MA: Development of a Highly Improved Autoclave Cleaning Process for the Ammonothermal Growth of High-Purity Nitrides

4. Dezember 2025

Tian Lu –

The ammonothermal method is widely considered to be one of the most promising techniques for growing nitride semiconductor crystals. However, a major challenge lies in the high levels of oxygen and water impurities that are commonly present in the resulting crystals. This study therefore aims to develop an efficient autoclave cleaning process to reduce these background impurities within the system. The experimental approach combines high-temperature baking with argon flushing, and the concentrations of residual oxygen and water vapor inside the autoclave were monitored quantitatively using zirconia- and phosphorus pentoxide-based sensors, respectively.
The results show that only two argon flushes are sufficient to significantly reduce the oxygen concentration. The residual oxygen impurities in the system are primarily attributed to the argon 6.0 used in the experiments, which has an intrinsic oxygen content of around 1.6 ppm. During heating in the 90-550 °C temperature range, the oxygen concentration dropped below the sensor’s detection limit, accompanied by a notable decrease in temperature, indicating the autoclave’s inner wall has a strong oxygen adsorption capability. Water vapor was released across the entire temperature range, with the most pronounced release occurring between 90-290 °C. Although a sharp temperature drop was also observed in the 500-550 °C range, the water vapor concentration did not increase significantly. This suggests that hydroxyl desorption was occurring at this stage, a process that cannot be effectively detected by the current humidity sensor.
These findings suggest that extending the heating and monitoring durations and integrating a gas purification system are essential for enhancing the efficiency of autoclave cleaning and facilitating the growth of high-purity nitride crystals via the ammonothermal method.