Electrical properties of nanocrystalline CdSe thin films prepared by thermal vacuum evaporation

Abstract

Thin films of CdSe with thicknesses of 50, 75 and 100 nm were prepared by physical vapour deposition using a 'one-step' or a 'step-by-step' deposition approach. The influence of the deposition conditions and film thickness on the microstructure and electrical properties has been explored by means of atomic force microscopy (AFM), dark conductivity, photoconductivity and thermally stimulated conductivity measurements. The AFM results have shown that smaller grains are formed in thinner films and that the size decrease is enhanced when the step-by-step deposition approach is used. A significant increase of the dark current activation energy with decreasing layer thickness has been registered and identified with a Fermi-level shift. A decrease of dark conductivity and photoconductivity has been observed with decreasing layer thickness which has been connected with both a size-induced increase of the interface defect density and appearance of new 'faster' recombination centres. The observed decrease is stronger in step-by step layers, in which the density of incorporated oxygen is higher. The oxygen creates new acceptor defects and causes band bending at grain boundaries. From the thermally stimulated conductivity data two kinds of defect states have been resolved situated at about 0.55 eV and 0.67 eV below the conduction band. A simultaneous fitting method has been applied to determine the main trap parameters.

Quantum chemistry of quantum dots: Effects of ligands and oxidation

“…28 Clearly, 650 nm corresponds to a band gap ͑1.9 eV͒ that is too narrow for strong quantum confinement in a QD that small, and is much closer to the bulk band gap. More controlled experiments for nanocrystalline thin films show, 29 that increased density of oxygen is, in fact, the reason that leads to the defect states appearing 0.6 eV below the band gap.…”

The effects of deposition parameters on CdS thin films optoelectronic properties

“…3The grain size must be increased in order to reduce the resistivity of the sample. It can be stated that the carriers concentration is directly proportional to the processing parameters, which include, the substrate temperature, film thickness and annealing temperature [9,10] . The Hall measurement indicated that all the fabricated films are ntype i.e.…”

Effect of thickness on structural, optical, electrical and morphological properties of nanocrystalline CdSe thin films for optoelectronic applications

“…They found that the crystallinity was increased with substrate temperature while the band gap energy was decreased. A study of electrical properties of thermally evaporated CdSe thin films was undertaken by Aneva et al [26]. They observed that the dark and photo conductivity were increased with film thickness.…”