Effect of Sodium Based Transparent Binders on the Optical Properties of GaSe Thin Films

Abstract

The effect of sodium based transparent binders on the optical properties of vacuum evaporated GaSe thin films are explored by means of optical reflectivity and transmittance of the binder, GaSe and GaSe/binder interfaces in the incident light wavelength range of 300-1100 nm. The analysis of the absorption coefficient spectra for the three samples revealed a pronounced red shift in the direct allowed electron transition's energy band gap of the GaSe. In addition, the band tail states of GaSe, which was observed at ~ 0.25 eV, disappeared upon binder coating. The binder coated GaSe films screen the energy band gap of the GaSe as band tail state in its energy band gap. On the other hand, the analysis of the dielectric spectra of the binder coated GaSe thin films displayed an abnormal enhancement in the optical conductivity of the double layer. The optical conductivity, which was modeled in accordance to Lorentz theory, displayed significant change in the free carrier density, the drift mobility, the electron collision time and the effective mass of GaSe upon binder coating. The study ends with the result that the sodium-based binder behaves as a fully transparent optical window to the optoelectronically sensitive GaSe thin films.