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

Abstract

We have analyzed the properties of as-deposited InSe thin films, deposited onto well cleaned glass substrates under a vacuum of 10⁻⁵ Torr, 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 1.44 eV. Under low field (<1×10⁵ V 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 ₀), 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 210–290 K, thermionic conduction mechanism plays a dominant role and its activation energy was calculated. At high field (>2×10⁵ V 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 ₀), 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.