Photoluminescence from Si nanocrystals exposed to a hydrogen plasma

Abstract

Si nanocrystals embedded in SiO 2 films were exposed to an atomic H plasma at different temperatures. Photoluminescence intensity from the nanocrystals increases with increasing exposure time, followed by saturation that depends on the exposure temperature. The saturation level depends on the final exposure temperature and shows no dependence on the thermal history of exposure. This behavior is shown to be consistent with a model in which the steady-state passivation level is determined by a balance between defect passivation and depassivation by H, with the activation energy for the passivation reaction being larger than that for the depassivation reaction.

Photoluminescence enhancement of Si nanocrystals embedded in SiO2 by thermal annealing in air

“…For the annealed sample, in contrast, a strong and nearly symmetric PL is observed which peaks near 803 nm and spans from 650 to 960 nm with a full width at half maximum of about 140 nm. This PL spectrum is consistent with those usually observed for Si nanocrystals embedded in the SiO 2 matrix [19]. Compared with our previous work [7], however, much stronger PL is observed from SiNCs/SiO 2 in the present work, with the PL intensity of Si-NCs/SiO 2 about 100 times stronger than that of a-SiO x .…”

“…The density of dangling bonds decreases as the passivation progresses, therefore, the PL intensity increases with the passivation time, which also accounts for the observation that the passivation of dangling bonds and consequently the increase of PL intensity tend to saturate. The saturation of the PL intensity increase of Si-NCs/SiO 2 with passivation time was also observed in oxygen passivation [22] and hydrogen passivation [18,19].…”

“…Brongersma et al reported that thermal oxidation resulted in a substantial blue shift due to a continuous decrease in the average nanocrystal size [21]. Jung et al showed that atomic hydrogen passivation led to an increase in PL intensity without changing the size and the density of Si nanocrystals, and the PL intensity saturated at a level depending on passivation temperature [19]. They believed that the temperature-dependent saturation of the PL intensity was associated with a difference in activation energies for the passivation and depassivation.…”

“…Therefore passivating dangling bonds can increase luminescence intensity. Passivation is usually achieved by thermal annealing of Si-NCs/SiO 2 in a hydrogen-containing gaseous environment such as pure H 2 gas [15], mixed H 2 /N 2 gas [16][17][18] or atomic hydrogen plasma [19,20]. Passivation can also be performed by thermal oxidation [21] or by directly exposing the sample to atomic oxygen plasma [22].…”

Oxygen-passivated enhancement of photoluminescence from SiO2 films containing Si nanocrystals

“…These reactions can occur simultaneously during the passivation treatment. The present results are in well consistent with those for hydrogen passivation and depassivation of P b centers [21], in which it has been shown that two reactions are thermally activated processes with the activation energy for the passivation reaction being larger than that for the depassivation reaction. As a consequence, the similarity between hydrogen and oxygen passivation suggests that the oxygen passivationenhancement of PL intensity is also due to competition between passivation and depassivation of non-radiative recombination defects.…”