The influence of implantation conditions on dopant activation in Al-implanted 4H-SiC: A MD study applying an Al potential fitted to DFT barriers

The non-monotonic dependence of Al dopant activation on implantation temperature in 4H-SiC has been experimentally observed, but its atomistic origin remains unclear.

We present a molecular dynamics (MD) study of Al implantation at $500$,K and $900$,K over seven doses from $1\times10^{13}$ to $7.5\times10^{14}$,cm$^{-2}$, followed by up to $100$,ns of annealing at $1500$--$2500$,K.

Using the Gao-Weber potential combined with a reparameterized Morse potential for Al-SiC interactions fitted to DFT migration and kick-in/out barriers, we show that implantation at both temperatures reduces Frenkel-pair formation and extended amorphous pockets compared with room-temperature implantation.

Above the Al solubility limit ($>10^{20}$,cm$^{-3}$), however, annealing reveals a non-monotonic temperature dependence.

Samples implanted at $900$,K form larger, kinetically stable interstitial clusters that persist throughout annealing and act as sinks and trapping centers for Al, reducing substitutional incorporation.

Although the $500$,K samples initially exhibit lower crystallinity, they contain a significantly larger fraction of substitutional Al after annealing.

The simulations identify two regimes: a low-dose regime dominated by isolated point defects and small complexes, and a high-dose regime characterized by defect clustering and planar-defect formation with strong implantation-temperature dependence.

These results explain the experimentally observed optimal implantation window between $500$ and $900$,K and suggest that controlled nanoscale amorphization at $500$,K enhances activation through regrowth-assisted incorporation while suppressing extended defects.

The simulations also identify a new basal-plane diffusion path for Al and an activation mechanism involving kick-out of a carbon antisite; both were confirmed by DFT-NEB calculations.