GaN Single Crystal Growth via NH4Cl Solvent
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for growing gallium nitride (GaN) crystals face challenges such as high defect levels, particularly threading dislocations, which affect the quality and reliability of GaN-based optoelectronic and electronic devices, including high dislocation density, opacity, and strain due to lattice mismatch and thermal expansion mismatch.
Innovation Solution
A method involving temperature gradient recrystallization in a supercritical fluid solvent, using a nucleation center and a GaN source material with a controlled temperature distribution to grow GaN crystals, achieving a dislocation density less than 10^4 cm^-2 and eliminating tilt boundaries, resulting in a true single crystal with improved photoluminescence and optical transparency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods (HVPE, liquid Ga growth) are used to grow GaN crystals, then crystal growth is achieved, but high dislocation density (10^7-10^10 cm^-2) and high defect levels are produced
Solution Approach 1:
The invention changes the fundamental growth parameters by using ammonium chloride (NH4Cl) as a solvent instead of conventional solvents like liquid gallium or supercritical ammonia. This parameter change enables growth at lower temperatures (below 1000°C) and achieves unprecedented dislocation densities below 10^4 cm^-2, directly resolving the technical contradiction between achieving crystal growth and minimizing defects
Solution Approach 2:
The invention introduces NH4Cl as an intermediary solvent that facilitates GaN crystal growth. The NH4Cl decomposes to provide nitrogen and chlorine, which react with gallium to form GaN crystals. This intermediary approach enables controlled growth with minimal dislocations and defects, improving both manufacturing precision and device reliability
2Illumination intensity
If GaN crystals are grown in liquid Ga or conventional methods, then crystals are produced, but they exhibit opacity with absorption coefficient of about 200 cm^-1 in visible spectrum
Solution Approach 1:
The invention changes the growth solvent parameter to NH4Cl, which enables production of optically transparent GaN crystals with absorption coefficients below 10 cm^-1 in the visible spectrum. This parameter change eliminates the opacity problem inherent in crystals grown by conventional methods using liquid Ga or other solvents
3Manufacturing precision
If conventional heteroepitaxial growth on non-GaN substrates (sapphire, SiC) is used, then GaN layers are formed, but lattice mismatch and thermal expansion mismatch generate additional defects
Solution Approach 1:
The invention uses NH4Cl as a homogeneous growth environment that allows GaN crystals to grow with minimal lattice mismatch. The ammonium chloride solvent creates a uniform chemical environment that reduces defect formation, eliminating the need for complex substrate preparation and multiple fabrication steps required by heteroepitaxial methods
4Manufacturing precision
If temperature gradient recrystallization in supercritical fluid is used, then dislocation density is reduced below 10^4 cm^-2, but the process requires high pressure and temperature conditions
Solution Approach 1:
The invention changes the solvent parameter to NH4Cl, which has favorable decomposition characteristics that enable low-temperature crystal growth. The NH4Cl decomposes at temperatures below 1000°C, releasing nitrogen and chlorine that facilitate GaN formation. This parameter change achieves low dislocation density without requiring the extreme high temperatures and pressures needed by supercritical fluid methods
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 method produces GaN single crystals with a dislocation density below 10^4 cm^-2, peak photoluminescence at 3.38-3.41 eV, and reduced optical absorption, enhancing the performance and reliability of GaN-based devices by minimizing defects and strain.
Implementation Method 1
temperature gradient recrystallization in a supercritical fluid solvent
Implementation Method 2
controlled temperature distribution to grow GaN crystals
Implementation Method 3
solvent is supersaturated in the first region of the chamber such that there is a temperature gradient between the nucleation center and the GaN source material
Implementation Method 4
controlled temperature distribution to grow GaN crystals
Implementation Method 5
temperature gradient recrystallization in a supercritical fluid solvent
Data Source
AI summary
There is provided a GaN single crystal at least about 2.75 millimeters in diameter, with a dislocation density less than about 104 cm−1, and having substantially no tilt boundaries. A method of forming a GaN single crystal is also disclosed. The method includes providing a nucleation center, a GaN source material, and a GaN solvent in a chamber. The chamber is pressurized. First and second temperature distributions are generated in the chamber such that the solvent is supersaturated in the nucleation region of the chamber. The first and second temperature distributions have different temperature gradients within the chamber.