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Heterostructure tunnel field-effect transistors (HTFET) are promising candidates for low-power applications in future technology nodes, as they are predicted to offer high on-currents, combined with a sub-60 mV/dec subthreshold swing. However, the effects of important quantum mechanical phenomena like size confinement at the heterojunction are not well understood, due to the theoretical and computational difficulties in modeling realistic heterostructures. We therefore present a ballistic quantum transport formalism, combining a novel envelope function approach for semiconductor heterostructures with the multiband quantum transmitting boundary method, which we extend to 2D potentials. We demonstrate an implementation of a 2-band version of the formalism and apply it to study confinement in realistic heterostructure diodes and p-n-i-n HTFETs. For the diodes, both transmission probabilities and current densities are found to decrease with stronger confinement. For the p-n-i-n HTFETs, the improved gate control is found to counteract the deterioration due to confinement. [ABSTRACT FROM AUTHOR]

Terahertz (THz) signals can be generated by the periodic motion of ballistic electron bunches inside a quantum well cavity surrounded by two asymmetric resonant tunneling structure implemented in an InAlAs/InGaAs heterostructure. The electron bunches are produced in an adjacent active quantum well by optical excitation with a femtosecond laser pulse, and transferred into the cavity by resonant tunneling. The device contains also a superlattice that eliminates the electrons, which exit the cavity in the direction of the active quantum well. In consequence, the device output consists of a train of ultrashort pulses, of less than 100 fs, which preserve their coherence. Electrical signals up to few tens of THz can be obtained, depending on the resonant filter or antenna placed at the end of the device. [ABSTRACT FROM AUTHOR]

We investigate ballistic transport and quantum interference in a nanoscale quantum wire loop fabricated as a GaAs/AlGaAs field-effect heterostructure. Four-terminal measurements of current and voltage characteristics as a function of top gate voltages show negative bend resistance as a clear signature of ballistic transport. In perpendicular magnetic fields, phase-coherent transport leads to Aharonov–Bohm conductance oscillations, which show equal amplitudes in the local and the nonlocal measurement at a temperature of 1.5 K and above. We attribute this observation to the symmetry of the orthogonal cross junctions connecting the four quantum wire leads with the asymmetric quantum wire ring. [ABSTRACT FROM AUTHOR]

The authors have fabricated and studied a ballistic one-dimensional p-type quantum wire using an undoped AlGaAs/GaAs heterostructure. The absence of modulation doping eliminates remote ionized impurity scattering and allows high mobilities to be achieved over a wide range of hole densities and, in particular, at very low densities where carrier-carrier interactions are strongest. The device exhibits clear quantized conductance plateaus with highly stable gate characteristics. These devices provide opportunities for studying spin-orbit coupling and interaction effects in mesoscopic hole systems in the strong interaction regime where rs>10. [ABSTRACT FROM AUTHOR]

This letter revises the interpretation of recent experiments showing quantized conductance on GaAs/GaAlAs constrictions or point contacts in terms of coherent ballistic and sequential transport. Our calculations show by using a first iterative self-consistent procedure that the experimental data can also be reconciled with sequential transport. The mean free path concept in the constriction is discussed in comparison with that of the reservoirs. We conclude that, for the higher modes, the former is much smaller than the latter, implying that in the constriction the transport may be sequential. [ABSTRACT FROM AUTHOR]