III-Nitride LED Template Strain Reduction
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Solution Overview
Problem
Semiconductor light emitting devices face challenges with strain in III-nitride layers, leading to reduced quantum efficiency and difficulty in growing thicker or higher InN composition layers due to structural mismatch and strain, which affects emission wavelength and device performance.
Innovation Solution
A template structure is used to reduce strain in the light emitting layer by incorporating low temperature InGaN layers and varying the lattice constant, along with controlling threading dislocation density and surface roughness, to enable thicker and higher InN composition layers with reduced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional growth templates are used, then the device structure is simple, but strain in the light emitting layer increases reducing quantum efficiency
Solution Approach 1:
The template is segmented into multiple functional layers: a first low-temperature layer (e.g., GaN) grown at 500-700°C, a second low-temperature layer (e.g., InGaN) grown at 500-700°C, and optionally a third high-temperature layer grown at 900-1100°C. Each layer serves specific functions in strain management and lattice constant expansion, collectively improving quantum efficiency while maintaining manageable structural complexity.
Solution Approach 2:
The patent changes growth temperature parameters to achieve different lattice constants. Low-temperature growth (500-700°C) produces layers with expanded lattice constants that better match the light emitting layer, reducing strain. The temperature parameter is strategically varied during sequential layer growth to optimize lattice matching without requiring complex structural modifications.
2Adaptability or versatility
If thicker light emitting layers are grown to achieve longer wavelength emission, then wavelength capability improves, but strain increases causing structural defects
Solution Approach 1:
The template layers are grown in advance before the light emitting layer to pre-establish an optimized lattice constant. The first and second low-temperature layers are deposited beforehand to create a lattice-matched foundation that can support thicker light emitting layers without accumulating excessive strain, enabling longer wavelength emission while maintaining structural integrity.
Solution Approach 2:
The low-temperature InGaN layer acts as an intermediary between the substrate and the light emitting layer. It mediates the lattice mismatch by providing an intermediate lattice constant that gradually transitions from the substrate to the light emitting layer composition, allowing thicker layers to be grown without defect formation.
3Adaptability or versatility
If higher InN composition is incorporated to achieve longer wavelength emission, then wavelength capability improves, but strain and dislocation density increase
Solution Approach 1:
Different regions of the template have different compositions and properties optimized for their local function. The first low-temperature layer has one composition (e.g., GaN), the second layer has a different composition (e.g., InGaN with specific InN content), and each is locally optimized to manage strain in the specific wavelength range target. This local quality differentiation allows high InN composition in the light emitting layer while controlling dislocation density through the graded template structure.
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 reduces strain in the light emitting layer, increasing the critical thickness for layer growth, minimizing defects, and enhancing quantum efficiency and wavelength capabilities of III-nitride LEDs.
Implementation Method 1
The template may expand the lattice constant in the light emitting layer over the range of lattice constants available from conventional growth templates
Implementation Method 2
or is formed by a process including a thermal anneal or thermal cycled growth step
Data Source
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AI summary
In a Ill-nitride light emitting device, the device layers (10) including the light emitting layer are grown over a template (22, 26) designed to reduce strain in the device, in particular in the light emitting layer. Reducing the strain in the light emitting device may improve the performance of the device. The template may expand the lattice constant in the light emitting layer over the range of lattice constants available from conventional growth templates. Strain is defined as follows: a given layer has a bulk lattice constant abulk corresponding to a lattice constant of a free standing material of a same composition as that layer and an in-plane lattice constant ain-plane corresponding to a lattice constant of that layer as grown in the structure. The amount of strain in a layer is l(ain-plane -abulk) | / abulk. In some embodiments, the strain in the light emitting layer is less than 1%.