Effect of interface states on the electrical properties of W, WSi x, and WAlx Schottky contacts on GaAs
Abstract
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.