Distinguishing impurity concentrations in GaAs and AlGaAs, using very shallow undoped heterostructures

TL;DR

This paper presents a method to create very shallow, gateable undoped 2D electron gases in GaAs/AlGaAs, enabling detailed impurity and interface analysis crucial for improving epitaxial growth and device performance.

Contribution

The authors develop a novel fabrication and analysis technique to extract impurity, interface, and surface charge information from shallow 2DEGs, advancing understanding of material quality.

Findings

Quantitative impurity concentration data obtained

Mobility evolution with 2DEG depth characterized

Method enables better control of heterostructure quality

Abstract

We demonstrate a method of making a very shallow, gateable, undoped 2-dimensional electron gas. We have developed a method of making very low resistivity contacts to these structures and systematically studied the evolution of the mobility as a function of the depth of the 2DEG (from 300nm to 30nm). We demonstrate a way of extracting quantitative information about the background impurity concentration in GaAs and AlGaAs, the interface roughness and the charge in the surface states from the data. This information is very useful from the perspective of molecular beam epitaxy (MBE) growth. It is difficult to fabricate such shallow high-mobility 2DEGs using modulation doping due to the need to have a large enough spacer layer to reduce scattering and switching noise from remote ionsied dopants.