LED Chip DBR Structure for Wide-Angle Reflectance Control
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Solution Overview
Problem
Existing GaN-based light emitting diode chips face challenges in achieving high reflectance across various angles of incidence due to the narrowing of the stop band and generation of ripples in the spectrum bandwidth, particularly when using a distributed Bragg reflector (DBR) with a patterned sapphire substrate.
Innovation Solution
The DBR is designed with specific optical thickness variations in alternating high and low refractive index layers, including a first region with varying optical thicknesses for improved reflectance near the central wavelength and longer wavelengths, a second region for shorter wavelengths, and a third region to prevent ripples, ensuring high reflectance across a wide spectrum range and various angles of incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a DBR with alternating high and low refractive index layers each having optical thickness equal to λ/4 is used, then high reflectance is achieved at the central wavelength, but the stop band becomes narrow and ripples occur at various angles of incidence
Solution Approach 1:
The patent applies local quality by dividing the DBR structure into multiple regions (first region, second region, third region) where each region has different optical thickness characteristics. The first region has layers with optical thickness greater than λ/4, the second region has layers with optical thickness less than λ/4, and the third region has alternating thicknesses. This spatial variation in layer thickness optimizes reflectance for different angles of incidence across the visible spectrum, resolving the angular dependence problem while maintaining high reflectance.
2Illumination intensity
If the stop band is widened by stacking DBR1 for longer wavelengths and DBR2 for shorter wavelengths, then high reflectance over the entire visible range is achieved, but the structure complexity increases
Solution Approach 1:
The patent segments the DBR structure into three distinct regions: a first region with high optical thickness layers for long wavelength reflection, a second region with low optical thickness layers for short wavelength reflection, and a third region with alternating thicknesses to suppress ripples. This segmentation approach widens the stop band across the entire visible range while maintaining a systematic and manufacturable structure.
Solution Approach 2:
The patent employs parameter changes by varying the optical thickness of alternating high and low refractive index layers across different regions. The optical thickness is systematically adjusted from greater than λ/4 in the first region to less than λ/4 in the second region, with the third region providing intermediate values. This continuous parameter variation enables broad-spectrum high reflectance while controlling structural complexity.
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 design enhances luminous efficacy by maintaining high reflectance and preventing ripples, effectively reflecting light across a wide spectrum range and angles of incidence, thereby improving light extraction efficiency.
Implementation Method 1
a distributed Bragg reflector (DBR) disposed at one side of the light emitting structure so as to reflect light emitted from the light emitting structure
Implementation Method 2
the DBR includes first material layers having a high index of refraction and second material layers having a low index of refraction, the first and second material layers being alternately stacked one above another
Data Source
AI summary
A light emitting diode chip including a light emitting structure and a distributed Bragg reflector (DBR) having first, second, and third regions and including first material layers having a low index of refraction and second material layers having a high index of refraction, in which the first material layers include a first group having an optical thickness greater than 0.25λ+10%, a second group having an optical thickness in a range of 0.25λ−10% to 0.25λ+10%, and a third group having an optical thickness less than 0.25λ−10%, the first region has alternately disposed first and second groups, the second region has the third group, the first material layers in the third region have a first material layer having an optical thickness less than 0.25λ and greater than 0.25λ, the second material layers have a smaller average optical thickness than the first group of the first material layers.