Structure of the GaP(001)-4×2-In surface investigated with LEED, STM, photoelectron spectroscopy, and ab initio calculations

Surface structures at the initial stage of indium adsorption on GaP(001) are studied by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), photoelectron spectroscopy (PES), and ab initio calculations. After indium deposition on the P-rich GaP(001)-2×1 surface followed by annealing at 400–450 °C, ×4 LEED spots were observed along the [110] direction. STM images obtained after 400 °C annealing show a 4×2-In reconstruction with row and hump structures. PES result for the 4×2-In surface shows existence of In atoms in two different chemical environments; one with In-In bonding and the other with In surrounded by phosphorus atoms at the surface. These LEED, STM, and PES results are consistent with the ζ structure, which was proposed for cation-rich clean surfaces of III-V semiconductors containing arsenic or antimony. Several plausible models derived from the original ζ model are examined by first-principles calculations for the GaP(001)-4×2-In surface.