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Chemical reactions and Schottky-barrier characteristics of W(200-nm-thick)/Si(0–2.5-nm)/GaAs contacts annealed at 800 °C have been investigated. The Si interfacial layer and the W film were sputter deposited successively on chemically etched GaAs substrates to fabricate Schottky-barrier diodes. The W/Si/GaAs diodes show nearly the same Schottky-barrier characteristics as tungsten-silicide (WSi0.6)/GaAs diodes. By using secondary ion mass spectrometry, the Si layer is found to suppress Ga and As atom diffusion from GaAs substrates into W films during annealing at 800 °C for 60 min. A reduction of natively oxidized GaAs surfaces is also observed at the initial stage of Si layer deposition by x-ray photoemission spectroscopy. These results suggest that the Si layer eliminates native oxides from GaAs surfaces, resulting in tungsten-silicide/GaAs intimate contact formation at the interface, and the Si stuffs diffusion paths of Ga and As atoms at W grain boundaries with W-Si-O ternary compounds.

We construct a kink solution on a non-BPS D-brane using Berkovits' formulation of superstring field theory in the level truncation scheme. The tension of the kink reproduces 95% of the expected BPS D-brane tension. We also find a lump-like solution which is interpreted as a kink-antikink pair, and investigate some of its properties. These results may be considered as successful tests of Berkovits' superstring field theory combined with the modified level truncation scheme.

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