Gallium ARSENIDE(100) and Zinc SELENIDE(100): Surfaces and Interfaces with Metals.

GaAs(100) and ZnSe(100) surfaces and interfaces are studied by using high resolution photoemission spectroscopy, contact potential difference measurement, low energy electron diffraction and Auger spectroscopy. These surfaces are prepared by capping and decapping techniques on MBE-grown samples. Highly reproducible ordered surfaces are obtained at various annealing temperatures. Researches are performed to correlate these surface atomic structures to their electronic properties. Chemistry, growth mode and band bending at GaAs(100) and ZnSe(100) interfaces with metals are also investigated. On GaAs(100) surfaces, the band bending is independent of surface reconstruction ((1 x 1) --> c(4 x 4) --> c(2 x 8) --> (4 x 2)). The work function undergoes large variations of up to 400 meV between the (2 x 4)-c(2 x 8) and (4 x 2)-c(8 x 2) structures. These variations are attributed to surface dipoles, which are explained by applying a simple electron counting model to each reconstruction. The studies of Ga/ and Pb/GaAs(100) reveal that both interfaces are abrupt and unreacted. With Ga, the Fermi level (E_{rm F}) converges toward a position 0.68 eV above the valence band maximum (VBM). The room temperature deposition of Pb leads to E_{rm F} stabilization at 0.57 eV above VBM. The evolution of the band bending as a function of metal coverage in both cases supports models based on metal-induced gap states. We have investigated the Se-rich (2 x 1) and Zn -rich c(2 x 2) ZnSe(100) surfaces. The (2 x 1) reconstruction corresponds to a complete monolayer of Se dimers. The c(2 x 2) reconstruction corresponds to a half-monolayer vacancy structure. We find a 150 meV decrease in surface electron affinity at the (2 x 1) --> c(2 x 2) transition, consistent with the model for GaAs(100) surfaces. Dramatic differences in chemical behavior have been found between Al/ and Au/ZnSe(100) interfaces. Au forms an abrupt, non-reactive interface with ZnSe, in contrast to significant chemical reaction at the Al/ZnSe interface. The stabilized Fermi level positions for Al and Au on ZnSe(100) are 2.15 eV and 1.15 eV above VBM. We also find that the Au/p-ZnSe Schottky barrier height can be reduced by 0.25 eV by introducing a 2-3 monolayer Se interlayer between the metal and the semiconductor.