Dopant concentration dependences and symmetric Fermi-level movement formetal/n-type andp-type GaAs(110) interfaces formed at 60 K

Abstract

The coverage-dependent Fermi-level movement for Ag, Co, and Ti interfaces formed at 60 K on $n$-type and $p$-type GaAs is shown to be symmetric but dependent on the bulk dopant concentration. Photoemission results show that $E_F$ remains close to the band edges until ∼1 monolayer for doping of 1×${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$ while $E_F$ movement is induced by far fewer adatoms for doping of 2×${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$ with overshooting for $p$-type GaAs. Remarkable surface chemical and structural insensitivity is reflected by similar band-bending trends for adatoms which exhibit very different reactivities and amounts of substrate disruption. We conclude that $E_F$ movement is controlled by the coupling between adatom-induced states and those of the substrate at low temperature, with strong dependence on the bulk doping of the semiconductor.