Semiconductor Light Emitting Device Rear Reflector Structure
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Solution Overview
Problem
Nitride semiconductor light emitting devices suffer from reduced light extraction efficiency due to total internal reflection, leading to undesired light emission and loss, necessitating a method to enhance light reflectance without excessive changes in wavelength bands and incident angles.
Innovation Solution
A semiconductor light emitting device with a rear reflector structure featuring a light transmissive dielectric layer and a reflective metallic layer, optionally with a distributed Bragg reflector (DBR) or omni-directional reflector (ODR) structure, combined with a planarization layer to improve light reflectance and heat dissipation, and an uneven substrate surface to increase contact area and light orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional flat reflector structure is used on the rear surface, then the device structure is simple, but light reflectance is insufficient and light extraction efficiency is reduced due to total internal reflection
Solution Approach 1:
The reflector structure employs a composite design combining a light transmissive substrate, a light transmissive dielectric layer with high refractive index, and a reflective metallic layer. This multi-material composite structure achieves superior light reflectance by leveraging the optical properties of each material: the high refractive index dielectric layer enhances light reflection at the interface, while the metallic layer provides strong reflective capability, together improving light extraction efficiency from the active layer.
Solution Approach 2:
The invention introduces an uneven portion on the rear surface of the light transmissive substrate, transitioning from a flat two-dimensional surface to a three-dimensional structured surface. This dimensional change increases the surface area and creates multiple light reflection paths, thereby enhancing overall light reflectance and extracting more light that would otherwise be lost through total internal reflection.
2Power
If a high refractive index semiconductor layer is used, then light generation is efficient, but total internal reflection increases causing light to be emitted in undesired directions or lost
Solution Approach 1:
The light transmissive dielectric layer with high refractive index acts as an intermediary between the semiconductor layer and the reflective metallic layer. This intermediate layer with optimized refractive index helps to reduce total internal reflection by providing a gradual transition in refractive index, allowing more light to reach the reflective metallic layer and be redirected in desired directions, thereby reducing light loss while maintaining efficient light generation.
3Reliability
If a simple reflective metallic layer is used, then manufacturing is simple, but reflectance varies excessively with wavelength bands and incident angles
Solution Approach 1:
The reflector structure combines a light transmissive dielectric layer with a reflective metallic layer in a composite configuration. The dielectric layer with high refractive index is positioned adjacent to the semiconductor layer, while the metallic layer provides broad-spectrum reflection. This composite structure achieves consistent reflectance across different wavelength bands and incident angles by leveraging the complementary optical properties of both materials, maintaining reliability without excessive manufacturing 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 solution achieves high overall reflectance and improved light emission efficiency by maintaining consistent reflectance across different wavelength bands and incident angles, enhancing the semiconductor light emitting device's luminance and heat dissipation capabilities.
Implementation Method 1
a semiconductor layer constituting the LED has a high refractive index as compared with external air, an encapsulated material, or a substrate, reducing a critical angle determining an incident angle range in which light can be emitted. As a result, a considerable amount of light generated from an active layer is totally internally reflected
Implementation Method 2
The light transmissive dielectric layer may include a plurality of dielectric layers having different refractive indexes and alternately stacked
Implementation Method 3
a rear reflective part including a reflective metallic layer disposed on the second main surface
Implementation Method 4
The plurality of dielectric layers may have a distributed Bragg reflector (DBR) structure
Implementation Method 5
the second main surface having an uneven portion formed thereon
Implementation Method 6
A light emitting diode (LED) is a semiconductor device able to emit light of various colors due to electron-hole recombination occurring at a p-n junction between p-type and n-type semiconductors when current is applied thereto
Data Source
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AI summary
There is provided a semiconductor light emitting device including: a light transmissive substrate; a light emitting part; first and second electrodes electrically connected to the first and second conductivity type semiconductor layers, respectively; and a rear reflective part including a reflective metallic layer, and a light transmissive dielectric layer interposed between the light transmissive substrate and the reflective metallic layer.