Semi-Insulating GaN Substrates via Ammonothermal Growth
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Solution Overview
Problem
Current methods for manufacturing semi-insulating gallium nitride crystals face challenges such as high dislocation densities, poor transparency, and high costs, with existing substrates being electrically conductive and limited in size, making them unsuitable for large-scale optoelectronic device production.
Innovation Solution
A method involving the use of high-quality gallium nitride seed crystals and a polycrystalline nutrient material processed in supercritical ammonia with a getter and compensatory dopants to achieve low-cost, transparent, and high-crystallographic quality semi-insulating gallium nitride crystals, which are then recrystallized to form large, semi-insulating substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MOCVD method is used to deposit GaN from ammonia and organometallic compounds, then deposition can be performed successfully, but bulk layer formation is difficult and dislocation densities are high
Solution Approach 1:
The invention changes the fundamental parameters of the deposition process by switching from conventional MOCVD to ammonothermal method, using supercritical ammonia as solvent and operating at elevated temperatures and pressures to achieve low dislocation density bulk GaN layers
Solution Approach 2:
The invention introduces an intermediary substance (ammonia) that serves dual purposes: as a solvent for transporting GaN from polycrystalline to single crystal form, and as a medium that enables controlled crystallization with reduced dislocation densities
2Reliability
If transition metal dopants are added to compensate donor species and impart semi-insulating character, then resistivity increases, but crystal quality deteriorates and free standing bulk wafers cannot be obtained
Solution Approach 1:
The invention uses oxygen as a disposable dopant that can be easily introduced and controlled during the ammonothermal growth process, replacing expensive and problematic transition metal dopants while maintaining semi-insulating properties
Solution Approach 2:
The invention changes the doping approach by using oxygen instead of transition metals, and controls the doping level through process parameters to achieve both semi-insulating character and high crystal quality simultaneously
3Reliability
If high pressure and high temperature crystallization from molten mixture is used, then highly resistive GaN bulk crystals are obtained, but crystal size is limited to about 1 cm
Solution Approach 1:
The invention uses supercritical ammonia as an intermediary solvent that enables transport and crystallization of GaN at lower pressures compared to molten salt methods, allowing growth of larger crystals up to 2 inches in diameter
Solution Approach 2:
The invention changes the pressure regime from very high pressure (0.5-2.0 GPa) to moderate pressure (up to 730 atm), and utilizes the unique properties of supercritical ammonia to enable large-scale crystal growth while maintaining high resistivity
4Reliability
If Fe or Co doping is performed by ammonothermal method, then semi-insulating GaN crystals are synthesized, but crystals become colored (reddish/amber or black) instead of transparent
Solution Approach 1:
The invention replaces transition metal dopants (Fe, Co) that cause coloring with oxygen dopant that maintains transparency, while still achieving semi-insulating properties through controlled oxygen incorporation during ammonothermal 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 enables the production of high-quality, semi-insulating gallium nitride substrates with low dislocation densities and improved transparency, suitable for large-scale optoelectronic applications, while reducing production costs and achieving resistivity suitable for commercial electronic use.
Implementation Method 1
dissolving polycrystalline GaN in supercritical ammonia and recrystallizing it onto one or more single crystal GaN seed plates
Implementation Method 2
recrystallizing it onto one or more single crystal GaN seed plates
Implementation Method 3
The oxygen content in the bulk GaN may be greater than 1×10^18 atoms per cubic centimeter and less than 1×10^20 atoms per cubic centimeter, and the bulk GaN may have a semi-insulating character
Data Source
AI summary
A large-area, high-purity, low-cost single crystal semi-insulating gallium nitride that is useful as substrates for fabricating GaN devices for electronic and/or optoelectronic applications is provided. The gallium nitride is formed by doping gallium nitride material during ammonothermal growth with a deep acceptor dopant species, e.g., Mn, Fe, Co, Ni, Cu, etc., to compensate donor species in the gallium nitride, and impart semi-insulating character to the gallium nitride.