Coulomb-blockade effect observed at room temperature in Ge nanocrystalline films deposited by the cluster-beam evaporation technique

The temperature-dependent current–voltage (I–V) characteristics have been studied across the thickness of Ge nanocrystalline films prepared by the cluster beam evaporation technique. It is found that a film with a thickness of 30 nm, deposited on a substrate kept at 77 K, does not exhibit any distinct step-like feature in the I–V characteristics at room temperature. However, with the lowering of the temperature, a “Coulomb gap” is observed and a pronounced step-like feature appear in the I–V characteristics suggesting the Coulomb blockade (CB) effect. It is hypothesized that the observed CB effect in these nanocrystalline thin films results from a very highly selective electron transport process where the electron transport is dominated by one local well-defined current path with the largest conductance. The result of similar measurements on a photo-oxidized sample, which shows a signature of a step-like feature in the I–V characteristics, even at room temperature, supports this hypothesis.