Influence of composition on structural properties and optical parameters of thermally evaporated Ge_10-xSe₆₀Te₃₀In_x (0 ≤ x ≤ 6) thin films

Abstract

Thin films of Se based chalcogenide glassy alloys Ge_10-xSe₆₀Te₃₀In_x (x = 0, 2, 4, 6) were deposited on to glass substrate by vacuum evaporation technique. Glassy nature of the film has been confirmed by DSC and XRD technique. Optical characterization of the thin films has been investigated by analyzing the absorption spectra measured at normal incidence in the spectral range 300–1000 nm. The optical constants viz absorption coefficient (α), extinction coefficient (k), optical band gap (E_g), and refractive index (n) have been studied. It has been observed that absorption coefficient (α) increases with increase in photon energy (hν). Extinction coefficient (k) is found to decrease with the increase of wavelength. Both absorption coefficient (α) and extinction coefficient (k) are found to decrease with In concentration for all compositions under considerations. Optical band gap (E_g) is evaluated and found to increase with increasing In content in Ge-Se-Te matrix. Refractive index (n) of the sample investigated has been estimated using Moss equation and is recorded to have a decreasing trend with increasing In incorporation in the ternary alloy. A correlative study of the optical bandgap and electronegativity of alloys indicate that optical band gap has increasing trend with decrease of electronegativity.

Keywords:

• Amorphous semiconductor
• chalcogenide glass
• thin films
• optical constants
• optical band gap

Acknowledgments

Authors are thankful to Dr. A.M. Awasthi and Dr. Mukul Gupta, UGC-DAE Consortium for Scientific Research Indore, India for providing the facility for DSC and XRD measurements. We are also thankful to Prof. S. K. Tripathi, Department of Physics, Punjab University, Chandigarh, India for continuous support and encouragement.