Landolt-Börnstein - Group III Condensed Matter

Electronic Transport. Part 1: Quantum Point Contacts and Quantum Wires · 3.6 Impurities

Abstract

This chapter discusses subsidiary role of impurity scattering in determining the device characteristics of a perfect quantum point contact (QPC). Nevertheless, in real devices the effects of impurities cannot be ignored, and the characteristics of nominally identical devices are frequently significantly different. The QPC characteristics permit the spectroscopy of an impurity state, which has been investigated as a function of temperature and magnetic field. A particularly elegant method exploited to investigate the nature of the confining potential, or rather its modification due to impurities, relies upon the lateral shifting of a channel position when different voltages are applied to split-gate electrodes. In such experiments the resistance associated with a given number of conducting subbands shifts with the applied differential voltage, and reflects the change in transmission resulting from changes in the local potential. Although the temperature dependence of the carrier concentration of 2DEG is relatively weak, the pinch-off voltage of the QPC moves to significantly lower negative voltages as the carriers within a doped layer freeze out. Irradiation has the effect of increasing the carrier density within a dopant layer, and hence leads to the observation of more negative pinch-off voltages for the QPC. Typical electron focusing spectra are plotted as a function of the applied field for temperatures between 7K and 50mK.

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Title
Electronic Transport. Part 1: Quantum Point Contacts and Quantum Wires · 3.6 Impurities
Book Title
Electronic Transport. Part 1: Quantum Point Contacts and Quantum Wires
In
3 Quantized transport
Book DOI
10.1007/b55682
Chapter DOI
10.1007/10479560_19
Part of
Landolt-Börnstein - Group III Condensed Matter
Volume
34B1
Editors
  • B. Kramer
  • Authors
  • D. Wharam
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