Multi-Quantum Well LED Structure for Phosphor-Free White Light
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Solution Overview
Problem
Current light emitting diodes (LEDs) using nitride semiconductors struggle to produce white light efficiently, requiring multiple LEDs or phosphors, which increase costs and complexity, and suffer from reduced efficiency due to Stokes' shift and light absorption losses.
Innovation Solution
A single-chip LED design with a lower active layer emitting light below 500 nm and an upper active layer emitting light above 500 nm, utilizing a multi-quantum well structure with varying barrier layers and doping profiles to enhance light intensity and reduce phosphor usage, allowing for white light emission without external phosphors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-chip LED is designed to emit multi-band light, then the manufacturing process is simplified and phosphor usage is reduced, but the light intensity of shorter-wavelength bands decreases under low current density conditions
Solution Approach 1:
The active layer is divided into multiple quantum well structures with different compositions, where each well layer emits light at different wavelengths. This segmentation allows the single-chip LED to produce multi-band light while maintaining sufficient intensity in each band through optimized well layer design.
Solution Approach 2:
Different regions of the active layer are designed with different impurity doping concentrations and well layer compositions. The lower active layer has higher indium content for shorter wavelength emission, while the upper active layer has lower indium content for longer wavelength emission. This local quality variation enables each region to optimize its light emission characteristics for the target wavelength band.
2Illumination intensity
If phosphors are used to convert wavelength and produce white light, then mixed color light can be achieved, but efficiency decreases due to Stokes' shift and additional costs are incurred
Solution Approach 1:
The invention extracts and eliminates the phosphor conversion step from the traditional LED structure. Instead of using a single blue LED with phosphor coating, the design directly integrates multiple quantum well structures that emit different wavelengths simultaneously, removing the source of Stokes' shift energy loss and phosphor-related costs.
Solution Approach 2:
The active layer structures are designed to self-generate the required multi-band light emission through their inherent quantum well properties. The different well layers automatically emit at different wavelengths based on their composition, eliminating the need for external phosphor materials to convert wavelengths.
3Illumination intensity
If multiple light emitting diodes are used together to emit different monochromatic light, then white light can be produced, but device complexity and manufacturing complications increase
Solution Approach 1:
Multiple quantum well structures that would traditionally require separate LED chips are merged into a single integrated active layer. The lower and upper active layers with different compositions are stacked vertically within one chip, combining multiple light emission functions into a single device structure, thereby simplifying the overall system while maintaining multi-color output capability.
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 solution enables efficient white light emission with improved light intensity and reduced phosphor requirements, simplifying the manufacturing process and enhancing light extraction efficiency, even under low current density conditions.
Implementation Method 1
the lower active layer emits light having a wavelength shorter than that of the upper active layer
Implementation Method 2
at least one of the plurality of barrier layers includes a first barrier layer and a second barrier layer having an n-type impurity doping concentration lower than that of the first barrier layer
Data Source
AI summary
A light emitting diode and a light emitting device having the same, in which the light emitting diode can include a first conductivity type semiconductor layer; a second conductivity type semiconductor layer; a lower active layer disposed there between; and an upper active layer disposed between the lower active layer and the second conductivity type semiconductor layer. The lower active layer can emit light having a wavelength shorter than that of the upper active layer, the upper active layer can include a plurality of well layers and a plurality of barrier layers, at least one of the plurality of barrier layers can include a first barrier layer and a second barrier layer having an n-type impurity doping concentration lower than that of the first barrier layer, and the first barrier layer can be closer to the first conductivity type semiconductor layer than the second barrier layer.