Electrical and optical studies on Pb-modified amorphous Ge–Se–Te films

Abstract

PbxGe42−xSe48Te10 (3 ⩽ x ⩽ 15) and Pb20GexSe70−xTe10 (17 ⩽ x ⩽ 24) amorphous thin films were prepared by thermal evaporation of corresponding bulk glasses on glass substrates. A p-type to n-type conduction change was observed at the compositions with x = 9 at wt% Pb and x = 21 at wt% Ge in PbxGe42−xSe48Te10 (3 ⩽ x ⩽ 15) and Pb20GexSe70−xTe10 (17 ⩽ x ⩽ 24) films, respectively. The optical bandgap of these thin film samples was determined from optical absorption data. The composition dependence of optical bandgap of the thin films is interpreted on the basis of the variation of the average bond energy in these amorphous semiconductors with change in composition. The direct current electrical resistivity of these samples was measured in the temperature range of 310–400 K. The sheet resistance and the activation energy for electrical conduction of the films decreased with increasing Pb content in the PbxGe42−xSe48Te10 (3 ⩽ x ⩽ 15) series, whereas the sheet resistance and the activation energy for electrical conduction exhibited a maximum at 21 at wt% of Ge in the Pb20GexSe70−xTe10 (17 ⩽ x ⩽ 24) series. The electronic conduction in the Pb–Ge–Se–Te films in the 310–400 K regime has been attributed to the band transport mechanism.