Dopant concentration dependences and symmetric Fermi-level movement for metal/n-type and p-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 \ensuremath{\sim}1 monolayer for doping of 1\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ while ${E}_{F}$ movement is induced by far fewer adatoms for doping of 2\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ 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.