A topotactic reaction between nickel and gallium arsenide

During the fabrication of a Schottky barrier diode for use at microwave frequencies a thin layer of nickel is evaporated on to a gallium arsenide crystal followed by an evaporated layer of gold. During the bonding of contacts to the base of the crystal, a temperature approaching 400 °C is reached. It has been demonstrated that a reaction takes place between the gallium arsenide and the evaporated layers resulting in the formation of a monocrystalline layer of nickel arsenide in a topotactic relationship to the substrate and an ordered alloy of gold and gallium. A number of X-ray diffraction techniques have been employed to analyse the reaction products and identify the topotactic relationships for substrates of both 〈001〉 and 〈111〉 orientation.