Nitride Semiconductor Light Emitting Element Sapphire Substrate Thickness Optimization
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Solution Overview
Problem
Conventional nitride semiconductor light emitting elements with sapphire substrates face inefficiencies in light extraction due to the thickness of the sapphire substrate, which affects the proportion of light output and extraction efficiency, particularly when the substrate thickness is reduced for chip formation.
Innovation Solution
Optimizing the thickness of the sapphire substrate relative to the chip size, specifically making it 0.45 to 1 times the average length of the chip's sides, improves light extraction efficiency by enhancing the proportion of sideways output light, thereby increasing the overall light extraction from the nitride semiconductor light emitting elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the sapphire substrate thickness is reduced to facilitate chip dicing and handling, then the ease of manufacture and chip division is improved, but the light extraction efficiency deteriorates due to increased total internal reflection at the back surface
Solution Approach 1:
The patent converts the harmful effect of total internal reflection at the back surface into a beneficial light extraction mechanism. By optimizing the substrate thickness to be equal to or greater than the chip size, the light that would normally be trapped by total internal reflection is instead allowed to reach the back surface and exit sideways, transforming a loss mechanism into a useful light output path that extracts approximately 95% of emitted light.
2Loss of energy
If the sapphire substrate thickness is increased to improve light extraction efficiency, then the light extraction efficiency is improved, but the ease of chip dicing and handling deteriorates
Solution Approach 1:
The patent changes the critical parameter of substrate thickness from the conventional range (100 μm ± 30 μm) to a new range where thickness is equal to or greater than the chip size. This parameter change simultaneously optimizes both light extraction efficiency (achieving approximately 95%) and maintains manufacturability, as the thick substrate can still be diced using conventional methods while providing superior optical performance.
3Ease of operation
If the conventional substrate thickness of 100 μm ± 30 μm is used, then the ease of chip handling is maintained, but the light extraction efficiency is limited due to total internal reflection at the back surface
Solution Approach 1:
The patent shifts the light extraction paradigm from a primarily vertical extraction mode (through the thin back surface) to a sideways extraction mode (through the side surfaces). By increasing the substrate thickness to match or exceed chip size, the light propagation path extends into the lateral dimension, allowing light to exit through the side surfaces of the chip, thereby achieving approximately 95% light extraction efficiency while maintaining conventional chip handling practices.
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 optimization allows for the efficient extraction of approximately 95% or greater of the emitted light from the nitride semiconductor light emitting elements, improving light extraction efficiency and addressing the limitations of conventional substrate thickness in nitride semiconductor light emitting elements.
Implementation Method 1
a back-surface-emitting type nitride semiconductor light emitting element that outputs light from an active layer to the outside of the element through the sapphire substrate
Implementation Method 2
the light traveling toward the upper surface is reflected by the upper surface of the chip downward, so that the reflected light together with the light traveling toward the lower surface is transmitted through the sapphire substrate
Data Source
AI summary
A nitride semiconductor light emitting element comprises a sapphire substrate, and a light emitting element structure portion that has a plurality of nitride semiconductor layers formed on the sapphire substrate. The nitride semiconductor light emitting element is a back-surface-emitting type nitride semiconductor light emitting element that outputs light from the light emitting element structure portion to an outside of the element through the sapphire substrate. The nitride semiconductor light emitting element is divided into a chip whose planarly-viewed shape is a square or a rectangle. A thickness of the sapphire substrate is 0.45 to 1 times an average length of sides of the planarly-viewed shape of the chip.