On the mechanisms of strain release in molecular-beam-epitaxy-grown In xGa1-xAs/GaAs single heterostructures

In x Ga1-x As/GaAs single heterostructures have been grown by molecular-beam epitaxy with different growing rates and In molar fractions.Indium composition, layer thickness, and residual strain have been measured mainly by Rutherford backscattering/channeling spectrometry and the results on selected samples compared with the results of other techniques like Auger electron spectroscopy and single- and double-crystal x-ray diffraction. Cathodoluminescence, x-ray topography, transmission electron microscopy, and ion dechanneling have been employed to observe dislocations and to characterize their nature and density. While the onset of misfit dislocations has been found to agree with the predictions of the equilibrium theory, the strain release has been found to be much lower than predicted and the results are compared with the available metastability or nucleation models. Present results are in best agreement with nucleation models. Moreover, annealing experiments show that these heterostructures are at (or very close to) thermodynamic equilibrium.