Effect of structure on current transfer in cadmium telluride films of different thickness

The mechanism of conductivity of polycrystalline high-resistivity films of cadmium telluride is proposed on the basis of the model of potential barriers between crystallites. According to this model, a decrease in the height of potential barriers upon external displacement is accompanied by an increase in the conductivity of the films and has an activation nature. The films were obtained by vacuum deposition in a quasi-closed volume. It has been established that the value of intercrystalline energy barriers for films obtained under various technological conditions is in the range of ~ 0.3-0.5 eV. A correlation was found between the intercrystalline energy barriers and the sizes of crystallites for films obtained at different temperatures of the substrate and annealing. Based on the temperature dependence of the conductivity, as well as the photoconductivity of polycrystalline samples, it can be argued that the Ev + 0.47 eV level is the main supplier of free carriers, but the dominant role in the conductivity is played by intercrystalline barriers. Thus, the conductivity of polycrystalline films depends on the number of barriers not linearly, as shown in the literature, but exponentially. With an increase in the thickness of the films, the number of energy barriers connected in series between the electrodes increases proportionally. Therefore, with a constant potential difference (V = 100 V) between the film electrodes, the voltage applied to one barrier will be inversely proportional to the film thickness, which leads to a linear decrease in conductivity with increasing film thickness.

Keywords

Authors

References