LED Epitaxial Layer Smooth Surface for Light Extraction
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Solution Overview
Problem
Current light emitting diodes (LEDs) have inefficient light emission due to their narrow angular spread direction and high total internal reflection, limiting their ability to replace conventional light sources for general illumination.
Innovation Solution
A light emitting diode structure with an epitaxial layer and electrodes, where the epitaxial layer surface has a root-mean-square roughness less than 3 nm to minimize surface plasmon absorption and enhance light extraction by using a smooth reflective electrode, such as silver, to reduce specular reflection and increase light escape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional LED structure with rough surface is used, then manufacturing is easier, but light extraction efficiency is poor due to high total internal reflection and surface plasmon absorption
Solution Approach 1:
The patent changes the surface roughness parameter of the epitaxial layer from conventional rough surfaces to a smooth surface with RMS roughness less than 3 nm. This parameter change reduces surface plasmon absorption and total internal reflection, thereby improving light extraction efficiency without significantly complicating the manufacturing process
Solution Approach 2:
The patent employs a composite structure consisting of multiple epitaxial layers with different compositions (AlGaN, InGaN, GaN) and a smooth surface reflective electrode. This composite material approach optimizes both light extraction efficiency and electrical performance while maintaining manufacturability
2Loss of energy
If a smooth surface with RMS roughness less than 3 nm is created, then light extraction efficiency is improved by reducing surface plasmon absorption, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies a precise surface roughness parameter (RMS less than 3 nm) for the epitaxial layer. This parameter control is achieved through optimized epitaxial growth conditions, including temperature, pressure, and gas flow control during the growth process, balancing manufacturing precision requirements with light extraction improvement
Solution Approach 2:
The smooth surface is created during the epitaxial growth process itself through preliminary optimization of growth conditions, rather than requiring subsequent surface treatment steps. This preliminary action reduces the need for additional precision machining or surface finishing operations
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 smooth surface of the LED structure improves light extraction efficiency by minimizing surface plasmon absorption and increasing reflectance, allowing more light to escape and be utilized effectively, thereby enhancing the LEDs' ability to replace conventional light sources.
Implementation Method 1
the epitaxial layer structure has a RMS (root-mean-square) roughness less than 3 nm on a surface wherein the second electrode is formed
Implementation Method 2
using a smooth reflective electrode, such as silver, to reduce specular reflection and increase light escape
Data Source
AI summary
A light emitting diode comprising an epitaxial layer structure, a first electrode, and a second electrode. The first and second electrodes are separately disposed on the epitaxial layer structure, and the epitaxial layer structure has a root-means-square (RMS) roughness less than about 3 at a surface whereon the first electrode is formed.