282 / 2017-12-07 00:57:19

First-principles investigations of point defects at 4H-SiC/SiO2 interface

SiC/SiO2,interface,First-principles,defects

全体主题 > Device characterization and modeling

Summary
The electronic structure of point defects at 4H-SiC/SiO2 interface is investigated by density functional theory. The results demonstrate characteristic features of the point defects at the SiC/SiO2 interface, including carbon vacancy, silicon vacancy, divacancy, and antisite pair. The defect energy level leads to Fermi energy changes, while the density of states of defect energy level is largely related to electronic state of several atoms in the vicinity of the defect. Formation energy is particularly high for Si vacancy, and is related to the different chemical potential that differs from C-rich to Si-rich interface.

Motivation
SiC can be easily oxidized into SiO2, which is a unique advantage among the wide-gap semiconductors. However, this great advantage for device manufacturing is still marred by the large density of interface states at the SiC/SiO2 interface1. This disadvantage limits the large-scale manufacturing of mental-oxide-semiconductors2. Extensively research of defects at the interface is needed to improve the performance of SiC MOS devices. Recent years, many studies of point defects in SiC are carried out by Electron paramagnetic resonance, Photoluminescence, Deep-level transient spectroscopy, etc. Carbon vacancy(VC), silicon vacancy3(VSi), divacancy(Vdi), and antisite pair are considered to exist at the interface, but the electronic structure and the stability of defects still needs revealing. We model the four type defects at the interface to understand mechanism of these defects affecting the electronic structure of the SiC/SiO2 interface.

Results
This paper centers on the electronic states calculation about the defects at 4H-SiC/SiO2 interface (Fig. 1(a)). Using first-principles, the model is formed with 4H-SiC and SiO2 of cristobalite structure. Four defects at the SiC/SiO2 interface are shown in Fig. 1 (b) (c) (d) (e), along with DOS for each structure compared with the perfect interface shown in Fig. 2 (a). For further understanding how defects affect the electronic structure and energy, local density of states is performed in Fig. 2 (b) (c) (d) (e). Through further analysis, we discovered that several atoms near the defect play a key role for defect energy level at the interface. Formation energy for each defect changes with different chemical potential from C-rich to Si-rich structure (Fig. 2 (f), Tab. 1).

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2 Iskandarova I, Khromov K, Knizhnik A, et al. The role of neutral point defects in carrier mobility degradation in bulk 4H-SiC and at 4H-SiC/SiO2 interface: First-principles investigation using Green's functions, J. Appl. Phys, vol. 117, no. 17, 175703 (2015).
3 Coutinho J, Torres V J B, Demmouche K, et al. Theory of the carbon vacancy in 4H -SiC: Crystal field and pseudo-Jahn-Teller effects, Phys.rev.b, vol. 96, no. 17, 174105 (2017).