Oscillating Germanium Profile Silicon Quantum Wells
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Solution Overview
Problem
The valley degree of freedom in silicon quantum dots of Si/SiGe heterostructures complicates the control of qubit states in quantum computing due to energy splitting between valley states being comparable to electron spin states, making it difficult to achieve clean control of qubit states.
Innovation Solution
A semiconductor heterostructure with a quantum well of strained, germanium-seeded silicon positioned between two quantum barriers, featuring an oscillating germanium concentration profile, which increases the valley splitting in the conduction band, allowing for clean control of qubit states without interference from valley splittings, achieved through pulsed chemical vapor deposition techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional Si/SiGe heterostructures are used with uniform germanium concentration, then the quantum well provides electron confinement, but the valley splitting is too small (comparable to spin splitting) causing unwanted complications in qubit control
Solution Approach 1:
The patent applies local quality by creating a non-uniform germanium concentration profile within the quantum well, specifically using oscillating profiles with peaks and valleys at specific positions. This local variation in composition is designed to enhance valley splitting in specific regions while maintaining overall electron confinement, directly addressing the problem of insufficient valley splitting in conventional uniform structures.
Solution Approach 2:
The patent changes the germanium concentration parameter from a uniform distribution to an oscillating distribution with specific wavelengths and amplitudes. By tuning these parameters (concentration amplitude, oscillation wavelength, number of oscillations), the valley splitting can be optimized to be significantly larger than spin splitting, enabling clean qubit control without unwanted valley transitions.
2Manufacturing precision
If the germanium concentration is increased to enhance valley splitting, then valley splitting increases, but the quantum well strain and material quality may deteriorate
Solution Approach 1:
Instead of uniformly increasing germanium concentration throughout the quantum well, the patent uses localized oscillating concentration profiles with peak concentrations only at specific positions. This allows valley splitting enhancement through local high-concentration regions while maintaining lower average germanium content, preserving overall material quality and reducing strain-related defects.
Solution Approach 2:
The patent employs periodic oscillations in germanium concentration rather than continuous high concentration. The oscillating profile creates alternating high and low concentration regions, which enhances valley splitting through the high-concentration peaks while allowing relaxation in the low-concentration regions, preventing cumulative strain damage and maintaining material reliability.
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 increased valley splitting of at least 80 μeV enables clean control of qubit states, eliminating the uncontrolled degree of freedom and facilitating manipulation of qubit energy splittings within a desirable range for quantum computing applications.
Implementation Method 1
the energy splitting between valley states is comparable to the energy splitting between electron spin states
Implementation Method 2
silicon quantum dots formed in the silicon well of an Si/SiGe heterostructure have been used to trap electrons in qubits
Implementation Method 3
a quantum well comprising strained, germanium-seeded silicon positioned between the first quantum barrier and the second quantum barrier
Implementation Method 4
growing a quantum well layer of strained, germanium-seeded silicon on a first quantum barrier layer comprising germanium or a germanium-silicon alloy via pulsed chemical vapor deposition
Data Source
AI summary
Semiconductor heterostructures, methods of making the heterostructures, and quantum dots and quantum computation devices based on the heterostructures are provided. The heterostructures include a quantum well of strained silicon seeded with a relatively low concentration of germanium impurities disposed between two quantum barriers of germanium or a silicon-germanium alloy. The quantum wells are characterized in that the germanium concentration in the wells has an oscillating profile that increases the valley splitting in the conduction band of the silicon quantum well.