Nanocrystalline CdTe films deposited by high-pressure sputtering: carrier transport at low temperature

Electrical conductivities of nanocrystalline CdTe films deposited onto quartz substrates by high-pressure (similar to 20 Pa) DC magnetron sputtering were studied as a function of temperature (188-298 K). The grain size varied within 4 to 4.7 nm with the variation of deposition temperature (T-s) within 253 to 273 K. The conductivity (sigma) showed (T-0/T)(P) dependence with p similar to 0.5 indicating the presence of a Coulomb gap near the Fermi level. Efros-Shklovskii (ES) hopping was found to be the predominant carrier conduction mechanism in the nanocrystalline CdTe films. The width of the Coulomb gap varied within 27-41 meV depending on the deposition conditions. Cross-over from ES to Mott's hopping was observed. The existing theoretical models were used for estimating hopping energy (29 to 42 meV) and hopping distance (2.8 to 5.1 nm) in the films. (C) 1999 Elsevier Science S.A. All rights reserved.