Resonant magnetotunneling via quantum confined states

We have measured the low temperature current-voltage characteristics ( I ( V )) of GaAs/A1As resonant tunnelling diodes with sub-micron lateral dimensions. Additional peaks in I ( V ) are observed due to resonant tunnelling via one-dimensional quantum wire states. In the presence of a magnetic field oriented perpendicular to the current and parallel to the wire the peaks show a complex splitting evolving into a regular series at high field with upt to 20 resonances. For the smallest device we are able to deduce the probability density of the lowest three bound states from the magnetic field dependence of the current and show that the confining potential is close to parabolic. For a magnetic field which is perpendicular to both the current and the wire a much weaker dependence on magnetic field is observed confirming the one-dimensional nature of our device. Finally, in the presence of a field oriented parallel to the current a continuous transition from electrostatic (at low field) to magnetic confinement (at high field) is observed.