All contemporary microelectronics is based on utilization of single-crystalline silicon, and it is unlikely that any other semiconductor will be able to supplant it in near future. During the past few years, researchers at Belgorod State University  (BelGU) have been investigating properties of carbonic coatings applied upon silicon. Such coatings enable to make the material harder and more resistant to mechanical failure. Besides, the coating allows to modify electrophysical properties of silicon as required. In their new work, Alexander Kolpakov  and his colleagues at the research laboratory of ion-plasmous technology development and implementation at Belgorod State University have investigated properties of carbonic coating alloyed by nitrogen atoms. The article about the research will be published in the next issue of the “Russian Nanotechnologies” journal. The research has been sponsored by Federal Target Program “Scientific and research and educational staff of innovative Russia ».

Carbonic coating properties are determined by the shape of electron clouds of carbon atoms. In case of sp³-hybridization of electron clouds, a carbon atom turns out to be inscribed into an imaginary pyramid with a triangular base: four electron clouds surrounding the nucleus diverge from each other at an angle of 109 degrees. Such electron structure is typical of diamond atoms. A large share of bonds with sp³-hybridization conditions high density of coating (up to 3 g/cm³) and a larger width of forbidden gap  (up to 5.5 eV). Increasing the share of sp²-hybridization atoms, which is typical of graphite, decreases the coating density and the forbidden gap width. Changing conditions of carbonic coating formation enables to control phase correlation and to obtain a material with preset properties.

The researchers have demonstrated that increasing the share of nitrogen atoms included in the carbonic coating augments the share of sp²-hybridization atoms and improves electroconductivity of the material. As a matter of fact, this happens only up to a certain limit: when there are too many nitrogen atoms, carbon nitride molecules are being formed in the coating, and electroconductivity begins to decrease again. The authors have also investigated dependence of coating properties on its depth. It has been found out that as the coating depth decreases, its specific conductance reduces.

Scanning of nitrogen-alloyed carbonic coating surfaces that were obtained via the scanning probe microscopy method. Illustration by the research authors

Investigation of the coating surface structure via scanning probe microscopy has proved that clusters from 10 through 100 nm in dimension (depending on the coating depth per se) are found in its structure. On their surface, electrophysical properties of the material change. Perhaps, these structural peculiarities will find application in electronics in the future.

An alloyed carbonic coating possesses semiconducting properties, and its electroconductivity can be controlled by changing the environment temperature. At the same time, electrophysical properties of the “silicon-coating” complex are changing. By applying carbon coatings with different nitrogen content, the forbidden gap width of the complex can be changed from 1.12 eV (the width of forbidden gap, which is typical of silicon) up to 0.19 eV. This property of coatings “make their application in nanotechnology and microelectronics promising”, the authors state.

Source of information:

A. Ya. Kolpakov, I.V. Sudzhanskaya, M.E. Galkina, I. Yu. Goncharov, A.I. Poplavsky, S.S. Manokhin “Influence of nitrogen alloyed degree  степени легирования азотом and width on electroconductivity and morphology of nano-dimensional carbonic coatings on silicon ”. Russian Nanotechnologies, # 3–4, 2011.

Kazantseva Anastasya