Gettered Polycrystalline GaN for Ammonothermal Crystal Growth
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Solution Overview
Problem
Conventional methods for growing gallium nitride crystals, such as ammonothermal synthesis, face challenges with significant impurities leading to colored crystals, which affect optical absorption and electrical conductivity, and are costly and inefficient.
Innovation Solution
A method involving a polycrystalline group III metal nitride material with a columnar structure and controlled oxygen content, processed using a crucible with a getter to minimize impurities and achieve a wurtzite structure with low optical absorption, is developed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ammonothermal synthesis is used to grow gallium nitride crystals, then crystal growth is achieved, but significant impurities are incorporated leading to colored crystals with poor optical and electrical properties
Solution Approach 1:
The polycrystalline nitride raw material is pre-treated by heating in ammonia atmosphere before crystal growth to reduce oxygen and other impurities. This preliminary purification step ensures lower impurity content in the final crystals, addressing the contradiction between achieving crystal growth and minimizing impurities that cause coloration and poor optical properties
Solution Approach 2:
The invention controls specific parameters including oxygen content below 100 ppm, water content below 100 ppm, and ammonia pressure between 73-300 atm during crystal growth. By optimizing these parameters, the process achieves high optical transparency while maintaining reliable crystal growth, resolving the contradiction between productivity and optical quality
2Productivity
If conventional MOCVD method is used for GaN deposition, then deposition is achieved from gas phase, but bulk layer formation is difficult due to limited growth rates
Solution Approach 1:
The invention employs ammonothermal synthesis that utilizes phase transitions of ammonia (liquid to supercritical fluid) to enable high-rate bulk crystal growth. The supercritical ammonia acts as a transport medium that dissolves polycrystalline nitride and deposits it as high-quality single crystals, achieving both high productivity and low dislocation density by exploiting the unique properties of supercritical phase
Solution Approach 2:
Supercritical ammonia serves as an intermediary medium that facilitates mass transport of gallium nitride from polycrystalline source to crystal growth interface. This intermediary enables efficient bulk material transfer while maintaining low dislocation densities, resolving the contradiction between growth rate and crystal quality
3Ease of manufacture
If polycrystalline nitride raw material is used for ammonothermal growth, then crystal growth is enabled, but residual impurities cause optical absorption and degrade electrical conductivity
Solution Approach 1:
The polycrystalline nitride raw material undergoes preliminary heating treatment in ammonia atmosphere to remove oxygen and volatile impurities before being used as source material. This pre-purification step ensures that even though polycrystalline material is used for scalable manufacturing, the resulting single crystals achieve high electrical conductivity with impurity levels below 100 ppm
Solution Approach 2:
The entire crystal growth process is conducted in an inert ammonia atmosphere that prevents oxidation and contamination of the polycrystalline nitride raw material and growing crystals. This controlled inert environment maintains electrical conductivity by preventing oxygen incorporation, while still allowing scalable manufacturing using polycrystalline starting material
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, improved optical transparency, and enhanced electrical properties, suitable for various optoelectronic applications.
Implementation Method 1
providing a getter at a level of at least 100 ppm with respect to the group III metal
Implementation Method 2
The composition has an oxygen content in the group III metal nitride material provided as a group III metal oxide or as a substitutional impurity within a group III metal nitride is less than about 10 parts per million (ppm)
Implementation Method 3
processing the nitrogen-containing material with the group III metal in the chamber to form a polycrystalline group III metal nitride in at least the crucible
Implementation Method 4
heats the chamber to a determined temperature
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.