Electron ratchet effect in semiconductor devices and artificial materials with broken centrosymmetry

Studies on nonlinear electron transport in nanometer-sized semiconductor devices with broken centrosymmetry are reviewed. In these devices, an applied alternating (rocking) electric field induces a net flow of electrons in the direction perpendicular to that of the applied field. Such an electron ratchet effect has been observed in a number of differently designed devices, fabricated from two types of semiconductor material systems. The functionality is interpreted with an extended Buttiker-Landauer formula. We show that the devices operate at both cryogenic and room temperatures and at frequencies up to at least 50 GHz. Based on a similar microscopic mechanism, we have also constructed, to the best of our knowledge, the first artificial electronic nanomaterial that operates at room temperature. The promising possibilities for practical applications, such as rectification, microwave detection, second-harmonic generation, etc., are also discussed.