Sublimation behavior of AlN in nitrogen and argon at conditions used for high-temperature annealing

High-temperature annealing (HTA) is one of the most promising techniques to produce high-quality, cost-efficient AlN templates for further epitaxial growth of AlGaN devices. Unfortunately, the yield of this process seems to be limited due to the restricting face-to-face configuration that is typically used, in which contaminations of the template surface can occur easily. A high yield is crucial for process transfer into industry. Indeed, templates that are annealed in open-face configuration suffer from surface degradation due to excessive AlN evaporation during the course of the annealing process. To highlight the physics that are restricting the open-face approach of the process, sublimation behavior of AlN at temperatures and atmospheres typically used in HTA processes has to be examined. In this study, we use the Knudsen effusion mass spectrometry technique to confirm the previously published results on equilibrium partial pressures of species above AlN. Based on the experimentally determined data and further AlN sublimation experiments, the apparent sublimation coefficient of AlN in N-2 and Ar atmospheres at HTA process conditions can be derived. Despite N-2 having a stabilizing effect on AlN during HTA, the still high decomposition rates of several hundred nanometers per hour can explain the excessive damage that is typically observed if AlN/sapphire templates are annealed in an open-face configuration. Finally, based on theoretical considerations, a strategy to reduce the sublimation of AlN during HTA in open-face configuration is suggested.

Automated summary

High-temperature annealing is a promising technique for producing high-quality AlN templates, but its yield is limited due to contamination on the template surface when using the face-to-face configuration. Open-face annealing leads to excessive AlN evaporation and surface degradation. By studying AlN sublimation behavior at typical HTA conditions, the limiting factors of the open-face approach can be identified.