Germanium wafers for strained quantum wells with low disorder

TL;DR

This paper demonstrates high-quality strained Ge/SiGe heterostructures grown on Ge wafers, achieving low disorder and high mobility in two-dimensional hole gases, suitable for advanced quantum computing applications.

Contribution

It introduces a method for growing low-dislocation Ge/SiGe heterostructures on Ge wafers, significantly reducing disorder compared to traditional Si wafer substrates.

Findings

Threading dislocation density reduced by nearly an order of magnitude.

Achieved maximum mobility of 3.4×10^6 cm^2/Vs in 2D hole gases.

Low percolation density of 1.22×10^{10} cm^{-2}.

Abstract

We grow strained Ge/SiGe heterostructures by reduced-pressure chemical vapor deposition on 100 mm Ge wafers. The use of Ge wafers as substrates for epitaxy enables high-quality Ge-rich SiGe strain-relaxed buffers with a threading dislocation density of (6$\pm$1)$\times$10$^5$ cm$^{-2}$, nearly an order of magnitude improvement compared to control strain-relaxed buffers on Si wafers. The associated reduction in short-range scattering allows for a drastic improvement of the disorder properties of the two-dimensional hole gas, measured in several Ge/SiGe heterostructure field-effect transistors. We measure an average low percolation density of (1.22$\pm$0.03)$\times$10$^{10}$ cm$^{-2}$, and an average maximum mobility of (3.4$\pm$0.1)$\times$10$^{6}$ cm$^2$/Vs and quantum mobility of (8.4$\pm$0.5)$\times$10$^{4}$ cm$^2$/Vs when the hole density in the quantum well is saturated to (1.65$\pm$0.02)$\times$10$^{11}$ cm$^{-2}$. We anticipate immediate application of these heterostructures for next-generation, higher-performance Ge spin-qubits and their integration into larger quantum processors.