GaN LED Nano-Patterned Substrate Thermal Management
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Solution Overview
Problem
Gallium nitride (GaN) based light-emitting diodes (LEDs) face challenges with thermal and electrical performance due to the use of sapphire substrates, which have poor thermal conductivity and electrical isolation, and the removal of these substrates can cause cracking and device degradation.
Innovation Solution
A method involving the formation of a nano-patterned substrate with a dielectric material layer and a nano-mask layer, followed by epitaxy semiconductor growth, wafer bonding, and selective substrate removal using radiation energy and mechanical force to minimize stress and enhance thermal and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sapphire substrate is used for GaN-LED, then electrical isolation is achieved, but thermal conductivity is poor
Solution Approach 1:
The sapphire substrate is segmented into multiple small islands separated by grooves, transforming a continuous poor thermal conductor into discrete thermal zones. This segmentation allows heat to be managed locally while preserving the electrical isolation function of the sapphire material.
Solution Approach 2:
A dielectric material layer is introduced as an intermediary between the segmented sapphire substrate and the LED structure. This intermediate layer facilitates thermal management while maintaining electrical isolation, bridging the thermal and electrical requirements.
2Temperature
If sapphire substrate is removed to improve thermal performance, then thermal conductivity improves, but cracking occurs leading to device degradation
Solution Approach 1:
The sapphire substrate is pre-segmented into islands with grooves formed before LED fabrication. This preliminary structuring creates stress relief pathways that prevent cracking during subsequent processing and operation, allowing the substrate to be removed or thinned without compromising device integrity.
Solution Approach 2:
By dividing the continuous sapphire substrate into discrete islands, the mechanical stress that causes cracking during substrate removal is distributed and reduced. The grooves act as stress relief features that prevent crack propagation across the entire substrate.
3Illumination intensity
If nano-patterned substrate is formed, then light extraction is enhanced, but manufacturing complexity increases
Solution Approach 1:
The nano-pattern introduces curved and non-planar features on the substrate surface, creating multiple light extraction pathways. The curved interfaces between sapphire islands, dielectric layer, and LED structure enhance light coupling and extraction efficiency.
Solution Approach 2:
The grooved nano-patterned substrate creates a porous-like structure with voids and interfaces that scatter and extract light more efficiently. The periodic arrangement of grooves and islands provides multiple opportunities for light to escape the high-refractive-index LED structure.
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 improves the thermal and electrical performance of GaN-LEDs by reducing mechanical stress and enabling efficient substrate removal, thereby preventing cracking and enhancing light extraction and device reliability.
Implementation Method 1
applying a radiation energy to the nano-composite layer
Data Source
AI summary
A light-emitting diode structure includes an AuSn or AuIn-containing bonding layer over a substrate, a metal layer disposed over the bonding layer, a p-type doped gallium nitride (p-GaN) layer disposed over the metal layer, a n-type doped gallium nitride (n-GaN) layer approximate the p-GaN layer, a multiple quantum well structure disposed between the n-GaN and p-GaN layers, and a conductive contact disposed on the n-GaN layer. The n-GaN layer includes a rough surface with randomly distributed dips. The nano-sized dips have diameters distributed between about 100 nm and about 600 nm, have a dip density ranging from about 107 grains/cm2 to about 109 grains/cm2, and are spaced from each other with an average spacing S, average diameter D, and a ratio S/D that ranges between about 1.1 and about 1.5. The conductive contact is disposed on some of the nano-sized dips of the rough surface.