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The effect of a single dotlike defect on the transport through a quantum dot single electron transistor weakly coupled to external leads is studied. It is found that the conductance profile is changed significantly by the quantum mechanical tunneling between the dot and the defect and the interactions between them, both of which are dependent on the distance between the dot and the defect, as also by the morphology of the defect. In particular, we find that even a very small strength of interdot interaction has a major influence on the transport and must be taken into account in device fabrication. [ABSTRACT FROM AUTHOR]

The electron microscopy was used to characterize the AlN interlayer in AlxGa1-xN/AlN/GaN heterostructures grown by plasma assisted molecular beam epitaxy (PAMBE). We show that the AlN interlayer grown by PAMBE is without gallium and oxygen incorporation and the interfaces are coherent. The AlN interlayer has the ABAB stacking of lattice planes as expected for the wurtzite phase. High purity of AlN interlayer with the ABAB stacking leads to larger conduction band offset along with stronger polarization effects. Our studies show that the origin of lower sheet resistance obtained by PAMBE is the purity of AlN interlayer. [ABSTRACT FROM AUTHOR]