SURFACE-STRUCTURE, LATTICE-DYNAMICS, AND RAMAN-SPECTROSCOPY OF SULFUR PASSIVATED INP(001)

The sulphur-passivated InP(001) surface is studied theoretically using density-functional methods and experimentally using Raman spectroscopy. The lowest energy structure is a very striking (2 X 2) reconstruction with the S atoms displaced from the bridge sites to form short and long dimers, belonging to Two distinct sublayers. The underlying In layer remains integral, but the P layer below it also splits into two sublayers. This structure is used to calculate the [001] interplanar force constants and the backscattering Raman spectrum. Two peaks arising from surface-layer vibrations, predicted to be at 190 and 257 cm(-1), are observed experimentally.