Hopping conduction in nanocrystalline ZnSe films deposited by high pressure d.c. magnetron sputtering

Electrical properties of nanostructured ZnSe films deposited onto quartz substrates by high pressure (~20 Pa) d.c. magnetron sputtering technique were studied. The grain size varied within 4 to 4.4 nm with variation of deposition temperature (Ts) from 233 to 273 K. The variation of the electrical conductivity (σ) with temperature was measured in the temperature range of 120–240 K. The conductivity showed ( T 0 T ) p dependence with variation of p within 0.4 to 0.6 indicating the presence of a Coulomb gap (~0.03 eV) near the Fermi level. Efros-Shklovskii hopping (with average p = 0.5) was predominant at low temperature which changed to Mott's hopping with increasing temperature. The existing theoretical models were used to determine the range of hopping energy (0.027 to 0.037 eV) and hopping distance (4.2 to 5.8 nm) in nanocrystalline ZnSe films. Applicability of the percolation model was tested. The effective potential barrier offered by the intergrannular insulating region was found to increase from 0.004 to 0.094 eV with the decrease of grain size from 4.43 to 3.98 nm.