Abstract
A quasicolumnar structure of GaAs quantum wells with mean column diameters of d=1–10 μm is observed in narrow 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] 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 Å). The luminescence measurements show that the thickness 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 =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.
- Received 13 March 1991
DOI:https://doi.org/10.1103/PhysRevB.44.8792
©1991 American Physical Society