Coulomb blockade observed in a Ge nanocrystalline thin film from a macroscopic-size device and its enhancement by photo-oxidation

Temperature dependent current–voltage (I–V) characteristics have been studied across the thickness of Ge nanocrystalline films (hereafter referred as nanofilm) prepared by cluster beam evaporation technique using a macroscopic size electrode. The nanofilms of thicknesses of about 20 nm deposited at liquid nitrogen substrate temperature (Ge-LNT) show the Coulomb blockade (CB) effect whereas for that deposited on substrates at 300 K (Ge-RT), no evidence of single electron tunneling could be observed. The difference is attributed to a difference in the nature of electron transport across the two kinds of the nanofilms. The photo-oxidation, which leads to size uniformity of the nanocrystals, is employed to observe its effect on I–V characteristics of the Ge nanofilm. It is found that the CB characteristics are enhanced in photo-oxidised Ge-LNT nanofilms, which can be explained in the light of a highly selective conduction process in the nanofilm.