Negative-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>U</mml:mi></mml:math>carbon vacancy in 4<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>H</mml:mi></mml:math>-SiC: Assessment of charge correction schemes and identification of the negative carbon vacancy at the quasicubic site

Abstract

The carbon vacancy (${V}_{C}$) has been suggested by different studies to be involved in the ${Z}_{1}$/${Z}_{2}$ defect-a carrier lifetime killer in SiC. However, the correlation between the ${Z}_{1}$/${Z}_{2}$ deep level with ${V}_{C}$ is not possible since only the negative carbon vacancy (${V}_{\mathrm{C}}^{\ensuremath{-}}$) at the hexagonal site, ${V}_{\mathrm{C}}^{\ensuremath{-}}$($h$), with unclear negative-$U$ behaviors was identified by electron paramagnetic resonance (EPR). Using freestanding $n$-type 4$H$-SiC epilayers irradiated with low energy (250 keV) electrons at room temperature to introduce mainly ${V}_{C}$ and defects in the C sublattice, we observed the strong EPR signals of ${V}_{\mathrm{C}}^{\ensuremath{-}}$($h$) and another $S$ = 1/2 center. Electron paramagnetic resonance experiments show a negative-$U$ behavior of the two centers and their similar symmetry lowering from ${C}_{3v}$ to ${C}_{1h}$ at low temperatures. Comparing the Si and C ligand hyperfine constants observed by EPR and first principles calculations, the new center is identified as ${V}_{\mathrm{C}}^{\ensuremath{-}}$($k$). The negative-$U$ behavior is further confirmed by large scale density functional theory supercell calculations using different charge correction schemes. The results support the identification of the lifetime limiting ${Z}_{1}$/${Z}_{2}$ defect to be related to acceptor states of the carbon vacancy.