Measuring carrier density in parallel conduction layers of quantum Hall systems

TL;DR

This paper presents an experimental method to accurately measure carrier densities in parallel conduction layers within quantum Hall systems, enabling better characterization of heterostructures and quantum wells.

Contribution

It introduces a quantitative analysis technique for determining charge densities and mobilities in parallel layers, including a simple formula for estimating carrier density from a single Hall measurement.

Findings

Quantitative determination of doping layer charge density.

Observation of magnetic freeze-out in heterojunctions.

Estimation of carrier density in a second subband using a simple formula.

Abstract

An experimental analysis for two parallel conducting layers determines the full resistivity tensor of the parallel layer, at magnetic fields where the other layer is in the quantum Hall regime. In heterostructures which exhibit parallel conduction in the modulation-doped layer, this analysis quantitatively determines the charge density in the doping layer and can be used to estimate the mobility. To illustrate one application, experimental data show magnetic freeze-out of parallel conduction in a modulation doped heterojunction. As another example, the carrier density of a minimally populated second subband in a two-subband quantum well is determined. A simple formula is derived that can estimate the carrier density in a highly resistive parallel layer from a single Hall measurement of the total system.