Exploration of the Limits to Mobility in Two-Dimensional Hole Systems in GaAs/AlGaAs Quantum Wells

TL;DR

This study investigates how the mobility of two-dimensional hole systems in GaAs/AlGaAs quantum wells varies with density, revealing a nonmonotonic relationship with a peak mobility at intermediate density, and discusses underlying scattering mechanisms.

Contribution

It provides the first detailed analysis of the density-dependent mobility in 2D hole systems in GaAs/AlGaAs quantum wells, highlighting nonmonotonic behavior and potential scattering mechanisms.

Findings

Mobility peaks at 2.3×10^6 cm^2/Vs at a density of 6.5×10^10 cm^-2.

Mobility decreases at higher densities, contrary to typical expectations.

Interface roughness alone cannot explain the mobility drop at high density.

Abstract

We report on the growth and electrical characterization of a series of two-dimensional hole systems (2DHSs) used to study the density dependence of low temperature mobility in 20 nm GaAs/AlGaAs quantum wells. The hole density was controlled by changing the Al mole fraction and the setback of the delta-doping layer. We varied the density over a range from 1.8 $\times$ 10$^{10}$ cm$^{-2}$ to 1.9 $\times$ 10$^{11}$ cm$^{-2}$ finding a nonmonotonic dependence of mobility on density at T = 0.3 K. Surprisingly, a peak mobility of 2.3 $\times$ 10$^6$ cm$^2$/Vs was measured at a density of 6.5 $\times$ 10$^{10}$ cm$^{-2}$ with further increase in density resulting in reduced mobility. We discuss possible mechanisms leading to the observed non-monotonic density dependence of the mobility. Relying solely on interface roughness scattering to explain the observed drop in mobility at high density requires roughness parameters which are not consistent with measurements of similar electron structures. This leaves open the possibility of contributions from other scattering mechanisms at high density.