AlN Crystal Growth Defect Reduction via Seed Preparation
Solution Overview
Problem
The growth of large-diameter bulk aluminum nitride (AlN) crystals is hindered by planar defects, which degrade crystal quality, reduce thermal conductivity, and impact optical transparency, making it challenging to produce high-quality AlN substrates for opto-electronic and electronic devices.
Innovation Solution
The solution involves a seed crystal free of planar defects, a defect-free seed attachment to a seed holder using a dense film, and controlled thermal gradients to minimize void formation and stress, allowing for high-quality AlN crystal growth with reduced planar defect densities and increased growth rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If large-diameter bulk AlN crystals are grown using conventional seeded growth techniques, then the crystal size and diameter can be increased, but planar defects form and degrade crystal quality
Solution Approach 1:
The seed crystal is prepared in advance with a specific orientation and defect-free structure before the bulk crystal growth process. The seed is carefully selected and positioned to ensure that the growth process initiates from a high-quality template, preventing planar defects from forming during subsequent crystal growth.
Solution Approach 2:
The patent optimizes growth parameters including temperature gradients, pressure conditions, and vapor flow rates to control the crystal growth process. By carefully controlling these parameters, the method achieves high growth rates while maintaining crystal quality and preventing planar defect formation in large-diameter crystals.
2Productivity
If high growth rates are achieved in AlN crystal growth, then productivity increases, but planar defects form and reduce thermal conductivity
Solution Approach 1:
The patent employs optimized temperature gradients and pressure conditions to achieve high growth rates without forming planar defects. The growth process is controlled to maintain thermal conductivity by preventing defect formation, thus simultaneously improving productivity and maintaining material reliability.
Solution Approach 2:
The growth process is monitored and controlled to detect and prevent planar defect formation. By implementing feedback control of growth parameters, the method maintains high growth rates while ensuring that thermal conductivity is preserved through prevention of defect-related degradation.
3Productivity
If planar defects are present in AlN crystals, then crystal growth can proceed, but optical transparency is reduced
Solution Approach 1:
A defect-free seed crystal is used to initiate growth, ensuring that the entire crystal structure develops without planar defects that would scatter light. This preliminary preparation of the growth template maintains optical transparency throughout the crystal while allowing productive growth to occur.
Solution Approach 2:
Growth parameters are optimized to achieve high growth rates while maintaining optical quality. The controlled environment and parameter optimization prevent planar defect formation, ensuring both productivity and optical transparency are achieved simultaneously.
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 growth of large-diameter, high-quality AlN crystals with reduced planar defect densities, enhancing crystal quality, thermal conductivity, and optical transparency, making them suitable for high-power and opto-electronic applications.
Implementation Method 1
vapor comprising or consisting essentially of aluminum and nitrogen is condensed within a growth chamber, thereby forming an AlN single crystal that increases in size along a growth direction
Implementation Method 2
a first (e.g., axial) non-zero thermal gradient is formed and maintained within the growth chamber in a direction substantially parallel to the growth direction, and a second (e.g., radial) non-zero thermal gradient is formed and maintained within the growth chamber in a direction substantially perpendicular to the growth direction
Data Source
AI summary
Bulk single crystal of aluminum nitride (AlN) having an areal planar defect density≤100 cm−2. Methods for growing single crystal aluminum nitride include melting an aluminum foil to uniformly wet a foundation with a layer of aluminum, the foundation forming a portion of an AlN seed holder, for an AlN seed to be used for the AlN growth. The holder may consist essentially of a substantially impervious backing plate.