GaN Substrate Tilt Angle for Crack Resistance
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Solution Overview
Problem
GaN substrates grown on heterogeneous substrates are prone to cracking and have high production costs due to low growth rates and crystal defects, leading to stress and reduced device characteristics, especially when indium-containing layers are grown, resulting in low luminous efficiency due to internal strain and piezoelectric fields.
Innovation Solution
A GaN substrate with a primary surface tilted between 20 to 160 degrees relative to the C-plane, particularly in the [1-100] direction, is developed to enhance fracture toughness and reduce cracking, with a preferred angle range of 71 to 79 degrees for optimal cleavage characteristics, thereby minimizing internal strain and improving device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If GaN substrate is grown on heterogeneous substrate, then production cost is reduced and growth rate is improved, but crack resistance deteriorates and device characteristics worsen
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the heterogeneous substrate and the GaN layer. This buffer layer gradually transitions the lattice structure and thermal expansion properties, allowing the GaN to grow with reduced stress and fewer cracks while maintaining the benefits of using a cost-effective heterogeneous substrate.
Solution Approach 2:
The patent modifies the substrate surface properties by controlling the tilt angle of the primary surface relative to the C-plane. By adjusting this geometric parameter, the patent optimizes stress distribution and crack propagation resistance, enabling better crack resistance while maintaining high growth rates on heterogeneous substrates.
2Adaptability or versatility
If indium-containing layer is grown on GaN substrate, then emission wavelength is adjusted, but internal strain increases and piezoelectric field strengthens causing low luminous efficiency
Solution Approach 1:
The patent applies different tilt angles to different regions or layers of the substrate. By locally adjusting the primary surface tilt angle in the indium-containing layer, the patent reduces the piezoelectric field strength in that specific region, thereby improving carrier recombination and luminous efficiency while maintaining the desired emission wavelength.
Solution Approach 2:
The patent introduces a new dimensional parameter - the tilt angle of the primary surface - to control the piezoelectric field. By rotating the growth direction relative to the C-plane, the patent creates a geometric configuration that reduces internal strain and enhances carrier recombination efficiency.
3Object-generated harmful factors
If primary surface is tilted at large angle with respect to C-plane, then piezoelectric field is reduced, but crack resistance deteriorates
Solution Approach 1:
The patent optimizes the tilt angle parameter to a specific range (20-160 degrees) where it achieves the desired balance. By precisely controlling this geometric parameter, the patent reduces the piezoelectric field strength sufficient to improve carrier recombination while maintaining crack resistance through optimized stress distribution.
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
The tilted GaN substrate significantly reduces cracking and enhances production yield by maintaining high fracture toughness and improving luminous efficiency, making it suitable for short-wavelength light emitting devices like laser diodes with reduced piezoelectric fields and improved cleavage properties.
Implementation Method 1
a large piezoelectric field is produced in the indium-containing layer to lower a recombination probability, resulting in low luminous efficiency
Implementation Method 2
The GaN-based compound semiconductor is grown by a method such as Molecular Beam Epitaxy (MBE) or Metal Organic Chemical Vapor Deposition (MOCVD)
Data Source
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AI summary
A gallium nitride (GaN) substrate hard to break and capable of enhancing a production yield is provided. The GaN substrate comprises a primary surface. The primary surface is tilted at an angle in the range of 20 to 160 degrees with respect to the C-plane of the substrate. The substrate has a fracture toughness of more than or equal to 1.36 MN/m3/2.