Dislocation formation during the growth of large diameter, undoped GaAs single crystals

Abstract

Dislocations can form in a perfect crystal, that is in quasi-equilibrium with its melt, either via stresses exceeding the critical resolved shear stress or through dislocation loop formation resulting from precipitation of point defects. For crystals growing under very low thermal gradients, thermoelastic stress is not the primary dislocation formation mechanism, nor is there sufficient point defect supersaturation to form dislocation loops. Dislocations can form only through heterogeneous stresses arising at the solid-liquid interface such as those due to point defect concentration gradients originating from non-uniform incorporation across steps in the interface. Control of point defect concentrations either via dopant additions or via stoichiometric control can lead to a reduction in the dislocation density. Growth of undoped GaAs in a how-walled chamber, wherein the arsenic partial pressure in equilibrium with the melt is carefully controlled, can yield nearly dislocation-free material.