Strain relaxation in InGaAs epilayers on GaAs by means of twin formation

Strain relaxation in In0.045Ga0.955As epilayers grown by molecular beam epi taxy on (001) vertical gradient freeze Bridgman GaAs substrates has been as sessed by monochromatic synchrotron X-radiation topography. A striation pat tern parallel to the [110] direction was observed in every topograph of a s ample grown with a non-uniform temperature distribution. Such a pattern has never been seen in specimens grown with a uniform temperature across the w afer:From a detailed analysis of the contrast, it is concluded that twins w ere formed. These twins, which were associated with oval defects, appear to relax the strain in the epilayer without misfit dislocation formation.