that Bi modification of the amorphous semiconducting thin f ilms does not induce a clear-cut carrier sign reversal. This is in con trast to the observation of a p-n transition in bulk glassy compositio ns Ge20Te80-xBix at x = 3.5. This dissimilarity may be explained by th e fact that the bonding in the bulk glass and the corresponding thin f ilm may be different. This fact is possibly responsible for creation o f some additional Bi-induced p-type defects with increase in Bi concen tration. The optical energy gap has been found to be approximately equ al to twice the thermal activation energy in all the four compositions studied in this work.