Effect of thickness and cold substrate on transport properties of thermally evaporated CdTe thin films

Abstract

The correlation between the structural characteristics (stoichiometry and crystallite size) of CdTe films and their electronic transport properties were the aims of the present study to bring attention to the dual importance of grain size and conversion of the semiconductivity type with changing film thickness. Two main parameters were considered: the substrate temperature and film thickness. Transport properties were influenced by grain boundaries as well as by native doping. Optical measurements showed two main direct transitions at energies: E 1 ≈ 1.55 eV (fundamental gap) and E 2 ≈ 2.49 eV (due to valence band splitting). Both transitions were found to be thickness dependent with a marked change at a film thickness of about 300 nm. In the case of low substrate temperature, the scaling relation between resistivity and grain size showed a deviation from linear behavior at a size of 20 nm and the transmission coefficient is reduced. Also, the deposition on cold substrate enhanced both dark and photoconductivity for films of thickness ≥300 nm. It is also proved that the carrier transport was affected by the transmission coef-ficient for carriers to pass a single grain boundary as well as the number of grain boundaries per mean free path.

Optimization of Thickness and Number of Layers for CdTe Films Deposited by Stacked Elemental Layers Method and Annealed in Different Environments

“…The extrapolation of the linear part of the curves to the photon energy axis would give the optical energy band gap. The results give optical band gap ranging between 1.36 and 1.51 eV (Table 3) which is in fair agreement with those reported in the literature for the CdTe polycrystalline material (1.5 eV) [19]. It should be noted that as the number of layers of the films (for the same thickness) increased the energy gap becomes more close to the value of the CdTe single crystal.…”

Effect of Layer Sequence on Formation of CdTe Thin Film Prepared by Stacked Elemental Layers

“…The values of the energy gab with sample preparation condition are given in Table (1). The values of the energy gap ranged from 1.50 to 1.65 eV in agreement with that of CdTe polycrystalline material [16].…”