Effect of Iso-Electronic GaAs Dopants on the Dislocation Density of

The addition of 1% In to LEC GaAs has been reported to reduce the dislocation density in this material; similar data exists for Sb doping. Several effects have been inferred to explain these phenomena, the most prevailing one stating that the solid stoichiometry is affected by an as yet unknown mechanism. Similar postulations have been made to explain the growth of semi-insulating GaAs. A thermodynamic model is described, based on earlier work, that shows a broadening of the existence region of GaAs when In or Sb are added to GaAs. Comparing the solidus phase diagrams of Inor Sb-doped GaAs to undoped GaAs shows that addition of either one of these two iso-electronic dopants has a similar effect on the solid stoichiometry as adding more As to the melt. However, the increased pressure problems in LEC growth of GaAs, normally associated with adding As, are circumvented if instead In or Sb are added to the melt. From our calculations it is also shown that the addition of the iso-electronic dopants A1 or P to GaAs would not result in the same effect on the solid stoichiometry. Published experimental evidence supports this and shows that no dislocation reduction and semi-insulating GaAs is obtained with the use of these dopants. The model described in this paper explains the postulation that iso-electronic doping is of critical significance in controlling the solid stoichiometry and thereby obtaining zero dislocation density LEC GaAs and semi-insulating GaAs.