LED Device with Uniform Current Density via Local Quality
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Solution Overview
Problem
Conventional LED devices face limitations in high current density due to efficiency 'droop' and reliability issues, such as current crowding and thermal gradients, which hinder cost reduction and energy savings compared to traditional lighting methods.
Innovation Solution
High current density LED devices are fabricated using bulk gallium and nitrogen containing substrates with polar, semipolar, or nonpolar materials, achieving increased light output per unit area through optimized epitaxial growth and design, including vertical injection geometries and reduced dislocation densities to maintain high external quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If current density is increased to generate more lumens per unit area, then productivity improves, but efficiency droop occurs and reliability deteriorates
Solution Approach 1:
The patent applies local quality by creating non-uniform current density distribution through specifically designed contact electrode geometries and positions. The current density is locally optimized to be higher in regions where it contributes most to light output while maintaining lower densities in regions prone to efficiency droop and reliability issues, thereby achieving high productivity without sacrificing device reliability
Solution Approach 2:
The patent changes the current density parameter from a uniform distribution to a controlled non-uniform distribution. By adjusting the contact electrode design parameters (geometry, position, size), the current density profile is optimized to maintain high overall current density for productivity while preventing localized excessive density that causes efficiency droop and reliability degradation
2Ease of manufacture
If current density is increased to reduce cost, then manufacturing cost decreases, but efficiency droop reduces internal quantum efficiency
Solution Approach 1:
The patent uses local quality by designing contact electrodes that create regions of optimized current density. This allows the device to operate at high overall current density (reducing cost) while maintaining high internal quantum efficiency in the active regions by preventing excessive current concentration, thus avoiding efficiency droop
Solution Approach 2:
The patent applies partial action by not uniformly increasing current density across the entire active area. Instead, it selectively increases current density in specific regions that contribute most to light output, while maintaining moderate densities in other regions. This achieves cost reduction through higher overall density without the full penalty of efficiency droop that would occur with uniform high density
3Use of energy by moving object
If current density is increased to improve energy savings, then energy efficiency improves, but thermal gradients and current crowding cause performance degradation
Solution Approach 1:
The patent addresses thermal gradients and current crowding by creating a non-uniform current density profile through optimized contact electrode design. This local quality approach ensures that current density is distributed to maximize energy efficiency while preventing excessive concentration in specific regions that would generate harmful thermal gradients and current crowding effects
Solution Approach 2:
The patent converts the potential harm of high current density (which causes thermal gradients and current crowding) into a benefit by strategically distributing the current. The contact electrode geometry is designed to guide current flow in a way that utilizes high density where it produces light efficiently while avoiding regions where it would create harmful thermal effects, thus transforming a potential problem into a performance advantage
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 LEDs with current densities exceeding 175 A/cm² and external quantum efficiencies of 40% or higher, providing improved reliability and efficiency while reducing the semiconductor material required, thus lowering costs and enhancing energy savings.
Implementation Method 1
High current density LED devices are fabricated using bulk gallium and nitrogen containing substrates with polar, semipolar, or nonpolar materials, achieving increased light output per unit area through optimized epitaxial growth and design
Implementation Method 2
one or more active regions are formed overlying the surface region, with a current density of greater than about 175 Amps/cm2 characterizing the one or more active regions
Data Source
AI summary
A light emitting diode device has a bulk gallium and nitrogen containing substrate with an active region. The device has a lateral dimension and a thick vertical dimension such that the geometric aspect ratio forms a volumetric diode that delivers a nearly uniform current density across the range of the lateral dimension.