Tunnel Junction Design and Characterization in Si:P Single Electron Transistors

Atomically precise Si:P quantum devices are a promising architecture for scalable solid-state quantum computing. Quantification and control of the tunnel coupling between device components at the atomic scale is essential to successful donor-based quantum information processing (e.g. gate-tunable exchange coupling, electron spin readout, and ultrasensitive charge sensing all require precise control over tunnel coupling). We report on reproducibility of tunnel coupling as measured in atomically precise single electron transistors (SETs). We systematically vary gap separations on the nanometer scale, observing orders of magnitude changes in resistance. Combining low-temperature transport measurements with the orthodox theory of Coulomb blockade, we have extracted tunnel resistances in SETs and analyze to what degree resistances depend on applied voltages. We analyze the relationship between the tunnel conductance and physical barrier parameters and will discuss the limits of lithographically defining an atomically abrupt Si:P tunnel junction. We find the behavior of the tunnel junctions in these devices to be of exceptional quality and will discuss potential reasons for these improvements compared to previous devices fabricated in a similar manner.