# Light effective hole mass in undoped Ge/SiGe quantum wells

## TL;DR

This study measures the density-dependent effective hole mass in undoped Ge/SiGe quantum wells, revealing a very light mass that varies with electron density, which is promising for quantum computing applications.

## Contribution

It provides the first detailed measurement of hole effective mass in undoped Ge/SiGe quantum wells across a wide density range, confirming theoretical predictions.

## Key findings

- Effective hole mass of 0.061m_e at 2.2×10^{11} cm^{-2}
- Mass increases with density as predicted by theory
- Extrapolated zero-density mass of ~0.05m_e, the lightest for planar quantum dots

## Abstract

We report density-dependent effective hole mass measurements in undoped germanium quantum wells. We are able to span a large range of densities ($2.0-11\times10^{11}$ cm$^{-2}$) in top-gated field effect transistors by positioning the strained buried Ge channel at different depths of 12 and 44 nm from the surface. From the thermal damping of the amplitude of Shubnikov-de Haas oscillations, we measure a light mass of $0.061m_e$ at a density of $2.2\times10^{11}$ cm$^{-2}$. We confirm the theoretically predicted dependence of increasing mass with density and by extrapolation we find an effective mass of $\sim0.05m_e$ at zero density, the lightest effective mass for a planar platform that demonstrated spin qubits in quantum dots.