研究目的
To investigate the change in solubility of gallium nitride (GaN) in supercritical ammonia under addition of a mixed mineralizer, and whether the mixing ratio can control the temperature dependence of the solubility.
研究成果
The solubility of GaN in supercritical ammonia can be controlled by the mixing ratio of mineralizers (NH4Cl with NH4Br or NH4I), with the temperature dependence intermediate between that of single mineralizers. This approach may enable better control in ammonothermal crystal growth for producing high-quality GaN substrates.
研究不足
The measurement uncertainty in solubility is within ±10%, and uncertainties in temperature and pressure are ±2 °C and ±2 MPa, respectively. Differences in solubility data compared to other studies (e.g., Schimmel et al.) are not fully explained, indicating potential limitations in experimental setup or mineralizer stability.
1：Experimental Design and Method Selection:
The solubility was measured using the mass-loss method in supercritical ammonia with mixed mineralizers (NH4Cl + NH4Br and NH4Cl + NH4I) at temperatures from 450 to 550 °C and pressure of 100 MPa. The van't Hoff equation was applied to analyze the heat of solution.
2：Sample Selection and Data Sources:
GaN crystals grown by hydride vapor phase epitaxy (HVPE) were used. Mineralizers (NH4Cl, NH4Br, NH4I) with specified purities were purchased and dried. Ammonia with high purity was obtained.
3：List of Experimental Equipment and Materials:
Autoclave for high-pressure and high-temperature experiments, weighing instruments for mass measurements, and materials including GaN, mineralizers, and ammonia.
4：Experimental Procedures and Operational Workflow:
Samples were prepared by weighing chemicals at desired molar ratios. The autoclave was heated to specified temperatures and pressures, and solubility was determined by mass loss after experiments. Uncertainties in temperature and pressure were ±2 °C and ±2 MPa, respectively.
5：Data Analysis Methods:
Solubility data were analyzed using the van't Hoff equation to calculate heat of solution. Measurement uncertainty in solubility was within ±10%.
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