Electronic structures of Si(111) in the 7 x 7 <-> "1 x 1" phase transitionstudied by surface second-harmonic generation

Surface second-harmonic generation (SHG) of Si(III)-7 x 7 shows an increase in intensity for the surface-state transition (56%) and the strain-induced E-0' interband transition (32%) in response to the phase transition to "1 x 1" taking place around 1100 K. The SHG surface-state transition in "1 x 1 " is assigned as the redshifted S-3 --> U-1 transition in 7 x 7 from the ob servation of no discernible changes in the resonant characteristics. From t he symmetry and atomic geometry of the electronic states responsible for SH G,the intensity jump is related to the dissolution of the stacking fault in the "1 x 1" phase. (C) 2001 Elsevier Science B.V. All rights reserved.