GaN Flux Growth Substrate Shielding Nitrogen Face
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Solution Overview
Problem
Existing methods for growing gallium nitride (GaN) single crystals on hetero-substrates often result in crystal cracks due to lattice constant and expansion coefficient mismatches, and three-dimensional growth on the nitrogen-face of self-standing substrates leads to poor crystal quality and material waste.
Innovation Solution
A method involving a self-standing substrate with a c-plane main surface is used, where the nitrogen-face is either not exposed to the flux mixture or shielded, allowing growth only on the gallium-face, with the substrate positioned to maximize uniform flux distribution and prevent crystal growth on the nitrogen-face.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a hetero-substrate is used for growing GaN single crystal, then the substrate can be provided, but cracks are likely to be generated due to lattice constant and expansion coefficient differences
Solution Approach 1:
The patent uses a self-standing substrate made of the same Group III nitride-based compound semiconductor material as the crystal to be grown, ensuring homogeneous lattice constant and expansion coefficient. This eliminates the lattice mismatch and thermal expansion difference between hetero-substrates, preventing crack generation during high-temperature growth and cooling processes.
2Productivity
If a self-standing substrate with c-plane main surface is used, then crystal growth can occur, but three-dimensional growth occurs on the nitrogen-face causing poor crystal quality and material waste
Solution Approach 1:
The patent applies different surface treatments to different faces of the self-standing substrate: the gallium-face is treated to promote uniform two-dimensional crystal growth, while the nitrogen-face is treated to suppress crystal growth. This local differentiation ensures high crystal quality on the gallium-face while preventing three-dimensional growth and material waste on the nitrogen-face.
3Productivity
If the nitrogen-face is exposed to flux mixture, then crystal growth occurs, but material waste increases and crystal quality deteriorates
Solution Approach 1:
The patent extracts or removes the nitrogen-face from the flux mixture environment by positioning the substrate such that only the gallium-face is exposed to the flux mixture. This selective exposure prevents unnecessary crystal growth on the nitrogen-face, eliminating material waste while maintaining high productivity through efficient use of the exposed gallium-face for crystal growth.
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 growth rate, homogeneity, and quality, reducing material waste and crack formation, thereby improving yield and production efficiency.
Implementation Method 1
nitrogen (N) is reacted with a Group III element of gallium (Ga), aluminum (Al), or indium (In) in a flux mixture containing an alkali metal, to thereby grow a Group III nitride-based compound semiconductor crystal
Implementation Method 2
a line normal to the +c-plane of the seed crystal is maintained in a direction within ±30° with respect to a horizontal plane
Data Source
AI summary
In the production of GaN through the flux method, deposition of miscellaneous crystals on the nitrogen-face of a GaN self-standing substrate and waste of raw materials are prevented. Four arrangements of crucibles and a GaN self-standing substrate are exemplified. In FIG. 1A, a nitrogen-face of a self-standing substrate comes into close contact with a sloped flat inner wall of a crucible. In FIG. 1B, a nitrogen-face of a self-standing substrate comes into close contact with a horizontally facing flat inner wall of a crucible, and the substrate is fixed by means of a jig. In FIG. 1C, a jig is provided on a flat bottom of a crucible, and two GaN self-standing substrates are fixed by means of the jig so that the nitrogen-faces of the substrates come into close contact with each other. In FIG. 1D, a jig is provided on a flat bottom of a crucible, and a GaN self-standing substrate is fixed on the jig so that the nitrogen-face of the substrate is covered with the jig. A flux mixture of molten gallium and sodium is charged into each crucible, and a GaN single crystal is grown on a gallium-face under pressurized nitrogen.