CHARGING EFFECTS IN SMALL-AREA MODULATION-DOPED DOUBLE-BARRIER HETEROSTRUCTURES

Charging effects on resonant tunneling are studied in modulation-doped double-barrier heterostructures. We observe a blockade of the tunneli ng current around zero-bias in small-area devices, while in large-area devices we observe a tunneling current with a zero-threshold bias due to the modulation doping. The blockade voltage width varies in propor tion to the inverse square of the conducting diameter, and agrees well with the calculated charging energy for a single electron. At the hig h voltage end of this blockade region we observe step-like current-vol tage features and fine structure in the form of small peaks and should ers. This fine structure is related to the interplay between charging and size quantization effects.