Crystallization behaviour of amorphous Si_(0.5)Ge_(0.5) films observed by positron annihilation

摘要

The crystallization behavior (ordering) of undoped and boron-doped Si_(0.5)Ge_(0.5) films, deposited on SiO_2/Si(001) substrate by molecular beam epitaxy in high vacuum at room temperature, were studied by XRD, HRTEM and in situ by Doppler broadening spectroscopy using monoenergetic positrons. Some decomposition features of SiGe solid solutions were demonstrated via splitting the XRD peaks at high temperatures. The SiGe decomposition was detected in the precrystalline state of the SiGe undoped and doped films in the temperature range from 450 to 600 K by compaering S- and W-parameters of SiGe with that of amorphous silicon and germanium. In conclusion, we discuss model of internim ordering states before crystallization.