Flux-Soluble Substrate Dissolution for GaN Crystal Growth
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Solution Overview
Problem
Conventional methods for growing Group III nitride compound semiconductor crystals using the flux method face challenges such as high dislocation density, crack generation, and increased production costs, particularly when using GaN single-crystal free-standing substrates, and issues with maintaining Group III element content during crystal growth.
Innovation Solution
The method involves growing semiconductor crystals on a substrate partially or entirely formed of a flux-soluble material, which is then dissolved in the flux, either during or after crystal growth, to reduce dislocation density, control impurity concentration, and lower production costs by using less expensive materials like silicon or GaAs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a GaN single-crystal free-standing substrate is employed as a base substrate, then crack generation in the semiconductor crystal is suppressed, but production cost increases significantly
Solution Approach 1:
The invention employs a sapphire substrate as a temporary, inexpensive base for growing the semiconductor crystal layer. After the crystal layer reaches sufficient thickness and quality, the sapphire substrate is removed (etched away), leaving only the high-quality GaN crystal. This disposable approach avoids the need for expensive free-standing GaN substrates while achieving crack-free crystals.
Solution Approach 2:
The invention separates the substrate function from the crystal growth function. The sapphire substrate serves only as a temporary support during growth, while the actual crystal quality is determined by the grown layer itself. This segmentation allows using cheap substrates for support while achieving high crystal quality in the separate grown layer.
2Ease of manufacture
If a template substrate formed by growing GaN on a sapphire substrate through MOCVD is employed as a seed crystal, then production cost is reduced, but a large number of cracks are generated in the semiconductor crystal during removal from the reaction chamber due to thermal expansion coefficient difference
Solution Approach 1:
The sapphire substrate is used as a temporary, inexpensive support that is discarded after serving its purpose. It enables cost-effective crystal growth but is removed afterward since it causes cracks due to thermal expansion mismatch. This disposable approach resolves the contradiction between low cost and crack-free crystals.
Solution Approach 2:
The invention extracts the problematic sapphire substrate from the final product structure. The substrate is used during growth but then removed (extracted) before the crystal is considered complete, eliminating the source of crack generation while maintaining the cost advantage of using sapphire as a growth substrate.
3Device complexity
If no Group III element is supplied to the flux during crystal growth, then production process is simplified, but the Group III element content of the flux is reduced, resulting in decreased crystal growth rate
Solution Approach 1:
The invention changes the composition parameters of the flux by adding Group III elements during the growth process. This parameter adjustment maintains the Group III element content in the flux, thereby sustaining a high crystal growth rate throughout the growth period without overly complicating the production process.
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 crack density, increases crystal growth rate, and simplifies substrate removal, while reducing production costs by employing inexpensive flux-soluble materials and allowing for controlled impurity addition, resulting in high-quality semiconductor crystals with reduced dislocation density.
Implementation Method 1
dissolving the flux-soluble material in the flux from a surface of the substrate that is opposite the surface on which the semiconductor crystal is grown
Data Source
AI summary
The present invention provides a method for producing a Group III nitride compound semiconductor crystal, the semiconductor crystal being grown through the flux method employing a flux. At least a portion of a substrate on which the semiconductor crystal is to be grown is formed of a flux-soluble material. While the semiconductor crystal is grown on a surface of the substrate, the flux-soluble material is dissolved in the flux from a surface of the substrate that is opposite the surface on which the semiconductor crystal is grown. Alternatively, after the semiconductor crystal has been grown on a surface of the substrate, the flux-soluble material is dissolved in the flux from a surface of the substrate that is opposite the surface on which the semiconductor crystal has been grown. The flux-soluble material is formed of silicon. Alternatively, the flux-soluble material or the substrate is formed of a Group III nitride compound semiconductor having a dislocation density higher than that of the semiconductor crystal to be grown.