Abstract
Current voltage ( I–V ) characteristics have been studied at various temperatures in vacuum evaporated thin films of a-Se 85− x Te 15 Bi x ( x= 0, 1, 2, 3, 4, 5) glassy alloys. Ohmic behavior is observed at low electric field while at high electric field ( E ∼10 4 V/cm) current becomes superohmic. An analysis of the experimental data reveals that in case of samples with 0–2 at% Bi, the experimental data fit well with the theory of space charge limited conduction (SCLC) for uniform distribution of localized states in the mobility gap. Such type of behavior is not observed at higher concentration of Bi in the present glassy system. Due to high conductivity in these samples, joule heating due to large currents may prohibit the SCLC mechanism. Density of localized defect states near Fermi level is determined for these samples by fitting the data in the theory of SCLC. The results indicate that density of defect states increases with Bi addition to binary Se 85 Te 15 alloy. This is explained in terms of electronegativity difference of Bi as compared to host elements.
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