Extended Temperature Field Facilitates 90 mm AlN Crystal Growth and HEMT Device Validation

In the AlN crystal growth process, the expansion of the diameter leading to the inhomogeneity of the temperature field is gradually prominent, and how to realize the effective expansion of the temperature field has become a key issue in the growth of large-size AlN single crystals. Based on this, this paper simulates three ways of expanding the temperature field through finite element simulation; it is found that only the thermal field structure with expanded heater diameter has a larger axial gradient, a faster gas transport rate, and growth rate, but the high growth rate also leads to larger tensile stress and BPD density inside the crystal. In contrast, the temperature field structure with equal proportional expansion leads to a relatively small axial gradient and slower growth rate due to the increase in the height of the heater. The stress and dislocation density are relatively small, which is favorable for alleviating the problem of cracking large AlN single crystals. The final choice was to use an equal scale expansion scheme for temperature field optimization. The 90 mm AlN single crystal was grown, and the AlN-based HEMT device was validated. This work provides a new path for the subsequent growth of large AlN single crystals.