Model band structure of reconstructed (111) 2 × 1 surface of silicon

We have computed the electronic band structure for a model of the 2 × 1-reconstructed (111) surface of Si, based on 2 two-dimensional net of dangling bonds. A pairing of surface atoms is assumed, involving a displacement and a tilting of the dangling bonds towards each other. The energy gap that separates the two bands of surface states obtained increases with the degree of reconstruction, which is taken as a parameter. Experimental data, particularly surface optical absorption, find a satisfactory explanation in terms of this calculation, which indicates in Si (111) 2 × 1 a shift of the surface atoms by about 8% of their ideal distance.