Absorption of Si, Ge, and SiGe alloy nanocrystals embedded in SiO2 matrix

Abstract

Using the atomistic s p 3 d 5 s ∗ tight-binding method, we calculate the optical absorption spectra due to phononless optical transitions in Si, Ge, and SiGe alloy nanocrystals embedded in an amorphous dielectric SiO 2 matrix. For the SiO 2 matrix, we use a virtual crystal approximation assuming the cubic crystalline structure, similar to β crystobalite, in the proximity of the nanocrystal surface. The optical absorption is analyzed in detail: its dependency on the Ge content and nanocrystal size and the role of the SiO 2 matrix are revealed. Our recent experimental measurements of the optical absorption in co-sputtered thin SiO 2 films with arrays of Si, Ge, and SiGe alloy nanocrystals are discussed and compared with the simulations.