Density-functional study of atomic and electronic structures of multivacancies in silicon carbide

作者：Iwata Jun Ichi^*; Shinei Chikara; Oshiyama Atsushi^*

来源：Physical Review B, 2016, 93(12): 125202.

DOI：10.1103/PhysRevB.93.125202

We report the density-functional calculations that provide a firm theoretical framework to identify the multivacancies and unravel the underlying physics in the most stable silicon carbide polytype 4H-SiC. The calculations with the generalized gradient approximation (GGA) for the Si and C monovacancy, V-Si and V-C, have clarified the significantly lower formation energy of the C vacancy accompanied by the efficient pairing relaxation of the surrounding Si dangling bonds. Our GGA calculation also predicts a stable next-neighbor VCVC divacancy which is lower in the formation energy than the usual nearest-neighbor divacancy VCVSi discussed in the past. We also perform the calculations with the hybrid functional and confirm the stability of the next-neighbor VCVC divacancy. Our calculations indeed clarify that it is possible to detect the VCVC with its peculiar hyperfine coupling constants by the electron paramagnetic resonance (EPR) measurements. Based on the structural characteristics and the energetics for the monovacancy, we further propose an extended dangling-bond-counting (EDBC) model to choose the energetically favorable topological network of the vacant sites for the multivacancy. The GGA calculations combined with the EDBC model reveal that V-3 and V-6 are energetically favorable. The stable V-3 is a nearest-neighbor complex of V-C-V-Si-V-C, whereas the V-6 is the high-symmetry V-5 (the central V-Si surrounded by four V-C) plus a symmetry-breaking next-neighbor V-C. We perform the GGA calculations for the electronic structure of such V-3 and V-6 and discuss the possibility of detecting these multivacancies. In particular, the EPR-detected ANN1 center is provisionally identified as the doubly positive trivacancy V-C-V-Si-V-C.

• 出版日期2016-3-3