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Thickness-dependent optimization of Er3+ light emission from silicon-rich silicon oxide thin films.

Cueff S, Labbé C, Jambois O, Garrido B, Portier X, Rizk R - Nanoscale Res Lett (2011)

Bottom Line: The Er3+ photoluminescence at 1.5 μm, normalized to the film thickness, was found five times larger for films 1 μm-thick than that from 50-nm-thick films intended for electrically driven devices.More Si excess has significantly increased the emission from "thin" films, up to ten times.This paves the way to the realization of highly efficient electrically excited devices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), ENSICAEN, CNRS, CEA/IRAMIS, Université de Caen, 14050 CAEN cedex, France. richard.rizk@ensicaen.fr.

ABSTRACT
This study investigates the influence of the film thickness on the silicon-excess-mediated sensitization of Erbium ions in Si-rich silica. The Er3+ photoluminescence at 1.5 μm, normalized to the film thickness, was found five times larger for films 1 μm-thick than that from 50-nm-thick films intended for electrically driven devices. The origin of this difference is shared by changes in the local density of optical states and depth-dependent interferences, and by limited formation of Si-based sensitizers in "thin" films, probably because of the prevailing high stress. More Si excess has significantly increased the emission from "thin" films, up to ten times. This paves the way to the realization of highly efficient electrically excited devices.

No MeSH data available.


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Transmission electron microscope images, of samples deposited at 500°C for two different thicknesses. (a) 50 nm and (b) 1,400 nm. In "thin" film (a) no Si-nc was detected throughout the whole area of the sample, while in "thick" film (b) numerous well-crystallized Si-ncs are seen with diameter as high as 5 nm. The observed darker regions in (b) are accounted for Er-clusters and are observed also in some regions of "thin" films.
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Figure 4: Transmission electron microscope images, of samples deposited at 500°C for two different thicknesses. (a) 50 nm and (b) 1,400 nm. In "thin" film (a) no Si-nc was detected throughout the whole area of the sample, while in "thick" film (b) numerous well-crystallized Si-ncs are seen with diameter as high as 5 nm. The observed darker regions in (b) are accounted for Er-clusters and are observed also in some regions of "thin" films.

Mentions: Accordingly, the PL properties of typical "thin" and "thick" layers deposited at 500°C can be compared. Figure 3 shows typical variations of the PL intensity (normalized to the thickness) of emission, both from Si-ncs around 750 nm, and from Er ions around 1.5 μm (see inset), as a function of the annealing temperature (Ta). The influence of Ta on the agglomeration of Si excess was previously studied [19] and it was shown that the value of %Siagglo increases almost linearly versus Ta before reaching a complete agglomeration at 1,100°C, whatever the temperature of deposition and the %Siexcess. Three major observations can be made: (1) Er PL shows the same evolution for both "thin" and "thick" samples, with an optimum for Ta = 900°C, (2) The Si-nc-PL detected from the thick sample rises spectacularly for Ta = 1,100°C. This opposite behavior of the Si-nc and Er emissions for thick films has been already observed and explained [20,21]. By contrast, no Si-nc PL emission is detected from the thin films, even after a 1,100°C annealing. This phenomenon is due to the low fraction of agglomerated Si (see Figure 2), and is confirmed in Figure 4 by TEM images of both thin and thick samples annealed at 1,100°C that shows the presence of well-defined crystallized Si-ncs in thick samples but not in the thin one. Such inhibition of the nucleation of Si-nc in thin films was already assumed in several studies based on PL results [6,10] but these TEM images are direct evidence of this phenomenon. (3) The Er emission is almost four times lower for the thin sample for all Ta. Such a gap between the Er PL from the "thin" and "thick" samples deserves further attention. The above-mentioned limitations (stress) and depth-dependent optical effects (LDOS, interference) related to the film thinness are to be circumvented and/or considered. To estimate the impact of both interference-induced variations of the pumping and LDOS effects, we made calculations based on the methods described in Refs. [9] and [10], respectively. Their specific contributions at a distance z from the substrate were then estimated, and their product integrated over the thickness has allowed the calculation of their combined contributions, Ical, on the measured Er PL intensity, IPL. The calculated intensity Ical is compared in Figure 5a to IPL. For the sake of comparison, both Ical and IPL are normalized to the highest values, at 1,400 nm where the stress effect on the Er PL intensity can be relatively neglected. While IPL shows an abrupt decrease at about 200 nm, indicated by the vertical dashed line of Figure 5b, Ical shows a smaller reduction down to a level significantly higher than the corresponding level for IPL. An approximately five-time lowering of IPL and nearly 1.5 times decrease of Ical occur at the thickness threshold of approximately 200 nm, beyond which the above-mentioned limitations are less effective. The additional reduction of IPL, compared to Ical can be attributed to a stress effect which affects the formation and homogeneity of the sensitizers.


Thickness-dependent optimization of Er3+ light emission from silicon-rich silicon oxide thin films.

Cueff S, Labbé C, Jambois O, Garrido B, Portier X, Rizk R - Nanoscale Res Lett (2011)

Transmission electron microscope images, of samples deposited at 500°C for two different thicknesses. (a) 50 nm and (b) 1,400 nm. In "thin" film (a) no Si-nc was detected throughout the whole area of the sample, while in "thick" film (b) numerous well-crystallized Si-ncs are seen with diameter as high as 5 nm. The observed darker regions in (b) are accounted for Er-clusters and are observed also in some regions of "thin" films.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211489&req=5

Figure 4: Transmission electron microscope images, of samples deposited at 500°C for two different thicknesses. (a) 50 nm and (b) 1,400 nm. In "thin" film (a) no Si-nc was detected throughout the whole area of the sample, while in "thick" film (b) numerous well-crystallized Si-ncs are seen with diameter as high as 5 nm. The observed darker regions in (b) are accounted for Er-clusters and are observed also in some regions of "thin" films.
Mentions: Accordingly, the PL properties of typical "thin" and "thick" layers deposited at 500°C can be compared. Figure 3 shows typical variations of the PL intensity (normalized to the thickness) of emission, both from Si-ncs around 750 nm, and from Er ions around 1.5 μm (see inset), as a function of the annealing temperature (Ta). The influence of Ta on the agglomeration of Si excess was previously studied [19] and it was shown that the value of %Siagglo increases almost linearly versus Ta before reaching a complete agglomeration at 1,100°C, whatever the temperature of deposition and the %Siexcess. Three major observations can be made: (1) Er PL shows the same evolution for both "thin" and "thick" samples, with an optimum for Ta = 900°C, (2) The Si-nc-PL detected from the thick sample rises spectacularly for Ta = 1,100°C. This opposite behavior of the Si-nc and Er emissions for thick films has been already observed and explained [20,21]. By contrast, no Si-nc PL emission is detected from the thin films, even after a 1,100°C annealing. This phenomenon is due to the low fraction of agglomerated Si (see Figure 2), and is confirmed in Figure 4 by TEM images of both thin and thick samples annealed at 1,100°C that shows the presence of well-defined crystallized Si-ncs in thick samples but not in the thin one. Such inhibition of the nucleation of Si-nc in thin films was already assumed in several studies based on PL results [6,10] but these TEM images are direct evidence of this phenomenon. (3) The Er emission is almost four times lower for the thin sample for all Ta. Such a gap between the Er PL from the "thin" and "thick" samples deserves further attention. The above-mentioned limitations (stress) and depth-dependent optical effects (LDOS, interference) related to the film thinness are to be circumvented and/or considered. To estimate the impact of both interference-induced variations of the pumping and LDOS effects, we made calculations based on the methods described in Refs. [9] and [10], respectively. Their specific contributions at a distance z from the substrate were then estimated, and their product integrated over the thickness has allowed the calculation of their combined contributions, Ical, on the measured Er PL intensity, IPL. The calculated intensity Ical is compared in Figure 5a to IPL. For the sake of comparison, both Ical and IPL are normalized to the highest values, at 1,400 nm where the stress effect on the Er PL intensity can be relatively neglected. While IPL shows an abrupt decrease at about 200 nm, indicated by the vertical dashed line of Figure 5b, Ical shows a smaller reduction down to a level significantly higher than the corresponding level for IPL. An approximately five-time lowering of IPL and nearly 1.5 times decrease of Ical occur at the thickness threshold of approximately 200 nm, beyond which the above-mentioned limitations are less effective. The additional reduction of IPL, compared to Ical can be attributed to a stress effect which affects the formation and homogeneity of the sensitizers.

Bottom Line: The Er3+ photoluminescence at 1.5 μm, normalized to the film thickness, was found five times larger for films 1 μm-thick than that from 50-nm-thick films intended for electrically driven devices.More Si excess has significantly increased the emission from "thin" films, up to ten times.This paves the way to the realization of highly efficient electrically excited devices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), ENSICAEN, CNRS, CEA/IRAMIS, Université de Caen, 14050 CAEN cedex, France. richard.rizk@ensicaen.fr.

ABSTRACT
This study investigates the influence of the film thickness on the silicon-excess-mediated sensitization of Erbium ions in Si-rich silica. The Er3+ photoluminescence at 1.5 μm, normalized to the film thickness, was found five times larger for films 1 μm-thick than that from 50-nm-thick films intended for electrically driven devices. The origin of this difference is shared by changes in the local density of optical states and depth-dependent interferences, and by limited formation of Si-based sensitizers in "thin" films, probably because of the prevailing high stress. More Si excess has significantly increased the emission from "thin" films, up to ten times. This paves the way to the realization of highly efficient electrically excited devices.

No MeSH data available.


Related in: MedlinePlus