Undoped Strained Ge Quantum Well with Ultrahigh Mobility of Two Million.

Area of Science:

• Semiconductor Physics
• Materials Science
• Quantum Computing

Background:

• Fabrication of high-quality germanium quantum wells is crucial for advanced electronic devices.
• Reducing threading dislocation density (TDD) is essential for high-performance semiconductor heterostructures.
• Achieving high carrier mobility in germanium-based systems is a key challenge for quantum applications.

Purpose of the Study:

• To develop a novel method for fabricating undoped Ge quantum wells (QWs) with suppressed TDD.
• To investigate the impact of SiGe barriers on strain and carrier mobility in Ge QWs.
• To explore the potential of strained germanium as a platform for quantum computation.

Main Methods:

• Fabrication of an undoped Ge QW beneath a 32 nm relaxed Si_0.2Ge_0.8 shallow barrier.
• Utilizing a graded SiGe bottom barrier (Si_0.2Ge_0.8 at 650 °C and Si_0.1Ge_0.9 at 800 °C) to create a sharp interface and suppress TDD.
• Incorporating in-plane parallel strain (ε_∥ strain -0.41%) within the Ge QW via the SiGe barrier.
• Fabricating heterostructure field-effect transistors (HFETs) with a shallow buried channel.

Main Results:

• Successfully suppressed threading dislocation density (TDD) in the undoped Ge QW.
• Introduced significant in-plane parallel strain (ε_∥ strain -0.41%) in the Ge QW.
• Achieved ultrahigh two-dimensional hole gas (2DHG) mobility exceeding 2 × 10⁶ cm²/(V s).
• Observed a very low percolation density of (5.689 ± 0.062) × 10¹⁰ cm^-2.
• Fractional quantum Hall effect indications observed at high density and magnetic fields.

Conclusions:

• The developed fabrication method effectively suppresses TDD and introduces beneficial strain in Ge QWs.
• The achieved ultrahigh 2DHG mobility demonstrates the potential of strained germanium for high-performance electronic devices.
• Strained germanium serves as a promising noise mitigation material for quantum computation, offering long coherence times and fast all-electrical manipulation.