When matter is confined to sufficiently small regions of space, its electronic properties can change dramatically through the mechanism of quantum confinement. This concept has been demonstrated in 2-D (well), 1-D (wire), and 0-D (dot) confined materials. By controlling the size, shape, and composition of nanostructures in the strong confinement region, properties such as optical absorption and emission, electronic density of states, and phonon modes can be rationally tuned for a desired application. This requires precise control of material dimensions in the sub-10 nm range. We have developed the use of ALD for fabrication of quantum wells and quantum dots, and demonstrated tunable material properties by simply controlling the number of ALD cycles and the nucleation behavior. This allows for fabrication of complex hybrid structures with tunable properties such as quantum dot-nanowire composites with a degree of control that would be very difficult to achieve by any other technique. We utilize a variety of atomic-scale microscopy and spectroscopy techniques to quantify these properties, and study their use in optoelectronic and energy-conversion devices.
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