TRANSPORT IN SUBMICRON RESONANT-TUNNELING DEVICES

We have investigated the I(V) characteristics of a sub-micron gated GaAs/(AlGa)As resonant tunnelling diode. We find that, relative to a large area device, there is additional structure at both,high and low source-drain bias. The low bias features are shown to be due to the presence of impurities in the quantum well. This is confirmed by experiments on delta-doped large area devices. Using the gate on the sub-micron devices we are able to control the current through a single donor state. The high voltage structure occurs within the main resonance and only in forward bias where the peak-to-valley ratio (PVR) is poor. We ascribe the poor PVR to a lateral variation of the resonance condition and discuss the high voltage structure in these devices, and in similar two-terminal devices, in the light of this hypothesis.