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01-02-2020 | MICROCRYSTALLINE, NANOCRYSTALLINE, POROUS, AND COMPOSITE SEMICONDUCTORS
Dielectric Spectroscopy and Features of the Mechanism of the Semiconductor–Metal Phase Transition in VO2 Films
Published in: Semiconductors | Issue 2/2020
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Abstract
In the range of 0.1–106 Hz, the temperature-induced transformation of the frequency dependences of the dielectric-loss tangent tanδ(f) as well as the Cole–Cole diagrams for undoped vanadium-dioxide films are investigated. The measurements are carried out in the temperature range T = 273–373 K. It is shown that the shape of the Cole–Cole diagrams for all films depends slightly on the temperature in the specified interval, while the frequencies f0 corresponding to the peaks of the function tanδ(f) increase with temperature. The thermal-hysteresis loops of the frequency positions f0(T) of the peaks are measured. When interpreting the data of dielectric spectroscopy, a complex equivalent electrical circuit of the sample is used; it makes it possible to detect the presence of two types of grains with different electrical properties in undoped VO2 films. The presence of two types of grains determines the features of the semiconductor–metal phase-transition mechanism in VO2 films.