The depth profile of the defect structure in strained and partially relaxed Ga0.8In0.2As/GaAs multilayers is investigated with the method of X-ray grazing-incidence diffraction. Both in-plane and out-of-plane parameters are obtained from the subsurface region between five and a few hundred nm.
The strength of the method is demonstrated on a sample series with similar thickness of the Ga0.8In0.2As sublayers, ta, but with varying thickness of the GaAs barrier, tb.The degree of relaxation R is directly obtained from the angular position of the in-plane Bragg peaks. For decreasing ta the peak maximum shifts to smaller angles which indicates an increase of R. Additionally the peak width is enlarged. This is explained by the orientational distribution of strain-reduced microdomains which are formed during the relaxation process. Their average size is estimated from the shape of the truncation rods which are recorded at the angular position of the in-plane Braggpeaks. The resulting size of about 100nm is additionally verified by high-resolution X-ray diffraction. The existence of microdomains is caused by a cross-hatched network of 60° misfit dislocations which is confirmed by TEM-measurements.