Photoconductivity of quantum wire structures

Ballistic pulses of non-equilibrium acoustic phonons, generated by a thin-film heater, have been used to probe the electron-phonon interaction in a short quantum wire (point contact). The wire was formed in a GaAs heterojunction using the split-gate technique. Incident phonons caused a transient decrease in conductance, Delta G, of the point contact. Giant oscillations in Delta G were observed as the wire was narrowed by increasing the negative gate bias. Peaks in Delta G occurred when the Fermi energy was close to the bottom of any one-dimensional (1D) subband. The model of direct electron backscattering by phonon absorption in the 1D channel is unable to account for the magnitude of the phonoconductivity response which is much larger than predicted, although it does predict correctly many other features of the phonoconductivity response. We believe that phonon absorption in the regions of two-dimensional electron gas (2DEG) near the point contact leads to an increase in electron temperature. The warm electrons enter the point contact wherein they relax by phonon emission and so are backscattered. We show that this model is able to account for all features of the measured phonoconductivity signal including its magnitude.