Refractive index, band gap and oscillator parameters of amorphous GaSe thin films

Abstract

GaSe thin films are obtained by evaporating GaSe crystals onto ultrasonically cleaned glass substrates kept at room temperature under a pressure of ~10 -5 Torr. The X-ray analysis revealed that these films are of amorphous nature. The reflectance and transmittance of the films are measured in the incident photon energy range of 1.1-3.0 eV. The absorption coefficient spectral analysis revealed the existence of long and wide band tails of the localized states in the low absorption region. The band tails width is calculated to be 0.42 eV. The analysis of the absorption coefficient in the high absorption region revealed an indirect forbidden band gap of 1.93 eV. The transmittance analysis in the incidence photon wavelength range of 500-1100 nm allowed the determination of refractive index as function of wave length. The refractive index-wavelength variation leads to the determination of dispersion and oscillator energies as 31.23 and 3.90 eV, respectively. The static refractive index and static dielectric constant were also calculated as a result of the later data and found to be 9.0 and 3.0, respectively.

Optoelectronical properties of polycrystallineβ -GaSe thin films

“…The value of direct allowed transition energy gap for the films is found to be 1.83 eV. This result differs from that we have previously reported for amorphous GaSe thin films [6] where the absorption coefficient analysis for the amorphous films revealed an indirect forbidden band gap of 1.93 eV. …”

“…The X-ray analysis reported [1,6] there revealed that the as grown films and the films grown at substrate temperature of 200°C are of amorphous nature. The films grown at substrate temperature of 300°C are of polycrystalline nature.…”

“…However, in spite of it is importance in optical applications, the data reported about the optical and photoconductive properties of these films still lack of details. Particularly, the refractive index, dielectric constant, dispersion values and temperature and illumination intensity dependence of photoconductivity of polycrystalline GaSe films are not widely considered [6]. The published optical data has reported the photovoltaic effect in these films [7].…”

“…The study allowed the identification of the transport mechanism in these films in addition to the hole traps domination by means of space charge limited current. In addition, the optical properties of the as grown amorphous GaSe thin films [6] have been investigated. The optical data analysis allowed the identification of the dispersive optical constants.…”

Characteristics of Optical and Photoconductive Properties in Bulk and Thin Film of TlS2Single Crystals

“…The exponent n can take one of the four values: 2, 1/2, 3, and 3/2, which define the type of the optical transition. Theoretically m is equal to 2, 1/2, 3, or 3/2 for the indirect allowed, direct allowed, indirect forbidden, and direct forbidden transitions, respectively [22]. For the case Fig.…”