Controlling Few-Donor Quantum Dots Coupled to SETs Using Surface Gates

Monolayer phosphorous dopant devices with high dopant confinement are an emerging methodology that allows the measurement and manipulation of single or few-dopant atom quantum dots for quantum computation and arrayed devices for analogue quantum simulation. STM fabrication of these devices provides a unique ability to create near perfect atomic structures on clean atomically ordered silicon in ultrahigh vacuum conditions. The devices are encapsulated in situ with a UHV grown ~30 nm epitaxial silicon layer followed by metallization for contact to the buried device components and top gates. In this talk we will present a single electron transistor (charge sensor) coupled to a few donor cluster where the chemical potential of the central island and the charge occupation on the few atom cluster are controlled via two capacitively coupled in-plane gates while current through the source/drain-leads and the SET island are used to determine the charge state. An external aligned metal gate on the surface is integrated ex situ using HfO2 as a dielectric. We confirm the functionality of the surface gates and measure a near zero-leakage current over a large gate range. Based on charge stability measurements, the surface gates have a similar lever arm as compared to the in-plane gates and therefore greatly expand the effective device gating range. We demonstrate the tuning of a few-donor cluster coupled to an SET charge sensor using surface gates while we use in-plane gates to load/unload individual electrons from the donor-cluster as well as demonstrate spin sensitive readout in a magnetic field. We will discuss the design, fabrication, and use of surface top gates to individually or globally address individual components in few-donor/quantum dot devices as well as a 2x2 arrayed device.