Strained Germanium on Silicon Laser for Optical Integration
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Solution Overview
Problem
Integrating germanium with silicon to form efficient optical devices for high-performance computing and data centers is challenging due to lattice constant mismatch and inefficient light emission properties of germanium as an indirect bandgap material.
Innovation Solution
Applying tensile strain to germanium layers grown on silicon using different thermal expansion coefficients and local stress techniques, combined with doping and hetero-junctions, to modify the bandgap behavior and enhance light emission and absorption efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If germanium is grown on silicon using heteroepitaxial growth, then high-quality crystalline germanium can be obtained, but crystal defects are introduced due to lattice constant mismatch
Solution Approach 1:
The patent applies tensile strain to the germanium layer by growing it on a relaxed silicon germanium buffer layer with a larger lattice constant. This parameter change in the substrate's lattice constant allows the germanium to maintain high crystalline quality while reducing misfit dislocations and other crystal defects caused by direct growth on silicon.
Solution Approach 2:
The patent introduces a silicon germanium buffer layer as an intermediary between the silicon substrate and the germanium layer. This buffer layer mediates the lattice mismatch by providing a gradual transition in lattice constants, thereby reducing crystal defects while maintaining high-quality germanium growth.
2Ease of manufacture
If germanium is used as an indirect bandgap material, then it can be integrated with silicon, but light emission efficiency is poor
Solution Approach 1:
The patent uses tensile strain to modify the band structure of germanium, transforming it from an indirect bandgap material to a direct bandgap material. This parameter change in the electronic band structure enables efficient light emission while maintaining compatibility with silicon integration.
Solution Approach 2:
The patent applies strain locally to the germanium layer through the silicon germanium buffer layer configuration, creating a region with modified electronic properties. This local quality change enables direct bandgap behavior in the germanium layer while maintaining indirect bandgap characteristics in the bulk material for silicon compatibility.
3Use of energy by moving object
If tensile strain is applied to germanium layers, then light emission efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent combines the strain induction mechanism with the heteroepitaxial growth process itself. By using a silicon germanium buffer layer that is naturally relaxed, the strain is induced during the growth process rather than requiring separate strain application steps, thereby reducing manufacturing complexity while maintaining improved light emission efficiency.
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
Enables the formation of high-performance germanium-based lasers and photo detectors with improved light emission and absorption capabilities, suitable for integrated optical communications with reduced manufacturing costs and increased processing speed.
Implementation Method 1
a difference between a heat expansion coefficient of the first layer and a heat expansion of the second layer imparts a tensile strain on the second semiconductor layer as the first and second semiconductor layers cool to an ambient operational temperature
Data Source
AI summary
The subject matter disclosed herein relates to formation of silicon germanium devices with tensile strain. Tensile strain applied to a silicon germanium device in fabrication may improve performance of a silicon germanium laser or light detector.