Effect of target materials on structural and electrical properties of unhydrogenated amorphous silicon thin films deposited by RF magnetron sputtering

The effect of target materials (single crystalline silicon (c-Si), polycrystalline silicon (p-Si)) and substrate temperatures on structural and electrical properties of a-Si thin films deposited on glass substrate by RF magnetron sputtering have been investigated. The purpose of this work was to find out the cost-effective materials for intrinsic layer in inorganic solar cell device. X-ray diffraction patterns of both sets of a-Si films showed similar broad hump indicating amorphous nature of thin film materials. AFM topographs indicated no target phase dependency on grain size (50–60 nm) and surface roughness (∼ 10 nm). Optical band gap values of all deposited films were calculated using Tauc´s plot from UV-Vis spectra, have values within the range 1.88 eV to 1.98 eV. In activation energy (Ea) study even in purely intrinsic phase dual activation energies in dark conductivity have been reported corresponding to high temperature (Ea ^High) and low temperature (Ea ^Low) regime. It is observed that Ea^Low was always lower in magnitude than Ea^High. The Ea^High originates due to dominant transport through the extended states (EC) at relatively higher temperature while at lower temperature, the extended state transport appears less feasible and the transport is dominated by the carrier hopping from one localized state to an empty localized state and carrier hopping from a localized (defect) state to an empty extended state. The values of activation energy in high temperature region (Ea^High for T ≫ 400 K) of a-Si samples were independent of sputter target used. The Ea^High value for samples deposited at RT was 0.59 eV and for sample deposited at 200°C was 0.58 eV. At high temperature regime electrical band gap from activation energy data for all deposited thin film materia- - l ∼ 1.2 –1.4 eV observed.