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(Color online) (a) Schematic drawings, typical RHEED patterns, and STM images of epitaxial (left) and nonepitaxial (right) Ge nanodots. For STM images, is the same for the two types of nanodots. (b) The average dot-radius estimated by a statistical analysis of the STM images, (c) the VBM position of Si from evaluated from energy shift, and (d) electrical conductance obtained from the gradient at zero current of curves taken at , plotted as a function of nominal Ge coverage. Solid lines indicate fitting curves, whereas dashed lines are guides for eyes. Error bars show standard deviation of size distribution of the nanodots. Filled and open symbols correspond to the epitaxial and nonepitaxial dots, respectively. The VBM position when states at the center of the band gap is shown in a dash-dotted line in (c), and a gray-hatched area corresponds to depletion and week-inversion region.
(Color online) (a) Schematic drawings displaying the conduction paths contributing to the measured conductance for the bare substrate and the two types of nanodot arrays on it. (b) Conductance of each path, and , plotted as a function of the average dot radius . Dot-size dependent change in from that of the bare substrate induced by shift of the VBM of Si (i.e., band-bending change) is also shown as solid and dashed lines for the epitaxial and nonepitaxial cases, respectively.
(Color online) [(a) and (b)] Temperature dependence of the conductance of the two types of nanodot arrays at noted average dot radii . [(c) and (d)] The activation energy evaluated from the above relationship (filled diamonds with error bars) plotted as a function of . Expected activation energies corresponding to overexcited electrons and holes are also shown as open squares and circles, respectively. Schematic drawings of the energy diagrams at the interfaces for the (e) epitaxial and (f) nonepitaxial nanodots.
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