ENERGY-LEVELS OF QUANTUM WIRES DETERMINED FROM MAGNETOPHONON RESONANCE EXPERIMENTS

We report the observation of magnetophonon resonances in quantum wires , fabricated by shallow etching on conventional high-mobility GaAs-Alx Ga1-xAs heterojunctions. It is shown that magnetophonon resonance meas urements can be used as an alternative transport tool for the characte rization of the subband spectrum of quantum wires. The method proves t o be particularly useful at low electron densities, when only a few su bbands are occupied and the standard magnetic depopulation characteriz ation technique can no longer be used. By variation of the electron de nsity in the wires through illumination with a red light-emitting diod e the one-dimensional (1D) subband spacing, as determined from magneto phonon resonance measurements, is found to increase with decreasing el ectron density and to be systematically higher than the subband spacin g obtained from simultaneous magnetic depopulation measurements. We gi ve an explanation of this observation, which indicates that the combin ation of both transport characterization methods provides information on the actual shape of the underlying confinement potential. In additi on, also the effective mass of the 1D electrons can be determined from the magnetophonon data. We observe a slight increase of the effective mass with decreasing carrier density and a strikingly large enhanceme nt of m with stronger confinement, achieved by deeper etching. We dis cuss several possibilities that could lead to this strong mass enhance ment. [S0163-1829(98)08503-8].