Influence of density of states on optical properties of GaSe thin film

Abstract

A systematic investigation on the effect of substrate temperature on the structure, optical absorption and density of states of vacuum evaporated gallium monoselenide (GaSe) thin films is reported. The X-ray diffraction analysis shows an occurrence of amorphous to polycrystalline transformation in the films deposited at higher-temperature substrates (573K). The compositional analysis is made with Auger Electron Spectroscopy (AES). The thickness of the film (175nm) is measured by a multiple beam interferometery. Optical characteristics of the GaSe sample have been analyzed using spectrophotometer in the photon energy range of 1.0 -4 eV. The absorption mechanism has been recognized and the allowed indirect as well as forbidden direct transitions have been found. As-deposited films show two indirect and allowed transitions due to spin-orbit splitting of the valence band, as reported here for the first time. Low field conduction have enabled us to determine the density of states in amorphous and poly-GaSe films. The amorphous and polycrystalline GaSe thin films have localized states density values of N (E F ) = 1.686 × 10 17 cm -3 eV -1 and 1.257 × 10 15 cm -3 eV -1 respectively. The experimental results are interpreted in terms of variations in the density of localized states due to progressive decrease of the unsaturated bonds during deposition.

Optical and electrical properties of GaSe thin films

“…The dependence of (αhω) 1/P on the photon energy (hω) was examined for different values of P and the results showed (αhω) 1/2 varies linearly with (hω), indicating a non-direct optical transition with energy 1.8 eV, in good agreement with the reported value for the sputtered GaSe films [14] and in contradictory with the reported results for thermally evaporated GaSe film [16]. Fig.…”

“…The presence of indirect optical transition was also supported with dissimilar energies values of 1.83 and 1.5 eV for sputtered [14] and vacuum evaporated amorphous GaSe film [15], respectively. Furthermore, other work revealed two indirect and one forbidden direct optical transitions with energies 1.1, 1.44 and 1.92 eV, for thermally evaporated GaSe films [16].…”

Temperature dependence of the energy gap, refractive index and optical‐oscillator parameters of amorphous GaxSe1–x (x = 0.4, 0.5, 0.6) thin films

“…The presence of non-direct optical transition was also supported with dissimilar energy values of 1.83 and 1.5 eV for sputtered [14] and vacuum evaporated amorphous GaSe film [15], respectively. Furthermore, other work revealed two non-direct and one forbidden direct optical transitions with energies 1.1, 1.44 and 1.92 eV, for thermally evaporated GaSe films [16]. Such contradictory results in the earlier studies, in addition to the fact that there is only one published work that considered the wavelength dependence of refractive index in the visible range for amorphous GaSe films [13], motivated us to undertake the present study.…”

Electrochemical growth of GaSe nanostructures and their Schottky barrier characteristics

“…The dependence of photo-current on the illumination intensity revealed the existence of two recombination centers in the GaSe crystals. Thamilselvan et al [12] reported the influence of heating the substrate on the conduction mechanism of the polycrystalline and amorphous GaSe thin films. Very recently, Siciliano et al [13] have investigated the influence of thermal oxidation on the GaSe thin film.…”