Coherent Far-Infrared Mode Pumping in Ballistic Electron Channels

Doctoral thesis, 1998

The influence of a high frequency electromagnetic field on transport properties of ballistic electron channels is investigated theoretically. We are primarily concerned with submicron-width channels formed by split-gate depletion of a two-dimensional electron gas at a GaAs/AlGaAs heterostructure interface. The pronounced quantization in the transverse direction of such channels opens the possibility to manipulate propagating electrons by inducing transitions between transverse modes by means of electromagnetic fields. Our investigations are focused on resonant mode coupling effects in long channels, induced by monochromatic far-infrared (FIR) fields polarized in the transverse direction of the channel. Within a single-particle transmission approach we predict the developing of spatial oscillations in the population of transverse modes, on a length scale much longer than the de Broglie wavelength. These oscillations have their correspondence in Rabi oscillations in atomic and molecular beams and in many other phenomena which exploit the resonant behavior of a two-level system. Different arrangements for detecting and exploiting this non-equilibrium situation are examined. A constriction in the channel leads to a retardation and a possibility for reflection of excited modes, while a widening leads to an acceleration and a possibility for excited modes to pass potential barriers. Such mechanisms affect the transmission probability and therefore lead to a change in the conductance. Also photovoltaic effects are found which eliminates the need for an external power supply. In the long run one can imagine to exploit this pumping mechanism in applications such as tunable narrow-band detectors and frequency demodulators, or even in transistors to which both the power and clock is distributed globally from the FIR field.