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Tailoring electron motion in artificial crystals
Friday, 18 April 2008, 16.00, W2.19 This work describes novel quantum transport phenomena in dilute nitride semiconductors - a class of semiconductor alloys in which a small amount of nitrogen (N) is incorporated in the lattice of III-V compounds such as GaAs. The incorporation of isoelectronic nitrogen on the pnictide (e.g. As) site gives rise to a highly-localised electronic state, whose interaction with the band states of the host crystal (e.g. GaAs) provides a parameter for tuning not only the energy bandgap, but also the effective mass and group velocity of conduction electrons. This, in turn, offers the possibility of studying a new regime of electron dynamics, not available in natural or synthesised crystal structures. Of particular interest is the emergence of a negative differential velocity effect, caused by the formation of a fully-developed energy gap in the conduction band of the host crystal. This is not only of fundamental interest, but also has potential for novel high-frequency (Terahertz, THz) electronic devices. The THz region of the electromagnetic spectrum, ranging from approximately 0.3 to 10 THz, is often referred to as the THz gap, due to the need for compact, solid state devices that can emit radiation in this frequency range in a selectable and tuneable way. Such devices are relevant for many emerging applications, such as THz imaging in biomedicine, security technology, environmental sensors, and for fundamental studies of, for example, excitations in semiconductors, gaseous plasmas, proteins and molecules, all of which can resonate at THz frequencies. |
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