Theoretical analysis of structure, thermodynamic properties, and optical properties of Ge-doped amorphous SiO2

Different stable geometric configurations of Ge doped amorphous SiO2 (a-SiO2) system, originating from one, two, or three Si atoms in various places of the a-SiO2 substituted by Ge atoms randomly have been investigated using interatomic potentials in this work. The most stable structures have been identified and corresponding evolutional rules obtained. The structural growth pattern for Ge-doped a-SiO2 system is that Ge atoms tend to spread far away from each other and keep away from the center. Furthermore, the thermodynamic properties including specific heat, Debye temperature, vibrational entropy, and so on are calculated from the structure with 16 Si atoms of the constructed a-SiO2 cell replaced by Ge atoms and with the biggest Ge-Ge distance. It can be seen that entropy of Ge doped system with larger specific heat is higher than that of the pure system with smaller specific heat. At last, optical properties including optical absorption spectrum and electron energy loss function of nGe-doped a-SiO2 (n=0-3, 8) system is also obtained.