Non-uniform strain relaxation in InxGa1-xAs layers

The deformation properties of the surface roughening associated with the strain relaxation process have been studied in a set of InxGa1-xAs single layers (0.10 less than or equal to x less than or equal to 0.50) grown by different epitaxial techniques on GaAs and InP substrates. Raman spectroscopy performed on samples showing a rough surface reveals that, as the probing depth is reduced, a shift of the GaAs-like longitudinal optical phonon frequency, as well as an increase of the normally forbidden transverse optical mode, are produced. These effects tend to disappear in samples showing a hat relief The results can be explained if a considerable strain relaxation together with a non-tetragonal distortion of the relaxed material occurred at the surface. Using the information on the surface geometry provided by atomic force microscopy and talystep measurements we have developed a simple elastic model which explains the observations.