Shear-Strained Silicon Quantum Wells for Valley Splitting
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Solution Overview
Problem
Existing silicon quantum dot qubits face challenges with variable and small energy spacing between ground and excited valley states due to degenerate valleys, leading to decoherence, which existing strategies like sharp interfaces and germanium concentration modulations struggle to address consistently.
Innovation Solution
Heterostructures with shear-strained silicon quantum wells seeded with germanium, featuring oscillating germanium concentration profiles and trenches aligned along the [110] crystallographic direction, enhance valley splitting through a combination of shear strain and Ge concentration oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sharp interfaces are engineered in thin quantum wells to achieve large valley splittings, then valley splitting increases, but device variability increases due to interface imperfections
Solution Approach 1:
The patent changes the approach from relying on interface sharpness to controlling bulk material parameters. Specifically, it uses shear strain (εxy) applied to the silicon quantum well and oscillating germanium concentration profiles to achieve valley splitting. This shifts the control mechanism from interface geometry to bulk material properties, reducing sensitivity to interface imperfections and improving device consistency.
Solution Approach 2:
The patent introduces local variations in germanium concentration within the silicon quantum well through oscillating profiles. These localized Ge-rich regions create specific strain fields and potential landscapes that enhance valley splitting. The local quality modification allows precise control of electronic structure without requiring perfect global interface sharpness.
2Reliability
If germanium concentration modulations are used to achieve large valley splittings, then valley splitting increases, but manufacturing complexity increases due to precise concentration control requirements
Solution Approach 1:
The patent merges two mechanisms—shear strain and germanium concentration oscillations—to achieve enhanced valley splitting. The shear strain provides a baseline enhancement, while the oscillating Ge concentration profiles provide additional tuning capability. This combination allows achieving large valley splitting through a more robust dual-mechanism approach rather than relying solely on precise concentration control.
3Ease of manufacture
If long-wavelength germanium modulations are used, then manufacturing is easier, but valley splitting is limited due to lack of shear strain
Solution Approach 1:
The patent creates a composite structure within the silicon quantum well by incorporating oscillating germanium concentration profiles. This composite material approach combines Si and Ge in a controlled oscillating pattern, leveraging the beneficial properties of both materials. The Ge-rich regions provide local strain and potential modulation, while the Si matrix maintains the overall quantum well structure, achieving both manufacturability and enhanced valley splitting.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The heterostructures achieve consistent and large valley splitting, improving qubit state control and spin-orbit coupling without relying on atomically sharp interfaces, enhancing scalability and reliability of quantum computing systems.
Implementation Method 1
This leads to a small energy spacing between ground and excited valley states, called valley splitting, which causes decoherence in qubits if not sufficiently large
Implementation Method 2
a quantum well comprising a layer of shear-strained germanium-seeded silicon disposed between the first quantum barrier and the second quantum barrier
Implementation Method 3
the layer of germanium-seeded silicon has an oscillating germanium concentration along its thickness direction (z)
Implementation Method 4
the one or more electrostatic gates are configured to apply a controllable potential to the quantum well that confines electrons in the quantum well in three dimensions
Data Source
AI summary
Heterostructures having germanium-seeded, shear-strained silicon quantum wells are provided. Also provided are gate-controlled qubits based on the heterostructures, and quantum computing systems based on the qubits. The heterostructures include a quantum well of germanium-seeded silicon positioned between two quantum barriers of germanium or a silicon-germanium alloy. The silicon of the quantum well is under a shear strain and is seeded with germanium such that the germanium concentration in the quantum well has an oscillating profile.