Morphology of GaAs-quantum-well interfaces grown by liquid-phase epitaxy

A quasicolumnar structure of GaAs quantum wells with mean column diameters of d=1--10 {μ}m is observed in narrow Al0.4{Ga}0.6$As/GaAs quantum wells prepared by liquid-phase epitaxy. The heterostructures are grown from a Ga solution at T{}650 ^∘{}C in a slider boat. Chemical lattice images confirm the presence of narrow quantum wells. The well width, however, can vary by one to two atomic layers over distances of order 9--16 nm. Photoluminescence measurements at T=2 K reveal a multiplet of lines for the excitonic [X(e-hh)ₙ₌₁] transition originating from different columns within each of which the mean well width averaged over the exciton diameter changes by much less than a step height (2.8 {}). The luminescence measurements show that the thickness Lz of the quantum wells varies between 2 and 6 monolayers, with microscopic roughness causing local thickness variations appreciably smaller than one monolayer. Line-shape analysis of the luminescence spectra quantifies the interfacial roughness in terms of a standard deviation σLz=0.2--0.4 monolayer. Time-resolved photoluminescence measurements reveal the same luminescence lifetime of {τ}{}270 ps at T=4 K for all spectral lines, with direct or indirect excitation of the quantum well. No significant carrier transfer is observed between the different columns. Cathodoluminescence is used to image the micrometer-scale variations in the quantum-well morphology.