| This thesis explored a low-cost fabrication process for producing highly ordered quantum nanostructures, including quantum dot arrays (QDAs) and vertical nanowire arrays. Nanochannel alumina (NCA) templates, produced using a two-step anodic oxidation process, with highly ordered nanohole arrays of inter-pore distance of 100nm, pore sizes of 45–90 nm and thickness of <200 nm were used as nanomasks after being bonded to GaAs substrates using van der Waals bonding. We realized the first successful molecular beam epitaxial (MBE) growth of highly ordered GaAs nanodot arrays on GaAs substrates under NCA masks. We revealed that the growth of GaAs nanodots under Al2O3 nanochannels is kinetically controlled by surface migration of Ga ad-atoms. We also realized the first MBE growth of QDAs of closely lattice-matched GaAs/AlGaAs and strained InGaAs/GaAs heterostructures on GaAs substrates under NCA masks. The nanodots of either single layer or multilayer heterostructures were truly defined by the nanochannels of the NCA masks, resulting in replication of the hexagonal arrays with 100 nm lattice spacing, and similar dot size and shape to the nanoholes of the NCA masks. The nanodots also exhibited excellent uniformity with a standard deviation of less than 5% in dot diameter distribution. Low temperature (4.2K) photoluminescence spectra of both single-well and double-well GaAs/AlGaAs QDAs showed strong and sharp photoemission, which confirmed the good crystal quality and dot size uniformity of the GaAs/AlGaAs QDAs. Photoemission from InGaAs QDs with GaAs barriers were also detected using low temperature (5K) cathodoluminescence (CL). CL spectra from different clusters of dots showed no measurable variation under the same excitation conditions, indicating uniform electronic structures. We also demonstrated MBE growth of ordered GaAs nanowire arrays using Au-catalyzed epi-growth and defining Au dots using NCA masks, and significantly improved wire diameter uniformity as compared to using random Au dots. The use of NCA masks and epitaxial growth was thus confirmed to provide a versatile approach for fabricating highly ordered quantum nanostructures, overcoming the limitations of conventional self-assembly processes (i.e. random locations, broad size distribution, and applicable only to certain materials). |
