Schottky barriers on atomically clean cleaved GaAs

We report here the first systematic study of the electronic properties of Al, Au, Ag and Cu Schottky barrier diodes on n-type GaAs. These diodes were formed on cleaved (110) surfaces in ultra-high vacuum (UHV) using similar conditions and evaporation rates during the initial stages of Schottky barrier formation as in the photoemission spectroscopy (PES) studies. Barrier height determinations using device measuring techniques (current-voltage (I-V), capacitive-voltage (C--V) and internal photoemission) are compared with the results from the PES studies. Essentially identical barrier heights are found from PES and the electrical measurements for the noble metals. The barrier height of the noble metal: n-GaAs system (0.9 eV) is larger than any simple metal on n-type GaAs previously reported. This is examined in light of recent work by Zur, McGill and Smith [22] and a model is suggested to explain it. Results of this study are found to be consistent with the unified defect model which has hypothesized that the barrier height is established by the energy levels of structural defects formed at the surface during the metal deposition.