# Hole weak anti-localization in a strained-Ge surface quantum well

## TL;DR

This study investigates weak anti-localization effects in a strained Ge quantum well, revealing spin-orbit coupling characteristics and effects of magnetic fields on hole transport, with implications for spintronic applications.

## Contribution

It provides the first detailed analysis of weak anti-localization in strained Ge quantum wells, including extraction of spin splitting energy and effects of magnetic field orientation.

## Key findings

- Weak anti-localization peak increases with hole density.
- Spin splitting energy estimated at ~1 meV.
- Weak anti-localization observed for magnetic fields parallel to the quantum well.

## Abstract

We report a magneto-transport study of a two-dimensional hole gas confined to a strained Ge quantum well grown on a relaxed Si0.2Ge0.8 virtual substrate. The conductivity of the hole gas measured as a function of a perpendicular magnetic field exhibits a zero-field peak resulting from weak anti-localization. The peak develops and becomes stronger upon increasing the hole density by means of a top gate electrode. This behavior is consistent with a Rashba-type spin-orbit coupling whose strength is proportional to the perpendicular electric field, and hence to the carrier density. By fitting the weak anti-localization peak to a model including a dominant cubic spin-orbit coupling, we extract the characteristic transport time scales and a spin splitting energy of ~1 meV. Finally, we observe a weak anti-localization peak also for magnetic fields parallel to the quantum well and attribute this finding to a combined effect of surface roughness, Zeeman splitting, and virtual occupation of higher-energy hole subbands.