Transport experiments in electron waveguides

Dain Curtis Miller, Purdue University

Abstract

T-shaped electron waveguide structures have been fabricated on AlGaAs/GaAs heterojunctions using electron-beam lithography and a shallow wet-chemical etch. The electrical width and carrier density of the narrow channels are estimated from their magnetoresistances. Two types of devices have been investigated at temperatures down to 30mK. T devices made on insulating substrates show conductance oscillations as the length of the stub is changed by depleting it with a Schottky gate on the surface. Although some of the frequencies observed fall in the range of expected frequencies, fringing fields from the gate complicate the interpretation of the oscillations. The effects of these fringing fields are greatly reduced by changing the substrate to P+ GaAs. Using the P+ substrate as a backgate, oscillations are observed in fixed-length T devices as the carrier density is varied. The observation of similar oscillations in straight wires implies that scattering in the waveguide is producing universal conductance fluctuations which mask the effects of device geometry. The conductance fluctuations are analyzed to estimate the phase-breaking length. Fabrication methods which produce waveguides free from disorder must be perfected before clear geometrical resonance can be observed in long narrow waveguide-type structures.

Degree

Ph.D.

Advisors

Datta, Purdue University.

Subject Area

Electrical engineering

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