Hexahedral Substrate Light Extraction for Semiconductor LEDs
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Solution Overview
Problem
Conventional nitride semiconductor light-emitting elements have low light extraction efficiency and are costly and time-consuming to produce, especially when multiple division grooves are formed on sapphire substrates, leading to increased absorption of laser beams and current leakage.
Innovation Solution
A semiconductor light-emitting element with a substrate having a hexahedral shape and a projecting and recessed structure on the first surface, and multiple reformed layers on the orthogonal surfaces, allowing efficient light transmission and extraction without cutting off light in specific directions, thereby enhancing light extraction efficiency and reducing production time and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple division grooves are formed on the sapphire substrate to extract light from side surfaces, then light extraction efficiency is improved, but production time and cost increase significantly
Solution Approach 1:
The patent applies preliminary action by forming reformed layers in the sapphire substrate before the laser division process. These pre-formed reformed layers guide the laser beams during substrate division, enabling the laser to automatically create appropriate division grooves without requiring multiple separate processing steps. This preliminary preparation reduces the number of processing steps and overall production time while maintaining effective light extraction from side surfaces.
Solution Approach 2:
The reformed layers act as an intermediary between the laser division process and the final division groove formation. These layers modify the laser beam interaction with the sapphire substrate, controlling where and how the division grooves form. This intermediary structure enables precise groove formation with fewer laser passes, reducing production time while achieving the desired light extraction efficiency.
2Illumination intensity
If multiple division grooves are formed on the sapphire substrate, then light extraction from side surfaces is enhanced, but laser beam absorption increases causing current leakage
Solution Approach 1:
The reformed layers are formed in advance at specific positions in the sapphire substrate where division grooves will eventually form. These pre-formed layers create controlled regions that guide laser beam propagation during the division process, ensuring that grooves are created only where needed and with appropriate depth control. This prevents excessive laser energy absorption that would otherwise cause current leakage in the light-emitting layer.
Solution Approach 2:
The reformed layers serve as an intermediary that mediates between the laser division process and the light-emitting structure. By controlling laser beam interaction at the substrate level before groove formation, these layers prevent uncontrolled laser energy absorption that could damage the light-emitting layer and cause current leakage, while still enabling effective side surface light extraction.
3Reliability
If the mesa end surface is spaced far from the chip end surface to avoid laser absorption, then current leakage is reduced, but light emission output decreases
Solution Approach 1:
The reformed layers act as an intermediary that enables close positioning of the mesa end surface to the chip end surface without causing current leakage. These layers control laser beam propagation and energy distribution, creating division grooves that safely terminate near the light-emitting structure without allowing harmful laser absorption. This intermediary control allows maximization of the light-emitting region area while maintaining electrical reliability.
Solution Approach 2:
The patent changes the physical and chemical parameters of the sapphire substrate by forming reformed layers with different properties from the bulk substrate. These modified regions have altered optical and mechanical characteristics that enable precise control of laser division grooves, allowing the mesa end surface to be positioned closer to the chip end surface without risking current leakage, thereby increasing the light-emitting region area and output.
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 significantly improves light extraction efficiency and reduces production time and cost by optimizing the substrate structure, allowing for higher light emission output without the need for extensive mesa end surface spacing, thus addressing the limitations of existing methods.
Implementation Method 1
The substrate has a property to allow transmission of light from the light-emitting layer
Implementation Method 2
In order to prevent light emitted from the side surface of the sapphire substrate from returning to the inside of the sapphire substrate as a result of total reflection by the side surface of the sapphire substrate
Data Source
AI summary
A semiconductor light-emitting element includes a substrate and a semiconductor stack portion provided on the substrate and having at least a first-conductivity-type semiconductor layer, a light-emitting layer, and a second-conductivity-type semiconductor layer. The substrate has a property to allow transmission of light from the light-emitting layer, and has a hexahedral shape including a first surface on which a semiconductor stack portion is provided, a second surface located opposite to the first surface, a pair of third surfaces orthogonal to the first surface and the second surface, and a pair of fourth surfaces orthogonal to the first surface and the second surface and different from the pair of third surfaces.