Epitaxial GaAs by close space vapor transport

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Abstract
The rate of transport of GaAs obtained with the close space vapor transport technique has been investigated as a function of the source (T) and substrate (θ) temperatures and of the source-substrate spacing for two different water vapor pressures (6.6 and ∼10−5 mm Hg) introduced with the H2 gas. Analysis of the results allow us (i) to determine the enthalpy and activation energy (2.1 and 3.1 eV, respectively) associated with the reactions taking place at the source and substrate surfaces and (ii) to deduce the existence of a third reaction occurring in the gas phase, whose activation energy has been measured (2.9 eV). Depending on the water vapor pressure, this third reaction occurs near the source (high water vapor pressure) or near the substrate (low water vapor pressure). We derive the equation governing the rate of transport, from which we calculate this rate per unit of source substrate spacing and of water vapor pressure as a function of both T and θ for constant values of θ and T, respectively.