The research has led to the development of magnetotunnelling spectroscopy as a probe of the complicated energy versus momentum dispersion curves of bound hole states in the valence band quantum well. It has been applied to the measurement of the hole dispersion curves in aluminium arsenic/gallium arsenic/aluminium arsenic quantum wells. Briefly, the technique works as follows. A magnetic field is applied parallel to the barriers. The effect of the magnetic field is to shift the voltage positions of the peaks in the current voltage characteristics by an amount given by the form of the hole dispersion curve. Thus the magnetic field and the applied voltage allow us sweep through different values of K(parallel), the in plane momentum of the tunnelling holes, and energy for the quantum well states. In this way, we are able to measure directly the negative effective mass behaviour and light heavy hole mixing of the valence band quantum well states.
We have used the technique to measure the hole dispersion curves for a valence band quantum well grown on a (311)A surface. This plane is highly asymmetric and the resonant magnetotunnelling spectroscopy (RMTS) technique has revealed clearly the remarkable and complex form of the valence band states.
Funding SchemeCSC - Cost-sharing contracts