Evidence for activated conduction in a single electron transistor

Conductance measurements are reported for quantum dots fabricated by patter n-dependent oxidation in silicon; the small size of these devices allows ob servation of single electron behavior to temperatures as high as 200 K. At temperatures above 6 K the zero-bias conductance peaks, periodic in gate vo ltage, are asymmetric, with heights that increase rapidly with increasing t emperature. These features suggest that the dominant conductance mechanism in this temperature range is thermal activation over one of the potential b arriers that localize electrons in the quantum dot. Quantitative comparison s are made between the data and the theory of Matveev and Glazman, includin g fits of the asymmetric line shapes. However, from these fits we find a po tential barrier height that is much smaller than the charging energy, indic ating that our data cannot be fully explained by this theory. At lower temp eratures, the conductance peaks become much less periodic, and the data in this regime suggest the presence of several quantum dots in series. (C) 200 1 American Institute of Physics.