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

Pure and Applied Chemistry

Vol. 74, Issue 9

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

S. N. Sharma2,**, S. M. Shivaprasad2, Sandeep Kohli3, and A. C. Rastogi2

1Materials Division, 2Surface Physics Group, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India; 3Department 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 mm) of Cd and CdTe embedded in amorphous TiO2 matrix. Here, the conduction is essentially by hopping mechanism via thermally activated tunneling.

* Special Topic Issue on the Theme of Nanostructured Advanced Materials

**Corresponding author

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