Strain-Inducing Nanostructures for Green LED Efficiency
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Solution Overview
Problem
Current green LEDs suffer from low internal quantum efficiency due to the 'green gap' challenge, where increasing Indium content to tune emission wavelength from blue to green results in efficiency drops, and existing nanostructuring methods only allow blue-shifting, not effectively improving green LED efficiency.
Innovation Solution
Fabricating nanostructures close to the light-emitting active region in semiconductor LEDs to induce strain, which can spectrally shift and broaden the emission spectrum by using a top-down technique, such as nano-sphere lithography, to create strain-inducing nanostructures that red-shift the emission, thereby increasing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If Indium content is increased to tune emission wavelength from blue to green, then emission wavelength is shifted to green region, but internal quantum efficiency drops drastically
Solution Approach 1:
The patent changes the strain parameter in the quantum well structure by fabricating nanostructures close to the active region. This strain modification allows tuning the emission wavelength to green region while maintaining high internal quantum efficiency, avoiding the efficiency drop that occurs with increased Indium content
Solution Approach 2:
The patent applies strain locally by fabricating nanostructures in close proximity to the active region rather than uniformly throughout the device. This localized strain induction enables wavelength tuning in the green region while preserving the overall high efficiency of the LED structure
2Length of moving object
If nanostructures are fabricated for strain relaxation, then emission wavelength is blue-shifted, but this does not improve green LED efficiency and requires long wavelength Indium-alloy based LEDs
Solution Approach 1:
Instead of relaxing strain to achieve blue-shift, the patent inverts the approach by inducing additional strain through nanostructure fabrication. This strain induction causes red-shift, enabling efficient green emission without requiring long wavelength Indium-alloy based LEDs or sacrificing green LED efficiency
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 approach enables the production of highly efficient green LEDs by red-shifting blue LEDs, creating long wavelength LEDs, and achieving phosphor-free white-light LEDs by extending the emission spectrum into the red region, addressing the 'green gap' and enhancing light extraction efficiency.
Implementation Method 1
Strain in a quantum well originates from a mismatch of growth temperature and the crystal structure of the material. By fabricating nanostructures that allow strain relaxation, the Quantum Confined Stark Effect (QCSE) in the active region of the LED, the multi-quantum wells (MQWs), can be reduced, thus shifting the emission wavelength to a shorter wavelength
Implementation Method 2
Such a nanostructure is capable of spectrally shifting the light emission to a longer wavelength, and/or broadening the emission spectrum of the light when the active region comprises more than one quantum heterostructure
Data Source
AI summary
A nanostructure fabricated on a semiconductor light-emitting device induces strain in the active region. The active device includes at least one quantum heterostructure, in which the strain changes the extent of Quantum Confined Stark Effect, and thus modifies the wavelength of light emission. By mixing strain relaxation and strain induction effects there is a spectral broadening of the light emission, providing polychromatic light emission.