Fabrication of quantum wires by in-situ ion etching and MBE overgrowth

We fabricate GaAs quantum wires (QW) that are completely embedded in epitax ial material. Here we report about an in-vacuo fabrication process, in whic h an ex-situ pre-patterned GaAlAs/GaAs heterostructure is in-situ etched an d subsequently transferred under ultra high vacuum conditions into the grow th chamber for epitaxial overgrowth. The insitu etching step involves a che mical assisted ion beam etching with subsequent chemical gas etching. The a im of our investigations is to optimize the in-vacuo process for the reduct ion of interface states between the etched and overgrown material. We have studied structural properties of such processed samples with cross-sectiona l scanning-electron microscopy and transmission-electron microscopy. The op tical and electronic properties of overgrown QW are investigated with magne to-transport measurements and far-infrared transmission spectroscopy. Overg rown QW show in comparison to conventional QW without overgrowth clearly in creased carrier densities and a reduced depletion zone at the QW side-walls . These results indicate the successful reduction of surface states and est ablish the potential of the suggested in-situ technique for the fabrication of quantum structures. (C) 2001 Elsevier Science B.V. All rights reserved.