GaN Substrate Thermal Expansion Control for Defect Reduction
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Solution Overview
Problem
Current Group III nitride semiconductor substrates face challenges such as lattice mismatch with sapphire substrates, leading to defects and reduced crystalline quality, which affects the performance of high-brightness LEDs and laser diodes, and existing methods for evaluating vacancy defect concentration are inadequate and difficult to implement on a large scale.
Innovation Solution
A high-quality Group III nitride semiconductor substrate with specific conditions: a thermal expansion coefficient ratio Δα/α ≤ 0.1, a dislocation density ≤ 2×10^6 cm^-2, and a total electrically active impurity concentration ≤ 1×10^19 cm^-3, which helps in suppressing vacancy defects and improving high-temperature operating characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a low temperature growth buffer layer is used to enable single crystal GaN growth, then epitaxial growth becomes possible, but the lattice mismatch between sapphire substrate and epitaxial GaN layer cannot be eliminated, resulting in numerous defects
Solution Approach 1:
The patent extracts and eliminates the sapphire substrate from the final product structure by creating a free-standing GaN substrate. This removes the source of lattice mismatch and thermal expansion differences, thereby eliminating the root cause of defects while preserving the ability to grow single crystal GaN
Solution Approach 2:
The patent changes the substrate material parameter from sapphire to GaN, and controls the thermal expansion coefficient ratio (Δα/α) to be not more than 0.1. This parameter change eliminates lattice mismatch issues and reduces defect density while maintaining single crystal growth capability
2Manufacturing precision
If high temperature MOVPE is used to grow GaN single crystal, then epitaxial growth is achieved, but temperature lowering after growth causes warpage due to thermal expansion coefficient difference between sapphire and GaN
Solution Approach 1:
The patent changes the substrate material to GaN with controlled thermal expansion coefficient (Δα/α ≤ 0.1), which matches GaN's thermal expansion characteristics. This eliminates the thermal expansion mismatch that causes warpage during temperature changes, while preserving high-quality epitaxial growth capability
3Productivity
If conventional GaN substrate methods are used, then substrate production is achieved, but vacancy defect concentration remains high, affecting high-temperature device performance
Solution Approach 1:
The patent controls the thermal expansion coefficient ratio (Δα/α) to be not more than 0.1 and maintains specific dislocation density (≤2×10^6 cm^-2) and impurity concentration (≤1×10^19 cm^-3). These parameter controls suppress vacancy defect formation and reduce defect concentration, improving high-temperature device reliability while maintaining production capability
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 substrate significantly reduces vacancy defect concentration and enhances the reliability and lifetime of LED elements, particularly under high-temperature conditions, by controlling substrate warpage, dislocation density, and impurity levels, resulting in improved thermal and optical properties.
Implementation Method 1
a ratio of Δα/α is not more than 0.1, where α is a thermal expansion coefficient calculated from a temperature change in outside dimension of the substrate, and Δα is a difference (α−αL) between the thermal expansion coefficient α and a thermal expansion coefficient αL calculated from a temperature change in lattice constant of the substrate
Data Source
AI summary
A Group III nitride semiconductor substrate is formed of a Group III nitride single crystal, and has a diameter of not less than 25.4 mm and a thickness of not less than 150 μm. The substrate satisfies that a ratio of Δα/α is not more than 0.1, where α is a thermal expansion coefficient calculated from a temperature change in outside dimension of the substrate, and Δα is a difference (α−αL) between the thermal expansion coefficient α and a thermal expansion coefficient αL calculated from a temperature change in lattice constant of the substrate.