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In this report, we review the results of our joint experimental and theoretical studies of electroninterference, and interaction, phenomena in open electron cavities known as quantum dots. The transport through these structures is shown to be heavily influenced by the remnants of their discrete density of states, elements of which remain resolved in spite of the strong coupling that exists between the cavity and its reservoirs. The experimental signatures of this density of states are discussed at length in this report, and are shown to be related to characteristic wavefunction scarring, involving a small number of classical orbits. A semiclassical analysis of this behaviour shows it to be related to the effect of dynamical tunnelling, in which electrons injected into the dot tunnel through classically forbidden regions of phase space, to access isolated regular orbits. The dynamical tunnelling gives rise to the formation of long-lived quasi-bound states in the open dots, and the many-body implications associated with electron charging at these resonances are also explored in this report.

In this paper, we combine the modified electrostatics of a one-dimensional transistor structure with a quantum kinetic formulation of Coulomb interaction and nonequilibrium transport. A multi-configurational self-consistent Green's function approach is presented, accounting for fluctuating electron numbers. On this basis we provide a theory for the simulation of electronic transport and quantum charging effects in nanotransistors, such as a gated carbon nanotube and whisker devices and one-dimensional CMOS transistors. Singleelectron charging effects arise naturally as a consequence of the Coulomb repulsion within the channel.

We report on a quantum collimation effect based on surface depletion regions in AlAs/GaAs nanocolumns with an embedded resonant tunneling structure. The considered MBE-grown nanodevices have been fabricated by means of a top-down approach that employs a reproducible lithographic definition of the vertical nanocolumns. By analyzing the scaling properties of these nanodevices, we discuss how a collimation effect due to a saddle point in the confining potential can explain an improved device performance of the ultimately scaled structures at room temperature.

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PACS: 73.40.Gk; 73.61.Ey Numerical simulations of AlN/GaN-based resonant tunnelling diode structures are presented, employing self-consistent real-time Green's functions. The simulated current-voltage characteristics show strong asymmetry effects due to polarization charges at the heterointerfaces in the doublebarrier region.Introduction During the last decade there has been tremendous progress in semiconducting III-nitride material science and technology. Early, very successful device applications in the field of optoelectronics (blue LEDs and laser diodes) and power microelectronics (HEMTs) have further driven the improvement of the materials and in turn of the devices. Even though the nitrides are far from the level of perfection seen in the technology of GaAs, the next natural step is towards quantum devices. In this sense, the resonant tunnelling diode (RTD) is an attractive candidate and offers the possibility of fundamental investigations of quantum phenomena as well as for modern device applications. Up to now, little attention has been paid to these types of structures and their functionality, when realized on the basis of nitride semiconductors.Kikuchi et al. [1] were the first to report the successful fabrication of RTDs based on AlN/GaN double-and multi-quantum well structures. The typical negative differential resistance (NDR) region in the current-voltage (I-V) characteristic was clearly observed, and, interestingly, a strong asymmetry was revealed: the NDR was only measured for one bias polarity and not for the opposite one (at least in the voltage range investigated). Due to the polarization charges built up at the wurtzite nitride heterojunctions, opposite electric fields are induced in the barrier and well regions of the device, which obviously are related to the observed asymmetry. Previous model calculations of GaNbased RTD structures showed that the effect of polarization fields is to shift the resonances in the transmission probability in comparison to the same hypothetical structure without polarization fields [2]. The model presented here goes a step further and deals with the self-consistent calculation of the current across the device structure under nonequilibrium conditions. This provides a direct comparison with the experiment and we are able to reproduce the measured asymmetry of the I-V characteristics.

We discuss the influence of the electron–electron interaction on transport properties of open quantum dot systems. Based on the idea of the Anderson model, we present interaction-induced temperature-dependent corrections to the conductance beyond the single-particle picture.

Dephasing of quantum dots presents an intrinsic limitation on their usage for quantum computing. We consider the dephasing of a double quantum dot caused by the Coulomb interaction with the nearby gate electrodes, and show that this occurs on a much longer timescale than dephasing due to phonons. However, the effect grows rapidly stronger as the system size decreases, and therefore it is expected to limit potential miniaturization of these systems.