Schottky Barrier Formation at Nonreactive Interfaces: Ga/Gaas(1Q0) and Pb/Gaas(10G)

The chemistry, overlayer morphology, and band bending occurring upon room temperature deposition of Ga and Pb on GaAs(lOO) are studied via high resolution photoemission spectroscopy, low energy electron diffraction and contact potential difference measurement. Both interfaces are abrupt and unreacted. At submonolayer coverage, Ga and Pb grow two dimensionally on GaAs(100). An ordered (1X2) superstructure is obtained for Pb(1/2 ML)/ GaA(100) by low temperature annealing of the interface (— 300 °C). Clustering is dominant at high coverage. With Ga, the Fermi level (E_F) converges toward a position 0.68 eV above the valence band maximum (VBM), in agreement with the position obtained for the GaAs(llO) surface. The room temperature deposition of Pb leads to E_fstabilization at 0.57 eV above VBM, independent of the initial surface stoichiometry (Ga or As rich). The evolution of the band bending as a function of metal coverage emphasizes in both cases the importance of adatom-induced states at low coverages and the transition to final E_fposition upon metallization, in support of models based on metal-induced gap states.