Electron transport in Ge nanocrystalline films deposited using the cluster beam evaporation technique

The carrier transport properties across Ge nanocrystalline films (hereafter referred to as nanofilms) deposited by the cluster beam evaporation technique have been thoroughly studied. A thin nanofilm deposited at liquid nitrogen substrate temperature (Ge-LNT) exhibits the Coulomb blockade characteristic at low temperatures, while that deposited at room temperature (Ge-RT) does not show any evidence of single electron tunneling. This is explained by the difference in the nature of the overall electron transport due to a structural difference between the two types of nanofilms. The electron transport between two adjacent nanocrystals in both types of nanofilms was also studied in detail. It was found that, under relatively low electric fields, a Ge-LNT nanofilm exhibited T−1/2 conductivity dependence, which could be explained by the variable range hopping model of Efros and Shklovskii [A. L. Efros and B. I. Shklovskii, J. Phys. C 8, L49 (1975)], while in the Ge-RT nanofilms, the conductivity-temperature dependence was explained by the variable range hopping mechanism as proposed by Mott and Greaves [N. F. Mott and E. A. Davis, Electronic Process in Non-Crystalline Materials (Clarendon, Oxford, 1979); G. N. Greaves, J. Non-Crystalline Solids 11, 427 (1973)] in the given temperature range.