AlGaN Cap Layer Gradient for LED Electron Overflow
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Solution Overview
Problem
Current semiconductor light emitting devices, particularly GaN-based LEDs, face inefficiencies due to electron overflow and low hole carrier density, leading to reduced light emitting efficiency and quantum efficiency, as existing techniques fail to effectively balance electron overflow suppression with the influence of spontaneous polarization in AlGaN layers.
Innovation Solution
The semiconductor light emitting device incorporates a specific configuration with an intermediate layer not substantially containing Al, a first AlGaN layer with a low Al composition ratio, and a second AlGaN layer with a higher Al composition ratio, strategically positioned between the light emitting portion and the p-type semiconductor layer to control electron overflow and enhance hole injection efficiency, while minimizing the adverse effects of spontaneous polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a cap layer with high Al composition ratio is introduced between the active layer and p-type clad layer to suppress electron overflow, then electron overflow is reduced, but spontaneous polarization effects increase and degrade quantum well performance
Solution Approach 1:
The patent applies local quality by creating a composition gradient in the AlGaN cap layer, where the Al composition ratio varies from the interface with the quantum well to the interface with the p-type clad layer. This gradient structure allows different regions of the same layer to have different properties: the region near the quantum well has lower Al composition to minimize polarization effects, while the region near the p-type clad layer has higher Al composition to enhance electron overflow suppression.
Solution Approach 2:
The patent changes the Al composition ratio parameter continuously or stepwise across the cap layer thickness. By controlling the Al composition ratio to increase from the quantum well interface toward the p-type clad layer interface, the patent optimizes the balance between suppressing electron overflow and maintaining quantum well performance, resolving the technical contradiction between these two opposing requirements.
2Loss of energy
If AlGaN layers with high Al composition ratio are used to form potential barriers, then electron overflow is suppressed, but the adverse effects of spontaneous polarization increase
Solution Approach 1:
The patent segments the cap layer into multiple sub-layers with progressively increasing Al composition ratios. This segmentation allows the structure to provide strong electron overflow suppression through the high-Al region while isolating the quantum well from the strongest polarization effects by positioning the lowest-Al region adjacent to the quantum well interface.
Solution Approach 2:
Different regions of the AlGaN cap layer are assigned different Al composition ratios tailored to their specific functions: the region adjacent to the quantum well uses lower Al composition to minimize polarization impact on quantum well performance, while regions farther from the quantum well use higher Al composition to maximize electron overflow suppression.
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 effectively reduces electron overflow and increases hole injection efficiency, resulting in improved light emitting efficiency by maintaining desired energy band characteristics and balancing Al composition ratios to optimize quantum well layer performance.
Implementation Method 1
The first layer includes Alx1Ga1-x1N and the second layer includes Alx2Ga1-x2N where the second Al composition ratio x2 is higher than the first Al composition ratio x1, creating a gradient structure that controls carrier transport
Implementation Method 2
balancing Al composition ratios to optimize quantum well layer performance while minimizing the adverse effects of spontaneous polarization
Implementation Method 3
how to recombine electrons and holes for light emission in an active layer
Implementation Method 4
semiconductor light emitting devices such as high-intensity ultraviolet to blue and green light emitting diodes (LED)
Data Source
AI summary
According to one embodiment, a semiconductor light emitting device includes an n-type semiconductor layer, a p-type semiconductor layer, a light emitting portion, a first layer, a second layer, and an intermediate layer. The semiconductor layers include nitride semiconductor. The light emitting portion is provided between the n-type semiconductor layer and the p-type semiconductor layer and includes a quantum well layer. The first layer is provided between the light emitting portion and the p-type semiconductor layer and includes AlX1Ga1-x1N having first Al composition ratio x1. The second layer is provided between the first layer and the p-type semiconductor layer and includes Alx2Ga1-x2N having second Al composition ratio x2 higher than the first Al composition ratio x1. The intermediate layer is provided between the first layer and the light emitting portion and has a thickness not smaller than 3 nanometers and not larger than 8 nanometers and includes Inz1Ga1-z1N (0≦z1<1).