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SiC: A review

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Literature Survey

Polytypes

3C-SiC

4H-SiC

Point defects

Vacancy

Silicon vacancy is a high-energy defect that can only be observed in heavily irradiated {SiC}\cite{Alfieri2012a} It is experimentally observed that silicon vacancies possess a peculiar high-spin configuration($S=\frac{3}{2}$) with three aligned spin resulting in a $-1$ charge state.[ref needed] ($\mathrm{O_{Si}}$)

A Jahn-Teller distortion of the silicon vacancy is not observed in any charge state.\cite{Torpo2001}

Large energy drop when transforming into the complex made of carbon vacancy and a carbon antisite ($\mathrm{V_cC_{Si}}$).[ref needed]

Carbon vacancy exists in the \(2+\) and $0$ charge states in {3C-SiC} and in $2^+$, $0$ and $2^-$ charge states in {4H-SiC}.

substitutional oxygen at carbon site (O<sub>C</sub>) inContrary to the silicon vacancy, the carbon vacancy exhibits a strong Jahn-Teller effect.\cite{Torpo2001}

541.74452341Oxygen in 3C-SiC

Substitutional oxygen on the carbon site ($\mathrm{O_C}$) is electrically active. $\mathrm{O_C}$ is a double effective mass-like donor in {3C-SiC}, like sulfur in silicon. The one-electron level of the defect is at $E_c-0.2$~{eV}. $\mathrm{O_C}$ is an on-center defect with T$_d$ symmetry.

Single positive charge state no metastable state was found, so this is an on-center defect with T$_d$ symmetry. The Si-o distance is sligtly shorter than in the neutral state.

In the case of O$_C^{2+}$, the SI-O distance is further shortened but the geometry is essentially the same as for the neutral and the single positive defect.

The occupation levels of the $\mathrm{O_C}$ double donor are at $E\left(2+/+\right)=E_v+2.13$~{eV} and at $E\left(+/0\right)=E_v+2.09$~{eV}.

They are two metastable configurations for oxygen at the silicon site ($\mathrm{O_{Si}}$) in the neutral state. In both configuration there is a double occupied level in the gap at $E_v+0.1$ and at $+1.1$~{eV} for C$_{2v}$ and T$_d$, respectively. Therefore $\mathrm{O_{Si}}$ is a hyperdeep double donor (or rather a double hole trap).

Oxygen in 4H-SiC

Due to high formation energy of $\mathrm{O_{Si}}$ in {3C-SiC}, the \textbf{oxygen at silicon site} in {4H-SiC} was not investigated.

The formation energy of \textbf{oxygen at carbon site} ($\mathrm{O_{C}^0}$) is $1.8$~{eV} higher in {4H-SiC} than in {3C-SiC}, because of the one-electron donor level occupied by two electron is situated about 1.0~{eV} higher in {4H-SiC} than in {3C-SiC}.

The double occupied level is at $E_v+3.2$~{eV} (for the k site) [not an effective-mass-like one as in {3C-SiC}]. Possible charge states of $\mathrm{O_{C}}$ are ($2+$, with $C_{3v}$ symmetry), ($+$) and ($0$), both with $C_{1h}$ symmetry. The (2+/+) and (+/0) occupation levels at the k site are at $E_v+3.1$~{eV} and $E_v+3.2$~{eV}.

The diference between k and h site were examined only for $\mathrm{O_{C}^{2+}}$. The total energy was lower at the h site by 0.11~{eV} and the Si-O bond length were about the same.

Fluorine in SiC

None to resume?!

Chlorine in 3C-SiC

For spin-average calculations, both $\mathrm{Cl_C}$ and $\mathrm{Cl_{Si}}$ act as donors in their neutral state. $\mathrm{Cl_C}$ retains its initial $\mathrm{T_d}$ symmetry, $\mathrm{Cl_{Si}}$ lowers it from $\mathrm{T_d}$ to $\mathrm{C_{3v}}$.

[discuss energy formation differences.]

For spin-polarized calculations, $\mathrm{Cl_C}$ retains tetragonal symmetry, while $\mathrm{Cl_{Si}}$ lowers it to trigonal.substitutional oxygen at carbon site (O<sub>C</sub>) in

Regarding interstitials, $\mathrm{Cl_i}$ in $\mathrm{T_d}$ or in $\mathrm{O_h}$ both retained its symmetry. Energy-wise, they have very high $\mathrm{E_{form}}$ thus they are unlikely to occur.

In sum, it is found that vacancies arising after implantation, rather than $\mathrm{Cl}$, can be held responsible for carrier compensation in n-type {SiC}, while for p-type {SiC} the presence of a compensating center, such as the $\mathrm{Cl_CAl_{Si}}$ complex, can be put forwsubstitutional oxygen at carbon site (O<sub>C</sub>) inard.substitutional oxygen at carbon site (O<sub>C</sub>) in

Method

Convergency Tests

Energy Cut-off

Ecut (eV)FFT gridEtotal (eV)ΔE (eV)
35058x58x64-542.46690454+0.0000
40062x62x68-542.40930972+0.0576
45066x66x72-542.32762253+0.1393
50068x68x76-542.22542586+0.2415
55072x72x80-542.24431883+0.2223
60074x74x84-542.25605694+0.2108
Ecut (eV)FFT gridEtotal (eV)ΔE (eV)
35058x58x64-538.17052187+0.0000
40062x62x68-538.07438469+0.0961
45066x66x72-537.98184250+0.1887
50068x68x76-537.87645909+0.2941
55072x72x80-537.89586716+0.2757
60074x74x84-537.90935670+0.2612
Ecut (eV)FFT gridEtotal (eV)ΔE (eV)
35058x58x64-541.99735253+0.0000
40062x62x68-541.90696915+0.0904
45066x66x72-541.81475011+0.1826
50068x68x76-541.71212207+0.2852
55072x72x80-541.72749107+0.2699
60074x74x84-541.74452341+0.2528
Ecut (eV)FFT gridΔEform (eV)
35058x58x64-3.7074
40062x62x68-3.7009
45066x66x72-3.6994
50068x68x76-3.6952
55072x72x80-3.6995
60074x74x84-3.6962

Bibliography

[1]
A. Mattausch, Ab-Initio Theory of Point Defects and Defect Complexes in SiC, University of Erlangen-Nuremberg, 2005.