Temperature dependencies of electrical resistivity and thermoelectric power of SnTe thin films

Abstract

The temperature dependences of electrical resistivity p and thermoelectric power S for the SnTe polycrystalline thin films with charge carrier concentration of(3 -5). 1021 cm3 have been obtained in the range of 80 -300 K. It was established that the p (T) and S (T) dependences had non-monotonous character. In the temperature range of (80 -150) K series of peculiarities in the form of steps and plateaux were observed most distinctly. Assumptions about the nature of these anomalies were made. The possible reasons for appearance of numerous temperature peculiarities are system's passing through different quantum states; the processes of self-organization taking place in an open system (heated thin film) at defmite levels of excitation (certain temperatures); microdomain structure of thin films; relaxation processes. The pronounced anomalies observed in the temperature ranges of 135-150 and 190-200 K were attributed to phase transitions caused by redistribution of non-stoichiometric defects.Effective application of materials based on the IV-VI compounds in IR-photoelectronics, thermoelectricity, lasers, 12 impossible without knowing temperature dependences of main electrical and thermal parameters. Temperature anomalies of properties can essentially affect the semiconductor parameters of a device. That is why determining the temperature ranges of instability of crystal lattice and/or electron subsystem is very important both from scientific and practical application points of viewThe objects of the present study are SnTe polycrystalline thin films. The SnTe semiconductor compound is characterized by high concentration (1020 1021 cm3) of native defects, mainly cation vacancies, caused by significant deviation from stoichiometry.2'3 This results in high concentration PH of p-type charge carriers, which can be controlled by changing the degree of deviation from stoichiometry.By now it has been established that at temperature T 100 K SnTe undergoes ferroelectric displacive phase transition (FPT),4'5 which is accompanied by the change in crystal lattice symmetry from cubic into rhombohedral and appearance of anomalies in temperature dependences of different physical properties61° in particular electrical resistivity p.1113 It was shown'4'11'15 that the increase of carrier concentration led to decrease of Tc and at PH > (7-8) . 1020 cm3 FPT was not observed. A number of authors6'7"6 suggested the existence of at least two phase transitions. When studying nuclear magnetic resonance, the authors of'7 detected "steps" in the temperature dependences of resonant fields of' '9Sn nuclei at T = 376/n (n = 1 -6). They suggested that the observed phenomena are connected with movement of the crystal lattice defects which affects local distribution of electron density under changing temperature. In'82° the temperature anomalies of p and the Hall coefficient RH were revealed in the ranges of 13 5-150 and 200-2 15 K in monocrystalline thin films of SnTe with charge carrier concentration PH = (3.5 -4.5). 1020 cm3 and bulk powder samples ...

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“…The carrier concentration for both SnTe and PbTe decreases with increase in mobility corresponding to temperature rise. This phenomenon of increase in carrier mobility with temperature shows the absence of scattering points due to the nano-textured grains and surface roughness of the deposited film [21]. The obtained results agree with the Petritz-mobility model explaining the temperature-dependent relationship between grain boundaries and carrier transportation [58,59].…”

“…However, conventional TEGs suffers from a rigid and brittle structure which limits their surface contact area and thus reduces heat recovery efficiency [20]. In this aspect, low-dimensional thin TE materials can realize higher zT than their bulk counterpart due to their low thermal conductivity associated with quantum confinement effect [21][22][23]. Meanwhile, thin film thermoelectric devices use less amount of materials compared to bulk thermoelectric generator (TEG) and provides easy integration with integrated circuits [24,25].…”