UV LED Mesa Structure Oxide Passivation for Light Extraction
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Solution Overview
Problem
Ultraviolet (UV) light emitting diode (LED) chips face reduced light extraction efficiency due to high absorption rates and lack of a concave-convex structure for preventing total reflection between the sapphire layer and aluminum nitride layer, which affects their performance in UV applications such as sterilization and disinfection.
Innovation Solution
A light emitting device with a mesa structure having a narrow horizontal width, where an oxide layer such as Al2O3 or SiO2 is formed on the side surfaces through a thermal oxidation process to reflect light emitted at angles greater than the critical angle, directing it at angles less than the critical angle for improved extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If p-GaN is formed on p-AlGaN to form an ohmic contact, then electrical contact is achieved, but light extraction efficiency is reduced due to high absorption rate of UV light by p-GaN
Solution Approach 1:
The device is divided into multiple functional regions including separate p-AlGaN contact regions and p-GaN light emission regions. The p-AlGaN layer is positioned to provide electrical contact while the p-GaN layer is positioned to emit light, spatially separating the contact function from the light emission function to reduce self-absorption of emitted UV light by the contact layer.
Solution Approach 2:
An AlN layer is introduced as an intermediary between the sapphire substrate and the p-AlGaN contact layer. This AlN layer forms a concave-convex structure that prevents total internal reflection at the sapphire-AlN interface, thereby improving light extraction efficiency while the p-AlGaN layer maintains its ohmic contact function.
2Ease of manufacture
If AlN is not bonded onto a roughened sapphire layer, then manufacturing is simplified, but a concave-convex structure for preventing total reflection cannot be formed
Solution Approach 1:
The sapphire substrate surface is pre-roughened before AlN layer deposition. This preliminary surface treatment creates the necessary concave-convex structure that prevents total internal reflection at the sapphire-AlN interface, enabling improved light extraction efficiency without requiring complex bonding processes.
Solution Approach 2:
The surface morphology parameter of the sapphire substrate is changed from smooth to roughened. This parameter change creates the concave-convex structure that disrupts total internal reflection pathways, allowing more UV light to be extracted from the device while maintaining a relatively simple manufacturing process.
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 enhances light extraction efficiency by preventing total reflection and reducing non-emission recombination, thereby increasing the external quantum efficiency of the UV LED chips.
Implementation Method 1
an oxide such as Al2O3 or SiO2 is formed on a side surface of the mesa structure through a thermal oxidation process. Accordingly, light emitted at an angle greater than a critical angle is reflected by an oxide layer and directed at an angle less than the critical angle
Implementation Method 2
an oxide such as Al2O3 or SiO2 is formed on a side surface of the mesa structure through a thermal oxidation process
Data Source
AI summary
A light emitting device includes a first light transmitting layer, a second light transmitting layer provided on the first light transmitting layer, a plurality of mesa structures provided on the second light transmitting layer and configured to generate light in an ultraviolet band, and passivation patterns provided on side surfaces of the plurality of mesa structures. Each of the plurality of mesa structures includes a first epitaxial pattern including an aluminum gallium nitride, a second epitaxial pattern provided on the first epitaxial pattern and including an aluminum gallium nitride, a third epitaxial pattern provided on the second epitaxial pattern and including an aluminum gallium nitride, and a fourth epitaxial pattern provided on the third epitaxial pattern and including a gallium nitride. A horizontal width of each of the plurality of mesa structures is in a range of about 5 μm to about 30 μm.