Results and model for single-gate ratchet charge pumping

Abstract

We show experimentally that, in the same Si devices, we can demonstrate multiple two-gate pumping modes but not single-gate mode. We contrast this with GaAs devices, which do show single-gate pumping at a high yield. We propose four mechanisms to explain the lack of plateaus in the Si devices in single-gate ratchet mode: operating the dot with a large number of electrons, a large ratio between the change in electrochemical potential energy and the change in the energy of the barrier (plunger-to-barrier ratio, Δptb) compared to the charging energy (Δptb/EC), nonlinear tunnel barriers, and phase offset leading to nonequilibrium heating. Our analysis shows that each of these could contribute to the lack of plateaus in single-gate ratchet pumping on Si devices but allow two-gate pumping methods to work with robust plateaus. It is easier for GaAs pumps to avoid these failure mechanisms due to their different architectures and cleaner gate turnoff curves. We propose several methods to reduce these sources of error, including reducing cross capacitances between gates. These recommendations may prove useful to other researchers in producing more robust, higher yield single-gate ratchet pumps.