Effects of hydrogen in the annealing environment on photoluminescence from Si nanoparticles in SiO2

Abstract

The role of hydrogen in enhancing the photoluminescence (PL) yield observed from Si nanocrystals embedded in SiO2 has been studied. SiO2 thermal oxides and bulk fused silica samples have been implanted with Si and subsequently annealed in various ambients including hydrogen or deuterium forming gases (Ar+4%H2 or Ar+4%D2) or pure Ar. Results are presented for annealing at temperatures between 200 and 1100 °C. Depth and concentration profiles of H and D at various stages of processing have been measured using elastic recoil detection. Hydrogen or deuterium is observed in the bulk after annealing in forming gas but not after high temperature (1100 °C) anneals in Ar. The presence of hydrogen dramatically increases the broad PL band centered in the near infrared after annealing at 1100 °C but has almost no effect on the PL spectral distribution. Hydrogen is found to selectively trap in the region where Si nanocrystals are formed, consistent with a model of H passivating surface states at the Si/SiO2 interface that leads to enhanced PL. The thermal stability of the trapped H and the PL yield observed after a high temperature anneal have been studied. The hydrogen concentration and PL yield are unchanged for subsequent anneals up to 400 °C. However, above 400 °C the PL decreases and a more complicated H chemistry is evident. Similar concentrations of H or D are trapped after annealing in H2 or D2 forming gas; however, no differences in the PL yield or spectral distribution are observed, indicating that the electronic transitions resulting in luminescence are not dependent on the mass of the hydrogen species.