Atomistic simulation of the interface structure of Si nanocrystals embedded in amorphous silica

An efficient means to obtain light emission from a silicon-based material would enable integrating both optical and electronic functionalities on the same silicon chips. The long radiative lifetimes have until recently obstructed efficient light emission from Si. A nanocrystalline approach has opened up a prospect for silicon in the optoelectronics application field. However, the structure of the nanocrystal-matrix interface, which appears to be important for the light emission, remains unclear. In the present work, by means of molecular dynamics atomistic models, small nc-Si embedded into defect-free a-SiO(2) are constructed using two different classical interatomic potentials. The models allow analysis of the defects at the interface which may serve as radiative and nonradiative recombination centers for excitons formed in nc's and, thus, be responsible for the optical properties of the structure. We analyzed the interface structures after a series of high-temperature annealing runs and subsequent relaxation at room temperature. The results show that the nc-Si/SiO(2) interface is organized by means of a thin suboxide layer (SiO(2)-x), which contains a considerable amount of undercoordinated defects as well. We also observed the spontaneous formation of silanone bonds (Si = O), frequently discussed in the literature to be centers with an important role on the optical properties of the nc structures.