Study of Modulation Doped Quantum Wires.

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We have demonstrated that GaAs, AlGaAs, InAs and InGaAs quantum wires were naturally formed on vicinal GaAs(110) surfaces with giant growth steps. These quantum wires were induced by the thickness and/or composition modulation at giant step edges. Transmission electron microscopy and photoluminescence (PL) measurements consistently confirmed the formation of quantum wires. Formation of InAs quantum wires was observed using scanning tunneling microscopy combined with molecular beam epitaxy. PL peaks of modulation doped GaAs quantum wires shifted with doping level and excitation intensity. Electronic resistance parallel to the wires was much lower than that perpendicular to the wires, showing the quantum wires were successfully modulation doped.The micro-PL spectra from single AlGaAs quantum wires at 4K inhibited one peak with low energy tail and sharp high energy Fermi edge. These features was quite different from those of GaAs quantum wires which showed many sharp lines which came from localized excitons, indicating that AlGaAs quantum wires were more uniform. There results were very consistent with the scanning cathodoluminescence images. Using scanning cathodoluminescence, electron-hole pairs were excited by electron beam through Al mask. The luminescence observed from the aperture in Al mask showed the one-dimensional exciton flow.