Off-Cut GaN Substrate Control for Low-Strain LD Production
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Solution Overview
Problem
The yield during laser diode (LD) production using c-plane GaN substrates obtained from common HVPE methods is low due to strains, pits, and substrate shape issues, necessitating improvements to enhance device performance.
Innovation Solution
A GaN substrate with a main surface inclined by 0° to 20° from the (0001) plane, having specific dislocation densities, reduced local strains, and controlled off-cut angle fluctuations, along with controlled impurity concentrations, is developed to address these issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a common HVPE method is used to obtain a GaN crystal, then the dislocation density is reduced, but local strains and pits remain on the main surface causing yield deterioration
Solution Approach 1:
The patent applies parameter changes by precisely controlling the off-cut angle of the main surface within 0° to 20° from the (0001) plane and controlling the fluctuation range of off-cut angle to 0.2 degrees or less. This parameter optimization eliminates local strains and pits while maintaining low dislocation density, thereby resolving the contradiction between manufacturing precision and production yield.
2Ease of manufacture
If the off-cut angle fluctuation is not controlled, then the substrate shape is easier to manufacture, but yield deterioration occurs due to substrate shape issues
Solution Approach 1:
The patent establishes specific parameter ranges for off-cut angle (0° to 20°) and its fluctuation (0.2 degrees or less), which optimizes the balance between ease of manufacture and production yield. These controlled parameters ensure substrate shape consistency without excessive manufacturing complexity.
3Device complexity
If impurity concentrations are not controlled, then the crystal growth process is simpler, but device performance deteriorates
Solution Approach 1:
The patent controls impurity concentrations including Si concentration at 5×10¹⁶ to 1×10¹⁸ atoms/cm³ and O concentration at 1×10¹⁶ to 1×10¹⁸ atoms/cm³. This parameter control ensures high device performance while maintaining a manageable crystal growth process through defined compositional ranges.
Data Source
Figure 1~2
Figure 3
Figure 4(a)~4(c)
AI summary
The present invention relates to a gallium nitride substrate having a main surface inclined by 0° to 20° from a (0001) plane and having an area of 15 cm2 or more. The main surface has a dislocation density of 5 × 106 cm-2 or less, and a number density of local strains in a crossed Nicols image obtained by a sensitive color method for the main surface is 0.5cm-2 or less.