Atomic geometry of the 2×2 GaP(111) surface

Abstract

Integral and fractional order beam low-energy electron-diffraction intensity-voltage (I-V) data have been taken on a bombardment-annealed GaP(111)-(2\ifmmode\times\else\texttimes\fi{}2) surface. We have compared these data with calculated I-V curves using a dynamical multiple scattering theory and found very good agreement for the following model: One out of every four Ga surface atoms is missing and the surface Ga-P bilayer is almost coplanar. Surface and deeper layer atoms undergo vertical and lateral displacements from bulk positions. Similar results in other systems suggest that the vacancy model applies on the (111) face of many compound semiconductors.