Thermopower-enhanced efficiency of Si/SiGe ballistic rectifiers

Injection-type ballistic rectifiers on Si/SiGe are studied with respect to the influence of gate voltage on the transfer resistance R T (output voltage divided by input current) for different positions of a local gate electrode. The rectifiers are trifurcated quantum wires with straight voltage stem and oblique current-injecting leads. Depending on the gate configuration, thermopower contributions arise from nearly pinched stem regions, which either cancel each other or impose upon the ballistic signal with same or opposite polarity. At best, this enhances R T to a maximum value of 470 Ω close to threshold voltage.