Group IV Semiconductor Bottom Junction for Flexible Multi-Junction Devices
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Solution Overview
Problem
Conventional optoelectronic devices, such as photovoltaic cells and LEDs, face inefficiencies due to lattice mismatch between growth substrates and layers, leading to reduced performance and increased costs, particularly when using Ge as a bottom junction in GaAs-based multi-junction devices.
Innovation Solution
The use of Group IV semiconductors like SiGe as a bottom junction in GaAs-based multi-junction optoelectronic devices, which provides better lattice matching and a higher band gap, improving efficiency by growing epitaxial layers with high growth rates and using techniques like epitaxial lift-off to form flexible devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Ge is used as a bottom junction in GaAs-based multi-junction devices, then the band gap is increased, but lattice mismatch occurs leading to reduced performance
Solution Approach 1:
The patent introduces an intermediate layer between the Ge bottom junction and the GaAs-based upper junctions. This intermediate layer serves as a buffer that gradually transitions the lattice constant, mediating the mismatch between Ge and GaAs. The intermediate layer allows the Ge junction to maintain its high band gap while preventing lattice mismatch from degrading device performance.
2Ease of manufacture
If conventional substrates are used for growth, then manufacturing is simplified, but lattice mismatch leads to increased costs and reduced efficiency
Solution Approach 1:
The patent changes the substrate parameters by using flexible substrates with specific thermal expansion coefficients and mechanical properties that accommodate the lattice mismatch. By selecting substrates with appropriate parameters (thermal expansion, flexibility), the device achieves both ease of manufacture and high efficiency, as the substrate can accommodate growth of multiple junctions with different lattice constants without requiring complex alignment procedures.
3Stability of the object's composition
If rigid structures are used, then structural stability is maintained, but device flexibility and adaptability are reduced
Solution Approach 1:
The patent employs flexible thin film structures for the multi-junction device. The device is grown as a thin film on a flexible substrate, allowing the entire structure to be bent or conformally mounted on curved surfaces. This flexible thin film approach maintains structural stability through the epitaxial growth quality and interface bonding, while providing the adaptability to be installed in various environments including curved or movable applications.
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
This approach enhances the light absorption and conversion efficiency of photovoltaic cells and light generation efficiency of LEDs, reducing costs and lattice mismatch issues, while maintaining device flexibility and adaptability to existing environments.
Implementation Method 1
enhances the light absorption and conversion efficiency of photovoltaic cells
Implementation Method 2
providing a second p-n structure formed by epitaxial growth on the first p-n structure
Data Source
AI summary
A multi-junction optoelectronic device and method of manufacture are disclosed. The method comprises providing a first p-n structure on a substrate, wherein the first p-n structure comprises a first base layer of a first semiconductor with a first bandgap such that a lattice constant of the first semiconductor matches a lattice constant of the substrate, and wherein the first semiconductor comprises a Group III-V semiconductor. The method includes providing a second p-n structure, wherein the second p-n structure comprises a second base layer of a second semiconductor with a second bandgap, wherein a lattice constant of the second semiconductor matches a lattice constant of the first semiconductor, and wherein the second semiconductor comprises a Group IV semiconductor. The method also includes lifting off the substrate the multi-junction optoelectronic device having the first p-n structure and the second p-n structure, wherein the multi-junction optoelectronic device is a flexible device.