Metal-semiconductor and condensed gas-semiconductor interface formation

Two adatom/III-V semiconductor interfaces were examined with high resolution synchrotron radiation photoemission spectroscopy. An investigation of a metal-semiconductor interface, Al/GaAs(110), was performed as a function of substrate temperature to correlate the evolving interfacial chemistry and morphology with band bending. Detailed examination shows a separation in energy of approximately 1.0 eV for the Al 2p binding energy for n- and p-type GaAs at submonolayer coverages. This equals the difference in band bending for the two substrates, demonstrating that the adatom energy reference is an intrinsic level of the semiconductor, not the Fermi level. Substrate band bending approaches its final value when E(sub f) becomes the energy reference for the overlayer, and this occurs at the onset of metallic overlayer behavior. The overlayer morphology, disrupted atom distribution, and band bending depends on the substrate temperature, while the amount of substrate disruption and the final value of E(sub f) in the gap at high coverage does not. Temperature-dependent band bending observed below a monolayer can be understood by considering the importance of a surface photovoltage. Studies of a condensed gas-semiconductor interface, O2/GaAs(110), were conducted at 20 K to examine the dynamics of photo-induced oxidation. Detailed core level analysis of photon exposure-dependent data demonstrate that As(+1)- and As(+3)-like bonding configurations form in a step-wise fashion with approximately equal reaction probabilities for the two steps. The high sticking coefficient for O2 at 20 K makes it possible to locally oxide the surface ten orders of magnitude more efficiently than in equivalent experiments at 300 K. Reaction cross sections determined from modeling the dynamics of the reaction processes indicate that an oxidation mechanism involving secondary electrons is operative. Results are also presented for the competition between continued reaction and photon-induced oxygen desorption, where desorption occurres via a first order process.