Photon energy dependence of crystallization of Si1−xGex films by soft X-ray irradiation

Abstract

Amorphous silicon germanium (a-Si1−xGex) films were crystallized by irradiation with soft X-rays of various photon energies. The crystallization upon soft X-ray irradiation is related to Ge concentration, photon energy, and photon flux density. The Ge atom was the trigger for the crystallization of the SiGe film because the atomic migration of Ge atoms was enhanced by electron excitation during soft X-ray irradiation, compared with Si atoms. As the photon energy decreased from 130 to 50 eV, the crystalline fraction increased. In the Si0.5Ge0.5 film, the ratio of peaks attributable to the crystal phases to those attributable to the amorphous phases of Si–Si, Si–Ge, and Ge–Ge bonds changed with irradiated photon energy. This is explained by the relationship between the orbital energies of Si 2p and Ge 3d and the photon energy of irradiated soft X-rays, because the electron excitation probability was determined by this relationship. Therefore, it is considered that soft X-ray irradiation crystallization occurred via the exitation of electrons from the core level.