Electronic structure of the (111) surface of semiconductors

The electronic structure of the (111) surface of semiconductors is investigated using the bond-orbital model. The semi-infinite solid is represented by a system which has the two-dimensional periodicity of the (111) surface, but the third dimension is terminated after a finite number of layers, which leads to a convergent electronic band structure. Since there is an abundance of experimental data on Si(111), we have examined this material in great detail. The total densities of states and the energy-band structures are presented for ideal, relaxed, and (2×1) reconstructed Si(111). The effect of the reconstruction is to split the universal surface states, $S_1$, $S_2$, and $S_3$, into various bands. In particular, we have been able to explain various features of the recent angular resolved photoemission from cleaved Si(111) without invoking any new surface states. The calculated electronic structure of ideal Ge(111) and diamond (111) is briefly discussed. The chemisorption of hydrogen on Si(111) is also studied. The surface states of the compound semiconductors, e.g., AIP are found to have similar features to the elemental semiconductors. However, their energy locations depend on the nature of the surface (i.e., anion or cation type). We compare our results with photoemission experiments.