Substrate temperature dependence of electrical conduction in nanocrystalline CdTe:TiO<sup>2</sup> sputtered films

Sharma, S. N.; Shivaprasad, S. M.; Kohli, Sandeep; Rastogi, A. C.

doi:10.1351/pac200274091739

Pure Appl. Chem., 2002, Vol. 74, No. 9, pp. 1739-1749

http://dx.doi.org/10.1351/pac200274091739

Substrate temperature dependence of electrical conduction in nanocrystalline CdTe:TiO² sputtered films

S. N. Sharma¹*, S. M. Shivaprasad², Sandeep Kohli³ and A. C. Rastogi¹

¹ Materials Division, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India
² Surface Physics Group, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India
³ Department of Chemistry, Colorado State University, Fort Collins, CO 80523, USA

Abstract: TiO² thin films with high volume fraction (∼5070 %) of CdTe nanoparticles were prepared by radio frequency (rf) magnetron sputtering from a composite TiO²:CdTe target. With increase in substrate temperature Ts from room temperature (RT ∼300 K) to 373 K, a transition from an ordered structure exhibiting metallic-type conduction to a disordered structure exhibiting nonmetallic-type conduction was observed for annealed nanocrystalline CdTe:TiO² films. The annealed RT-deposited films showed a large coalescence of distinct islands (size ∼0.30.7 µm) mainly of Cd and CdTe, and as result, a 3D network was realized. For metallic regime films, electrical conduction is essentially due to electrical percolation through Cd/CdTe crystallites embedded in an amorphous TiO² matrix. However, the annealed high Ts films consisted of noncoalescent, small islands (size ∼0.150.3 µm) of Cd and CdTe embedded in amorphous TiO² matrix. Here, the conduction is essentially by hopping mechanism via thermally activated tunneling.