The electron conductivity of the surface states and the sub-surface space charge layer originating from the Si(111)-(4 x 1)–In reconstruction were measured as a function of temperature. The conductivity of the surface states fell sharply around 130K, with decreasing temperature; revealing a metal–insulator phase transition of the surface reconstruction. In contrast, the influence of the phase transition upon the conductivity of the space charge layer was limited to temperatures above 60K. This implied that the surface Fermi level remained strongly pinned, in spite of the phase transition; indicating the presence of free carriers in the surface states, down to quite low temperatures.

Phase Transition of the Si(111)4 x 1–In Surface Reconstruction Investigated by Electron Transport Measurements. T.Uchihashi, U.Ramsperger: Surface Science, 2003, 532-535, 685-9