UV LED Mesa Branch Structure for Lower Light Loss and Voltage
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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 lack of reflective metal layers, leading to inefficient current spreading and light loss.
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 the n-bump and p-bump cover 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 a reflective metal layer is adopted as the n-type ohmic contact layer to reduce light loss, then light output is improved, but in deep-UV light emitting diodes the n-type ohmic contact layer cannot be formed of reflective metal and occupies large area causing significant problems
Solution Approach 1:
The patent transitions from a planar contact layer to a three-dimensional bump structure. The n-type ohmic contact is formed as an n-bump that protrudes upward, allowing the contact to be made at the peak while the sides remain exposed. This dimensional change enables the use of non-reflective metal materials while still achieving good electrical contact and allowing light to escape from the side surfaces without being absorbed by a planar contact layer.
Solution Approach 2:
The contact structure is segmented into distinct components: the n-bump for electrical contact, the mesa for light generation and side surface exposure, and the p-bump for the opposite polarity contact. This segmentation allows each component to perform its specific function optimally - the n-bump provides electrical connection without blocking light, the mesa provides light emission from side surfaces, and the p-bump provides the opposite contact.
2Ease of manufacture
If the mesa width is increased to reduce side surface area, then manufacturing is simplified, but distance from n-type ohmic contact layer to central region increases causing inefficient current spreading and high forward voltage
Solution Approach 1:
The patent uses the vertical dimension to solve the current spreading problem. By forming n-bump and p-bump structures that protrude upward from the mesa, the electrical contacts are positioned closer together in the vertical direction while the mesa can maintain a wider horizontal footprint for manufacturing simplicity. The current spreads efficiently through the vertical path from the bump peaks through the active region.
Solution Approach 2:
The mesa structure exhibits local quality variations: the top region contains the active layer and quantum wells for light generation, the side surfaces allow light extraction, and the bottom region provides mechanical support and thermal management. The n-bump and p-bump are strategically positioned at specific locations to optimize current injection while allowing the mesa width to be optimized for manufacturing.
3Reliability
If p-type GaN layer is used for ohmic contact to achieve good electrical contact, then electrical characteristics are improved, but UV light entering the p-type semiconductor layer is absorbed and lost
Solution Approach 1:
The patent forms the p-type ohmic contact as a p-bump structure that protrudes upward, similar to the n-bump. This allows the p-type contact to be made at the peak where it provides good electrical connection, while the sides of the mesa remain exposed for light extraction. The p-bump structure minimizes the volume of p-type material that light must traverse, reducing absorption losses while maintaining electrical contact quality.
4Reliability
If n-type ohmic contact layer occupies large area to ensure adequate contact, then electrical contact is improved, but light traveling towards the n-type ohmic contact layer is absorbed and lost
Solution Approach 1:
The patent resolves this contradiction by forming the n-type ohmic contact as a three-dimensional bump structure rather than a planar layer. The n-bump provides adequate electrical contact area through its vertical extent and peak surface, while its compact footprint minimizes the horizontal area that blocks light. The side surfaces of the mesa around the n-bump remain exposed for light extraction, allowing light to escape laterally without passing through the contact material.
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 structure enhances light output and reduces forward voltage by increasing the surface area for light reflection and efficient current distribution, addressing the limitations of conventional deep-UV light emitting diodes.
Implementation Method 1
each of the n-bump and the p-bump covers upper and side surfaces of the mesa
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.