Adam A. Bahishti

Effects of laser irradiation on optical properties of a-Se100−x Te x thin films

The effect of laser irradiation on the optical properties of thermally evaporated Se100−x Te x (x=8, 12, 16) chalcogenide thin films has been studied. The result shows that the irradiation causes a shift in the optical gap. The results have been analyzed on the basis of laser irradiation-induced defects in the film. The width of the tail of localized state in the band gap has been evaluated using the Urbach edge method. As the irradiation time increases, the values of the optical energy gap for all compositions decrease, while tail energy width increases. It is also observed that the optical energy gap decreases with increasing Te content in the alloy. These changes are a consequence of an increment in disorder produced by laser irradiation in the amorphous structure of thin film.

Dc conductivity and High Field Behavior of Se 100-x Te x Alloy

The dc conductivity has been carried out in vacuum-evaporated thin films of amorphous Se100-xTex(x = 4, 8, 12, 16) in the temperature range of (317–378 K). It is found that dc conductivity increases and the activation energy (ΔE) decreases with increase of Te concentration. The conduction is explained on the basis of tunneling of carrier in the band tail of localized state. The high field measurement has been observed at various fixed temperature, a dc voltage (0–400 V) was applies across the sample. I–V characteristic data show that at low electric fields an ohmic behavior is observed. However, at high electric field super ohmic behavior is observed. Analysis of the data show the absence of space charge limited conduction (SCLC) in all glassy alloys as ln I/V versus V curves are not found to be straight lines. Instead ln I/V versus V 1/2 are found to be straight line, with high correlation coefficient. This suggests the conduction process is either of the Pool-Frenkel or Schottky emission. A detailed analysis show that dominant mechanism is Pool-Frenkel type conduction.