Nitride Semiconductor Light Emitting Device Warpage Reduction
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Solution Overview
Problem
Nitride semiconductor light emitting devices formed on sapphire substrates face issues with reduced light emitting area due to electrode placement, increased current density, heat generation, and warpage caused by substrate removal, leading to decreased reliability and efficiency.
Innovation Solution
The method involves forming grooves in the stacked nitride semiconductor layers to create a sacrifice layer that is filled and later removed, allowing for efficient light emission from the sides and reducing warpage by dividing the GaN layer, thereby improving the mechanical strength and reliability of the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sapphire single crystal substrate is used, then excellent nitride semiconductor properties can be achieved, but the device generates excessive heat due to low heat conductivity
Solution Approach 1:
The device is divided into two separate sides with electrodes positioned on opposite surfaces. The n-type electrode is formed on the bottom surface while the p-type electrode is formed on the top surface, allowing current to flow vertically through the light emitting layer rather than horizontally. This segmentation resolves the heat generation issue by eliminating the need for both electrodes to be on the same side, thereby reducing localized current density and heat accumulation.
2Illumination intensity
If both positive and negative electrodes are positioned on one side, then light extraction can be achieved, but current density increases locally causing heat generation
Solution Approach 1:
Instead of positioning both electrodes on the same side (conventional approach), the invention inverts the arrangement by placing the positive electrode on the top surface and the negative electrode on the bottom surface. This inversion allows current to flow vertically through the light emitting layer, reducing localized current density and heat generation while maintaining effective light extraction through the transparent substrate.
3Ease of manufacture
If the n-type semiconductor is exposed by etching the light emitting layer to form the negative electrode, then electrode formation is achieved, but the light emitting area is reduced
Solution Approach 1:
The negative electrode is formed on the bottom surface of the substrate rather than on the top surface by etching through the light emitting layer. This dimensional change allows the electrode to be positioned in a different plane, eliminating the trade-off between ease of manufacture and light emitting area. The light emitting layer remains intact on the top surface while the bottom surface provides access for electrode formation.
4Temperature
If a conductive substrate is attached and the sapphire substrate is removed, then heat dissipation is improved, but warpage occurs due to mechanical strength reduction
Solution Approach 1:
A support structure is formed on the bottom surface of the substrate before removing the sapphire substrate. This preliminary action provides mechanical reinforcement to the device, preventing warpage that would otherwise occur when the rigid sapphire substrate is removed. The support structure maintains structural integrity while allowing the device to benefit from improved heat dissipation.
5Strength
If the GaN layer is divided to reduce warpage, then mechanical strength is improved, but light emission from sides may be affected
Solution Approach 1:
The GaN layer is divided into multiple regions with different properties. The light emitting layer maintains its integrity in areas where light emission is critical, while other regions are divided to reduce warpage and improve mechanical strength. This local differentiation allows the device to simultaneously achieve both mechanical stability and effective light emission without compromising either function.
Data Source
AI summary
The present invention provides a production method for a nitride semiconductor light emitting device, which warps less after removing the substrate, and which can emit light from the side thereof; specifically, the present invention provides a production method for a nitride semiconductor light emitting device comprising: forming stacked layers by stacking at least an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer on a substrate in this order; forming grooves which divide the stacked layers so as to correspond to nitride semiconductor light emitting devices to be produced; filling the grooves with a sacrifice layer; and forming a plate layer on the p-type semiconductor layer and the sacrifice layer by plating.