Top-gated germanium nanowire quantum dots in a few-electron regime

Top gated quantum dots (QDs) have been fabricated from n-type chemically synthesized germanium nanowires (GeNWs) by constricting its length with metal electrode contacts. With an intermediate HfO2 thin film, the constricted GeNW was fully covered by an Omega-shaped top-gate. The QD was probed and characterized by single-electron transport measurements at liquid helium temperature and has been found to reach a few-electron regime, in which the number of confined electrons was tunable from zero. The absolute zero-electron was confirmed with a charge stability diagram, and it was revealed that the extremely small QD arose from potential fluctuations due to phosphorus donors.