Mesoscopic conductance fluctuations in impurity-assisted resonant tunnelling

We have studied fluctuations in the differential conductance of resonant tunnelling diodes which incorporate a δ-layer of donor impurities in the centre plane of the quantum well. The system is well-suited to studying this type of conductance fluctuation, as we can control the number and position of the impurity states and also vary their effective linewidth by the application of a magnetic field perpendicular to the current direction.