Reflective Mounting Substrates for LED Light Extraction
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Solution Overview
Problem
Group III nitride light emitting diodes (LEDs) used in white light applications face reduced external quantum efficiency when grown on silicon substrates due to light absorption, which diminishes the initial advantages of higher-quality epitaxial layers formed on silicon carbide substrates when integrated into LED lamps with phosphors.
Innovation Solution
A light emitting diode structure featuring a Group III nitride active structure bonded to a reflective mounting substrate that reflects at least 50% of emitted light frequencies, using materials like aluminum oxide, boron nitride, or titanium dioxide, which supports the active structure and minimizes light absorption, thereby enhancing external quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Group III nitride LEDs are grown on silicon substrates, then manufacturing cost is reduced and ease of manufacture is improved, but external quantum efficiency deteriorates due to light absorption by the silicon substrate
Solution Approach 1:
A reflective mounting substrate is introduced as an intermediary between the silicon substrate and the active structure. This mediator reflects light that would otherwise be absorbed by the silicon substrate back toward the active structure, thereby maintaining the ease of manufacturing on silicon while recovering the lost light output and improving external quantum efficiency.
2Loss of energy
If Group III nitride LEDs are grown on silicon carbide substrates, then external quantum efficiency is improved due to reduced light absorption, but manufacturing cost increases and ease of manufacture deteriorates
Solution Approach 1:
The invention uses a inexpensive silicon substrate as a temporary growth platform for forming high-quality Group III nitride epitaxial layers. After the active structure is formed, the silicon substrate is discarded and replaced with a reflective mounting substrate. This allows leveraging the manufacturing advantages of silicon without suffering its light absorption drawbacks in the final device.
3Loss of energy
If a reflective mounting substrate is added to the LED structure, then external quantum efficiency is improved by reducing light absorption, but device complexity increases
Solution Approach 1:
The reflective mounting substrate serves multiple functions simultaneously: it provides mechanical support for the active structure, acts as a light reflector to improve external quantum efficiency, and can be integrated with standard LED packaging processes. By combining these functions in a single component, the added complexity is minimized while achieving multiple benefits.
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 reflective mounting substrate significantly increases the external quantum efficiency of the LED by reducing light absorption and enhancing light extraction, maintaining the quality of Group III nitride layers even after substrate removal and integration into LED lamps.
Implementation Method 1
The mounting substrate includes a material that is other than a Group III nitride and that reflects at least fifty percent of light having the frequencies emitted by the active structure
Data Source
AI summary
A light emitting diode is disclosed that includes a light emitting active structure formed from the Group III nitride material system, a bonding structure supporting the Group III nitride active structure, and a mounting substrate supporting the bonding structure. The mounting substrate includes a material that reflects at least fifty percent of light having the frequencies emitted by the active structure.