High-spatial-resolution photoluminescence studies on misfit dislocations in lattice-mismatched III-V heterostructures

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Abstract
The effect of misfit dislocations on the electro-optical behaviour of strained III-V heterostructures has been studied by high-resolution spatially resolved photoluminescence (PL) imaging. Both epitaxial layers under tensile stress (in this study GaAs on InGaAs) as well as layers under compressive stress (InGaAs on GaAs) have been examined. Dislocation lines in both (011) directions are observed in both systems. In contrast to the compressive system, where no as-grown morphological asymmetry is observed, the dislocations in the tensile system have been preferably formed in the (011) direction. This is explained by assuming (i) that the relaxation of the strained layer is initiated by the most mobile dislocation in GaAs, which is the arsenic glide As(g) dislocation, and (ii) that cross-slip of these As(g) dislocations is only possible in the compressive system. PL imaging reveals the presence of many non-radiative deep levels around the dislocation lines and also shows an opto-electronic asymmetry of the two (011) directions for both systems, in contrast to the as-grown morphology. For the compressive system this is explained by the difference in depletion between the dislocation lines along the (011) direction, of which the core is believed to consist of Ga atoms, and those along the (011) direction, formed with As atoms. For the tensile system just the opposite holds. DSL (defect-revealing) etching confirms the results obtained with PL imaging.