The use of undoped GaAs heterostructures allows ambipolar devices where the carrier type (electrons or holes) is solely determined by the polarity of the top-gate voltage. This is not possible in modulation-doped sample, and allows for ambipolar devices with both N-type and P-type elements.
We are interested in a class of devices known as a single-electron pumps. At low temperatures, these devices produce quantized current plateaus at I = nef, where e is the electron charge, f is the radio frequency (RF) of an ac signal applied to a local gate , and n is the number of electrons pumped from source to drain during each RF cycle.
These pumps do not require an applied source-drain bias, operate at high frequencies (~1 GHz), and are distinct from adiabatic turnstile pumps, which require a finite source-drain bias and a minimum of two RF gates to operate. Following the 2019 re-definition of the ampere in the International System of Units (SI), non-adiabatic single electron pumps have emerged as candidates to serve as primary standards for accurately measuring a ~1 nA current. During every RF cycle, an electron is “scooped” from the source reservoir and ejected into the drain reservoir. Note only one gate is operated at high frequencies. By tuning the barrier gates, the number n of pumped electrons can be precisely controlled, producing the current I = nef. The ability to eject individual electrons controllably is an important element of future quantum devices, such as an on-demand quantum light source or devices that exploit electron optics.