Tunneling spectroscopy in the hopping regime

Charge transport across tunneling junctions of n-doped Ge has been investigated experimentally and theoretically. Using tunneling spectroscopy we were able to observe the density of states and the effect of the electron-electron interaction on the excitation spectrum of samples, in which hopping is the transport mechanism close to equilibrium. To analyze the data of the measurements we derive an expression for the tunneling current in the hopping regime. We use our expression for the tunneling current in order to analyze the character of the transitions. Doing so, we show that in the experiment only transitions with at most small energy transfer were relevant.