The Si (100) surface: A theoretical study of the unreconstructed surface

The potential, charge density, and energy spectrum of an ideal unreconstructed Si (100) surface is obtained self-consistently. Two bands of surface states that arise from broken surface bonds are found in the energy gap between the valence and conduction bands. One band (1 eV wide) has its electron density localized about a line through and normal to the surface atoms, with a node on the atoms; the other band (2. 5 eV wide) has its charge located around a line through a row of surface atoms, again having nodes on the surface atoms. The role these surface states play in surface reconstruction as well as in understanding the surface-state spectrum of stepped Si (111) -surface bands is discussed. Additional surface states within the valence band are found and their significance discussed.