Dependences of the Transport Scattering Time and Quantum Lifetime on the Two-Dimensional Electron Gas Density in Modulation-Doped Single GaAs Quantum Wells with AlAs/GaAs Short-Period Superlattice Barriers

TL;DR

This study investigates how transport scattering time and quantum lifetime depend on electron density in GaAs quantum wells with superlattice barriers, revealing the roles of remote donors and background impurities in scattering processes.

Contribution

It provides a new expression for the effective remote ionized donor concentration considering X-valley electrons, explaining the observed dependence of scattering times on electron density.

Findings

Transport scattering time and quantum lifetime increase with electron density.

An abrupt increase in scattering times occurs above a critical electron density.

Background impurity scattering limits the ratio of transport to quantum lifetime at high densities.

Abstract

The dependences of the transport scattering time {\tau}t, quantum lifetime {\tau}q, and their ratio {\tau}t/{\tau}q on the density ne of the electron gas in modulation-doped single GaAs quantum wells with AlAs/GaAs short-period super-lattice barriers are investigated. The experimental dependences are explained in terms of electron scattering by remote ionized donors with an effective two-dimensional concentration n*R and background impurities with a three-dimensional concentration nB. An expression for n*R(ne) is obtained including the contribution of X-valley electrons localized in AlAs layers to the suppression of scattering by the random potential of remote donors. It is shown that the experimentally observed abrupt increase in {\tau}t and {\tau}q with an increase in ne above a certain critical value nec is related to a decrease in n*R. It is established that the drop in {\tau}t/{\tau}q observed for electron densities ne > nec occurs because scattering by the random potential of background impurities in this two-dimensional system with a decrease in n*R limits an increase in {\tau}t more considerably than an increase in {\tau}q.