Coupling between in-plane and longitudinal motion in resonant tunnelling structures

We investigate tunnelling transport in an asymmetric double-barrier structure with heavily doped contacts by use of a quantizing magnetic field applied perpendicular to the layers. We find that for bias voltages in the region of the resonance, the current-voltage (I-V) characteristics exhibit step-like features that shift to higher biases with increasing magnetic field. Our experimental results clearly show two distinct regions in the I-V curves where tunnelling is controlled by Landau 'ladder' formation in either the well or the barriers. It is shown that electrons with relatively large in-plane energy tunnel conserving their in-plane energy rather than their in-plane momentum.