Origin of hydrogen passivation in $4H$-SiC

Carbon vacancy ${\mathrm{V}}_{\mathrm{C}}$ is the dominant detrimental defect in SiC, and hydrogen passivation of ${\mathrm{V}}_{\mathrm{C}}$ is often used to facilitate its application in electronic devices. However, the exact nature of hydrogen passivation of ${\mathrm{V}}_{\mathrm{C}}$ in $4H$-SiC remains inconclusive in view of the available divergent experiment and theoretical findings. Here, using the Heyd-Scuseria-Ernzerhof screened hybrid density functional calculations, we demonstrate that the ${\mathrm{V}}_{\mathrm{C}}$ defect can capture up to four hydrogens, and the electrically active levels within the band gap can be entirely passivated, in line with recent reported experimental observations. This paper, thus, casts light on the role of hydrogen passivation in SiC.

Figure 1

Formation energies as a function of Fermi level for carbon vacancy at both h-site ${\mathrm{V}}_{\mathrm{C}}\left(\mathrm{h}\right)$ and k-site ${\mathrm{V}}_{\mathrm{C}}\left(\mathrm{k}\right)$ in $4H$-SiC under C-poor condition. The zero of the Fermi level is at the valence band maximum (VBM) of $4H$-SiC. The slope of the formation energy segment gives the defect charge state and the Fermi level at which the slope changes denote the transition energy level $\varepsilon \left(q/q^{\prime }\right)$.

Figure 2

The stable atomic configuration for neutral defect systems of (a) ${\mathrm{V}}_{\mathrm{C}}$, (b) ${\mathrm{V}}_{\mathrm{C}}+1\mathrm{H}$, (c) ${\mathrm{V}}_{\mathrm{C}}+2\mathrm{H}$, (d) ${\mathrm{V}}_{\mathrm{C}}+3\mathrm{H}$, (e) ${\mathrm{V}}_{\mathrm{C}}+4\mathrm{H}$, and (f) ${\mathrm{V}}_{\mathrm{C}}+2\mathrm{O}$ in $4H$-SiC. The blue-colored ball is for Si, the brown one is for C, the magenta one is for H, the orange one is for O, and the four Si neighbors of ${\mathrm{V}}_{\mathrm{C}}$ are emphasized in green for convenience. The calculated isosurface plots the charge density difference for H and O incorporation in $4H$-SiC $\left(0.01e/\mathrm{Boh}{\mathrm{r}}^3\right)$. The electron charge accumulation is shown in gray areas, whereas the electron depletion is not being displayed for viewing convenience.

Figure 3

The single-particle defect levels for ${\mathrm{V}}_{\mathrm{C}}, {\mathrm{V}}_{\mathrm{C}}+n\mathrm{H} (n=1-4)$ and ${\mathrm{V}}_{\mathrm{C}}+2\mathrm{O}$ defects in $4H$-SiC in the neutral charge state. The upward and downward arrows stand for the up- and down-spin states of the occupied electron, respectively, while the unoccupied hole state is depicted by open dot.