Comparative study of Fermi energy pinning and adatom bond character: Antimony versus the column 3 elements (Al, Ga, In) on GaAs (110) and GaSb (110)

Abstract

New results which probe the nature of a defect mechanism responsible for pinning the Fermi energy within the band gap on the (110) surfaces of the 3-5 compounds are presented. From these results it is concluded that to first order the Fermi energy pinning position is independent of the fundamental difference between the Sb-GaAs chemical bond and the column 3 metal-GaAs bond. Furthermore, based on the defect mechanism for the Schottky barrier formation proposed by Spicer and Lindau, the present data can be most easily understood if the defect is more complex than a single surface lattice vacancy. Previously, investigations of column 3 metals on both n- and p-type GaAs, by photoemission electron spectroscopy, revealed a systematic difference in surface Fermi energy stabilization in the gap, with p-type samples pinning 0.25 eV below n-type samples. In the present work, it is shown that antimony, a column 5 element, yields essentially the same Schottky barrier height as the column 3 metals when adsorbed on GaAs (110). A strong similarity in the barrier height is also noted when Sb adsorption is compared to Ga adsorption on GaSb (110). The observed tendency for n-type GaSb to pin closer to the valence-band maximum than GaAs is consistent both with the Spicer/Lindau defect mechanism and with the ‘‘anion rule’’ of McCaldin, McGill, and Mead. These results are important for the theory of Schottky barrier formation and for Schottky barrier device fabrication.