Simulations of the Optical Properties of Silicon Nanoparticles Embedded in Silicon Nitride

There is currently a strong interest in the material science community in the optical properties of silicon nanoparticles embedded in silicon nitride. These nanostructures are CMOS-compatible materials which exhibit efficient and fast light emission. The optical properties of these embedded silicon nanoparticles are studied using first-principles Density Functional Theory simulations. We present simulations of the structural, electronic and optical properties of nitrogen-doped silicon nanoparticles both in the gas phase and embedded in a silicon nitride environment. These simulations point to the crucial role played by nitrogen atoms bonded to the surface of small ($\sim$ 1nm) silicon nanoparticles in the light emission mechanism of SiN$_x$ films. We compare the calculated optical gaps and radiative lifetimes of the nanoparticles with recent experimental measurements of light-emitting silicon-rich silicon nitride films obtained by PE-CVD deposition followed by low temperature (500-900 $^\circ$C) thermal annealing. This work was performed under the auspices of the U.S. Dept. of Energy at the University of California/Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48.