Cathodoluminescence of GaAs/(Al,Ga)As and (In,Ga)N/GaN heterostructures grown by molecular beam epitaxy

For GaAs/(Al,Ga)As quantum wells (QWs) fabricated by molecular beam epitaxy (MBE), variations of the QW thickness of less than one mono-layer (ML) with lateral correlation lengths on a micrometer scale have been revealed by cathodoluminescence spectroscopy and imaging. GaAs QWs grown on GaAs (100) substrates with a miscut towards (111)B exhibit pronounced surface corrugations accompanied by composition fluctuations of the barrier layers. For (In,Ga)N/GaN multiple QWs, the superposition of piezoelectric fields and electric fields induced by surface polarization causes a vertical variation of the QW confinement energy. The carrier recombination properties of GaN-based QWs are governed by the interplay of piezoelectric fields and exciton localization due to lateral parameter variations. The importance of localization effects depends not only on the structural quality of the QWs but also on the well width.