Significance Statement
Materials that reserve their properties at high radiation levels and elevated temperatures are of great necessity in electronic engineering. Silicon carbide is the most promising for operations under the variance of external influence. However, its high production cost makes it unsuitable for wide utilizations in electronic devices. The alternative has been to develop technologies for obtaining elements for electronic devices on the base polycrystalline such as nanocrystalline silicon that can grow at significantly lower temperature, slightly cheaper and has characteristics that are significantly similar to those of the silicon carbide single crystals.
In a recent paper published in Super lattices and Microstructures Professor Alexander Semenov and colleagues from the Institute for Single Crystals of National Academy of Sciences of Ukraine investigated electron transport in nanocrystalline Silicon Carbide films obtained by direct ion deposition. Their aim was to study the mechanism of electrical conductivity of nanocrystalline silicon carbide films obtained by direct ion deposition, in a wide range of temperatures.
First, electrophysical properties had to be investigated on a series of samples of nanocrystalline films of varying microstructure on a leucosapphire single crystalline substrate. Heteropolytype and monopolytype films created by the layers of nanocrystalline silicon carbide of varying polytypes were also studied. The researchers also used an electron microscope to micro analyze presence of any impurities in the films used. Conductivity measurements by the four-contact method using direct current was employed so as to clarify the mechanism of charge transfer in the obtained films and check for temperature dependence of their electrical resistance.
The authors of this paper observed that no impurities were present in the films except for oxygen in insignificant percentages. It was also noted that the excess silicon in silicon carbide caused by self-doping gave rise to electronic conduction in the semiconductors. Electrical resistance of the samples of the investigated complex inhomogeneous systems was analyzed using varying physical models of the techniques of charge transfer of semiconductor type. From this analysis, the research team was able to note that the mechanisms of conduction of the monopolytype and heteropolytype films were different.
The monopolytype films were observed to possess temperature dependencies of electrical resistance that was in conformity with the thermal activation mechanism described by the Arrhenius relation. The team eventually noted that within the temperature interval from 2 K to 110 K the temperature dependence on the conductivity in the considered film corresponded to a known function. At this point charge transport in the low temperature region was realized with the participation of intercrystalline amorphous regions.
From the above empirical analysis, it is clear that charge transport in nanocrystalline silicon carbide films with electronic conduction caused by the internal defects created by the excess silicon ions has an intricate character and cannot be defined by a single mechanism. Intercrystalline regions are seen not to exert noticeable effect on the electron transport. In the heteropolytype films, the main contribution to electrical conductivity can be attributed to the contact regions of the heterojunction where charge transmission is realized by tunneling via the energy barriers generated by the conduction band offset in the contact regions of the heterojunction.
The obtained nanocrystalline SiC films are affordable functional SiC based material for the development of new devices in electronics.
Reference
A. Kozlovskyi, A. Semenov, S. Skorik. Electron transport in Nano crystalline Silicon Carbide films obtained by direct ion deposition. Superlattices and Microstructures volume 100 (2016) pages 596-604
Institute for Single Crystals, STC “Institute for Single Crystals”, National Academy of Sciences of Ukraine, 60 Nauky Ave., 61001 Kharkiv, Ukraine.
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