Low disordered, stable, and shallow germanium quantum wells: a playground for spin and hybrid quantum technology

TL;DR

This paper demonstrates a high-mobility, shallow germanium quantum well with low disorder, suitable for advanced spin and hybrid quantum devices, achieving record mean free paths and tunable carrier control.

Contribution

It introduces a high-mobility, shallow Ge/SiGe heterostructure with sharp interfaces and low disorder, advancing the platform for quantum technology applications.

Findings

High mobility of 5×10^5 cm^2/Vs in shallow Ge channel

Mean free path of approximately 6 μm

High g-factor up to 7 and low effective mass of 0.09 m_e

Abstract

Buried-channel semiconductor heterostructures are an archetype material platform to fabricate gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface, however nearby surface states degrade the electrical properties of the starting material. In this paper we demonstrate a two-dimensional hole gas of high mobility ($5\times 10^{5}$ cm$^2$/Vs) in a very shallow strained germanium channel, which is located only 22 nm below the surface. This high mobility leads to mean free paths $\approx6 \mu m$, setting new benchmarks for holes in shallow FET devices. Carriers are confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The top-gate of a dopant-less field effect transistor controls the carrier density in the channel. The high mobility, along with a percolation density of $1.2\times 10^{11}\text{ cm}^{-2}$, light effective mass (0.09 m$_e$), and high g-factor (up to $7$) highlight the potential of undoped Ge/SiGe as a low-disorder material platform for hybrid quantum technologies.