TEMPERATURE-DEPENDENT FORMATION OF INTERFACE STATES AND SCHOTTKY BARRIERS AT METAL MOLECULAR-BEAM EPITAXY GAAS(100)JUNCTIONS

We report temperature-dependent cathodoluminescence spectroscopy (CLS) and internal photoemission spectroscopy (IPS) studies of metal/molecular-beam epitaxy GaAs(lOO) interfaces. For Au, Cu, and A1 deposited at 90 K on clean, ordered GaAs(100) surfaces under ultrahigh vacuum conditions, we observe low intensity, metal-induced optical transitions centered at 0.85 eV. Upon room temperature (RT) annealing, this emission feature increases in intensity, corresponding to an increased density of midgap states. For Al, an additional excitation-energy-dependent emission is evident at 1.2 eV due to states even more localized near the interface. RT IPS measurements for metals deposited on GaAs at 90 K give well-defined Schottky barriers. We obtain stable and reproducible Schottky barrier heights of 1.05 and 0.93 eV for Au/GaAs and Cu/GaAs, respectively. For Al/GaAs, we obtain a Schottky barrier height as low as 0.3 eV with significant, time-dependent variations up to 0.41 eV. After 400 °C annealing, the Schottky barrier height increases to 0.57 eV. These results demonstrate that the barrier height and the formation of metal-induced states are temperature dependent. The correlation between CLS and IPS results indicates that the barrier height depends on the presence of metal-induced interface states and their metal-specific interface reactions. The values of the Schottky barrier height determined here are in close agreement with those obtained from our earlier soft x-ray photoemission studies. Our CLS and IPS results emphasize the detailed role of interface states couppled with chemical interactions for Schottky barrier formation at metal/GaAs interfaces. © 1990, American Vacuum Society. All rights reserved.