A comparative thermodynamic analysis of impurity incorporation in vapor phase epitaxial InP and GaAs

The maximum extent of unintentional Si incorporation has been defined for deposition of GaAs and InP by both the chloride and hydride processes. The extents were determined on the basis of constrained chemical equilibrium being achieved in the CVD reactor. The input species consisted of the input gas components and excess condensed phases of the group 3 source material and quartz reactor wall. The work performed included incorporation of a novel psuedo-steady state constraint for the liquid source, identifying vapor species not included before, and establishing the vapor composition relation to the point defect structure. The results indicate that Si incorporation levels can be significant. In general, the activity of Si was less in the hydride system and with the compound source in the chloride system. Furthermore, the activity of Si decreased significantly with temperature, small additions of H2O, HCl or VCl3 to the mixing zone, and replacing the H2 carrier gas by an inert in the chloride system. However, the activity of Si displayed a maximum with system pressure and was somewhat insensitive to input composition. Reviews of the literature are included for the thermochemical properties employed and unintentional doping in experimental GaAs and InP VPE films. Algorithms for computing complex chemical equilibrium using both stoichiometric and non-stoichiometric approaches were generated.