A gigahertz single-electron (SE) pump with a semiconductor charge island is promising for a future quantum current standard. However, high-accuracy current in the nanoampere (10^-9 A) regime is still difficult to achieve because the performance of SE pumps tends to degrade significantly at frequencies exceeding 1 GHz. NTT (Japan) and NPL (UK) have shown robust pumping via a single-trap level in silicon up to 7.4 GHz where the pump current exceeds 1 nA.

NTT scientist Gento Yamahata and co-workers fabricated based an electron pump based on a single atomic trap site in silicon. This was measured at NPL using their high accuracy small current calibration system.

While conventional pumps lose accuracy rapidly at frequencies above about 1 GHz, they found that the trap-based pump continued to work up to 7.4 GHz, generating a current of more than 1 nA. At these highest speeds the current was in error by a small amount around 20 parts per million, but nevertheless this represents a benchmark result for high speed electron pumping and the starting point for promising future work.

This research was published open-access in Scientific Reports from the Nature Publishing Group:
G. Yamahata, S. P. Giblin, M. Kataoka, T. Karasawa and A. Fujiwara, “High-Accuracy current generation in the nanoampere regime from a silicon single-trap electron pump”, Scientific Reports 7, 45137 (2017).