On the origin of resonance features in reflectance difference data of silicon

The physical origin of sharp resonances in reflectance difference spectrosc opy (RDS) data at the critical points of the dielectric function of bulk Si , previously assigned to surface-bulk transitions, to photon localization o r to optical transitions from bound dimer states to excited dimer states is investigated. We show that uniaxial in plane stress of bulk Si induces sha rp resonances at exactly these critical points of Si via the piezo-optic ef fect. In the recent literature, it was shown that surface reconstruction as well as dimerization exerts anisotropic stress, e.g. along the dimer direc tion, and the resulting strain is extending into the bulk. In our contribut ion, we simulate this surface strain by externally stressing different Si f aces and compare ex situ measured RDS data of Si(0 0 1), Si(1 1 1) and Si(1 1 0) surfaces with RDS data measured in situ and density functional theory calculations. (C) 2001 Elsevier Science B.V. All rights reserved.