Gettered Polycrystalline GaN for Low-Impurity Ammonothermal Growth
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Solution Overview
Problem
The challenge in manufacturing polycrystalline nitride materials for gallium nitride crystal growth is the presence of impurities, which affect the optical and electrical properties of optoelectronic devices, and existing methods are costly and inefficient in producing high-quality bulk gallium nitride crystals with low impurity levels.
Innovation Solution
A method involving the use of a polycrystalline group III metal nitride material with a columnar structure, specific grain size, and controlled oxygen content, along with a getter to reduce impurities, is employed. This method includes processing a group III metal in a crucible with a nitrogen-containing material under controlled temperature and pressure to form a crystalline nitride with a wurtzite structure and low optical absorption coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional MOCVD method is used to deposit GaN, then deposition can be performed from ammonia and organometallic compounds, but growth rates are slow and dislocation densities are high
Solution Approach 1:
The patent employs ammonothermal synthesis which utilizes phase transitions of ammonia (between liquid, gas, and supercritical states) to transport gallium nitride material. The process involves heating polycrystalline GaN in liquid ammonia to form a supersaturated solution, then allowing crystallization upon cooling or pressure reduction, achieving both high growth rates and low dislocation densities through controlled phase changes.
Solution Approach 2:
The patent uses an inert ammonia atmosphere throughout the synthesis process. Liquid ammonia provides a chemically inert environment that prevents oxidation and contamination of the gallium nitride material while enabling high-temperature processing without introducing dislocations or defects that would occur in oxidizing atmospheres.
2Productivity
If ammonothermal synthesis is used to grow GaN crystals, then scalability is improved, but significant levels of impurities cause crystals to be colored and reduce optical transparency
Solution Approach 1:
The patent performs preliminary purification of the polycrystalline GaN raw material before ammonothermal synthesis. The material is pre-treated to remove oxygen and other impurities that would otherwise incorporate into the growing crystals and cause coloration. This preliminary action ensures that the scalable ammonothermal process produces optically transparent crystals suitable for optoelectronic devices.
Solution Approach 2:
The patent carefully controls process parameters including temperature, pressure, and ammonia composition during ammonothermal synthesis. By optimizing these parameters, the process achieves both high scalability and production of optically transparent crystals with minimal impurity incorporation, resolving the contradiction between scalable production and optical quality.
3Ease of manufacture
If chemical vapor reaction process is used to synthesize polycrystalline nitride, then GaN powder can be produced, but oxygen impurities are present at levels from 16 to 160 ppm
Solution Approach 1:
The patent replaces conventional chemical vapor reaction processes that introduce oxygen impurities with ammonothermal synthesis in an inert ammonia atmosphere. This fundamental change in the chemical environment eliminates oxygen incorporation into the GaN lattice, producing material with oxygen content below detection limits while maintaining ease of manufacture through a streamlined single-step process.
Solution Approach 2:
The patent changes the chemical parameters of the synthesis process by using liquid ammonia as both solvent and atmosphere rather than conventional vapor-phase chemistry. This parameter change fundamentally alters the impurity profile of the produced GaN, eliminating oxygen while maintaining nitrogen incorporation, thereby achieving superior purity without complicating the manufacturing process.
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 cost-effective production of high-quality gallium nitride crystals with reduced impurities, resulting in clear and haze-free crystals suitable for optoelectronic devices, improving their efficiency and performance.
Implementation Method 1
providing a getter at a level of at least 100 ppm with respect to the source material into the chamber such that the getter contacts the source material
Implementation Method 2
processing the nitrogen-containing material with the group III metal in the chamber to form a polycrystalline group III metal nitride
Implementation Method 3
heating the chamber to a determined temperature
Implementation Method 4
pressurizing the chamber to a determined pressure
Data Source
AI summary
A gettered polycrystalline group III metal nitride is formed by heating a group III metal with an added getter in a nitrogen-containing gas. Most of the residual oxygen in the gettered polycrystalline nitride is chemically bound by the getter. The gettered polycrystalline group III metal nitride is useful as a raw material for ammonothermal growth of bulk group III nitride crystals.