The Application of Thermodynamics to Molecular Beam Epitaxy

Thermodynamics is most rigorously applied to systems at equilibrium. In its extension to MBE, the interaction with kinetics, the effect of chemical over-potential and the concept of local equilibrium are briefly described. The growth of GaAs is considered in detail, as experimental data is available for comparison. While in general in MBE, kinetic barriers to reactions are expected to confuse thermodynamic guidelines, it is found that under conditions where the best quality layers are obtained their impact is slight. Kinetically induced defects can be reduced to the part per billion range. Against this background the main competing (contaminating) reactions and doping processes are examined. Potential (elemental sulphur) and impractical (elemental zinc) dopants can be identified, without recourse to MBE, from existing thermochemical data. Kinetic barriers, when they occur, are more clearly revealed by the analysis. These barriers seldom involve the commonly assumed dopant incorporation step.