In low-magnification, plan-view photoluminescence images of a nominally lattice-matched, undoped GaAs/GaInP heterostructure, a random distribution of isolated dark spots was observed. The dark spots were attributed to crystal dislocations, where non-radiative recombination was augmented by transitions involving defect-related energy levels between the conduction and valence bands. It was noted that, when the laser excitation intensity was reduced, the darkened regions expanded. At lower excitation, the density of photo-generated electrons and holes was reduced, and they were more likely to reach the defective region before encountering a partner for radiative recombination. When the behaviour was modelled using a simulation that allowed for Laplacian diffusion and defect-related recombination only through mid-bandgap energy levels, good agreement between experimental and simulated images was not obtained. However, if allowance was made for an arbitrary distribution of defect levels, such that the occupation of the levels and bands could change independently, there was more flexibility in fitting the density-dependent recombination rates. The more sophisticated model produced results that were more consistent with experimental images.

Excitation-Dependent Recombination and Diffusion Near an Isolated Dislocation in GaAs. T.H.Gfroerer, C.M.Crowley, C.M.Read, M.W.Wanlass: Journal of Applied Physics, 2012, 111[9], 093712