Space charge limited current, variable range hopping and mobility gap in thermally evaporated amorphous InSe thin films

We have analyzed the properties of as-deposited InSe thin films, deposited onto well cleaned glass substrates under a vacuum of 10^-5Torr, using X-ray diffraction, Rutherford back scattering, energy dispersive analysis of X-rays, optical transmittance and current-voltage (120-390 K) measurements. Allowed and indirect transition was identified and the mobility gap was determined as 1.44eV. Under low field ( < 1 × 10⁵V cm^-1) and in the temperature range of 130-200 K, the conductivity in the films was behaving like that of Mott's variable-range hopping (VRH) type. Mott's parameters such as characteristics temperature (T_O), hopping range (R_hop), hopping energy (W_hop), values of localized states density N (E_F), and activation energy (E_a) were estimated. In the temperature range 210-290K, thermionic conduction mechanism plays a dominant role and its activation energy was calculated. At high field ( > 2 × 10₅V cm^-1) and in the temperature range of 300-390 K, space charge limited conduction currents (SCLC) mechanism was observed and the related parameters, such as electron density (n_o), trap density (n_t), the ratio between free electron density to the total electron density (θ), mobility (μ) and the effective mobility (μ_eff) of the InSe film of typical thickness 265 nm were calculated and the results are discussed.