Dislocation reduction in GaAs crystal grown from the Czochralski process

Abstract

The dislocation density in the gallium arsenide (GaAs) crystal is generated by excessive thermal stresses during the Czochralski (CZ) growth process. A constitutive equation which couples the dislocation density with the plastic deformation is employed to simulate the dislocation density in the crystal. The temperature distribution in the crystal during the growth process is obtained by solving the quasi-steady-state (QSS) heat-transfer equation. The thermal stresses induced by the temperature distribution are calculated using the finite-element method. The crystal is assumed to be an axisymmetrical ingot. The resolved shear stress (RSS) in each slip system is obtained by stress transformation. The RSS in each slip system is no longer axisymmetric. The dislocation motion and multiplication in each slip system are simulated using the constitutive equation. The total dislocation density in the crystal is obtained by summing the dislocation densities in all of the slip systems. Since the thermal stresses are sensitive to the temperature gradients and the dislocations move faster at a higher temperature, the dislocation densities are generated most near to the solid-melt interface. The dislocation density is also found to be affected by the growth orientation, growth speed, ambient temperature and the radius of the crystal. The dislocation density in GaAs crystals grown with the different growth orientation, growth speed, and crystal radius at various ambient temperatures has been calculated so that the influence of these growth parameters on the dislocation density can be understood. Consequently, the growth parameters can be controlled to reduce the dislocation density generated in the crystal during the CZ growth process.