We report on the fabrication and characterization of a few-electron quantum dot controlled by a single gate electrode. Our device has a double-quantum-well design, in which the doping controls the occupancy of the lower well while the upper well remains empty under the free surface. A small air-bridged gate contacts the surface, and is positively biased to draw laterally confined electrons into the upper well. Electrons tunneling between this accumulation-mode dot and the lower well are detected using a quantum point contact (QPC), located slightly offset from the dot gate. The charge state of the dot is measured by monitoring the differential transconductance of the QPC near pinch-off. Addition spectra starting with N=0 were observed as a function of gate voltage. DC sensitivity to single electrons was determined to be as high as 8.6%, resulting in a signal-to-noise ratio of ~9:1 with an equivalent noise bandwidth of 12.1 kHz. Analysis of random telegraph signals associated with the zero to one electron transition allowed a measurement of the lifetimes for the filled and empty states of the one-electron dot: 0.38 ms and 0.22 ms, respectively, for a device with a 10 nm AlInAs tunnel barrier between the two wells.
@article{arxiv.0910.3631,
title = {Single-Gate Accumulation-Mode InGaAs Quantum Dot with a Vertically Integrated Charge Sensor},
author = {E. T. Croke and M. G. Borselli and M. F. Gyure and S. S. Bui and I. I. Milosavljevic and R. S. Ross and A. E. Schmitz and A. T. Hunter},
journal= {arXiv preprint arXiv:0910.3631},
year = {2010}
}