Vacancy-Interstitial Pair-Formation Mechanism of X-Ray-Irradiation-Induced Crystallization in Amorphous Silicon Studied by ab initio Molecular Dynamics Simulation

ABSTRACTWe have studied the microscopic mechanism of the X-ray-irradiation-enhanced crystallization in amorphous silicon (a-Si) based upon an ab initio molecular-dynamics simulation. We find that the bistable dangling-bonds (sp3- and sp2-like structures) exhibit a large lattice relaxation and are strongly related to the X-ray-irradiation-induced vacancy-interstitial-pair formation. The vacancy-interstitial-pair formation reduces the formation energy of the vacancy to zero and enhances the crystallization with small migration energy of the vacancy. The crystallization rate in X-ray-irradiated a-Si is dominated by the migration energy of the vacancy in this mechanism because the formation energy is zero in X-ray-irradiated a-Si and one order of magnitude larger than the migration energy without X-ray irradiation.