Effects of oxygen impurities in W films on W/GaAs Schottky-barrier contacts

Schottky-barrier characteristics and chemical reactions of contacts between oxygen-contained W films and GaAs substrates annealed up to 800 °C have been investigated. Phase transformation from β-W to α-W of the oxygen-contained W films (3 at. % oxygen), sputter deposited in Ar and O2 gas mixture, is observed at temperatures around 650 °C. Electrical degradation of the contacts, especially in capacitance-voltage (C-V) characteristics, is found after annealing above 650 °C. Oxygen accumulation at the W/GaAs interfacial region and Ga and As atom diffusion into the W films are found by secondary-ion mass spectrometry during annealing. Formation of a Ga2O3 layer at the interfacial region is also detected by x-ray photoemission spectroscopy and transmission electron microscopy. These results suggest that Ga2O3-layer formation is related to the electrical degradation. The C-V characteristics can possibly be explained by series capacitance of an interfacial oxide layer and a depletion layer together with an assumption of nonuniform carrier distribution in the GaAs substrate.