(001) Surfaces of GaP and InP: structural motifs, electronic states and optical signatures

We present ab initio calculations on the energetics and geometry, as well as electronic and optical properties of InP and GaP(001) surfaces. Cation-rich conditions lead to the formation of asymmetric cation-anion dimers on top of a (2 x 4) reconstructed cation-terminated surface. Anion-rich surfaces form c(4 x 4) reconstructions. Based on the DFT-LDA electronic structure, we compute the reflectance anisotropy of the energetically favoured (2 x 4) reconstructions. Strong anisotropies in the low-energy region arise from transitions between a-like cation-cation bonding states and empty dangling bonds. Transitions involving P dimer states and surface modified bulk wave functions contribute at higher energies. The application of GW corrections leads to non-uniform shifts of characteristic peaks and changes the line shape, considerably improving the agreement with experiment. (C) 2000 Elsevier Science B.V. All rights reserved.