UV LED Electrode Structure for Better Ohmic Contact and UV Reflection
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Solution Overview
Problem
Conventional UV semiconductor light emitting devices have low light efficiency due to significant light absorption in the p-type contact layer, which is not transparent to UV light.
Innovation Solution
The semiconductor light emitting device incorporates a contact electrode with varying aluminum composition ratios across its depth, and a metal layer with a reflective layer and a barrier layer to improve Ohmic contact characteristics and light reflection, thereby enhancing light efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type contact layer is used to achieve Ohmic contact with the AlGaN layer, then the electrical contact characteristics are improved, but the light efficiency deteriorates due to UV light absorption in the contact layer
Solution Approach 1:
The patent extracts the light-absorbing p-type contact layer from the optical path by using a flip chip bonding technique to mount the LED chip on a substrate, allowing UV light to be emitted through the transparent sapphire substrate rather than passing through the opaque p-type contact layer. This separates the electrical contact function from the optical transmission path.
Solution Approach 2:
The patent applies different material compositions to different regions: the p-type contact layer uses AlInGaN with low GaN/Al content for good Ohmic contact, while the multiple quantum well structure uses AlGaN with higher Al content for UV light emission. The transparent substrate is used specifically for optical output, creating localized optimization of material properties for different functions.
2Illumination intensity
If AlGaN layer is used to achieve short wavelength UV emission, then the light wavelength is improved, but the Ohmic contact characteristics deteriorate because AlGaN does not make good Ohmic contact with metal
Solution Approach 1:
The patent uses composite material structures: AlInGaN contact layers with specific composition ratios (low GaN/Al content) are combined with AlGaN active layers (high Al content) to achieve both good Ohmic contact properties and short wavelength UV emission properties in different regions of the device.
Solution Approach 2:
The patent varies the composition parameters of the AlInGaN contact layer, specifically controlling the GaN and Al content to be low, which changes the electrical and optical properties to enable both good Ohmic contact and UV light transmission. The Al content is specifically controlled to balance contact quality and optical properties.
3Loss of energy
If a transparent substrate is used to emit UV light through the substrate, then the light efficiency is improved, but the device complexity increases due to the need for flip chip bonding technique
Solution Approach 1:
The patent inverts the conventional light emission direction by using flip chip bonding to mount the LED chip upside down on a substrate, so that UV light is emitted through the transparent sapphire substrate rather than through the top surface. This structural inversion enables the transparent substrate to serve as the optical output window while maintaining good electrical contacts.
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 improved Ohmic contact characteristics and light reflection mechanisms result in enhanced forward voltage characteristics and light efficiency for deep ultraviolet light emission.
Implementation Method 1
a metal layer disposed on the contact electrode... including a reflective layer to reflect light
Implementation Method 2
a barrier layer disposed on the reflective layer to prevent diffusion of metal atoms or metal ions from the reflective layer
Implementation Method 3
an active layer disposed on the first semiconductor layer to emit ultraviolet light... light is emitted by a material contained in a device using electric energy, and have inorganic semiconductors emitting light generated by recombination of electrons and holes
Implementation Method 4
a first electrode disposed on the first semiconductor layer and being in Ohmic contact with a portion of the first semiconductor layer... to improve Ohmic contact characteristics
Data Source
AI summary
A semiconductor light emitting device includes: a first semiconductor layer; an active layer disposed on the first semiconductor layer to emit ultraviolet light; a second semiconductor layer disposed on the active layer; a contact electrode disposed on the first semiconductor layer; a first electrode including a plurality of metal layers having a first portion and a second portion adjacent to the first portion; and a second electrode disposed on the second semiconductor layer; a first bump disposed on the first electrode and electrically coupled to the first semiconductor layer by the first electrode; and a second bump disposed on the second electrode and electrically coupled to the second semiconductor layer by the second electrode, wherein the first semiconductor layer is formed of AlGaN and has an energy larger than the ultraviolet wavelength energy generated in the active layer, wherein the first portion of the plurality of metal layers is in contact with the contact electrode and the second portion of the plurality of metal layers is disposed on and in contact with first semiconductor layer, and all of the plurality of metal layers have irregular top surfaces, respectively.