Surface states on cleaved (111) silicon surfaces

Abstract

Conductivity changes resulting when single crystal silicon is cleaved in ultrahigh vacuum have been measured parallel to the cleavage plane over various temperature ranges for gold doped and high resistivity boron doped silicon. The resulting change of conductivity is related to the position of the surface states in the forbidden band and to the quantity of charge, in the surface states, which has been trapped from the bulk. Analysis of the data shows a high density of surface states on the atomically clean cleaved surface, centered 0.28 ± 0.08 eV above the valence band edge. The density of surface states depends on the model chosen, but is at least 10 12 cm −2 eV −1. These results are in good agreement with theoretical expectations and other types of experimental results. Oxygen adsorption is observed to introduce different surface states, also of high density but centered 0.6 ± 0.15 eV above the valence band edge at the surface. Low temperature measurements on gold doped silicon crystals show that probably no conduction takes place through the surface states themselves, either on clean or oxidized surfaces. These results are used to discuss possible models of the surface state distributions.