HIGH MAGNETIC-FIELD STUDIES OF RESONANT TUNNELING VIA SHALLOW IMPURITIES IN DELTA-DOPED QUANTUM-WELLS

We have observed a new sub-threshold peak in the I(V) characteristics of double-barrier resonant tunneling structures. By investigating a range of intentionally delta-doped and control layers we can relate this peak to resonant tunneling through the bound state of a shallow donor impurity in the quantum well. We have 'studied the dependence of the voltage position of this peak on the magnitude of a magnetic field applied either parallel or perpendicular to the plane of the quantum well. In the parallel orientation the donor peak shifts slightly to lower voltage whereas the threshold of the continuum resonance shows the usual large quadratic shift to higher voltage. The amplitude of the donor-related peak is reduced in the presence of a magnetic field. We present a theoretical model to explain this behaviour and show how the results can be used to probe the spatial form of the impurity wavefunction in the quantum well.