AlGaN Interlayer Suppresses Reflection in GaN Light-Emitting Devices
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Solution Overview
Problem
Group III nitride semiconductor light-emitting devices suffer from poor light extraction efficiency due to reflection at the interface between the p-contact layer and the transparent electrode, primarily because of the significant difference in refractive indices between p-GaN and ITO.
Innovation Solution
A semiconductor layer with an Al composition ratio of 10% to 50% and a thickness of 2 Å to 50 Å is introduced between the p-contact layer and the transparent electrode, with a refractive index lower than the p-contact layer but higher than the transparent electrode, to reduce reflection and enhance light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-GaN layer is used as the p-contact layer, then good electrical contact is achieved, but light extraction efficiency deteriorates due to total internal reflection at the interface with the transparent electrode
Solution Approach 1:
An AlGaN layer with intermediate refractive index is introduced between the p-GaN contact layer and the ITO transparent electrode. This intermediary layer acts as an optical mediator that gradually transitions the refractive index from 2.3 (p-GaN) to 1.9 (ITO), reducing the abrupt index mismatch and minimizing total internal reflection at the interface.
Solution Approach 2:
The refractive index parameter is gradually changed by using an AlGaN layer with specific aluminum composition ratio (10-50 mol%). By controlling the Al composition, the refractive index of the intermediate layer is optimized to be between that of p-GaN and ITO, creating a gradual transition that reduces optical reflection losses while maintaining electrical contact properties.
2Reliability
If the refractive index difference between p-contact layer and transparent electrode is large, then electrical contact is maintained, but light reflection increases and light extraction efficiency decreases
Solution Approach 1:
The AlGaN intermediate layer serves as an optical mediator that bridges the refractive index gap between the p-contact layer and transparent electrode. This mediator layer reduces the abrupt optical impedance mismatch, allowing more light to be extracted from the device while the electrical contact function is preserved through the underlying p-GaN layer.
Solution Approach 2:
A composite structure is formed by combining p-GaN, AlGaN, and ITO layers. This multi-layer composite structure leverages the complementary properties of each material: p-GaN provides electrical contact, AlGaN provides refractive index transition, and ITO provides transparency. The composite structure achieves both electrical functionality and optical efficiency.
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 introduction of the semiconductor layer effectively suppresses reflection between the p-contact layer and the transparent electrode, significantly improving the light extraction efficiency of the Group III nitride semiconductor light-emitting device.
Implementation Method 1
the p-contact layer has a refractive index for blue light of about 2.3, and the transparent electrode has a refractive index for blue light of about 1.9, thus the refractive indices are quite different. Therefore, a part of the light emitted from the light-emitting layer cannot be extracted from the device because the light is totally reflected at the interface between the p-contact layer and the transparent electrode.
Implementation Method 2
a part of the light emitted from the light-emitting layer cannot be extracted from the device because the light is totally reflected at the interface between the p-contact layer and the transparent electrode.
Data Source
AI summary
The present invention provides a Group III nitride semiconductor light-emitting device exhibiting improved light extraction efficiency. An AlGaN semiconductor layer is formed in contact with and on a p-GaN p-contact layer, and an ITO transparent electrode is formed in contact with and on the semiconductor layer. The semiconductor layer comprises AlGaN having an Al composition ratio of 10 mol % to 50 mol %, and has a thickness of 2 Å to 50 Å. The semiconductor layer has a refractive index at an emission wavelength lower than that of the p-contact layer, and larger than that of the transparent electrode. By forming such a semiconductor layer, the reflection is suppressed between the p-contact layer and the transparent electrode, thereby improving the light extraction efficiency.