Investigation of Mobility Limiting Mechanisms in Undoped Si/SiGe Heterostructures

TL;DR

This study investigates the electron mobility limitations in undoped Si/SiGe heterostructures, identifying background oxygen as a key factor and demonstrating high-quality 2DEGs suitable for quantum dot applications.

Contribution

It provides a detailed analysis linking background oxygen levels to mobility in undoped Si/SiGe heterostructures, highlighting their potential for quantum computing devices.

Findings

Maximum mobility of 160,000 cm^2/Vs achieved

Strong correlation between oxygen concentration and mobility

Valley splitting of approximately 150 microeV at 1.8 T

Abstract

We perform detailed magnetotransport studies on two-dimensional electron gases (2DEGs) formed in undoped Si/SiGe heterostructures in order to identify the electron mobility limiting mechanisms in this increasingly important materials system. By analyzing data from 26 wafers with different heterostructure growth profiles we observe a strong correlation between the background oxygen concentration in the Si quantum well and the maximum mobility. The highest quality wafer supports a 2DEG with a mobility of 160,000 cm^2/Vs at a density 2.17 x 10^11/cm^2 and exhibits a metal-to-insulator transition at a critical density 0.46 x 10^11/cm^2. We extract a valley splitting of approximately 150 microeV at a magnetic field of 1.8 T. These results provide evidence that undoped Si/SiGe heterostructures are suitable for the fabrication of few-electron quantum dots.