Inelastic cotunneling in the Coulomb-blockade transport of donor-atom transistors

We report finite-bias characteristics of electrical transport through phosphorus donors in silicon nanoscale transistors, which we observe inelastic-cotunneling current the Coulomb-blockade region. The cotunneling appears like a resonant-tunneling peak emerging from excited state and sustain within blockade regions. These features are unique, since currents have so far been reported either as broader hump or continuous increment current. This finding is ascribed purely due to excitation-related inelastic involving ground states. Theoretical calculations were performed for two-level quantum dot, supporting our experimental observation.