Effects of Interface Disorder on Valley Splitting in SiGe/Si/SiGe Quantum Wells

TL;DR

This study investigates how interface disorder affects valley splitting in SiGe/Si/SiGe quantum wells, revealing that interface imperfections and electric fields significantly influence electronic properties crucial for quantum computing.

Contribution

It provides an atomistic analysis of interface disorder effects on valley splitting, highlighting the limitations of simplified models and emphasizing the importance of interface interactions.

Findings

Electric fields increase valley splitting fluctuations.

Interface disorder causes significant valley splitting variability.

Ordered alloy models help understand bonding effects on valley splitting.

Abstract

A sharp potential barrier at the Si/SiGe interface introduces valley splitting (VS), which lifts the 2-fold valley degeneracy in strained SiGe/Si/SiGe quantum wells (QWs). This work examines in detail the effects of Si/SiGe interface disorder on the VS in an atomistic tight binding approach based on statistical sampling. VS is analyzed as a function of electric field, QW thickness, and simulation domain size. Strong electric fields push the electron wavefunctions into the SiGe buffer and introduce significant VS fluctuations from device to device. A Gedankenexperiment with ordered alloys sheds light on the importance of different bonding configurations on VS. We conclude that a single SiGe band offset and effective mass cannot comprehend the complex Si/SiGe interface interactions that dominate VS.