Effect of deposition conditions on the microstructure and gas-sensing characteristics of Te thin films

Effect of deposition temperature, post-deposition annealing and substrate crystallinity on the microstructure and gas sensitivity of tellurium thin films has been investigated. As the substrate temperature during deposition is increased, due to increased mobility of adatoms, microstructure of films gradually changes from a smooth amorphous nature at low temperatures to polycrystalline films showing dendritic growth at high temperatures. It is also seen that improvement in crystalline nature of substrate leads to enhancement in grain size of the deposited films. Post-deposition annealing is found to have much less influence on the film morphology compared to films deposited on heated substrates. For films deposited at same temperature (on different substrates), gas sensitivity improves with reduction in the grain size. This has been attributed to increase in effective surface area for gas–film interaction. On the contrary, for films deposited at different temperatures, increase in grain size (higher deposition temperature) leads to better sensitivity. This has been understood to arise from reduced intragrain defect density. Small grain size and reduced defect density are seen to be conducive to better gas sensitivity of the films.