Clarification of the GaP(001)(2x4) Ga-rich reconstruction by scanning tunneling microscopy and ab initio theory

We infer the structure of the GaP(001)(2x4) surface from a study of scanning tunneling microscopy (STM) images obtained under UHV conditions on metal-organic vapor phase epitaxy grown samples. STM images are compared with results of first-principles calculations for models energetically most favorable under Ga-rich growth conditions. The comparison shows that the GaP(001)(2x4) surface unit cell consists of a mixed Ga-P dimer on top of a complete gallium layer, hence ruling out the Cia-Ga dimer model