Light Emitting Element Transparent Electrode Light Extraction
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Solution Overview
Problem
The existing light emitting elements, such as those described in JP-A-2008-288548, face limitations in light extraction efficiency due to absorption of emitted light by the buffer electrode or n-electrode, rather than effective reflection.
Innovation Solution
A light emitting element is constructed with a p-side transparent contact electrode made of ITO, a first reflecting layer formed on top, and a second reflecting layer above a p-side insulating film opening, allowing emitted light to be reflected back into the light extracting direction without absorption, enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a buffer electrode and n-electrode are used to reflect light, then light extraction efficiency is improved, but light is absorbed by these electrodes instead of being effectively reflected
Solution Approach 1:
A transparent reflecting layer is introduced as an intermediary between the electrode and the light emitting layer. This layer mediates the interaction between light and electrode, enabling light to be reflected back into the extracting direction without being absorbed by the electrode, thus resolving the contradiction between light extraction efficiency and energy loss
Solution Approach 2:
The transparent reflecting layer is designed to be transparent to the specific wavelength of light emitted by the light emitting layer. This selective transparency allows the layer to reflect light effectively while maintaining transparency to the emitted light, solving the contradiction between reflection capability and light absorption
2Illumination intensity
If a metallic reflecting film is formed above the diffusion electrode, then light reflection is improved, but light extraction efficiency enhancement is limited due to absorption by buffer electrode or n-electrode
Solution Approach 1:
The transparent reflecting layer serves as an intermediary that enables effective light reflection without the harmful absorption effect of the underlying electrode. This intermediary layer allows the system to achieve both good light reflection and enhanced light extraction efficiency simultaneously
3Loss of energy
If a transparent contact electrode is used, then light absorption is reduced, but carrier diffusivity may be compromised
Solution Approach 1:
The contact electrode structure uses a composite configuration combining a transparent material (such as ITO) with the electrode layer. This composite structure maintains both the transparency needed to reduce light absorption and the electrical conductivity required for carrier diffusion, resolving the contradiction between optical and electrical performance
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
This configuration significantly enhances light extraction efficiency by reflecting emitted light back into the extracting direction, reducing absorption and improving overall light output without compromising carrier diffusivity or increasing driving voltage.
Implementation Method 1
a contact electrode on a p-side contact layer of a p-type semiconductor layer is formed of ITO transparent to light emitted from an active layer
Implementation Method 2
a first reflecting layer is formed thereon... the emitted light can be reflected back to the light extracting direction
Implementation Method 3
a second reflecting layer is formed on a p-side first insulating film opening of the first reflecting layer... the emitted light can be reflected back to the light extracting direction at a high rate without being absorbed
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A light emitting element includes a semiconductor laminate structure including a first semiconductor layer (21) of a first conductivity type, a light emitting layer (22), and a second semiconductor layer (23) of a second conductivity type different from the first conductivity type, a part of the second semiconductor layer and the light emitting layer being removed to expose a part of the first semiconductor layer, a first reflecting layer (50) on the semiconductor laminate structure and including an opening (55,56), the opening being formed in the exposed part of the first semiconductor layer, a transparent wiring electrode (30,40,41) for carrier injection into the first semiconductor layer or the second semiconductor layer through the opening, a second reflecting layer (60) formed on the transparent wiring electrode and covering a part of the opening so as to reflect light emitted from the light emitting layer and passing through the opening back to the first semiconductor layer.