Effect of interface states on the electrical properties of W, WSi _x, and WAl_x Schottky contacts on GaAs

Barrier heights of refractory W, WSix, and WAlx Schottky contacts deposited on n-GaAs with different surface treatments have been electrically characterized by current-voltage, capacitance-voltage, and internal photoemission measurements. Internal photoemission measurements indicate that the Fermi level pins approximately at midgap (φn ≅0.7-0.8 eV). The current-voltage barrier heights were consistent with internal photoemission for diodes with little oxide at the GaAs/metal interface. For an oxide layer of about 2.5 nm, current-voltage barrier heights as high as 0.9 eV were observed. Capacitance-voltage barrier heights were found to be 0.9-1 eV with a weak dependence on interface oxide. A theoretical model was developed to explain these results. A large density of states (5×10 13-1014/cm2) at the GaAs/metal interface which exchanges charge mainly with the metal appears to explain well our experimental capacitance-voltage and current-voltage data.