Room-temperature negative differential resistance in single-atom devices

We report the observation of negative differential resistance (NDR) in single-atom single-electron devices based on arsenic, phosphorus and potassium dopants implanted in a silicon host matrix. All devices exhibit NDR, with the potassium-based one exhibiting NDR at room temperature because of the larger charging and confinement energies. Our experimental results are reproduced with a simple model that assumes sequential electron tunnelling through two series-connected charge centres, each having two discrete energy levels. The model utilises the nonequilibrium Keldysh diagram technique, and its accuracy is improved by introducing an effective local temperature that depends on the dissipated power and by semi-classical averaging of fluctuations of the dopant spectra. Our control experiments on undoped devices revealed the bandgap boundaries of the silicon host matrix which we successfully modelled using a single-barrier approximation. The use of unconventional dopants in silicon with high characteristic energies, such as potassium, is a major step forward toward the implementation of room-temperature single-atom electronics.