Computer Simulations of Epitaxial Recrystallization and Amorphous-to-Crystalline Transition in 4H-SiC

Molecular dynamics (MD) methods have been employed to study the epitaxail recrystallization and amorphous-to-crystalline (a-c) transition in 4H-SiC, with simulation times of up to a few hundred ns and at temperatures ranging from 1000 to 2000 K. Three nano-sized amorphous layers with the normal of a-c interfaces along the [-12-10], [-1010] and [0001] directions, respectively, were created within a crystalline cell to investigate the anisotropies of recrystallization processes. The amorphous structures were analyzed using a topological method, which indicates the complete loss of long-rang order, and the existing short-range disorder is quantified by the fraction of homonuclear bonds. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layers. The amorphous layer with the a-c interfaces normal along the [-12-10] direction can be completely recrystallized at the temperatures of 1500 and 2000 K, but the recrystallized region is defected with dislocations and stacking faults. The temperatures required for complete recrystallization are in good agreement with those observed at experiments. On the other hand, the recrystallization processes for the a-c interfaces normal along [-1010] and [0001] directions are hindered by the nucleation of polycrystalline phases. These secondary ordered phases have been identified as 4H- and 3C-SiC with different crystallographic orientations to the original 4H-SiC. The bond mismatches at the interfaces between different microcrystals result in the formation of number stacking faults. The temperature is an important parameter to control the nucleation of secondary ordered phase, whereas the size of amorphous region has a significant effect on their growth. These results are in good agreement with the previous experimental observations. One of the most important results is that the epitaxial recrystallization of amorphous layer with a-c interface along the c axis is much slower than those long the basal plane, which provides atomic-level insights into the anisotropies in the different activation energies for recrystallization.
Based on a model developed in the previous annealing simulations of 3C-SiC, the activation energy spectra for recrystallization along the three directions have been determined. In general, the activation spectra show that there is a number of activation energy peaks associated with different recrystallization processes. These activation energy values for full recrystallization are in the range of from 1.2 to 1.7 eV for the amorphous layers with the a-c interfaces along [-12-10] and [-1010] directions, and 1.1 to 2.3 eV for the amorphous layer with the a-c interfaces along [0001] direction. However, the highest activation energy of 2.3 eV is consistent with the experimental value of 2.1±0.5 eV reported for 6H-SiC. The internal energy distribution provides a detailed analysis of energy paths to recrystallization, and the nucleation and growth of the secondary ordered phases.