III-Nitride LED Strain Reduction via Segmented InGaN-GaN Templates
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Solution Overview
Problem
Semiconductor light-emitting devices face challenges with strain in III-nitride layers, leading to reduced external quantum efficiency and difficulty in growing thicker or higher InN composition layers due to structural mismatch and strain-related defects, which limits their performance and wavelength emission capabilities.
Innovation Solution
A template structure is used to reduce strain in the light-emitting layer by incorporating low-temperature InGaN and GaN layers with controlled lattice constants, threading dislocation density, and surface roughness, allowing for the growth of 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 leading to reduced external quantum efficiency
Solution Approach 1:
The template is segmented into multiple functional layers: a first GaN layer, an InGaN layer, and a second GaN layer. Each layer serves a specific purpose in managing strain and dislocation density, allowing the complex function of strain reduction to be divided into manageable segments that collectively improve external quantum efficiency.
Solution Approach 2:
The InGaN layer acts as an intermediary between the first and second GaN layers. This intermediate layer with intermediate lattice constant gradually transitions the strain, reducing the abrupt strain mismatch that would occur with a single-layer template, thereby reducing overall strain in the light emitting layer.
2Adaptability or versatility
If thicker layers with higher InN composition are grown, then wavelength emission capabilities are enhanced, but strain-related defects increase due to structural mismatch
Solution Approach 1:
The template parameters (lattice constant, thickness, composition) are specifically optimized to match and gradually transition to the light emitting layer parameters. The InGaN layer's indium content and thickness are tuned to provide the optimal lattice constant for reducing strain in thicker, higher InN composition layers, enabling improved wavelength emission with reduced defects.
Solution Approach 2:
The template structure with controlled strain characteristics is prepared in advance before growing the light emitting layer. This preliminary preparation of the template with specific lattice constant and strain properties creates a favorable foundation that enables subsequent growth of thicker, higher InN composition layers with reduced strain-related defects.
3Reliability
If the lattice constant in the light emitting layer is expanded, then strain is reduced, but the threading dislocation density may increase
Solution Approach 1:
Different regions of the template have different properties optimized for their local function: the InGaN layer is optimized for lattice constant expansion and strain reduction, while the GaN layers are optimized for providing structural stability and filtering dislocations. This local optimization allows strain reduction without excessive increase in threading dislocation density in the light emitting layer.
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 effectively reduces strain in the light-emitting layer, increasing the critical thickness for layer growth, minimizing defects, and enhancing the external quantum efficiency and wavelength emission capabilities of III-nitride light-emitting devices.
Implementation Method 1
a template structure to reduce strain in the light-emitting layer... an indium-containing layer such as InGaN... consisting of the same material as the first layer such that threading dislocation density and stacking fault density are reduced
Implementation Method 2
the device layers including the light emitting layer of a III-nitride device are grown over a template... an indium-free nucleation layer such as GaN grown directly on the substrate and an indium-containing layer such as InGaN grown over the indium-free layer
Data Source
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Figure 15~16
AI summary
A device comprising: a Ill-nitride structure comprising: a first layer (22), wherein the first layer is substantially free of indium; a second layer (26) grown over the first layer, wherein the second layer is a non-single crystal layer comprising indium; and device layers (10) grown over the second layer, the device layers comprising a Ill-nitride light emitting layer disposed between an n-type region and a p-type region. Reducing the strain in the light emitting device may improve the performance of the device. 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 anin-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 I (ain-plane-abulk)|/ abulk- In some embodiments, the strain in the light emitting layer is less than 1%.