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KMID : 0380319870390000015
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Journal of Korean Research Institute for Better Living
1987 Volume.39 No. 0 p.15 ~ p.26
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The effect of Sn doping on the physical properties of chalcogenide semiconductor As_2 Te_3
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Abstract
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D.C. electrical conductivity, optical absorption, and photoconductivity exper-iments on glassy semiconductor As_2 Te_3+Sn, for which the Sn concentration is 0,0.6, 4.3, and 6.7 at. % are investigated. The thin film samples are prepared by the thermal evaporation method.
Over the temperature range from 173K to 343K, the d.c. conductivity of the investigated samles is of the form σ=σ_0exp (-ΔE_a/KT) and d.c. con-ductivity except the 6.7 at. % samples is about 2.9X10^-4(Ω^-1cm^-1). In the Sn concentration less than 4.3 at. %, the tin additives on As_2 Te_3 seem to have little influence upon the d.c. conductivity and the low-temperature con-ductivity is due to variable range hopping.
Except 6.7 at. % sample, the activation energy of As_2 Te_3 is almost con-stant at 0.47 eV and an optical gap is 0.94 eV.
The value of pre-exponential factor σ_0 is about ∼10^3(Ω^-1cm^-1). From the optical absorption data, the photoconductivity increases with increasing Sn concentration and the optical energy gap decreases gradually with increasing Sn concentration. The reduction in the optical energy gap E_g is due to the bonds formed between an impurity atom and the surrounding host atoms.
It is shown that the value of the difference E_g-ΔE_a is independent of Sn concentration in As_2 Te_3, except 6.7 at. % sample. This is explained by the fact that, in As_2 Te_3 , both E_g and ΔE_a change little. The increase in the photoconductivity with increasing Sn concentration is due to the decrease of the recombination probability by the change of D^+ into D^- by Sn incor-poration result in the carrier life.
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