Evidence for sequential tunnelling and charge build-up in double barrier resonant tunnelling devices

Magnetoquantum oscillations in the tunnel current of double barrier n-GaAs/(AlGa)As/GaAs/ (AlGa)As/GaAs resonant tunnelling devices are shown to contain both resonant and non-resonant contributions. The former demonstrates the build-up of charge in the GaAs quantum well when electrons are resonant with the first subband of the well. A theoretical analysis of resonant tunnelling is in excellent agreement with the experimental data. Evidence of sequential tunnelling is found in the voltage range corresponding to the resonance when electrons tunnel into the second subband of the well. Near this resonance, the charge build-up in the well is estimated from the magnetotunnelling oscillations.