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

• Published in: Physica status solidi. A, Applications and materials science Vol. 202; no. 10; pp. 1925 - 1934
• Main Authors: El-Mongy, A. Abd, Hashem, H. M., Ramadan, A. A.
• Format: Journal Article
• Language: English
• Published: Berlin WILEY-VCH Verlag 01.08.2005; WILEY‐VCH Verlag
• Subjects: 68.55.Jk; 68.55.Nq; 73.61.Ga; 78.40.Fy; 81.15.Ef
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.200420050

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: E1 ≈ 1.55 eV (fundamental gap) and E2 ≈ 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. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)