Joint Study on the Novel Semiconductor Nanostructures

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Effect of quantum confinement and lattice relaxation on electronic states in GaAs/In_<0.2>Ga_<0.8>As/GaAs quantum dots has been studied. The quantum dots were fabricated by using electron beam lithography and wet chemical etching, and the photoluminescence measurements have been carried out to investigate the electronic states. Blue shift in the transition energy for smaller quantum dots was clearly observed, while the transition energy shifts to lower energy for larger dots. The blue shift is attributed to quantum confinement and the red shift to lattice relaxation. A simple empirical formula is given which well describes the observed energy shift.Hopping conduction in the Wannier-Stark reginme of a Landau-quantized superlattice has also been studied. We have measured current-voltage characteristics in GaAs/AlAs superlattices, analyzed them by taking into account acoustic deformation interaction, and find that two types of anti-resonances with different anti-resonance conditions occur in superlattices having high potential barrier. One type of the anti-resonances is due to the inter-well phase-factor and the anti-resonance condition depends on the superlattice period. The other type of the anti-resonances is due to the intra-well phase-factor and the anti-resonance condition depends on the well width. Since the superlattice period is different from the well width, the two types of anti-resonances occur in out phase in general. For a certain voltage region, however, the two types of anti-resonances occur in phase, and the anti-resonances are found to appear clearly in current-voltage characteristics.