Resonant tunneling in coupled quantum dots

Resonant tunneling in GaAs-AlGaAs triple barrier diodes is studied as a function of the diode diameter between d=8 μm and d=100 nm. We observe, only in the very small diodes, a novel spikelike fine structure in the current-voltage characteristics within the conventional resonant tunneling peaks. These spikes are assigned to resonant tunneling between coupled quantum dots. Furthermore, a much stronger quenching of the conventional resonance peaks at lower bias is observed with decreasing diode diameters as compared to the higher bias peaks. This effect is clearly reproducible and may be an indication that the low bias peaks employ different tunneling mechanisms than the high bias peaks.