Effect of Temperature Gradient on AlN Crystal Growth by Physical Vapor Transport Method

In this study, the effect of different temperature field distributions on the growth of AlN crystal via spontaneous nucleation by physical vapor transport (PVT) method was investigated through simulation and experiment. The axial temperature gradient increased from 6.71 K/cm to 10.85 K/cm, while the radial temperature gradient increased to 4.6 K/cm at first and then decreased with the rising of the crucible position. Combining with the growth dynamics theory, we found that the axial temperature gradient was the main factor affecting the growth rate of AlN crystal, and the radial temperature gradient was the driving force for expanding the diameter of AlN crystal. Temperature field simulation and growth dynamics analysis provided a theoretical guide for the growth experiments of AlN crystal. When the crucible relative position was 16%, the radial temperature gradient reached the maximum of 4.6 K/cm, and the size of the spontaneous nucleation grown AlN crystal was the largest. A 2 in. AlN boule was obtained under this temperature field after several runs, and a 5 × 6 mm, 600 μm thick AlN crystal wafer was obtained by slicing and polishing. Compared to the initial spontaneous nucleation, the single crystal size was enlarged from ∼600 μm to 6 mm. The HRXRD, Raman, and EBSD results showed that the grown AlN crystals had high structure quality and low stress. Our study provides an important reference for growing high quality, large-size AlN crystals.