Electrical and optical properties of thermally evaporated [formula omitted] films

Abstract

Thin films of Ge 20 In 5 Se 75 were prepared by the conventional thermal evaporation technique of presynthesize material on pyrographite and glass substrate. The chemical composition of the films has been checked using energy dispersive X-ray spectrometry. X-ray diffraction measurements have shown that Ge 20 In 5 Se 75 in powder and thin film form has an amorphous nature. Electrical measurements included the electrical conductivity and I–V characteristics of amorphous films. The electrical conductivity was found to increase with increasing temperature, and to decrease with increasing film thickness. The obtained results showed that the electrical conduction activation energy has two values of Δ E I and Δ E II indicating the presence of two different conduction mechanisms. The I–V characteristics of films are typical for a memory switch. The mean value of the threshold voltage V th decreases with increasing temperature and increases with increasing film thickness. The switching voltage activation energy ( ε ) was determined. Agreement between the obtained value of ratio ( ε / Δ E II ) with its value obtained theoretically on the basis of an electrothermal model was found. The spectral and optical parameters have been determined using spectrophotometric measurements of transmittance and reflectance in the wavelength range 400–2500 nm. The optical constants (refractive index ( n ) , absorption index ( k ) and absorption coefficient ( α ) ) have been determined. An allowed indirect transition with optical energy gap E g opt of 1.76 eV has been found.