III-Nitride Thin Template Growth for Strain-Relaxed InGaN LEDs
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Solution Overview
Problem
Current methods for producing high-efficiency green and red LEDs using InGaN active layers face challenges due to lattice mismatch and strain, leading to poor crystal quality and low external quantum efficiency, while porous GaN technology is complex and limited to small device sizes.
Innovation Solution
A method involving the growth of III-nitride devices on a thermally decomposed GaN decomposition layer, creating a mechanically flexible decomposition stop layer that allows for high In incorporation and reduced strain, enabling the production of high-quality InGaN layers with increased growth temperature and relaxed lattice constants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If InGaN active layers are grown on conventional substrates, then device structure is simple, but lattice mismatch and strain cause poor crystal quality and low external quantum efficiency
Solution Approach 1:
The patent segments the substrate system into multiple functional layers: a sacrificial GaN decomposition layer, a template layer, and the InGaN active layer. This segmentation allows each layer to serve its specific purpose - the decomposition layer provides lattice matching and is removed after growth, while the template layer maintains structural integrity, thereby achieving high crystal quality without overly complex fabrication
Solution Approach 2:
The patent introduces a GaN decomposition layer as an intermediary between the substrate and the InGaN active layer. This intermediary layer temporarily provides lattice matching during growth, then is selectively removed to release strain, enabling high-quality crystal growth that would otherwise be impossible on conventional substrates
2Manufacturing precision
If growth temperature is increased to improve crystal quality, then crystal quality improves, but Indium incorporation decreases due to composition pulling effect
Solution Approach 1:
The patent applies preliminary anti-action by pre-growing a GaN decomposition layer with specific lattice constants that compensate for the composition pulling effect. This layer is designed to counteract the strain that would normally prevent high Indium incorporation at elevated growth temperatures, allowing both high crystal quality and high Indium content to be achieved simultaneously
3Manufacturing precision
If porous GaN technology is used to reduce strain, then strain is reduced, but device complexity increases and device size is limited
Solution Approach 1:
The patent extracts the strain-reduction function from the complex porous GaN structure and implements it through a simpler sacrificial decomposition layer that is thermally decomposed. This extracted approach achieves the same strain reduction benefit without the fabrication complexity and size limitations of porous GaN technology
4Device complexity
If lattice mismatch is accommodated through strain, then device structure remains simple, but strain relaxation causes defects and reduces external quantum efficiency
Solution Approach 1:
The patent changes the physical-chemical parameters of the decomposition layer by thermally decomposing it after the InGaN active layer is grown. This parameter change (from solid GaN to decomposed state) causes the layer to shrink and release strain, thereby improving external quantum efficiency while maintaining relative structural simplicity
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 results in significantly improved crystal quality and external quantum efficiency, enabling the production of LEDs with longer peak emission wavelengths and broader application, including monolithic three-color LEDs, while simplifying the fabrication process and expanding substrate size capabilities.
Implementation Method 1
the decomposition layer is decomposed at a high temperature to obtain a mechanically flexible or compliant decomposition stop layer
Data Source
AI summary
A III-nitride based device is fabricated having an in-plane lattice constant or strain that is more than 30% biaxially relaxed, by creating a III-nitride based decomposition stop layer on or above a III-nitride based decomposition layer, wherein a temperature is increased to decompose the III-nitride based decomposition layer; and growing a III-nitride based device structure on or above the III-nitride based decomposition stop layer. The III-nitride based device structure includes at least one of an n-type layer, active layer, and p-type layer, and at least one of the n-type layer, active layer and p-type layer has an in-plane lattice constant or strain that is preferably more than 30% biaxially relaxed, more preferably 50% or more biaxially relaxed, and most preferably at least 70% biaxially relaxed.