Optical and transport properties of low-dimensional structures fabricated by cleaved edge overgrowth

Recent progress in the fabrication of GaAs/AlGaAs low-dimensional structure s by cleaved edge overgrowth (CEO) - a molecular beam growth technique that involves one or two regrowth steps on the sidewalls of an in situ cleaved layer structure - is reviewed. Ballistic electron transport in modulation-d oped quantum wires prepared in this way is characterized by pronounced quan tization of the conductance in integer multiples < 2e(2)/h. A magnetic fiel d oriented perpendicular to the quantum wires is found to increase the quan tized conductance values. While for a 400 Angstrom wide channel the canonic al values of n x 2e(2)/h are almost reached at a magnetic field strength of 4 T the corresponding conductance rise in a 250 Angstrom wide channel is m uch slower. In addition, the magnetic field dependence of the positions of the conductance steps as a function of an applied gate voltage which contro ls the electron density is distinctly different for wires of 400 and 250 A width. The optical, properties of atomically precise quantum dots which ori ginate at the right angle intersection of three quantum wells are character ized by narrow "atom-like" emission lines. Two different types of quantum d ot structures have been investigated using microscopic photoluminescence sp ectroscopy: linear arrays of weakly coupled dots, i.e. an one-dimensional q uantum dot superlattice and single as well as paired quantum dots. The latt er allow the assembly of "artificial molecules') out; of almost identical q uantum dots which can be considered as "artificial atoms" as the dot-to-dot distance is varied.