Transparent UV LED Structure With Tunnel Junction Light Extraction
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Solution Overview
Problem
Current UV and far-UV LEDs are inefficient due to optically absorbing components, which limit their light extraction efficiency and power output, and no fully transparent UV LEDs exist, hindering their commercial availability for applications like skin-safe and eye-safe disinfection.
Innovation Solution
A fully transparent UV or far-UV LED design is achieved by replacing optically absorbing components with transparent tunnel junctions and packaging materials, allowing top-side and bottom-side emission without lossy metal mirrors, and using a transparent substrate for maximum light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional UV LED components (p-GaN hole injection layer, metal mirrors) are used, then electrical functionality is achieved, but light extraction efficiency is reduced due to optical absorption
Solution Approach 1:
The patent extracts and removes the optically absorbing p-GaN hole injection layer and metal mirror components from the UV LED structure. By eliminating these lossy components, the device achieves full transparency to UV wavelengths while maintaining electrical functionality through alternative transparent structures such as transparent conductive oxides and transparent tunnel junctions.
2Loss of energy
If fully transparent materials are used throughout the device, then light extraction efficiency is maximized, but achieving sufficient hole injection becomes difficult
Solution Approach 1:
The patent introduces transparent tunnel junctions as intermediary structures that enable efficient hole injection into the active region while maintaining optical transparency. These tunnel junctions use quantum mechanical tunneling through thin barrier layers to transport holes without requiring absorbing materials, thus serving as a mediator between the need for electrical functionality and optical transparency.
Solution Approach 2:
The patent changes the electrical parameters (doping concentrations, layer thicknesses, band structures) of the transparent layers to optimize both hole injection efficiency and optical transparency. By carefully tuning these parameters, the device achieves sufficient carrier injection while maintaining full transparency to UV wavelengths.
3Loss of energy
If metal contacts cover the entire emitting area, then electrical contact is sufficient, but light emission is blocked by the metal
Solution Approach 1:
The patent transitions from planar metal contacts to transparent conductive oxide layers that can be deposited in conformal fashion across the device surface. This dimensional change allows electrical contact to be established through the transparent layer without blocking UV emission, as the TCO maintains optical transparency while providing electrical conductivity.
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 design significantly enhances light extraction efficiency, enabling high-power UV emission with minimal optical absorption, and allows for novel device configurations like series connections for AC power use, addressing the inefficiencies and commercial limitations of existing UV LEDs.
Implementation Method 1
a transparent tunnel junction, which is a highly doped p-n junction operated in reverse bias, injecting holes into the p-side of the LED via interband tunneling
Implementation Method 2
ultraviolet (UV) or far-UV light-emitting diodes (LEDs)
Data Source
AI summary
A fully transparent UV LED or far-UV LED is disclosed, in which all semiconductor layers except the active region are transparent to the radiation emitted in the active region. The key technology enabling this invention is the transparent tunnel junction, which replaces the optically absorbing p-GaN and metal mirror p-contact currently found in all commercially available UV LEDs. The tunnel junction also enables the use of a second n-AlGaN current spreading layer above the active region (on the p-side of the device) similar to the current spreading layer already found below the active region (on the n-side of the device). Therefore, small-area and/or remote p- and n-contacts can be used, and light can be extracted from both the top-side and bottom-side of the device. This fully transparent semiconductor device can then be packaged using transparent materials into a fully transparent UV LED or far-UV LED with high brightness and efficiency.