Wafer Bonding Virtual Substrates for Non-Lattice Matched Solar Cells

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Solution Overview

Problem

The monolithic growth process for multi-junction solar cells restricts the use of materials due to lattice matching requirements, limiting the integration of non-lattice matched III-V semiconductors and reducing photoelectric conversion efficiency.

Innovation Solution

Wafer bonding and layer transfer techniques enable the integration of non-lattice matched semiconductor materials by creating virtual substrates, allowing for the growth of optimized subcells without the need for metamorphic layers, thereby expanding the material options and improving efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If monolithic epitaxial growth process is used, then series connected layers forming subcells are achieved, but material selection is constrained by lattice matching requirements

Engineering Contradiction:

Improvephotoelectric conversion efficiencyVSAvoidmaterial selection flexibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The invention segments the monolithic growth process into separate stages: first growing a virtual substrate with optimized bandgap on a sacrificial substrate, then bonding this to the final substrate, and finally growing additional subcells. This segmentation allows each stage to be optimized independently, breaking the lattice matching constraint that would otherwise limit material selection throughout the entire structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The virtual substrate acts as an intermediary layer between the final substrate and the subcell layers. This intermediary enables the integration of non-lattice matched materials by providing a buffer that absorbs lattice mismatch, allowing broader material selection while maintaining the integrity of the epitaxial growth process.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If non-lattice matched materials are integrated, then material flexibility is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvematerial selection flexibilityVSAvoidfabrication process complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The virtual substrate is prepared in advance on a sacrificial substrate before being bonded to the final substrate. This preliminary action allows the complex task of integrating non-lattice matched materials to be performed in a controlled, pre-planned manner, simplifying the overall fabrication process by separating the complexity into a distinct preparatory stage.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention extracts the virtual substrate growth step from the main fabrication sequence, performing it separately on a sacrificial substrate. This extraction isolates the complexity of integrating non-lattice matched materials into a manageable, independent process module that can be optimized and repeated without affecting the main production line.

Inventive Principle:

Principle #2Taking out (Extraction)

3Adaptability or versatility

If virtual substrate method is used, then non-lattice matched materials can be integrated, but additional bonding and separation steps are required

Engineering Contradiction:

Improveintegration of non-lattice matched materialsVSAvoidfabrication throughput

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

The invention merges the virtual substrate growth with the subcell fabrication process by bonding the pre-grown virtual substrate to the final substrate and continuing epitaxial growth directly on top of it. This merging eliminates the need for separate handling and processing steps, thereby maintaining high productivity despite the additional bonding step.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The epitaxial growth process continues uninterrupted after bonding the virtual substrate to the final substrate. This continuity of useful action ensures that the additional bonding step does not significantly impact fabrication throughput, as the productive growth phase proceeds without interruption once the virtual substrate is in place.

Inventive Principle:

Principle #20Continuity of useful action

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 allows for the fabrication of high-efficiency multi-junction solar cells with optimized bandgaps, reducing manufacturing costs and improving the quality of the grown layers, leading to enhanced photoelectric conversion efficiency and flexibility in solar cell design.

Implementation Method 1

bonding the donor substrate to a handle substrate

Methodology Applied

Scientific EffectWafer bonding: Welding

Data Source

PatentUS10374120B2High efficiency solar cells utilizing wafer bonding and layer transfer to integrate non-lattice matched materials

Publication Date: 2019.08.06 KONINKLIJKE PHILIPS NV

AI summary

A method of making a virtual substrate includes providing a donor substrate comprising a single crystal donor layer of a first material over a support substrate, wherein the first material comprises a ternary, quaternary or penternary semiconductor material or a material which is not available in bulk form, bonding the donor substrate to a handle substrate, and separating the donor substrate from the handle substrate such that a single crystal film of the first material remains bonded to the handle substrate.