Controlling defect and Si nanoparticle luminescence from silicon oxynitride films with CO2 laser annealing

Abstract

We demonstrate that a focused CO2 laser beam (λ=10.6μm) can be employed to locally synthesize light emitting defects and Si nanoparticles in silicon rich oxynitride thin films. Films with a stoichiometry of SiO1.08N0.32 were prepared by plasma enhanced chemical vapor deposition with N2O and SiH4. Strongly absorbing CO2 laser light was then used to induce local heating in the films in air ambient using power densities in the range from 0 to 580W∕cm2 and times of 5s to 60min. High-resolution cross sectional transmission electron microscopy (TEM) images of the irradiated region revealed the presence of crystalline Si nanoparticles. Photoluminescence (PL) spectra taken from irradiated areas showed two distinct peaks around 570 and 800nm. From a combined TEM, Rutherford back scattering (RBS), forming gas annealing (FGA), PL, and PL lifetime study it is concluded that the 570nm peak with a short PL lifetime (<10ns) is related to defects characteristic of silicon suboxides and that the 800nm peak is due to exciton recombination inside the Si nanoparticles. The appearance of an isosbestic point in the PL spectra suggests that upon CO2 laser heating Si nanoparticles are formed at the expense of the luminescent defect structures, which are annealed out.