TRANSPORT AND OPTICS IN QUANTUM WIRES FABRICATED BY MBE OVERGROWTH ONTHE (110) CLEAVED EDGE

The MBE double-growth technique that we call cleaved-edge overgrowth h as, over the past several years, proved itself to be especially suitab le for making quantum wires of the very highest quality. We will revie w our recent progress in measuring the transport and quantum optics ch aracteristics of these wires, and the MBE growth issues that arise wit h cleaved-edge overgrowth fab-cation. Our transport experiments have r esulted in 250 Angstrom wide quantum wires with ballistic mean free pa ths exceeding 10 mu m. We verify the prediction that in the ballistic regime the electron conductivity in a quantum wire is independent of t he wire length and shows quantized steps proportional to e(2)/h. The d eviation of our observed step heights from exactly e(2)/h is taken as evidence for correlated electron behaviour. The electrons are tightly confined on three sides by atomically smooth GaAs/AlGaAs heterojunctio ns and in the fourth direction by an electric field. This results in a quantum wire of nominal square cross-section 250 x 250 Angstrom. Magn etotransport measurements reveal quantum wire sub-band separations in excess of 20 meV as well as the symmetries of the wave functions of th e one-dimensional modes. For optics studies our quantum wires are made using cleaved-edge overgrowth to form a line junction as two quantum wells are made to intersect with the cross-section forming a letter 'T '. This line intersection separately forms a quantum wire bound-state for holes, for electrons, and even for excitons. We have characterized our optical wires by PL, by PLE, and by scanning near-field optics. A n important application of this work is our demonstration of the first quantum laser using this T-geometry. (C) 1997 Published by Elsevier S cience Ltd.