Spectroscopy of a Single Si Donor by the Resonant Tunnelling Experiment

Resonant tunnelling via single impurities placed in a single barrier was experimentally studied.The typically observed structures in the currentvoltage characteristics seem to be paired.Such a pair can be interpreted as ground and excited states of an impurity, related to X xy and X z valleys, which is in agreement with the results obtained for big mesas.However, it is not clear why X xy states can be seen without any phonon participation.