Nitride Semiconductor Light Emitting Device Substrate Removal
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Solution Overview
Problem
Conventional nitride semiconductor light emitting devices face issues with substrate removal, leading to thermal damage and reduced luminance due to lattice mismatch between sapphire substrates and GaN single crystals, which limits current efficiency and makes the devices vulnerable to electrostatic discharge.
Innovation Solution
A method involving the sequential growth of nitride layers on a preliminary substrate, followed by selective removal and polishing to form uneven surface structures, which reduces thermal stress and allows for the retention of the substrate, enabling improved light extraction efficiency and electrode arrangement without complete laser lift-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a sapphire substrate is used for growing nitride single crystals, then single-crystal growth is enabled, but thermal stress is generated due to lattice mismatch causing damage to nitride single crystals
Solution Approach 1:
The substrate removal process is segmented into multiple steps: first polishing the bottom surface to reduce thickness, then selectively removing portions to form uneven surface structures, and finally removing remaining portions. This gradual segmentation approach reduces thermal stress concentration and prevents damage to the nitride single crystals during substrate removal.
Solution Approach 2:
The bottom surface of the sapphire substrate is polished to reduce its thickness before complete removal. This preliminary action weakens the substrate structure in advance, allowing for controlled removal that minimizes thermal stress and prevents damage to the grown nitride single crystals during the subsequent substrate removal process.
2Ease of manufacture
If complete laser lift-off is used to remove the substrate, then substrate removal is achieved, but thermal damage occurs to the light emitting structure
Solution Approach 1:
The bottom surface is polished to reduce substrate thickness before complete removal, creating a preliminary weakened state that allows for safer, more controlled removal processes that minimize thermal damage to the light emitting structure.
Solution Approach 2:
The substrate removal is divided into stages: initial polishing to reduce thickness, selective removal to form uneven structures, and final removal of remaining portions. This segmented approach replaces complete laser lift-off with a gentler, multi-step process that avoids thermal damage.
3Ease of manufacture
If electrodes are arranged horizontally on insulating substrate, then electrode formation is simplified, but current flow is narrowed decreasing current efficiency
Solution Approach 1:
Instead of arranging electrodes horizontally on the insulating sapphire substrate, the invention inverts the approach by removing the sapphire substrate and forming electrodes vertically on the nitride layers. This inversion enables broader current flow paths and improved current efficiency while maintaining ease of manufacture through the vertical electrode configuration.
4Strength
If sapphire substrate is retained throughout the process, then structural support is maintained, but light extraction efficiency is reduced
Solution Approach 1:
The sapphire substrate is segmented and partially removed rather than retained completely. The bottom surface is polished and portions are selectively removed to form uneven surface structures, providing structural support during processing while enabling improved light extraction efficiency in the final device configuration.
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 approach enhances the luminance, reliability, and light extraction efficiency of nitride semiconductor light emitting devices by minimizing thermal damage and facilitating vertical electrode arrangement, thereby improving current efficiency and reducing electrostatic discharge vulnerability.
Implementation Method 1
polishing a bottom surface of the preliminary substrate to reduce a thickness of the preliminary substrate
Implementation Method 2
the heat generated from a process of emitting a laser beam to the sapphire substrate 11
Implementation Method 3
the heat generated from a process of emitting a laser beam to the sapphire substrate 11 is transferred laterally along the sapphire substrate 11
Implementation Method 4
forming uneven surface structures by machining a surface of the preliminary substrate
Data Source
AI summary
There are provided a method of manufacturing a nitride semiconductor light emitting device and the nitride semiconductor light emitting device manufactured by the method, the method including: forming a light emitting structure by sequentially growing a first conductivity nitride layer, an active layer and a second conductivity type nitride layer on a preliminary substrate for nitride single crystal growth; separating the light emitting structure in accordance with a size of final light emitting device; forming a conductive substrate on the light emitting structure; polishing a bottom surface of the preliminary substrate to reduce a thickness of the preliminary substrate; forming uneven surface structures by machining the preliminary substrate; selectively removing the preliminary substrate to expose portions of the first conductivity type nitride layer; and forming electrodes on the portions of the first conductivity type nitride layer exposed by selectively removing the preliminary substrate.