BINARY ALAS/GAAS VERSUS TERNARY GAALAS/GAAS INTERFACES - A DRAMATIC DIFFERENCE OF PERFECTION

Large differences between the structural and chemical modifications binary AlAs and ternary Al0.4Ga0.6As barriers of GaAs quantum wells (QWs) upon undergoing growth interruption are found in an investigation of luminescence of type I and type II QWs. There are no increased trap incorporation but rapid smoothing and formation of interface islands larger than the diameter of type I excitons but smaller than the diameter of type II excitons is observed on the AlAs surface. Chemical lattice images obtained by high-resolution transmission electron microscopy visualize directly the structure of the interfaces. Areas without monoatomic steps in the interface plane extending more than 0.1-mu-m are observed at the top surface. The bottom interfaces show structure on the scale of the exciton diameter in agreement with the luminescence results. Superimposed to the in-plane variations of the interface positions is a grading extending over 2-4 monolayers in growth direction.