Al-Ga disorder in AlxGa1−xAs alloys grown by molecular beam epitaxy

A heterostructure, consisting of two GaAs quantum wells each of 40 Å width separated by a 40-Å Al0.5Ga0.5As barrier, has been grown by molecular beam epitaxy and examined optically for Al-Ga disorder (alloy clustering). The photoluminescent and excitation spectra showed no evidence of clustering, in marked contrast to results on a similar structure grown by metal-organic chemical vapor deposition. Thus any clusters present must be less than 40 Å in diameter. The spectra also support an island-like interface with steps of ∼one monolayer in height and ≳300 Å in lateral extent.