Abstract
The influence of nitrogen incorporation on the microstructure of dilute nitride films andquantum wells has been investigated using cross-section scanning transmission electronmicroscopy. The elemental distributions of Ga, In, N and As in GaInNAs andGaAsN films have been mapped by energy dispersive x-ray analysis. Below thesolubility limit for nitrogen, homogeneous GaAsN and GaInNAs compositionsare obtained of good crystalline quality near to the epilayer/GaAs interface. InGaAsN films containing nitrogen above the solubility limit a graded transition fromarsenide-like to nitride-like material occurs after some 50 nm of growth. GaInNAs filmscontaining nitrogen exceeding the solubility limit exhibit a ‘cellular’ microstructureconsisting of a gallium-depleted InGaAs centre with walls of a GaN-like composition.A similar segregation effect is observed in GaInNAs quantum wells containingnitrogen around and above the solubility limit. The formation of In-rich regionsoccurs within the wells, which causes three-dimensional growth at higher nitrogencontents, with the consequent initiation of growth defects. The electronic structure ofGaInNAs quantum wells has been investigated by mapping the variation in theplasmon frequency using electron energy loss spectrometry on a dedicated scanningtransmission electron microscope. Kramers–Kronig analysis of the singly scatteredlow-loss region yields a measure of the local effective valence electron density.
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