III Nitride LED Composite Electrode for Low Forward Voltage
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Solution Overview
Problem
III nitride semiconductor light emitting devices with reflective electrode layers face challenges in achieving good ohmic contact and sufficient light emission efficiency due to high contact resistance and absorption of ultraviolet light by the p-type contact layer, leading to increased forward voltage.
Innovation Solution
A composite layer with a reflective electrode portion and a contact portion made of AlxGa1-xN (0≦x≦0.05) is formed on the surface of the III nitride semiconductor laminate, opposite to the light extraction side, where the contact portion is thicker and covers the reflective electrode portion, allowing for good ohmic contact and effective light reflection without significant absorption of ultraviolet light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflective electrode layer is formed on the p-type semiconductor layer, then light reflectance is improved, but contact resistance increases and forward voltage increases
Solution Approach 1:
The patent divides the electrode structure into three distinct segments: a reflective electrode layer (first electrode layer) for light reflection, a p-type contact layer (second electrode layer) for electrical contact, and a barrier layer. This segmentation allows each layer to perform its specific function optimally without interfering with others, resolving the contradiction between reflectance and contact resistance.
Solution Approach 2:
The patent applies local quality by making each electrode layer have different properties suited to its function: the reflective electrode layer has high reflectance properties, while the p-type contact layer has high electrical conductivity and low contact resistance. This localized optimization resolves the contradiction by ensuring each region has the quality needed for its specific purpose.
2Reliability
If a p-type contact layer is formed to reduce contact resistance, then ohmic contact is improved, but ultraviolet light absorption increases
Solution Approach 1:
The patent segments the electrode structure so that the p-type contact layer is positioned below the reflective electrode layer, with a barrier layer separating them. This segmentation allows the p-type contact layer to provide good ohmic contact while the barrier layer and reflective electrode layer above it prevent ultraviolet light absorption and enable light reflection.
Solution Approach 2:
The barrier layer acts as an intermediary between the p-type contact layer and the reflective electrode layer. It prevents ultraviolet light from being absorbed by the p-type contact layer while allowing the reflective electrode layer to function properly, thus resolving the contradiction between ohmic contact and light absorption.
3Illumination intensity
If the reflective electrode layer directly contacts the p-type semiconductor layer, then light reflection is maximized, but forward voltage increases due to poor ohmic contact
Solution Approach 1:
The patent introduces a p-type contact layer between the reflective electrode layer and the p-type semiconductor layer, creating a segmented structure. This segmentation allows the reflective electrode layer to maximize light reflection while the p-type contact layer provides low-resistance electrical contact, thereby reducing forward voltage.
Solution Approach 2:
The p-type contact layer serves as an intermediary that bridges the reflective electrode layer and the p-type semiconductor layer. It enables both functions to coexist: the reflective electrode layer maintains high reflectance while the p-type contact layer ensures low contact resistance and reduced forward voltage.
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 improves light emission efficiency while maintaining low forward voltage, enabling both good ohmic contact and sufficient reflective electrode functionality.
Implementation Method 1
The reflective electrode layer reflects part of light produced in the light emitting layer, which is directed toward the p-side electrode, thus increasing the amount of light emitted out from the light extraction side.
Implementation Method 2
contact resistance can be reduced when this p-type contact layer is in contact with the p-side electrode as compared with the case where the p-type semiconductor layer is directly in contact with the p-side electrode. Thus, good ohmic contact can be obtained.
Implementation Method 3
the contact layer characteristically absorbs ultraviolet light, in particular, light at a wavelength of 365 nm or less
Data Source
AI summary
A III nitride semiconductor light emitting device with improved light emission efficiency achieved without significantly increasing forward voltage by achieving both good ohmic contact between an electrode and a semiconductor layer, and sufficient functionality of a reflective electrode layer, and a method for manufacturing the same. The III nitride semiconductor light emitting device has a III nitride semiconductor laminate including an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer; an n-side electrode, a p-side electrode; and a composite layer having a reflective electrode portion and a contact portion made of AlxGa1-xN (0≦x≦0.05) on a second surface of the III nitride semiconductor laminate. The second surface is opposite to a first surface on the light extraction side.