W. Drube

Inverse photoemission from surface and interface states of III–V semiconductors

We have measured unoccupied surface and interface states on Ga‐ and In‐derived III–V semiconductors with momentum‐resolved inverse photoemission. The position of the surface states is found to be unrelated to the fundamental band gap. Instead, a connection with the gap of p‐like states can be made. This finding is discussed in the context of theories of Fermi level pinning and band lineup, which use (virtual) gap states as a reference energy. Unoccupied metal‐induced gap states are found for transition metals (Y, Ti, V, Mn, Pd) on GaAs(110) and InP(110). Their energy tracks the Fermi level pinning position, suggesting that these states are connected with the pinning process. A tentative assignment in terms of nonbonding metal d states is given.

Layer-by-layer electronic structure at semiconductor-metal interfaces: band gap and magnetism

Epitaxial semiconductor-metal interfaces are studied with inverse photoemission. For Group-V elements (Sb,Bi) on III–V surfaces (GaAs(110),InP(110)) it is possible to distinguish electronic states of the first few layers. The metal layer at the interface becomes semiconducting. Interfaces of semiconductors with ferromagnetic metals, such as epitaxial GaAs(110)Fe, exhibit a change in magnetism. The ferromagnetic exchange splitting can be resolved very clearly in Fe by inverse photoemission. The bulk splitting of 2 cV is observed to collapse to < 0.7 eV for a monolayer of Fe on GaAs(110), probably due to FeAs bonding. It is suggested to use Au as an epitaxial barrier layer between GaAs and Fe since it is lattice-matched and does not suppress magnetism at the interface. Gold also plays the role of a surfactant, thereby making it possible to grow Fe in a layer-by-layer fashion.