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
Abstract: TiO2 thin films with high volume fraction
%) 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
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