Green LED Quantum Well Structure for Current-Stable Wavelength
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Solution Overview
Problem
State-of-the-art green LEDs exhibit a significant shift in emission wavelength with changes in operating current density, making it challenging to maintain consistent color temperature and rendering index in illumination systems.
Innovation Solution
The development of a light emitting diode (LED) device with a dominant wavelength greater than 520 nm, which changes by less than 7 nm as current density increases from 10 A/cm2 to 100 A/cm2, achieved through a gallium-nitride based epitaxy design with a quantum well and p-type layers, ensuring stability across varying current densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the operating current density of green LED is increased to achieve higher brightness, then the luminance increases, but the emission wavelength shifts to shorter wavelength causing color instability
Solution Approach 1:
The patent applies parameter changes by modifying the quantum well structure parameters (width, composition gradient) and barrier layer parameters to compensate for the current-induced wavelength shift. The quantum well is designed with specific indium composition gradients and width variations that counteract the blue-shift effect at high currents, maintaining stable green emission wavelength across a wide current density range from 10 to 100 A/cm2.
Solution Approach 2:
The patent uses composite material structure combining InGaN quantum well with GaN barrier layers, where the different materials have complementary properties. The InGaN well provides green emission while the GaN barriers confine carriers and electrons, and the composite structure's overall behavior compensates for current-induced wavelength shifts that neither material could achieve alone.
2Adaptability or versatility
If the current density is varied to control luminance levels, then the brightness can be adjusted, but the color temperature and rendering index cannot be maintained consistent
Solution Approach 1:
The patent employs parameter changes in the quantum well design, specifically using indium composition gradients and varying well widths to create a structure where the emission wavelength remains stable despite current density changes. This allows the LED to maintain consistent color temperature and rendering index across different luminance levels achieved through current variation.
3Illumination intensity
If green LED operates at high current density for high brightness applications, then the luminance is sufficient, but the emission wavelength shifts making it appear cyan or blue
Solution Approach 1:
The patent uses parameter changes by designing the quantum well with specific structural parameters (width, indium composition, gradient profiles) that are optimized to maintain accurate green color at high current densities. The barrier layer parameters are also adjusted to control carrier confinement and recombination characteristics, ensuring color accuracy is maintained even at high brightness levels.
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 solution provides a stable color output across a wide range of current densities, enabling consistent color temperature and rendering index in illumination systems, and allows for the same epitaxial wafers to be used for both low and high brightness applications.
Implementation Method 1
A light emitting diode (LED) is a semiconductor light source that emits visible light when current flows through it
Data Source
AI summary
Described are light emitting diode (LED) devices including a quantum well on a superlattice structure. The LED device has a dominant wavelength greater than 520 nm. The dominant wavelength changes less than 7 nm when the current density increases from 10 A/cm2 to 100 A/cm2 and a junction temperature of the device changes less than 20° C.