Nitride Semiconductor Substrate Lattice Uniformity Control
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Solution Overview
Problem
Nitride semiconductor light emitting devices fabricated on free-standing substrates exhibit significant variations in emission wavelength, output, and lifetime, leading to reduced device yield due to uneven lattice constants and newly generated dislocation densities.
Innovation Solution
A nitride semiconductor free-standing substrate with a controlled lattice constant variation of ±12 ppm or less is developed, achieved by managing impurity concentration distribution during crystal growth, specifically by flattening the GaN thick film before reaching 350 μm and ensuring only c-face growth at the surface, thereby reducing lattice constant variations in the substrate plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a GaN layer is grown on a sapphire substrate by ELO or FIELO method, then dislocation density is reduced, but lattice constant variation and newly generated dislocations occur during subsequent epitaxial growth, leading to device performance variation
Solution Approach 1:
The invention changes the growth parameters by controlling the thickness of the GaN layer at approximately 350 μm and ensuring c-face orientation at the surface. This parameter control prevents lattice constant variation and new dislocation generation during subsequent epitaxial growth, thereby improving device performance consistency while maintaining manufacturing precision.
Solution Approach 2:
The invention performs preliminary flattening of the GaN thick film surface before device fabrication. By ensuring the surface is flattened and maintains c-face orientation prior to growing the light emitting device structure, the invention prevents subsequent dislocation generation and lattice constant variation, thereby improving reliability without sacrificing manufacturing precision.
2Reliability
If the GaN thick film is grown thicker to reduce dislocation density, then initial dislocation density decreases, but lattice constant variation increases and new dislocations are generated during device structure growth
Solution Approach 1:
The invention optimizes the GaN layer thickness to approximately 350 μm and controls the surface orientation to be c-face. This specific parameter combination achieves low dislocation density while preventing lattice constant variation and new dislocation generation during subsequent epitaxial growth, resolving the contradiction between reliability and manufacturing precision.
Solution Approach 2:
The invention performs preliminary surface flattening and orientation control before device fabrication. By ensuring the GaN surface is properly flattened and oriented toward the c-face direction at the specified thickness, the invention prevents subsequent dislocation generation and maintains lattice constant uniformity, thereby achieving both high reliability and manufacturing precision.
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 significantly reduces variations in emission wavelength and output, increases the proportion of devices meeting desired performance criteria, and enhances the yield of nitride semiconductor light emitting devices by minimizing dislocation densities and lattice constant deviations.
Implementation Method 1
flattening the GaN thick film before reaching 350 μm
Implementation Method 2
Nitride semiconductor layers constituting these devices are epitaxially grown on a base substrate by a vapor phase growth method such as MOVPE (metalorganic vapor phase epitaxy), MBE (molecular beam epitaxy), HVPE (hydride vapor phase epitaxy)
Data Source
AI summary
A nitride semiconductor free-standing substrate formed of a free-standing nitride-based compound semiconductor crystal that has a variation in lattice constant of ±12 ppm or less.