Distributed Bragg Reflector Structure for Blue LED Light Extraction
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Solution Overview
Problem
Conventional light-emitting devices with distributed Bragg reflection (DBR) structures exhibit low reflectivity, especially for blue light and at various incident angles, which affects light extraction efficiency.
Innovation Solution
The proposed light-emitting device incorporates a DBR structure with multiple dielectric-layer pairs, where the first dielectric layer has a higher refractive index than the second, and the optical thickness ratios of both layers are optimized to enhance reflectivity across a wider wavelength range and incident angles, improving light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional DBR structure with uniform dielectric-layer pairs is used, then the structure is simple to manufacture, but the reflectivity is low especially for blue light and at various incident angles
Solution Approach 1:
The DBR structure is divided into multiple film stacks (first film stack, second film stack, third film stack) with different dielectric-layer pair configurations. Each film stack contains dielectric-layer pairs with different optical thickness ratios, allowing the structure to handle different incident angles and wavelengths effectively. This segmentation resolves the contradiction by creating a complex multi-stack structure that achieves high reflectivity across blue light wavelengths and various incident angles.
Solution Approach 2:
Different regions of the DBR structure (different film stacks) are assigned different local optical properties through varying dielectric-layer pair configurations. The first film stack has a first ratio of optical thicknesses, the second film stack has a second ratio, and the third film stack has a third ratio. This local quality variation enables each region to optimize reflectivity for specific incident angles and wavelengths, achieving high overall reflectivity for blue light.
2Reliability
If the optical thickness ratios of dielectric layers are optimized for normal incidence, then reflectivity at normal incidence is improved, but reflectivity at oblique angles deteriorates
Solution Approach 1:
The DBR structure is designed with multiple film stacks that collectively provide universal reflectivity performance across different incident angles. The first film stack optimizes for normal incidence with its first optical thickness ratio, while the second and third film stacks with different ratios compensate for oblique angle incidence. This multi-functional design ensures high reflectivity whether light enters at normal or oblique angles, resolving the contradiction between normal incidence optimization and angular adaptability.
3Ease of manufacture
If the DBR structure uses a single dielectric material pair, then manufacturing is simplified, but the wavelength range of high reflectivity is limited
Solution Approach 1:
The DBR structure employs composite dielectric material pairs (first dielectric material and second dielectric material with different refractive indices) arranged in multiple film stacks with varying optical thickness ratios. This composite structure extends the high reflectivity wavelength range to include blue light (450-480 nm) and broader spectral regions, while maintaining manufacturability through systematic repetition of the multi-stack pattern.
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 optimized DBR structure significantly increases reflectivity for blue light and across a broader wavelength range, enhancing light extraction efficiency and overall performance of the light-emitting device.
Implementation Method 1
a distributed Bragg reflection structure formed on the second surface of the substrate. The distributed Bragg reflection structure includes a first film stack and a second film stack; wherein the first film stack includes a plurality of first dielectric-layer pairs consecutively arranged
Implementation Method 2
The light from the active layer 146 can be reflected by the DBR structure 120
Implementation Method 3
The second dielectric layer has a refractive index higher than that of the first dielectric layer
Data Source
AI summary
A light-emitting device includes a substrate having a first surface and a second surface opposite to the first surface; a light-emitting stack formed on the first surface; and a distributed Bragg reflection structure formed on the second surface, wherein the distributed Bragg reflection structure includes a first film stack and a second film stack; wherein the first film stack includes a plurality of first dielectric-layer pairs consecutively arranged, the second film stack includes a plurality of second dielectric-layer pairs consecutively arranged, each of the first dielectric-layer pairs and each of the second dielectric-layer pairs respectively includes a first dielectric layer having an optical thickness and a second dielectric layer having an optical thickness; wherein the second dielectric layer has a refractive index higher than that of the first dielectric layer; wherein in each of the first dielectric-layer pairs of the first film stack, the optical thickness of the first dielectric layer to the optical thickness of the second dielectric layer have a first ratio, and in each of the second dielectric-layer pairs of the second film stack, the optical thickness of the first dielectric layer to the optical thickness of the second dielectric layer have a second ratio; wherein the first ratio is greater than the second ratio; and wherein the first film stack is farther from the second surface of the substrate than the second film stack.