Branched UV LED Mesa Structure for Lower Voltage and Light Loss
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Solution Overview
Problem
Conventional deep-UV light emitting diodes suffer from low power output and high forward voltage due to absorption of UV light by p-type and n-type semiconductor layers and inefficient current spreading, with limited use of side surface light emission.
Innovation Solution
A UV light emitting diode with a novel structure featuring a mesa with a main branch and sub-branches, where the n-ohmic and p-ohmic contact layers surround the mesa and cover its upper and side surfaces, allowing for reflection of UV light and improved current spreading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the mesa width is increased to reduce side surface area, then light loss through side surface is reduced, but current spreading efficiency decreases and forward voltage increases
Solution Approach 1:
The mesa is divided into multiple branches (main branch and sub-branches) to increase the total side surface area while maintaining efficient current distribution. This segmentation allows light emission from multiple side surfaces and improves current spreading without requiring a single large-width mesa
Solution Approach 2:
The invention transitions from a conventional single-wide mesa structure to a multi-branch mesa structure, effectively utilizing the dimensional arrangement of branches to increase surface area while maintaining compact footprint and efficient current paths
2Reliability
If the n-type ohmic contact layer is made larger to improve electrical contact, then electrical characteristics improve, but light absorption by the contact layer increases
Solution Approach 1:
The n-type ohmic contact layer is segmented into multiple regions corresponding to the mesa branches, allowing adequate electrical contact area while minimizing the continuous layer area that would absorb light. The contact layer follows the branched mesa structure rather than covering a large continuous area
Solution Approach 2:
The n-type ohmic contact layer is strategically positioned and sized to provide sufficient electrical contact at critical locations (under each mesa branch) while avoiding excessive area that would cause light absorption. Each contact region is optimized locally for its specific function
3Device complexity
If the p-type semiconductor layer is used for ohmic contact to simplify structure, then device complexity is reduced, but UV light absorption by the p-type layer increases
Solution Approach 1:
The p-type semiconductor layer is extracted from its conventional role as the primary ohmic contact layer. Instead, a separate n-type ohmic contact layer is introduced specifically for electrical contact, while the p-type layer focuses on its light-emitting function without the burden of providing ohmic contact, thereby reducing its light absorption
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
Enhances light output and reduces forward voltage by increasing the surface area for light reentry and efficient current distribution, addressing the limitations of conventional deep-UV light emitting diodes.
Implementation Method 1
The n-bump and the p-bump cover upper and side surfaces of the mesa... reflecting UV light emitted through the mesa side surface
Data Source
AI summary
An ultraviolet light-emitting diode includes: a substrate; an n-type semiconductor layer disposed on the substrate; a mesa disposed on the n-type semiconductor layer and including an active layer and a p-type semiconductor layer; an n-ohmic contact layer contacting the n-type semiconductor layer; a p-ohmic contact layer contacting the p-type semiconductor layer; an n-bump electrically connected to the n-ohmic contact layer; and a p-bump electrically connected to the p-ohmic contact layer, wherein the mesa includes a plurality of branches, the n-ohmic contact layer surrounds the mesa and is disposed in a region between the branches, each of the n-bump and the p-bump covers an upper surface and a side surface of the mesa, and the p-bump covers at least two of the branches among the plurality of branches. Therefore, an optical output can be increased by reducing light loss, and a forward voltage can be lowered.