Semi-Polar LED Efficiency Droop Mitigation
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Solution Overview
Problem
High power light emitting diodes (LEDs) face efficiency drop and non-uniform light emission due to polarization characteristics when driven at high current densities, leading to reduced performance and reliability.
Innovation Solution
A high power light emitting device with a nitride-based semiconductor structure grown on a semi-polar or non-polar substrate, featuring a multilayered wavelength conversion unit and optimized electrode configurations, including grooves and reflective layers, to enhance light extraction and heat management, allowing operation at current densities above 350 mA/mm2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high power LED is driven at high current density to increase power output, then the power output increases, but efficiency droop occurs and light emission becomes non-uniform
Solution Approach 1:
The patent applies local quality by creating asymmetric current distribution through non-polar/semi-polar growth surfaces and selective contact structures. The light emitting structure uses different contact configurations at different locations (first contact on n-type layer, second contact on p-type layer with specific geometry) to locally optimize current injection and reduce efficiency droop while maintaining high power output
Solution Approach 2:
The patent changes the crystal orientation parameter from conventional polar (c-plane) to non-polar (a-plane) or semi-polar orientations. This fundamental parameter change in the growth surface orientation modifies the polarization characteristics and current distribution, enabling high power operation without severe efficiency droop by altering the underlying physical parameters of the semiconductor structure
2Power
If a high power LED is driven at high current density to increase power output, then the power output increases, but light emission becomes non-uniform
Solution Approach 1:
The patent uses local quality through asymmetric contact structures and non-polar/semi-polar growth surfaces to create uniform current distribution across the active region. The selective placement of contacts and the specific crystal orientation ensure that current is distributed evenly, producing uniform light emission even at high power levels
Solution Approach 2:
The patent employs asymmetry in the contact structure configuration and crystal orientation to achieve symmetric uniform light emission. The asymmetric contact placement on non-polar/semi-polar surfaces creates a balanced current distribution that eliminates the non-uniformity typically seen in conventional symmetric polar LED structures at high current densities
3Use of energy by moving object
If the wavelength conversion unit is placed close to the light emitting diode to improve light coupling, then light coupling efficiency improves, but the wavelength conversion unit is damaged by heat generation
Solution Approach 1:
The patent introduces an intermediary heat dissipation structure between the light emitting diode and the wavelength conversion unit. This intermediary layer or structure acts as a thermal mediator that allows optical coupling while providing a heat sink function, protecting the wavelength conversion unit from excessive heat while maintaining efficient light transfer
Solution Approach 2:
The patent segments the device structure into distinct functional zones with separate thermal management for each. The light emitting structure, wavelength conversion unit, and heat dissipation components are spatially segmented and independently optimized, allowing the wavelength conversion unit to be positioned for optimal optical coupling while being thermally protected by dedicated heat dissipation pathways
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 high power LEDs to maintain excellent efficiency, reliability, and uniform light emission even at high current densities, reducing efficiency droop and heat generation while preventing damage to the wavelength conversion unit.
Implementation Method 1
a light emitting diode configured to emit near ultraviolet light
Implementation Method 2
a wavelength conversion unit having a multilayered structure including a first phosphor layer and a second phosphor layer
Data Source
AI summary
Disclosed herein are a light emitting device and a method of making the same. The light emitting device includes: a substrate including a first lead and a second lead; a light emitting diode disposed over the first lead of the substrate, including a second conductive-type semiconductor layer, an active layer, and a first conductive-type semiconductor layer, and emit near ultraviolet light; and a wavelength conversion unit disposed over the light emitting diode and spaced apart from the light emitting diode, wherein the light emitting structure has semi-polar or non-polar characteristics, the wavelength conversion unit has a multi-layered structure including a first phosphor layer and a second phosphor layer, and the light emitting diode is driven at a current density which is equal to or greater than 350 mA/mm2.