Study of defects and strain relaxation in GaAs/InxGa1-xAs/GaAs heterostructures using photoluminescence, positron annihilation, and x-ray diffraction

Strain relaxation and consequent generation of defects in GaAs/InxGa1-xAs/G aAs heterostructures with x=0.05-0.3 prepared by metalorganic chemical vapo r deposition have been studied using photoluminescence, positron beam, and x-ray diffraction techniques. Photoluminescence studies have indicated peak shifts and broadening in the spectra as the In concentration is increased. Broadening is attributed to defect generation, caused by In substitution b eyond the critical limit. Depth resolved defect-sensitive S-parameter measu rements, using a low energy positron beam, exhibit an increase in the S par ameter over a depth range corresponding to the In substituted layers as the In concentration is increased. The results are suggestive of the productio n of open volume defects like misfit dislocations in the In substituted lay er. A simplified analysis of positron beam data shows that a 5% In sample i s defect-free, indicating that it is pseudomorphic to the substrate. A 10% In sample is in the transition region, while higher In concentration sample s indicate a large concentration of defects. X-ray diffraction studies have revealed the in-plane and out-of-plane strains in the samples and it is fo und that increased In substitution leads to larger strains and an increased degree of strain relaxation. Using the experimentally determined strain pa rameters, a dynamical theory based simulation of x-ray profiles has been ma de for comparison with the measured profiles. The combined study of the thr ee techniques clearly establishes the interplay between the In substitution and strain relaxation leading to defect generation in the InGaAs system. ( C) 2000 American Institute of Physics. [S0021-8979(00)02012-0].