Atomic arrangements, bond energies, and charge distribution on Si(0 0 1) surfaces with the adsorption of a Ge dimer by DFTB calculations

The atomic arrangements and electrical properties of SiGe nanomaterials are of significance when used in novel nanoelectronic devices and optoelectronic devices. Atomic arrangements, bond energies, and charge distribution of a Ge dimer adsorbed on Si(0 0 1) surfaces with different initial heights and inclination angles are investigated by using the DFTB algorithm. Eight different stable adsorption modes of the Ge dimer on the Si slab surface are demonstrated. The variations of the structural and electrical properties of the eight modes are elucidated. Different initial conditions caused stable adsorption of Ge dimer on the surface or caused two single Ge atoms from the Ge dimer to fragment. The Ge dimer, with different inclination angles, is adsorbed on the top site, bridge site, or hollow site of the Si dimer on the surface. The bond length of the Ge dimer is stretched, and the two Ge atoms lose charges. The further the Ge atom is from the surface, the more charges it loses. The different adsorption sites of the Ge dimer affect the properties of the Si dimer on the surface. The top adsorption site mode exerts a greater influence on the bond length and bond energy of the Si dimer, while the bridge adsorption site mode exerts a greater influence on the electron distribution of the Si dimer. The properties of the Ge monoatomic adsorption are akin to the case of a Ge dimer being adsorbed on the bridge site. The different adsorption sites and inclination angles cause the EGap values of the systems to differ, and the effect of the inclination angle on different sites also differs. The Ge dimer and Ge monoatom not only have similar effects on the properties of the Si dimer, but also exert the similar effects on EGap, suggesting that changes in the Si surface are the main contributors to the change in EGap.