Inhomogeneities in multiple quantum wells investigated by SEM-Cathodoluminescence

The lateral cathodoluminescence distribution of GaAs/Ga1-xAlxAs-multiple quantum wells with a well thickness of 2nm grown by molecular beam epitaxy is inhomogeneous. The contrast between two neighbouring areas is caused by an average shift of the luminescence spectrum of about 15meV. This shift can be explained neither by well thickness variations nor by fluctuations of the Al-mole fraction of the barriersalone. At selected spots the shift amounts to 50meV or more. We compare the larger spectral splitting with the shift of spectra measured at and around oval defects.