The identification of dark-line defects in AlGaAs/InGaAs/GaAs heterostructures

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Abstract
We have investigated the correlation between the structure of and the nonradiative recombination at defects in AlGaAs/InGaAs/GaAs heterostructures using scanning cathodoluminescence (CL) and transmission electron microscopy (TEM). It is shown that the dark-line defects seen in scanning CL images do not always correspond to individual misfit dislocations even for relatively low mismatched epilayers. CL and TEM images from the same area reveal that there are structures which do correlate to the dark lines seen in CL. The density of dislocations at the interface determines which structure dominates the CL image. At very low misfit, the dark lines correspond to single 60° or edge dislocations, whereas at higher misfit the dark lines correspond to groups of dislocations. Contrary to previous studies in GaAlAsP/GaAlAs semiconductor heterostructures [J. Microsc. 118, 255 (1980)], we have found that edge dislocations at AlGaAs/InGaAs and InGaAs/GaAs interfaces are higher nonradiative recombination sites than 60° dislocations. TEM micrographs show that edge dislocations form more readily along one 〈110〉 direction, possibly explaining differences in residual elastic strain measurements along different 〈110〉 directions.