Buried Unstrained Germanium Channels: A Lattice-Matched Platform for Quantum Technology.

Area of Science:

• Semiconductor physics
• Quantum computing materials

Background:

• Strained germanium (ε-Ge) and silicon (ε-Si) quantum wells are key for spin-qubit processors.
• Metamorphic SiGe buffers used for these materials introduce defects, hindering device performance and scalability.

Purpose of the Study:

• To introduce an alternative platform for quantum processors.
• To eliminate the need for metamorphic buffers by using a heterojunction between bulk unstrained Ge and a strained SiGe barrier.

Main Methods:

• Fabrication of a heterojunction structure with a strained SiGe barrier on unstrained Ge.
• Characterization of the resulting two-dimensional hole gas (2DHG) using quantum transport measurements.
• Analysis of hole effective mass and g-factor dependence on density.

Main Results:

• Demonstration of a low-disorder 2DHG with high mobility (1.33 × 10^5 cm^2/Vs) and low percolation density (1.4 × 10^10 cm^-2).
• Observation of density-dependent in-plane effective mass and out-of-plane g-factor, indicating significant heavy-hole-light-hole mixing.
• Measurement of a larger in-plane g-factor in unstrained Ge compared to ε-Ge.

Conclusions:

• The proposed Ge/ε-SiGe heterojunction platform effectively eliminates metamorphic buffer defects.
• This platform shows promise for advanced quantum hardware due to strong spin-orbit interaction and potential for superconducting correlations.
• The observed properties are favorable for developing fast quantum processors and hybrid quantum systems.