UV LED P-Side Electrode Structure for Ohmic Contact and Reflectance
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Solution Overview
Problem
Current group III nitride semiconductor light emitting devices face challenges in forming ohmic contact with p-AlGaN or p-GaN layers while achieving high ultraviolet reflectance, leading to increased contact resistance and reduced light extraction efficiency.
Innovation Solution
A flip-chip type ultraviolet light emitting device is developed with a p-side electrode made of Ru, Rh, or their alloys, in contact with the p-type layer, and a DBR layer that reflects ultraviolet light, allowing for efficient light extraction and maintaining low contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If Al layer is used to form p-side electrode, then ultraviolet reflectance is improved, but contact resistance increases because Al cannot form ohmic contact with p-AlGaN or p-GaN
Solution Approach 1:
The p-side electrode is segmented into multiple functional layers: a first electrode layer (Ru, Rh, or alloy) that forms ohmic contact with the p-type layer, and a second electrode layer (Al or alloy) that provides high ultraviolet reflectance. This segmentation allows each layer to perform its specialized function, resolving the contradiction between contact resistance and reflectance.
Solution Approach 2:
The p-side electrode uses a composite structure combining different materials: Ru, Rh, or their alloys for ohmic contact properties, and Al or Al-based alloys for high reflectance. This composite approach integrates the beneficial properties of each material to simultaneously achieve low contact resistance and high ultraviolet reflectance.
2Reliability
If transparent electrode material such as ITO or IZO is used, then ohmic contact is improved, but ultraviolet reflectance decreases
Solution Approach 1:
The electrode structure is segmented into contact-functional layers (Ru, Rh, or alloy) and reflective layers (Al or alloy), allowing the transparent electrode material to be replaced by materials optimized for each specific function, thereby achieving both good ohmic contact and high reflectance.
Solution Approach 2:
The invention changes the material parameters of the electrode layers by selecting Ru, Rh, or their alloys for the first layer and Al or Al-based alloys for the second layer, optimizing the electrical and optical parameters to simultaneously achieve low contact resistance and high ultraviolet reflectance.
3Reliability
If p-side electrode thickness is increased to reduce contact resistance, then light extraction efficiency decreases due to increased light absorption
Solution Approach 1:
The p-side electrode is segmented into a thin first electrode layer for ohmic contact and a second electrode layer for reflectance, allowing the overall structure to achieve low contact resistance without increasing light absorption, thus maintaining high light extraction efficiency.
Solution Approach 2:
The composite electrode structure uses Ru, Rh, or their alloys combined with Al or Al-based alloys, where the first layer provides low contact resistance with minimal thickness and the second layer provides high reflectance, together achieving both low contact resistance and high light extraction 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 solution enables improved ultraviolet reflectance and light extraction efficiency while forming ohmic contact with the p-type layer, enhancing the performance of the light emitting device.
Implementation Method 1
an insulating DBR layer formed on and in contact with a part of the p-side electrode, and reflecting ultraviolet light with an emission wavelength
Data Source
AI summary
The present disclosure provides a light emitting device in which the ultraviolet reflectance can be improved while the p-side electrode can form ohmic contact with the p-type layer. A flip-chip type ultraviolet light emitting device includes an n-type layer, an active layer, a p-type layer, a p-side electrode formed on the p-type layer, including a layer in contact with the p-type layer and made of Ru, Rh, or an alloy containing those metals as a main component, and having a thickness that transmits ultraviolet light with an emission wavelength, an insulating DBR layer formed on and in contact with a part of the p-side electrode, and reflecting ultraviolet light with an emission wavelength, a second p-side electrode being electrically connected with the p-side electrode through a hole formed in a region on the p-side electrode of the DBR layer.