No abstract

A sharp step-like structure, which is seen in the current-voltage characteristic of a laterally confined AlGaAs/GaAs resonant tunnelling structure, is a novel manifestation of a quantum effect arising when one-dimensional wires feed electrons into a zero-dimensional quantum box. The authors can analyse the data to deduce a tunnelling time, an inelastic scattering time and the transmission probability for electrons in this system. The height of the current steps, Delta I, gives the electron tunnelling time, taue, via Delta I=e/2 taue, while the differential conductance gives the peak transmission probability, T0, via G approximately (e2/h)T0. The authors must invoke inelastic scattering to explain the low value of T0 approximately 9% obtained from the data, and so they find that tunnelling in their structure is sequential.

We report magnetotunneling through a quantum dot realized in a 200-nm-diameter Al"Gal As-GaAs double-barrier diode. Steplike current-voltage characteristics are observed at low temperatures in the low-bias regime and are assigned to tunneling though zero-dimensional states. With increasing magnetic field parallel to the current direction, the first six resonances shift to higher bias by the same amount. The data are discussed in terms of a simple model of electrostatic quantum confinement in a magnetic field, allowing for Coulomb-charging effects. W'e conclude that a more detailed theory is needed to obtain a clear explanation of the mechanism leading to the current steps.

Resonant tunneling is studied in an ultrasmall asymmetric GaAs-AI, Gal -"Asdouble-barrier diode

Resonant tunneling in GaAs-AlGaAs triple barrier diodes is studied as a function of the diode diameter between d=8 μm and d=100 nm. We observe, only in the very small diodes, a novel spikelike fine structure in the current-voltage characteristics within the conventional resonant tunneling peaks. These spikes are assigned to resonant tunneling between coupled quantum dots. Furthermore, a much stronger quenching of the conventional resonance peaks at lower bias is observed with decreasing diode diameters as compared to the higher bias peaks. This effect is clearly reproducible and may be an indication that the low bias peaks employ different tunneling mechanisms than the high bias peaks.