| Title: | Badanie rozpuszczalności azotku galu w amonotermalnym roztworze zasadowym w różnych warunkach fizykochemicznych |
| Project leader: | Karolina Grabiańska |
| Laboratory: | Laboratory of Ammonothermal Synthesis (NL-13) |
| Call/Programme name: | PRELUDIUM |
| Project number: | 2021/41/N/ST5/03669 |
| Implementation date: | 25.01.2022 24.01.2025 |
| Implementing entity: | Institute of High Pressure Physics |
| Total funding granted: | 209 840 zł |
| Funding for the entity: | 209 840 zł |
| Funding institution: | National Science Center |
Project description
| The main goal of this project is a comprehensive study of the gallium nitride (GaN) solubility in the ammonothermal alkaline solution with sodium amide (NaNH2) as the mineralizer. Gallium nitride crystals of the best structural quality are grown by ammonothermal method in a supercritical ammonia solution inside high pressure autoclaves. The idea of the ammonothermal process is the following: GaN, used as feedstock, is dissolved in supercritical ammonia in one zone of a high-pressure autoclave. The dissolved feedstock is transported to the second zone, where the solution is supersaturated and crystallization of GaN on native seeds takes place. An appropriate temperature gradient between dissolution and crystallization zones enables the convective mass transport. Some mineralizers are added to ammonia in order to enhance the solubility of GaN. Thus, the ammonothermal growth can be proceeded under different environment: basic or acidic. The type of environment is, obviously, determined by the choice of mineralizers. Ammonobasic growth makes use of alkali metals or their amides as mineralizers, while in ammonoacidic growth halide compounds are present. Basic mineralizers include mainly lithium, sodium, or potassium amide. The most frequently studied basic mineralizer is potassium amide (KNH2). However, a few data on the solubility experiments with the basic mineralizer NaNH2 can be found in the literature. The reason for this is the generally accepted opinion of the higher solubility of KNH2 in ammonia compared to NaNH2. It is stated and commonly believed that in the case of NaNH2 used as a mineralizer, a normal course of solubility is observed (it increases with increasing the temperature), the solubility of GaN does not dependent on the concentration of the mineralizer, NaNH2 dissolves very poorly in supercritical ammonia and NaNH2 does not contribute to the dissolution of GaN. On the other hand, the best, in terms of structural quality, and the largest, in terms of thickness and lateral size, crystals are grown by basic ammonothermal method with NaNH2 as the mineralizer and with a reverse course of solubility (it decreases with increasing the temperature; this is called a retrograde solubility mode). No doubt, this discrepancy should be explained. The GaN solubility as a function of temperature, pressure, dissolution time, mineralizer concentration and surface area of GaN feedstock will be investigated. The solubility of GaN in ammonobasic NaNH2–GaN–NH3 systems in the temperature range of 300–550 °C will be examined. First of all, the kinetics of the dissolution process will be investigated and time to reach a saturated solution will be determined. Then, the solubility of GaN as a function of temperature will be analyzed. The influence of ammonia pressure on the GaN solubility will also be studied. Finally, the influence of the mineralizer concentration on the dissolution process for selected values of temperature and pressure will be analyzed and determined. This project will allow to expand the basic knowledge of the NaNH2–GaN–NH3 system. No doubt, it can be the starting point for further work on the description of GaN crystallization under alkaline ammonothermal conditions. A proper analysis of the GaN solubility is absolutely needed. It will lead to a deeper understanding of the basic ammonothermal crystal growth process and a further, faster and better development of this technology. |