Group III Nitride Crystal Growth With Staged Alkali Metal Control
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Solution Overview
Problem
Existing methods for growing group III nitride single crystals, such as the flux method using a Ga-Na melt, result in the formation of inclusions and reduce crystal quality due to the presence of alkaline earth metals like Ca, leading to the generation of miscellaneous crystals and macrostep growth.
Innovation Solution
A method involving the use of a mixed melt with a controlled concentration of alkali metals, specifically Na, to form initial nuclei, followed by a planarization and thickening process, while adjusting the concentration of alkaline earth metals like Ca to promote lateral growth and prevent inclusions, using a jig and apparatus to manage metal addition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If alkaline earth metals such as Ca are added to the Ga-Na melt to improve wettability and prevent macrostep growth, then crystal quality is improved, but miscellaneous crystals are generated in large amounts making it difficult to form intended initial nuclei
Solution Approach 1:
The patent applies preliminary action by performing the initial nucleus formation step first with a Ga-Na melt containing minimal alkaline earth metals (0.001-0.05 mass%) to ensure reliable nucleus formation, then subsequently adding larger amounts of alkaline earth metals in later growth stages to improve crystal quality and prevent macrostep growth. This sequential approach resolves the contradiction by addressing each requirement at the appropriate stage.
Solution Approach 2:
The patent segments the crystal growth process into distinct stages: (1) initial nucleus formation with low alkaline earth metal content, (2) intermediate growth with increasing alkaline earth metal content, and (3) final thickening with high alkaline earth metal content. This segmentation allows each stage to optimize for its specific purpose, resolving the contradiction between reliable nucleus formation and high crystal quality.
2Manufacturing precision
If high concentration of alkaline earth metals is used to promote lateral growth and prevent inclusions, then macrostep growth is prevented, but miscellaneous crystal formation increases significantly
Solution Approach 1:
The patent uses preliminary action by establishing a foundation of intentional nuclei in the first growth stage with minimal alkaline earth metals, ensuring that subsequent stages with high alkaline earth metal concentrations will grow only the desired single crystals rather than generating miscellaneous crystals. This preliminary nucleus formation prevents harmful miscellaneous crystal formation in later high-concentration stages.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the alkaline earth metal concentration throughout the growth process: starting with 0.001-0.05 mass% for nucleus formation, increasing to 0.05-0.5 mass% for intermediate growth, and finally using 0.5-5.0 mass% for thickening. This controlled parameter change prevents miscellaneous crystal formation while achieving planar surfaces.
3Manufacturing precision
If repeated immersion and heating processes are performed to planarize the crystal surface, then macrostep growth is reduced, but the process complexity and time increase
Solution Approach 1:
The patent applies continuity of useful action by performing the planarization function continuously throughout the growth process rather than as separate repeated cycles. The alkaline earth metals are added progressively during continuous growth, maintaining planarization action throughout the entire thickening stage, which reduces total process time while achieving the same surface planarity.
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 crystal quality by reducing miscellaneous crystal formation and macrostep growth, resulting in improved planarization and thickening of group III nitride single crystals.
Implementation Method 1
immersing a seed substrate, on which a plurality of seed crystals each made of a group III nitride single crystal is formed, into a mixed melt including a group III metal and Na and stored in a crucible to grow a group III nitride single crystal from each seed crystal to thereby form a plurality of initial nuclei
Implementation Method 2
heated under a nitrogen atmosphere to grow the group III nitride single crystal from the initial nuclei and fill a gap between the initial nuclei adjacent to each other with the group III nitride single crystal to thereby form a planarized crystal surface
Implementation Method 3
immersing the seed substrate having the planarized crystal surface into a mixed melt stored in a crucible to thereby form a thickened group III nitride single crystal on the seed substrate
Data Source
AI summary
A method of growing a group III nitride single crystal, including steps of forming a plurality of initial nuclei on a seed substrate having seed crystals made of a group III nitride single crystal formed thereon by immersing the substrate into a mixed melt in a crucible; forming a planarized crystal surface by immersing into a mixed melt in a crucible and pulling up therefrom to heat the substrate; and forming a thickened group III nitride single crystal on the seed substrate. When forming the plurality of initial nuclei, a concentration of alkali metals or alkaline earth metals other than Na in the mixed melt is set to 0.001 mol % or less, and when forming the thickened group III nitride single crystal, a concentration of alkali metals or alkaline earth metals other than Na in the mixed melt is set higher than that when forming the plurality of initial nuclei.