GaAs/AlGaAs/InGaAs vertical triple barrier single electron transistors

A gated vertical sub-micron triple barrier structure with undoped Al0.22Ga0.78As barriers and In0.05Ga0.95As wells is used to study the properties of two weakly coupled quantum dots containing just a few electrons. We find that the conductance peaks become sparse as the ac excitation voltage is decreased when there is considerable mismatch between the ladders of energy levels in the two dot. Concurrently, the diamond shaped regions of Coulomb blockade are strongly disrupted. On the other hand, when the mismatch between energy levels is ''small''-comparable to or less than the level width-the evolution of conductance peaks in pairs in the presence of a magnetic field applied parallel tb the tunneling current is clearly seen and this can be related to spin-degeneracy.