Patterned LED Substrate With Hole Structure for Defect-Free Epitaxy
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Solution Overview
Problem
The existing patterned sapphire substrates with SiO2 protrusions for light-emitting diodes (LEDs) often suffer from defects in the longitudinal direction during epitaxial growth, leading to reduced light extraction efficiency due to electron-hole capture and recombination issues.
Innovation Solution
A light-emitting device with a patterned substrate featuring protrusions having a cone-shaped structure made of a different material than the supporting substrate, accompanied by a buffer layer and a hole structure above the top end of each protrusion, which alleviates stress and prevents defects by allowing lateral epitaxy and enhancing light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a patterned sapphire substrate with cone-shaped protrusions is used to enhance light extraction efficiency, then light extraction efficiency is improved, but defects in the longitudinal direction occur at the top of the protrusions during epitaxial growth
Solution Approach 1:
The patent applies preliminary action by forming a buffer layer on the side wall surfaces of the protrusions before epitaxial growth. This buffer layer is deposited in advance to cover the problematic regions where defects typically occur, preventing defects from forming during subsequent epitaxial growth while maintaining the light extraction enhancement benefits of the protrusion structure
Solution Approach 2:
The buffer layer acts as an intermediary between the patterned sapphire substrate and the epitaxial layer. It mediates the interaction by covering the defect-prone regions at the protrusion tops, allowing the epitaxial layer to grow defect-free while still benefiting from the underlying protrusion structure's light extraction enhancement
2Illumination intensity
If protrusions are formed on the sapphire substrate to improve light extraction, then light extraction efficiency is enhanced, but electron-hole capture increases reducing light-emitting efficiency
Solution Approach 1:
The patent applies the taking out principle by removing or eliminating the harmful effect of electron-hole capture at the protrusion tops. Through the buffer layer and controlled epitaxial growth, the defect sites that cause non-radiative recombination are eliminated, allowing electrons and holes to recombine radiatively and emit light efficiently while retaining the light extraction benefits
3Manufacturing precision
If a patterned substrate with protrusions is used to relieve stress and reduce defect density, then lattice quality is improved, but defects extend to the active layer during epitaxial growth
Solution Approach 1:
The buffer layer is deposited in advance on the protrusion side walls to create a defect-free foundation before epitaxial growth. This preliminary action prevents defects from the substrate-protrusion interface from propagating into the active layer during subsequent growth, maintaining both lattice quality and active layer integrity
Solution Approach 2:
The buffer layer serves as an intermediary barrier that prevents defect propagation from the patterned substrate through the protrusions to the epitaxial active layer. It mediates the stress and defect transmission, allowing the active layer to grow with high lattice quality free from substrate-induced defects
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 effectively reduces defects in the active layer, improves light-emitting efficiency, and increases the internal quantum efficiency of the LED, as evidenced by increased luminous intensity and enhanced protection against electrostatic discharge.
Implementation Method 1
The patterned sapphire substrate may relieve stress between a sapphire substrate and a GaN epitaxial layer during growth of the GaN epitaxial layer
Implementation Method 2
The at least one hole structure is located at a top of the cone of the at least one of the protrusions and extend into the epitaxial layered unit
Data Source
AI summary
A light-emitting device includes a patterned substrate, a buffer layer, an epitaxial layered unit, and at least one hole structure. The patterned substrate includes a supporting substrate having an upper surface, and a plurality of protrusions formed on the upper surface. Each of the protrusions includes a base and a cone sequentially stacked in such order on the upper surface. The cone is made of a material different from that of the supporting substrate. The buffer layer formed on a side wall surface of each of the protrusions and the upper surface of the supporting substrate exposed from the protrusions. The epitaxial layered unit is formed on the buffer layer opposite to the patterned substrate. The hole structure is disposed above a top end of at least one of the protrusions. A method for manufacturing the light-emitting device is also disclosed.