Cathodoluminescence of MBE-grown cubic AlGaN/GaN multi-quantum wells on GaAs (001) substrates

Cubic phase GaN/AlxGa1-xN Multi Quantum Well structures were grown by rf-plasma assisted molecular beam epitaxy (MBE) on GaAs (001) substrates. X-ray measurements showed a high phase purity of the epilayers and revealed an Aluminum incorporation between 9 % and 49 %, respectively. The QW luminescence was tuned between 3.25 eV and 3.4 eV by means of the variation of QW barrier Aluminum content and QW width. Strong Cathodoluminescence (CL) from the GaN QWs and the underlying cubic AlxGa1-xN bulk material was observed at room temperature. The spatial localization of the QW emission was unambiguously determined by depth-resolved CL measurements. Combined with a model of energy-dependent penetration, diffusion, and recombination, these variations indicate a value of about 20 nm for the minority carrier diffusion length within the AlxGa1-xN confinement layer. The assignment of AlxGa1-xN bulk and GaN luminescence was further supported by employing a simple effective-mass quantum mechanical model.