Optical and electronic properties of Bi-modified amorphous thin films of Ge₂₀Te_80-xBi_x

Abstract

A n investigation of the effect of addition of Bi impurities on the electrical, optical and thermoelectric properties of vacuum evaporated amorphous thin films of Ge,,Te,,_,Bi, (x = 0, 0.19, 2.93 and 7.35) has been carried out. The synthesized thin films were characterized by x-ray diffraction and electron probe microanalysis. Analysis of the results revealed that Bi modification of the amorphous semiconducting thin films does not induce a clear-cut carrier sign reversal. This is in contrast to the observation of a p-n transition i n bulk glassy compositions Ge,Te,,-,Bi, at x = 3.5. This dissimilarity may be explained by the fact that t h e bonding in the bulk glass and the corresponding thin film may be different. This fact is possibly responsible for creation of some additional Bi-induced p-type defects with increase in Bi concentration. The optical energy gap has been found to be approximately equal to twice the thermal activation energy in all t h e four compositions studied in this work.

Analysis of some optical parameters of the glasses of the system Bix(As2S3)100‐x

“…With the further increase in the content of dopant atoms, the trend of decrease continues. The same effect has also been observed with the other chalcogenide glasses with bismuth as dopant [7][8][9].…”

Electronic conduction in Bi‐modified amorphous thin films of Ge20Te80‐x Bi x exhibiting an absence of a p‐n transition

“…10. A qualitative explanation for the absence of a p-n transition in these films has been proposed by us (Bhatia et al 1995). In several other studies (Solin andPapatheodoru 1977, Nemanich, Cornell, Hayes andStreet 1978) on chalcogenides, it has been shown that thin films prepared by vacuum evaporation onto the substrates, held at temperatures below the glass-transition temperature, and of nominally the same composition as the coresponding bulk material, display very different types of bond distribution.…”

“…However, the mechanism of the p-n transition still remains poorly understood. In a recent communication we have reported that thin films of Ge 20 Te s0 _ x Bi x do not exhibit a p-n transition up to x=7-35 like the one observed in bulk glasses at x = 3-5at.% (Bhatia, Singh, Kitagawa, Kishore and Suzuki 1995). Contrary to this behaviour, the two systems Ge-S-Bi and Ge-Se-Bi show a p-n transition in both thin-film forms (Bhatia et al 1988).…”

“…The values of dielectric constant e t at room temperature used in the fitting have been estimated from optical spectra at longer wavelengths (Bhatia et al 1995). The various parameters used in the fitting procedure are summarized in the table.…”

Electrical conduction and photoconduction in Se80−xTe20Bixthin films

“…This problem can be overcome by alloying Se with some impurity atoms (Bi, Te, Ge, Ga, Sb, As, etc), which gives higher sensitivity, higher crystallization temperature and smaller ageing effects. Several workers have studied the effect of bismuth on the optical and electrical properties of chalcogenide materials [9][10][11]. However, not much work has been reported on the effect of bismuth on the photoconductivity of the Se-Te matrix.…”