GaN Wafer Surface Quality via Low-Angle X-Ray Diffraction
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Solution Overview
Problem
The production of high-quality group III nitride wafers is hindered by the difficulty in growing bulk GaN crystals due to their high melting point and nitrogen vapor pressure, leading to high defect densities and surface damage during slicing, which complicates device fabrication.
Innovation Solution
The method involves slicing group III nitride ingots to produce wafers, polishing the surfaces to remove damaged layers, and using x-ray diffraction with an incident beam angle less than 15 degrees to evaluate and ensure sufficient surface quality for device fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bulk GaN crystals are grown using conventional methods, then wafer production becomes possible, but high defect densities and surface damage occur due to high melting point and nitrogen vapor pressure
Solution Approach 1:
The patent changes the growth parameters by using ammonothermal method with supercritical ammonia as solvent, growing at temperatures below the melting point of GaN (typically 500-700°C at high pressure), which avoids the harmful effects of high temperature nitrogen vapor pressure while still enabling bulk crystal growth with low defect densities
Solution Approach 2:
The patent introduces supercritical ammonia as an intermediary solvent medium that enables GaN crystal growth at lower temperatures. The ammonia acts as a carrier for gallium and nitrogen, allowing controlled crystal formation without direct high-temperature processing that causes surface damage and defects
2Ease of manufacture
If wafers are sliced from bulk crystals, then device fabrication becomes possible, but surface damage occurs during the slicing process
Solution Approach 1:
The patent performs preliminary surface preparation by polishing and etching the wafer surfaces after slicing to remove the damaged layer created during the slicing process, restoring surface quality before device fabrication
Solution Approach 2:
The patent uses chemical etching with specific reagents to selectively remove damaged surface layers while preserving the underlying high-quality crystal structure, changing the surface state from damaged to pristine through chemical treatment
3Ease of operation
If conventional x-ray diffraction is used with high incident angles, then measurement is easier, but surface damage detection is insufficient
Solution Approach 1:
The patent employs asymmetric low-angle x-ray diffraction geometry where the incident angle is deliberately set low (e.g., 2-10 degrees) and different from the detection angle, creating an asymmetric measurement configuration that enhances sensitivity to surface and near-surface crystal quality while maintaining measurement feasibility
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 enables the production of group III nitride wafers with reduced defect densities, suitable for device fabrication, by effectively removing damaged layers and assessing surface quality through x-ray diffraction, thereby improving the reliability of the wafers for optoelectronic and electronic devices.
Implementation Method 1
tested with x-ray diffraction. The x-ray incident beam is irradiated at an angle less than 15 degrees, and diffraction peak intensity is evaluated.
Implementation Method 2
x-ray diffraction with an incident beam angle less than 15 degrees to evaluate and ensure sufficient surface quality
Data Source
AI summary
The invention provides, in one instance, a group III nitride wafer sliced from a group III nitride ingot, polished to remove the surface damage layer and tested with x-ray diffraction. The x-ray incident beam is irradiated at an angle less than 15 degree and diffraction peak intensity is evaluated. The group III nitride wafer passing this test has sufficient surface quality for device fabrication. The invention also provides, in one instance, a method of producing group III nitride wafer by slicing a group III nitride ingot, polishing at least one surface of the wafer, and testing the surface quality with x-ray diffraction having an incident beam angle less than 15 degree to the surface. The invention also provides, in an instance, a test method for testing the surface quality of group III nitride wafers using x-ray diffraction having an incident beam angle less than 15 degree to the surface.