Evidence of Activated Conduction in a Single Electron Transistor

Conductance measurements are reported for quantum dots fabricted by pattern-dependent oxidation in silicon; the small size of these devices allows observation of single electron behavior to temperatures as high as 200K. At temperatures above 6K the zero-bias conductance peaks, periodic in gate voltage, are asymmetric, with heights that increase rapidly with increasing temperature. These features suggest that the dominant conductance mechanism in this temperature range is thermal activation over one of the potential barriers that localize electrons in the quantum dot. Quantitative comparisons are made between the data and the theory of Matveev and Glazman, including fits of the asymmetric lineshapes. However, from these fits, we find a potential barrier height that is much smaller than the charging energy, indicating that our data cannot be fully explained by this theory. At lower temperatures, the conductance peaks become much less periodic, and the data in this regime suggest the presence of several quantum dots in series.