Tunneling Between Constrained Dimensionality Systems

Abstract

Systems of reduced dimensionality became a topic of increased interest during the last few years. To induce a one-dimensional system, a two-dimensional electron gas can be constrained to a thin stripe (“quantum wire”) by etching processes or electrostatic confinement. This confinement results in an additional set of quantized states. The knowledge of these one dimensional (ID) subband energies is one of the basic requirements to understand the physical properties of quantum wires such as the quenching of the quantum hall effect (Roukes et al., 1987), mobility modulations (Ismail et al., 1989) or boundary scattering (Thornton et al., 1989). One effect widely used to determine the ID-energy levels is the magnetic depopulation of the lD-subbands. This was done first by (Berggren et al., 1986) on a split-gate field effect transistor structure. Assuming a parabolic electrostatic confinement, the influence of an additional magnetic field can be analyzed analytically. It was shown (Berggren et al., 1986), that the additional magnetic field increases the ID subband spacing, so that lD-subbands are shifted above the Fermi energy if the magnetic field is increased. Consequently, these subbands are depopulated, resulting in an oscillating behavior of the magneto resistance. In contradiction to the 2D-case, a plot of the oscillation index versus inverse magnetic field (Landau-plot) is not linear and saturates at low magnetic fields. By fitting the experimental results, both the ID electron concentration n_1D and the subband energies are determined. From this, the widths of the conducting channels can be calculated.