Towards an optimum coupling between Er ions and Si-based sensitizers for integrated active photonics

Abstract

Series of Er-doped Si-rich silicon oxide layers were studied with the aim of optimizing the coupling between Er ions and the Si-based sensitizers. The layers were grown at substrate temperature between 400 and 600°C by the cosputtering of three confocal targets: Si, SiO2, and Er2O3. The influence of Si excess (5–15at.%) and annealing temperature (500–1100°C) was examined for two concentrations of Er ions (3.5×1020 and ∼1021cm−3). We report the first observation of significant Er photoluminescence (PL) from as-grown samples excited by a nonresonant 476nm line, with a lifetime in the range of 1.3–4ms. This suggests the occurrence of an indirect excitation of Er through Si-based entities formed during the deposition. A notable improvement was observed for both Er PL intensity and lifetime after annealing at 600°C. This temperature is lower than that required for phase separation, suggesting the formation of “atomic scale” sensitizers (Si agglomerates, for example) considered in recent work. For high Er doping (∼1021cm−3), an optimum Er PL was obtained for the sample grown at 500°C, annealed at 600°C, and containing ∼13at.% of Si excess. This high PL should correspond to an optimum fraction of coupled Er for this series, which was roughly estimated to about 11% of the total Er content for an excitation photon flux of few 1019phcm−2s−1. For the moderately Er-doped series (3.5×1020cm−3) grown at 500°C, the optimum Er PL was found for the samples containing about 9at.% silicon and annealed in the 600–900°C range. The time decay reached a value as high as 9ms for low Si excess (<6at.%) and 6–7.5ms for high values of Si excess. The fraction of Er ions coupled to sensitizers was similarly estimated for the best sample of this series and found to be as high as 22% of the total Er content.

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

“…However, our group has recently observed an Er-PL under these indirect excitation conditions on the as-deposited samples at about 500°C. 13,14 The Er emission was improved after annealing at about 500-600°C, and this aspect was also confirmed by another team on similarly sputtered layers. 15 We have assigned such an observation to the formation of Sibased sensitizers during the deposition process that are expected to be very small and dense, ensuring a noticeable coupling with the Er ions.…”

“…The Si excess was estimated by a Fourier transform infrared ͑FTIR͒ spectroscopy approach detailed elsewhere. 14 The refractive index and the thickness were measured using spectroscopic ellipsometry ͑SE͒.…”

On the interplay between Si-Er-O segregation and erbium silicate (Er2Si2O7) formation in Er-doped SiOx thin films

“…More details on the fabrication conditions can be found elsewhere [9]. APT experiments were performed using a LAWATAP-CAMECA using UV (343 nm) femtosecond laser pulses (350 fs).…”

Achieving optical gain in waveguide-confined nanocluster-sensitized erbium by pulsed excitation

“…This coupling is an active area of experimental research. 9,10 However, net gain in the system is only possible if gain from inverted Er 3+ is greater than loss due to carrier absorption.…”

“…However, it is possible that improved thin film fabrication can lead to higher Er incorporation. 10 Another way to increase gain is to make the active layer thicker. This allows the active layer to overlap a larger fraction of the confined TM mode, increasing the gain via the integral factor in Eq.…”