Theoretical study of polar interfaces of the (122) Sigma =9 grain boundary in cubic SiC

Abstract

The polar and non-polar interfacesof grain boundariesin the zinc blendestructure canbedefined bythestoichiometryin theinterfaceregion,andit ispossibletoconstruct two polar interfaces and one non-polar interface for a symmetrical-tilt grain boundary for which the interface comprises the polar surfaces. The atomic and electronic structures of polar interfaces of the {122) 2 = 9 grain boundary in S i c have been examined using the selfconsistent tight-binding method coupled with the supercell technique, and they have been comparedwithourpreviousresultsfor thenon-polarinterface. In thepresentatomicmodels consistingofazigzagarrangement of5-7units. whichisconsistent withan ~n ~~i m a g e , o n e polar interlace contains the C--C wrong bonds and another polar interface contains the Si-Si wrong bonds, although the non-polar interface contains both types of wrong bonds. The present calculated results indicate that as well as the non-polar interface the respective polar interfaces are possibly stable without the generation of any macroscopic electrostatic fieldsor excess free carriers, although thewrong bondsintroducelocalizedstatesat the band edges and an increase in the electrostatic energy similar to the non-polar interface. This is because the atomicchargesin SiCare mainlycaused by the bond polarization and the wrong bonds do not generate any extra carriers or deep states in Sic, unlike ionic solids or heterovalent compound semiconductors. The calculated energy of formation of the pair of polar interfaces is rather smaller than that of the non-polar interfaces, because the energy increasecaused by bonddistortionsissmaller in the polarinterfaces.which containonlyone type of wrong bond. By using the calculated binding energies, the relative stability of the polar and non-polar interfaces of the (122) E = 9 boundary in Sic has been analysed thermodynamically as a function of the atomic chemical potentials. The calculated thermodynamic potentials of the interfaces indicate that either one or the other polar interlace is always more stable than the non-polar interface for the allowable ranges of the atomic chemical potentials. There is a general discussion of the stability of the polar interfaces in Sic and in compound semiconductors.

Grain boundary structures in silicon carbide: Verification of the extended boundary concept

“…The defocus-dependence of the apparent thickness is considered to arise from the large strain near the boundary. According to the self-consistent tight binding calculation of the atomic and electronic structures in SiC reported by Kohyama et al [6], even if the interfacial bonds are well reconstructed, both bond-length and bond-angle distortions due to wrong bonds are fairly large, and the distortions spread over a few inter-atomic distances; these results are in good agreement with the observed strain contrast along boundaries. Thus, the wide extension observed by Ikuhara et al [2] is believed to originate from this strain effect.…”

Atomistic Modelling of Structures of Tilt Grain Boundaries and Antiphase Boundaries in ?-Silicon Carbide

“…The energies of stoichiometric h001i GBs for small tilt angles are plotted in The dots correspond to the calculated energies and the curves correspond to the fitted expression (8) sponding dislocations. For larger angles, however, the GBs with C atoms in the dislocation cores are the more stable stoichiometric GBs.…”

“…Instead, we follow the approach of Ref. [8] and compute the chemical potentials by assuming that the GB is in equilibrium with atomic reservoirs of Si and C, as it is done in the computation of energies of surfaces [28,29]. The upper limits of m Si and m C are given by the chemical potentials of the bulk phases, m bulk Si and m bulk C .…”

“…The first theoretical investigations of GBs and APBs in the zincblende structure have been performed by Holt [5,6]. Later on, Kohyama and coworkers have studied short period GBs in b-SiC using semi-empiric tight-binding methods [7,8 ] and ab initio calculations [9,10].…”

First-Principles Study of a {122} Σ = 9 Boundary in Cubic SiC: Relative Stability between Zigzag and Straight Models and Comparison with Electron Microscopy Observation

“…We deal with the non-polar interface of the {122} AE ¼ 9 boundary with respect to the direction of the polarity of the two grains, 19,20) because only the non-polar interface is consistent with the stable non-polar interfaces of the AE ¼ 3 boundaries at the triple junction as shown in Fig. 1.…”