AN X-RAY-DIFFRACTION STUDY OF THE LATTICE STRAIN RELAXATION IN MOVPE GAAS/GE HETEROSTRUCTURES

GaAs/Ge heterostructures were grown by metal-organic vapour phase epitaxy with different V/III flow ratios; the layer thickness was always much larger than the critical threshold for the elastic strain relaxation. The structural properties of the specimens were investigated by both x-ray topography and high-resolution x-ray diffractometry. It has been found that, at high V/III ratios, the layers are affected by a high density of stacking faults, whereas misfit dislocations are completely absent; the fault density decreases on decreasing the V/III value. A small, but significant strain relaxation has also been observed, thus demonstrating the effectiveness of the partial dislocations bordering the faults in relaxing the strain. At lower V/III ratios the dominant defects are the misfit dislocations to which the strain relaxation can be attributed.