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Abstract Low-dimensional Semiconductor Structures Guenther Bauer Institut fuer Halbleiterphysik, Universitaet Linz, Austria In metal-oxide-semiconductor structures, the backbone of integrated circuits, the electrons are confined at the interface between the oxide and the semiconductor in a narrow channel and are only free to move along the interface. This confinement of the carriers in a triangular potential has dramaitic consequences for the physical properties like a change the allowed energy states , an altered density of states, etc. Even mor perfect structures are realized by semiconductor heterostructures like GaAs/GaAlAs or Si/SiGe, where instead of an amorphous oxide interface two single crystaline materials form the triangular potential well for the carriers. Hence much higher carrier mobilities as in Si-MOS structures result. By growing layer sequences like GaAlAs/GaAs/GaAlAs rectangular quantum wells are realized and the energy states in the GaAs layers depend according to quantum mechanics on the thickness of the GaAs well and can be tuned with it. Apart from a whole range of physical phenomena like Quantum Hall and Fractional Quantum Hall effect, intersubband transitions, confined excitons, the high carrier mobilities and the altered density fo states are used in high frequency devices for communication, in lasers in modulators etc. Using techniques like lithography and etching from quantum well
structures quantum wires or quantum dots can be fabricated. In these
wires and dots the electron motion is confined to either one or to zero
dimensions. The two dimensional density of states changes from a
step-like increase with energy to an inverse root law or to a
delta-function comb. Quantum dots can be considered as "artificial
atoms" as the carriers are bound in all three dimensions.
Furthermore, such dots can be realized by selforganized growth, taking
advantage of the spontaneous transition from a layer by layer growth
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