Origin of energy dispersion inAlxGa1−xN/GaNnanowire quantum discs with low Al content

Individual GaN nanowires containing ${\text{Al}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{N}/\text{GaN}$ quantum discs (QDiscs) with Al content $x\ensuremath{\le}16\mathrm{%}$ have been investigated by microphotoluminescence, transmission electron microscopy, and theoretical modeling. Single quantum discs show narrow emission lines with a linewidth as low as 3 meV at energies above the GaN band gap while the emission of nanowires containing multiple quantum discs shows multiple peaks with total spectral broadening that depends on the Al content in the barrier. As assessed by simulations of the quantum confinement based on a three-dimensional effective-mass model, the main factors influencing the spectral dispersion are: (i) strain relaxation in the QDiscs, strongly affected by the presence of a lateral AlGaN shell with a progressively changing thickness formed during the barrier growth; (ii) monolayer fluctuations in the QDisc thickness.