Effect of hydrogen passivation on luminescence-center-mediated Er excitation in Si-richSiO2with and without Si nanocrystals

Abstract

The influence of hydrogen passivation on luminescence-center-mediated excitation of Er 3+ in Er-doped Si-rich SiO 2 films with significantly different microstructures is studied. Photoluminescence measurements are presented for samples containing no detectable silicon nanocrystals ͑annealed at 600°C͒ and for samples containing silicon nanocrystals ͑annealed at 1100°C͒ as a function of hydrogen passivation temperature. Passivation is found to have little effect on the Er 3+ photoluminescence intensity at 1535 nm in the samples that do not contain nanocrystals. In contrast, a pronounced increase in the Er 3+ photoluminescence intensity is observed in the samples containing Si nanocrystals, which is accompanied by a similar increase in the nanocrystal photoluminescence intensity and a gradual increase in the Si nanocrystal emission lifetime. This observation is attributed to two interrelated effects, namely, ͑a͒ an increase in the density of fully passivated optically active nanocrystals due to the passivation-induced removal of silicon dangling bonds and ͑b͒ a concurrent reduction in nonradiative Er 3+ relaxation from levels above the 4 I 13/2 level due to a direct interaction of excited Er 3+ ions with silicon dangling bonds. In addition, the observed counterintuitive gradual increase in the nanocrystal photoluminescence decay time upon passivation is successfully explained taking into account a passivation-induced change in the concentration of optically active nanocrystals with different sizes and the inhomogeneous nature of the nanocrystal-related emission band. It is shown that the combination of luminescence-center-mediated Er 3+ excitation and silicon-dangling-bond-induced Er 3+ de-excitation can explain at least 14 experimental observations reported by independent authors.

Efficient energy transfer from Si-nanoclusters to Er ions in silica induced by substrate heating during deposition

“…3,25 The slight shift to higher energies, in spite of T d increase, reflects some lowering in the average size of Si-nc which is quite compatible with the above-commented decrease in Si excess. It is also worth noting that this visible emission was similarly observed and attributed to Si-nc by Savchyn et al 9,26,27 for their samples annealed at 1000°C during only 100 s. On the contrary, no contribution is detected in our samples of the so-called luminescent centers ͑LCs͒ emitting at around 500 nm. 9 The presence of a significant Er-PL in our as-deposited samples ͑for T d Ն 200°C͒ excited with a nonresonant wavelength reveals the occurrence of an efficient energy transfer from Si-nc to Er 3+ .…”

Energy Transfer from Silicon Nanocrystals to Er3+ Ions Embedded in Silicon Oxide Matrix

“…The samples annealed by the RTP only are referred to as "as-annealed" samples and the samples annealed by the RTP and passivated are referred to as "passivated" samples. The purpose of the passivation is to remove the dangling bond defects surrounding Si nanostructures (Savchyn et al, 2008;Wilkinson & Elliman, 2003). In our study, we have varied the passivation time and found that after 30 minutes of the passivation, the emission intensity of exciton recombinations in Si nanocrystals as well as the exciton lifetime have reached the optimum values and saturated, showing that most, if not all, dangling bond defects have been effectively removed.…”

“…Prior to 2007, many research works reported that the main energy transfer mechanism is from Si nanocrystals to Er 3+ ions (Fujii et al, 2004;Heitmann et al, 2003;Kik & Polman, 2001;Polman & Veggel, 2004). However, recently, in 2007 and2008, one leading group in the field suggested that defect mediated energy transfer was the dominant mechanism (Savchyn et al, 2007(Savchyn et al, , 2008. In their work (Savchyn et al, 2007(Savchyn et al, , 2008, the origin of defects that transfer energy to Er 3+ ions was not discussed.…”

“…However, recently, in 2007 and2008, one leading group in the field suggested that defect mediated energy transfer was the dominant mechanism (Savchyn et al, 2007(Savchyn et al, , 2008. In their work (Savchyn et al, 2007(Savchyn et al, , 2008, the origin of defects that transfer energy to Er 3+ ions was not discussed. The controversial in the energy transfer mechanism has created much difficulty in improving Er 3+ emission efficiency.…”

“…nanostructures embedded in SiO 2 matrix has been extensively studied (Fujii et al, 2004;Heitmann et al, 2003;Kik & Polman, 2001;Polman & Veggel, 2004;Savchyn et al, 2007Savchyn et al, , 2008. Si nanostructures can be excited optically or electrically, then transfer the energy to Er 3+ ions which then decay radiatively giving emission peaked at 1.53μm, which coincides with the telecommunication wavelength.…”