THE EFFECT OF LIGHT ON THE CONDUCTIVITY AND THE ADSORPTIONDESORPTION PROCESSES OF THE ACCEPTORS ON THE SURFACE OF СdTe:Sb THIN FILMS
Semiconductor films of Cadmium telluride are frequently used for the production of gas sensors. The mechanism of such sensors is based on the change in conductivity caused by gas adsorption and desorption. However, the instability of the surface and its susceptibility to the environment may result in the instability of gas sensors. Therefore, the aim of this paper is to study the effect of light on the conductivity and on adsorption and desorption processes on the surface of CdTe:Sb thin films.
Samples of CdTe:Sb solid solutions were synthesized by sintering CdTe and Sb2Te3 composites of exact composition in vacuumed quartz ampoules. The samples were then deposited on glass substrates using vacuum thermal evaporation (~ 1.3 × 10-3 Pa) in a VUP-5 unit. The thickness of the films was 1 μm. The samples were then tempered in a vacuumed quartz ampoule at 750 °С for 100 hours.
The broadband photo-dielectric spectroscopy method was used in the experiments. In order to prevent electrode effects, alternating current measurements were performed. The electrode voltage was 1 V, and the current frequency was 1 Hz. All the measurements were performed at 20 С, stabilised by a nitrogen flow.
The study of the effect of light on the conductivity of СdTe:Sb thin films demonstrated that the change in productivity is determined by the quantum energy. The conductivity changes include two stages: a sharp increase at the initial stage and a subsequent decline. Exposure to light E < Eg, results in increased conductivity. The paper shows that the observed reduction in conductivity is caused by photodesorption of oxygen and/or water molecules from the surface of the sample. To interpret the obtained results, a two-layer conductivity model was used in the form of a chain with "parallel" connection between surface and volume conductivities. The nature of surface conductivity, as well as the effect of the frequency of the external alternating field on the results obtained, are to be detailed in our next paper.
The authors express their gratitude to M. V. Gapanovich, PhD in Chemistry, for his assistance in preparing the samples.
The reported study was supported by the Russian Foundation for Basic Research (project No.16-08-01234) and financed within the framework of the state order No. 01201361850.
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