Strain relief mechanisms and the nature of dislocations in GaAs/Si heterostructures

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Abstract
The nucleation and glide of misfit dislocations in the GaAs/Si system has been investigated using transmission electron microscopy. GaAs epilayers of different thicknesses were examined by electron microscopy (plan and cross section) and the elastic strain remaining in the film has been related to the average spacing of the misfit dislocations at the interface. The 1000-Å-thick GaAs epilayer contains mostly 60° misfit dislocations with an average spacing larger than the equilibrium dislocation spacing, which implies that the misfit strain is not fully relieved. The 2000-Å and thicker GaAs epilayers contain predominantly 90° misfit dislocations with an average spacing between the dislocations less than the equilibrium dislocation spacing. The formation of sessile 90° dislocations at the interface is explained on the basis of a reaction of two 60° dislocations. A model is developed based on minimum energy considerations to determine the strain-versus-thickness relationship. The theoretical predictions of strain relaxation are compared with experimental observations using high-resolution electron microscopy.