Spreading of Au dots on InP surfaces

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Abstract
Circular gold dots, measuring about 200 μm in diameter and either 150 or 300 nm in thickness, have been produced on {100}, {110}, and {111} substrates of indium phosphide by a combination of vapor deposition and photolithographic processing, annealed at temperatures ranging from 420–460 °C, and subsequently examined by optical microscopy. During annealing, a reaction product, bounded by well-defined crystallographic planes of the substrate, forms, expands parabolically with annealing time, and eventually saturates due to the limited supply of gold. Generally, reactions proceed at least three times faster at {100} and {110} planes than at {111}In planes, in which reactions proceed about three times faster than at {111}P planes. Analysis of concomitant reaction kinetics yields an activation energy of 8.6±3.0 eV for reactions at {111}In planes. Results are interpreted in terms of a preferential interfacial reaction at {111}In planes, which is controlled by solid-state diffusion and eventual escape of phosphorus.