Study of the optical and structural properties of multi quantum well structures grown on high-index surfaces
The MOVPE overgrowth of high [01@?1]-oriented ridges confined at sides by facets related to {n11} crystallographic planes is reported. We studied the influence of the side tilt on the thickness of the AlGaAs and GaAs epitaxial layers grown under the condition of the kinetic growth mode. The multi quantum well (MQW) structures were prepared on the sides of ridges tilted at 54.7^o, 45^o and 30^o to (100). The sidewall surface morphologies before and after epitaxial growth were evaluated and compared. We observed no tendency towards planarization towards a neighbouring high-index crystallographic plane, such as (211) and (311). We also showed that the quantum wells of the MQW structure make a smooth transition over the edge between the top surface and the facet as both AlGaAs and GaAs grew at similar rates on the surfaces.
Fabrication of GaAs symmetric pyramidal mesas prepared by wet-chemical etching using AlAs interlayer
We present a wet-chemical-etching method developed for the preparation of GaAs four-sided pyramid-shaped mesas. The method uses a fast lateral etching of AlAs interlayer that influences the cross-sectional profiles of etched structures. We have tested the method using H3PO4:H2O2:H2O etchant for the (100) GaAs patterning. The sidewalls of the prepared pyramidal structures together with the (100) bottom facet formed the cross-sectional angles 25° and 42° for mask edges parallel, resp. perpendicular to {011} cleavage planes. For mask edges turned in 45° according to the cleavage planes, 42° cross-sectional angles were obtained. Using the method, symmetric and more than 10-μm-high GaAs “Egyptian” pyramids with smooth tilted facets were prepared.
Photoluminescence excitation spectra in GaAs/AlAs trench‐buried quantum wires with 20 nm wide rectangular cross‐sectional shapes
Polarization‐dependent photoluminescence excitation spectra (PLE) are measured in GaAs/AlAs rectangular trench‐buried quantum wires (QWRs) with 20 nm width and various thicknesses. Experiments demonstrate that the polarization properties of the PLE spectra, which have several clear peaks corresponding to the optical transitions between quantized conduction and valence subbands, significantly depend on the cross‐sectional ratios of the rectangular wires. Quantum indices of these transition levels are assigned by comparing the experiments with theory. The distinctive optical features of the QWRs with the rectangular cross sections are discussed in relation to the characteristics of one‐dimensional valence subbands.