Positively charged carbon vacancy in three inequivalent lattice sites of6H−SiC: Combined EPR and density functional theory study

Abstract

The $Ky1$, $Ky2$, and $Ky3$ centers are the dominant defects produced in the electron-irradiated $p$-type $6H\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}$ crystals. The electron paramagnetic resonance study of these defects has been performed in the temperature range of $4.2--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at $X$, $K$, and $Q$ bands. The centers are characterized by the fourfold silicon coordination established on a basis of the observed hyperfine structure. At low temperatures both $Ky1$ and $Ky2$ defects reveal the ${C}_{S}$ symmetry that only slightly deviates from the ${D}_{2d}$ one. At high temperatures, the thermally activated reorientation from one Jahn-Teller distortion to the others causes the averaging of the $Ky1$ and $Ky2$ spectra in such a manner that their spin-Hamiltonians correspond to the axial symmetry. The $Ky3$ center has axial symmetry in all the temperature range under investigation. Its hyperfine parameters for the first-shell silicon atoms are substantially different from those determined for the $Ky1$ and $Ky2$ centers. Based on the density functional theory, the calculations of the electronic structure of a number of fourfold silicon coordinated defects have been carried out for the unambiguous identification of the observed defects through the comparison of experimentally determined and calculated hyperfine parameters. The present study proves an assignment of the $Ky1$, $Ky2$, and $Ky3$ centers to the positively charged carbon vacancy located in two quasicubic and hexagonal sites of the $6H\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}$ lattice, respectively. The features of the ${V}_{\mathrm{C}}^{+}$ defect related to the multivalley character of its potential energy surface are also discussed. It is shown that this defect can be localized in the minima of different symmetry depending on the occupied lattice site, and these minima are experimentally distinguishable by the values of hyperfine parameters.