Semipolar GaN LED Substrates for Radiative Recombination Efficiency
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Solution Overview
Problem
Conventional light bulbs dissipate most energy as thermal energy and have reliability issues due to thermal expansion, while GaN-based LEDs face challenges in achieving high intensity and efficiency, particularly in the green wavelength range, known as the 'green gap', and suffer from roll-over at high current densities.
Innovation Solution
The use of semipolar or nonpolar gallium nitride substrates for light emitting diodes (LEDs) combined with phosphors to emit polarized light, which enhances radiative recombination efficiency and overcomes the limitations of c-plane GaN-based LEDs, achieving improved light emission across a broader spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional c-plane GaN-based LEDs are used to achieve blue and green wavelength emission, then the device structure is simple and manufacturing is easier, but the radiative recombination efficiency is poor due to strong internal polarization fields that spatially separate electron and hole wave functions
Solution Approach 1:
The patent changes the crystal orientation parameter of the GaN substrate from conventional c-plane to semipolar or nonpolar planes. This parameter change fundamentally alters the polarization field characteristics, reducing the strong internal polarization fields that cause spatial separation of electron and hole wave functions in c-plane LEDs, thereby improving radiative recombination efficiency while maintaining manufacturing feasibility
Solution Approach 2:
The patent employs composite material structures including InGaN quantum wells grown on semipolar or nonpolar GaN substrates. This composite approach combines the beneficial properties of different materials and structures to achieve both high radiative recombination efficiency and practical manufacturability, overcoming the limitations of single-material systems
2Illumination intensity
If increased indium content is used in InGaN layers to extend emission wavelength to blue-green or green regime, then the emission wavelength is extended, but the crystal quality of InGaN films is degraded due to reduced growth temperature requirements
Solution Approach 1:
The patent changes the substrate orientation parameter to semipolar or nonpolar GaN planes, which enables better crystal quality control for high-indium InGaN layers. This parameter change allows the system to accommodate increased indium content while maintaining appropriate growth temperatures, thus extending emission wavelength to blue-green and green regimes without degrading crystal quality
3Device complexity
If conventional light bulbs are used for illumination, then the device structure is simple, but more than 90% of the energy used dissipates as thermal energy
Solution Approach 1:
The patent replaces the thermal radiation mechanism of conventional incandescent bulbs with electroluminescence in semiconductor LEDs. This substitution fundamentally changes the energy conversion mechanism from thermal to direct electrical-to-optical conversion, dramatically reducing energy dissipation as heat while achieving practical device structures for illumination applications
4Device complexity
If conventional light bulbs are used for illumination, then the structure is simple, but the light bulb routinely fails often due to thermal expansion and contraction of the filament element
Solution Approach 1:
The patent replaces the thermal-mechanical system of filament heating and glowing with the solid-state electroluminescence system. This substitution eliminates the thermal expansion and contraction cycles that cause filament failure, dramatically improving reliability while maintaining relatively simple device structures suitable for general illumination
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 approach results in higher efficiency and reliability for LEDs, enabling extended wavelength emission with minimal roll-over, particularly in the blue, green, and yellow regions, and allows for the creation of high-performance white light sources.
Implementation Method 1
enhances radiative recombination efficiency
Implementation Method 2
The entities are excited by the substantially polarized emission, which is direct or reflected or a combination to emit electromagnetic radiation second wavelengths
Data Source
AI summary
A packaged optical device includes a substrate having a surface region with light emitting diode devices fabricated on a semipolar or nonpolar GaN substrate. The light emitting diodes emit polarized light and are characterized by an overlapped electron wave function and a hole wave function. Phosphors within the package are excited by the polarized light and, in response, emit electromagnetic radiation of a second wavelength.