Anomalous resonant-tunneling effect in type II heterostructures

We have observed unusual negative differential-conductance features in the magneto-tunneling current–voltage characteristics of GaSb–AlSb–InAs–AlSb–GaSb heterostructures. These features are very narrow (∼2 mV) and shift to higher voltage with increasing magnetic field, both properties being in sharp contrast with those of the features associated with conventional resonant tunneling through Landau levels in the InAs well. The new results are explained by a three-step sequential tunneling process, in which two Landau levels – one empty and one occupied – are involved.