Subproject 4



Investigation of dissolution and crystallization equilibria as a basis for the ammonothermal crystal growth of nitrides


Knowledge of the solubility behavior of GaN in ammonothermal synthesis is the decisive prerequisite for mastering, controlling and operating the process under optimal conditions. The aim of this subproject is to determine the optimal parameters for the solubility of GaN under ammono basic conditions. The emphasis is on clarifying whether the solubility behaves retrograde with a constant filling level and mineralizer quantity. Furthermore, the solubility parameters as well as filling level, temperature, mineralizer quantity and reaction time are examined and optimized.

In addition, it should be shown both quantitatively and qualitatively that the thermal decomposition of the solvent ammonia occurs to a significant extent during the process. This creates a basis for further work to analyse the influence of thermal ammonia decomposition on the ammonothermal process. 

In the first project phase, a prototype of the double reactor was developed in order to test and optimize the sampling technology under high pressure. In the project years four to six, solubility data will be generated in the double reactor using the sampling technology developed and from this knowledge and optimization approaches for the ammonothermal process will be obtained.

By measuring ultrasonic velocity, the concentration and density of process liquids can be determined. This can be realized by means of a calibration curve from the correlation between the ultrasonic velocity and the concentration. Since these measurements can also be carried out through the walls, it should also be possible to monitor crystallization processes in situ in an autoclave by measuring the ultrasonic velocity. As an alternative direct measurement method, the second phase of the project aims to determine material parameters such as solubility and density by measuring the ultrasonic velocity in situ.