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 RT (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 RT to a maximum value of 470 Ohm close to threshold voltage.