InGaN Strain Buffer Layer for Nitride LED Efficiency
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Solution Overview
Problem
Nitride-based semiconductor light emitting devices face reduced internal quantum efficiency and deteriorated crystallinity due to strain between InGaN quantum-well and GaN quantum-barrier layers, leading to inefficient light emission.
Innovation Solution
Incorporating a strain buffer layer of InGaN with a lower average indium content than the active layer, positioned between the nitride semiconductor layers, to minimize stress and adjust indium content and thickness ratios (1.4<B/A<6.1) for improved light emitting efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If InGaN quantum-well layers are used to achieve blue or green light emission, then light emitting wavelength range is improved, but strain between well layer and barrier layer increases causing reduced internal quantum efficiency
Solution Approach 1:
An InGaN relief layer with high indium content is introduced as an intermediary layer between the n-type contact layer and the active layer. This relief layer acts as a mediator to relieve the strain accumulated between the InGaN quantum-well layers and GaN quantum-barrier layers in the active layer, thereby improving internal quantum efficiency while maintaining the desired light emitting wavelength range
Solution Approach 2:
The indium content parameter is strategically varied across different layers: the relief layer has high indium content (greater than the active layer) to provide lattice mismatch compensation, while the quantum-well layers maintain specific indium content (5-20%) to achieve target wavelengths. This parameter optimization resolves the contradiction between wavelength range and efficiency
2Illumination intensity
If InGaN quantum-well layers with high indium content are used to extend light emission to green range, then wavelength range is improved, but strain increases causing V-pit generation and interface roughness
Solution Approach 1:
The InGaN relief layer serves as a buffer intermediary that absorbs and compensates for the lattice mismatch caused by high indium content in the quantum-well layers. This prevents V-pit generation and maintains smooth interfaces between well and barrier layers, enabling green light emission without sacrificing crystallinity
Solution Approach 2:
The relief layer is formed in advance (before the active layer) to pre-compensate for the strain that will be generated by subsequent high-indium-content quantum-well layers. This preliminary strain management prevents interface roughness and V-pit formation during active layer growth
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
The strain buffer layer reduces piezoelectric fields and enhances crystallinity, resulting in improved recombination efficiency and light emitting efficiency of the active layer.
Implementation Method 1
Such strain generates a large piezoelectric field in the active layer, causing reduction of internal quantum efficiency of the active layer
Data Source
AI summary
The nitride-based light emitting device according to one embodiment includes a first nitride semiconductor layer doped with a first conductive impurity; a strain buffer layer formed on the first nitride semiconductor layer and comprised of InGaN; an active layer formed on the strain buffer layer and having a multi-quantum well structure in which a quantum-well layer and a quantum-barrier layer are alternately stacked one above another; and a second nitride semiconductor layer formed on the active layer and doped with a second conductive impurity opposite to the first conductive impurity, wherein the ratio B/A satisfies 1.4<B/A<6.1, where A is the product of an average indium content of the strain buffer layer and a thickness of the strain buffer layer and B is the product of an average indium content of the active layer and a thickness of the active layer.