Physical Origin of Hydrogen-Adsorption-Induced Metallization of the SiC Surface: $n$-Type Doping via Formation of Hydrogen Bridge Bond

We perform first-principles calculations to explore the physical origin of hydrogen-induced semiconductor surface metallization observed in $\beta \mathrm{\text{−}}\mathrm{SiC}(001)\mathrm{\text{−}}3\times 2$ surface. We show that the surface metallization arises from a novel mechanism of $n$-type doping of surface band via formation of hydrogen bridge bonds (i.e., Si-H-Si complex). The hydrogen strengthens the weak Si-Si dimers in the subsurface by forming hydrogen bridge bonds, and donates electron to the surface conduction band.

Figure 1

Structure of SiC surface with and without H adsorption. (a), (c), and (e) show the side view of the clean surface, the surface with H at top dimer, and the surface with H at both top and bottom dimers, respectively. (b), (d), and (f) show the corresponding top view. Red atoms stand for H atom, green for C, and yellow for Si. $T$ and $B$ indicate the top and bottom dimers which are active in H adsorption. $HB$ indicates the H-bridge bond.

Figure 2

Band structure of $\beta \mathrm{\text{−}}\mathrm{SiC}(001)\mathrm{\text{−}}3\times 2$ reconstruction surface with and without H adsorption. (a) Clean surface; (b) only dangling bonds of $T$ dimers are saturated by H; (c) dangling bonds of $T$ dimers are saturated and H-bridge bonds are formed by H atoms and $B$ dimers. The dashed lines denote the Fermi level. The inset shows the charge density in the plane of the H-bridge bond.