Mobility and quantum mobility of modern GaAs/AlGaAs heterostructures

TL;DR

This paper investigates how excess electrons in GaAs/AlGaAs heterostructures influence electron mobility, revealing that electron screening effects and impurity concentrations are key to optimizing high mobility in quantum wells.

Contribution

It provides a detailed theoretical analysis of electron localization, screening, and mobility limits, offering new insights into the factors affecting electron mobility in modern heterostructures.

Findings

Quantum mobility increases as the cube of the filled remote donor fraction.

Screening by excess electrons can surpass background impurity effects.

Method to estimate impurity concentrations from measured mobilities.

Abstract

In modern GaAs/Al$_x$Ga$_{1-x}$As heterostructures with record high mobilities, a two-dimensional electron gas (2DEG) in a quantum well is provided by two remote donor $\delta$-layers placed on both sides of the well. Each $\delta$-layer is located within a narrow GaAs well, flanked by narrow AlAs layers which capture excess electrons from donors. We show that each excess electron is localized in a compact dipole atom with the nearest donor. Nevertheless, excess electrons screen both the remote donors and background impurities. When the fraction of remote donors filled by excess electrons $f$ is small, the remote donor limited quantum mobility grows as $f^{3}$ and becomes larger than the background impurity limited one at a characteristic value $f_c$. We also calculate both the mobility and the quantum mobility limited by the screened background impurities with concentrations $N_1$ in Al$_x$Ga$_{1-x}$As and $N_2$ in GaAs, which allows one to estimate $N_1$ and $N_2$ from the measured mobilities. Taken together, our findings should help to identify avenues for further improvement of modern heterostructures.