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In-situ depositions and reactions are utilized in the study of phase formation from solid phase reactions. We report on the formation of epitaxial GaAs and the formation of NiAs or Ni2Ga3 by the exposure of Ni3GaAs to As4 or Ga fluxes. In-situ annealing of Ni on MBE-grown GaAs leads to Ni3GaAs, and subsequent reaction with As4 or Ga drives regrowth of GaAs. The structures were analyzed by RBS, XRD, TEM, and in-situ electrical measurements.

We have designed a device for measuring sound speeds in reactive liquids at high pressure and temperature. It has been tested in experiments on liquid-potassium metal at pressures up to 0.7 GPa and temperatures up to 423 K. The limitations on pressure and temperature were imposed by auxiliary instrumentation rather than the properties of the device, and it seems likely that it would be suitable for more extreme conditions. The data on potassium agree well with precise room-temperature data. The sound velocities measured as a function of pressure at various temperatures can be used to calculate equation-of-state parameters such as the bulk modulus and its pressure derivatives. The experiments on potassium indicate that bulk modulus can be determined to ±1%, its first pressure derivative to about ±5%, and second pressure derivative to about ±50% (the last for a run with a 0.7-GPa pressure range). The device should permit sound velocity measurements in a variety of liquids which are reactive, corrosive, and/or miscible with pressure media.

In situ electrical characterization is used to study the interface properties and the contact penetration during reactions at metal/semiconductor interfaces. Ni contacts were formed in situ by deposition through a removable molybdenum shadow mask on molecular beam epitaxy-grown n-type GaAs(100) c(4×4) As-rich surfaces. Annealing at 300 °C resulted in NixGaAs (x≈3) formation. Subsequent exposure of the NixGaAs to an As4 flux at 350 °C resulted in the formation of NiAs at the surface and the epitaxial regrowth of GaAs at the Ni3GaAs/GaAs interface. The Schottky barrier height (φbn=0.68 V, as deposited) increased with NixGaAs formation (φbn=0.87 V) and decreased slightly with subsequent As4 exposure (φbn=0.85 V). A thin buried n+ marker layer was used to determine changes in the metal/semiconductor interface position from in situ capacitance–voltage measurements. The marker-layer movement demonstrated consumption and subsequent regrowth of GaAs beneath the contact. The ideality factor obtained from current–voltage measurements for the contacts on regrown GaAs was ⩽1.11, which is indicative of the high electrical quality of the regrown GaAs.