UNILATERAL CURRENT WITH COULOMB STEPS IN 2 SMALL TUNNEL-JUNCTIONS OF TRAPEZOIDAL BARRIERS CONNECTED IN SERIES

We theoretically study single electron transport through voltage biase d two small tunnel junctions of trapezoidal barriers connected in seri es, and show that this structure possesses a characteristic feature of unilateral current accompanied with Coulomb steps. Due to such a char acteristic feature, the structure is expected to serve as a single ele ctron transistor giving a very good performance. Our analysis is based on the semi-classical tunnelling model, but the tunnel rates through each junction are determined by directly calculating a golden rule equ ation.