RESEARCH OF THE ELECTRICAL PROPERTIES OF LEAD CHALCOGENIDE FILMS FOR THE NEWEST ENERGY SOURCES
[3. Технічні науки]
Автор: Mazur Tetiana Mikhailivna, PhD, Associate Professor, Ivano-Frankivsk National Technical University of Oil and Gas, Ivano-Frankivsk, Ukraine; Mateik Galina Dmitrivna, PhD, Associate Professor, Ivano-Frankivsk National Technical University of Oil and Gas, Ivano-Frankivsk, Ukraine
Lead chalcogenide films are promising for creating active elements of micro- and optoelectronics on their basis: thermoelectric energy converters , detectors and sources of infrared radiation of the optical spectrum . It should be noted that the values of the performance characteristics of device structures and their stability over time are determined by the structural state and degradation processes that take place in thin-film materials used in the latest energy sources.
In the present work, films were prepared using thermal evaporation in a vacuum. The substrates were fresh chips (0001) of mica-muscovite at a temperature Ts = 500 – 600 K. The initial charge was prepared from a stoichiometric alloy, the deposition rate was in the range of 10–13 Å, and the thickness was approximately 0.3 μm . Electron-microscopic and electron-graphic study of the structure of the prepared films showed that they have a mosaic structure. The linear dimensions of the blocks were several times greater than the film thickness. As a result of the studies of the electrical properties, it was found that after the completion of the deposition process, the films had n-type conductivity. The electron concentration determined from Hall measurements depended on the substrate temperature Ts and increased from 6 1017 cm-3 at Ts = 500 K to 8 1018 cm-3 at Ts = 600 K, which caused a decrease in the resistivity of the films.
On Fig. 1 shows the time dependences of the resistivity of PbTe films deposited on mica at different substrate temperatures Ts. It can be seen that the holding resistivity tends to decrease with time. This fact shows that the processes associated with the ordering of the structure occur in the films, in particular, the processes of postcondensation recrystallization.
Fig. 1. Change in resistivity (ρ) of PbTe mosaic films as a function of annealing time (t). Substrate temperature Ts, K: 1 – 500; 2 – 560; 3 – 600. Points - experiment; solid lines – calculation according to (1).
The presented experimental results of the values of the resistivity of PbTe films at different Ts on the exposure time in vacuum (Fig. 1) can be analytically described by the exponential function:
Here ρn, ρ1 are the resistivities of the films, which depend on their state and are adjustable parameters; τ1 are the relaxation time constants for the corresponding changes in resistivity, determined on the basis of the approximation of the experimental curves by the analytical expression (1).
It should be noted that monotonic changes in the resistivity of the films are well approximated using one exponential function (1), which indicates the predominance of one specific physical process associated with the processes of postcondensation recrystallization.
1. D.M. Freik, V.M. Pasichnyak, O.L. Sokolov, B.S. Dzundza. Scattering features of charge carriers in epitaxial structures based on lead chalcogenides. Physics and Chemistry of Solid State. 2004. 5(3), P. 455-459.
2. V.M. Sherun, D.M. Freik, R.I. Puffy. Thermoelectricity of lead telluride and its analogues. Plai, Ivano-Frankivsk. 2000.
3. V. Prokopiv, I. Horichok, T. Mazur, O. Matkivsky, L. Turovska Thermoelectric materials based on samples of microdispersed PbTe and CdTe. Proceedings of the 2018 IEEE 8th International Conference on Nanomaterials: Applications & Properties (NAP - 2018). Zatoka, Odesa Region, 2018. P. 01SPN57-1 - 01SPN57-4. DOI: 10.1109/NAP.2018.8915357.