Nitride Semiconductor LED Active Layer Indium Gradient
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Solution Overview
Problem
Nitride semiconductor light emitting devices face reduced carrier recombination efficiency due to piezoelectric polarization, which increases driving voltage and degrades light emission performance.
Innovation Solution
The semiconductor light emitting device incorporates a multi-quantum well and quantum barrier layer structure with varying indium content and thickness, optimizing the active layer to minimize piezoelectric polarization effects, where quantum well layers with higher indium content are thicker and closer to the p-type semiconductor layer, and quantum barrier layers are thicker adjacent to these well layers to reduce polarization influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional active layer structure is used in nitride semiconductor LEDs, then the device can be manufactured with standard processes, but piezoelectric polarization causes spatial separation of electron and hole wave functions, degrading carrier recombination efficiency
Solution Approach 1:
The active layer is segmented into multiple quantum well layers (first, second, and third quantum well layers) with different indium contents and thicknesses, separated by quantum barrier layers. This segmentation allows each layer to be optimized for specific functions: the first quantum well layer with higher indium content enhances light emission, while the second and third layers with lower indium content improve carrier confinement and reduce piezoelectric polarization effects, thereby resolving the contradiction between maintaining manufacturing simplicity and improving recombination efficiency.
Solution Approach 2:
Different regions of the active layer are assigned different local properties: the first quantum well layer has higher indium content (e.g., 10-30%) for enhanced light emission, while the second and third layers have lower indium content (e.g., 0-10%) for reduced polarization. The quantum barrier layers have specific thicknesses (e.g., 2-5 nm) optimized for carrier confinement. This local quality differentiation enables each layer to address specific aspects of the recombination efficiency problem without requiring complete structural redesign.
2Illumination intensity
If the indium content in quantum well layers is increased to enhance light emission, then luminance efficiency improves, but piezoelectric polarization effects are amplified, increasing driving voltage
Solution Approach 1:
The patent systematically varies the indium content parameter across different quantum well layers: the first quantum well layer has higher indium content (e.g., 10-30%) to maximize light emission and luminance efficiency, while the second and third layers have progressively lower indium content (e.g., 0-10%) to reduce piezoelectric polarization. The thickness parameter is also optimized, with the first layer being thinner (e.g., 2-4 nm) and subsequent layers being thicker (e.g., 4-6 nm). These parameter changes enable the device to achieve high luminance efficiency while controlling driving voltage through reduced polarization in later layers.
3Reliability
If quantum well layers with higher indium content are used to improve light emission, then internal quantum efficiency increases, but the driving voltage increases due to enhanced piezoelectric polarization
Solution Approach 1:
The active layer is divided into multiple quantum well layers with progressively varying indium contents. The first quantum well layer has higher indium content to provide strong light emission and high internal quantum efficiency. The second and third layers have lower indium content to reduce the cumulative piezoelectric polarization effect. This segmentation strategy allows the device to maintain high internal quantum efficiency through the first layer while reducing driving voltage through the polarization-mitigating effect of the subsequent layers.
Solution Approach 2:
The quantum barrier layers act as intermediaries between the quantum well layers with different indium contents. These barrier layers (with thicknesses of e.g., 2-5 nm) provide a transition zone that helps manage the strain and polarization effects between layers with different compositions, enabling the higher indium content layers to contribute to high internal quantum efficiency while the overall structure maintains lower driving voltage through the buffering effect of the barrier layers.
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 configuration enhances carrier recombination efficiency and maintains uniform light wavelength, reducing the driving voltage increase while improving luminance efficiency.
Implementation Method 1
an active layer disposed between the n-type and p-type semiconductor layers and having a structure in which a plurality of quantum well layers and a plurality of quantum barrier layers are stacked alternately
Implementation Method 2
a thickness of a layer constituting an active layer and band gap energy thereof are optimized to minimize an influence of piezoelectric polarization affecting the active layer
Data Source
AI summary
A semiconductor light emitting device includes: n-type and p-type semiconductor layers; and an active layer disposed between the n-type and p-type semiconductor layers. The active layer has a structure in which a plurality of quantum well layers and a plurality of quantum barrier layers are alternately disposed, wherein the plurality of quantum well layers are made of AlxInyGa1-x-yN (0≦x<1, 0<y≦1) and each of the plurality of quantum well layers contains a different indium (In) content. And, among the plurality of quantum barrier layers, a quantum barrier layer adjacent to a quantum well layer having a higher indium (In) content is thicker than a quantum barrier layer adjacent to a quantum well layer having a lower indium (In) content.