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

TLDR: In this article, the influence of the deposition temperature Td on the Si-mediated excitation of Er ions within silicon-rich silicon oxide layers obtained by magnetron cosputtering was investigated.

Abstract: This study investigates the influence of the deposition temperature Td on the Si-mediated excitation of Er ions within silicon-rich silicon oxide layers obtained by magnetron cosputtering. For Td exceeding 200 °C, an efficient indirect excitation of Er ions is observed for all as-deposited samples. The photoluminescence intensity improves gradually up to a maximum at Td=600 °C before decreasing for higher Td values. The effects of this “growth-induced annealing” are compared to those resulting from the same thermal budget used for the “classical” approach of postdeposition annealing performed after a room temperature deposition. It is demonstrated that the former approach is highly beneficial, not only in terms of saving time but also in the fourfold enhancement of the Er photoluminescence efficiency.

Figures

FIG. 6. Behavior of the lifetime values of Er3+ at 1.53 m according to the deposited temperature detectable at the lower excitation photon flux. Inset: a typical PL decay trace of SRSO:Er collected for sample deposited at 600 °C. Note the PL decay dynamics is biexponential as described in Ref. 28.

FIG. 5. Color online PL spectra normalized to the thickness at a flux of 5 1018 photons cm2 /s of both Si-nc range 600–900 nm and of Er3+ ions range 1400–1700 nm for all deposition temperatures. Inset: Si-nc PL intensities compared to the Er-PL intensities according to the deposition temperature both normalized to unity .

FIG. 7. Color online Comparison of PL intensity of as-deposited samples recorded at 1.53 m and obtained after indirect excitation 476 nm and direct excitation 980 nm . Note that the results corresponding to the 980 nm excitation are multiplied by 104.

FIG. 4. Color online a Ellipsometry measurements of the refractive index at 633 nm and Si excess as estimated by FTIR techniques and the formula 1 in function of Td the curves are just a guide for the eyes . b SIMS measurements of the erbium concentration according to the deposition temperature.

FIG. 3. Color online Evolution of the wave number of SiO2:Er references and SRSO:Er samples for each deposition temperature.

FIG. 1. Color online rms roughness measured by AFM and layer thickness measured by SE as a function of deposition temperature Td. Two typical AFM micrographs scan area: 1 m2 are also shown for the depositions at RT and at 600 °C.

Frequently asked questions

Q1. What is the effect of a high surface mobility on the deposited elements?

a high surface mobility should lead to a progressive relaxation of the net-work through lower distortion of the atomic bond angles and an improved atomic rearrangement, together with better compactness. 

Q2. What are the contributions in "Efficient energy transfer from si-nanoclusters to er ions in silica induced by substrate heating during deposition" ?

In this paper, the influence of the deposition temperature on the optical properties of SRSO: Er thin films was carefully investigated. 

Q3. What is the reason for the thickness lowering?

A significant part of this thickness lowering may be due to a temperature-dependent sticking/desorption rate of the sputtered elements, already demonstrated for elemental oxygen on Si substrate,17 and/or the creation of volatiles species. 

Q4. What is the effect of the increase in Er-PL intensity with Td?

The increase in the Er-PL intensity with Td may originate from the formation of small Si-sensitizers, as already mentioned, and also from the improvement of the environment of Er3+ ions which is expected to increase the number of optically active Er3+ ions. 

Q5. What is the surface roughness of the deposited atoms?

The surface roughness is generally correlated with both mobility and growth rate of the deposited atoms, especially in this specific layer-by-layer deposition technique. 

Q6. What is the surface roughness of the deposited layers?

the surface roughness reflects some balance between the deposition rate and the surface mobility of the sticking elements. 

Q7. What is the evolution of the TO3 peak for the SiO2:Er reference?

The evolution of the TO3 peak for the SiO2:Er reference is considered as reflecting an evolution of the atomic arrangement rather than any Si excess. 

Q8. What is the reason for the decrease in Si excess?

In this regards, the Si excess lowering can be provoked by some increasing interactions/reactions between the deposited species, inducing the formation of volatile elements such as SiO for Td 300 °C, as supported by earlier studies. 

Q9. How much does the surface roughness rms change with temperature?

The roughness rms continuously softens from 1.6 to 0.3 nm when Td increases, with a steep decrease for Td between 300 and 600 °C. 

Q10. How does the Er-PL increase with Td?

under the resonant wavelength of 980 nm corresponding to a resonant direct excitation of Er i.e., without the Si-nc relays from the ground state 4I15/2 to the second excited level4I11/2, the Er-PL increases systematically up to Td=600 °C see Fig. 7 , reflecting a concomitant enhancement of the number of the optically active ions. 

Q11. What is the effect of the increase in the Er-PL?

Those concomitant effects lead to a positive paradox when the deposition temperature is raised from 200 to 600 °C: the PL of Er3+ still increases whereas both the Si excess and the Er concentration get lower. 

Q12. What is the effect of the increase in the Er-PL intensity at 700 °C?

On the other hand, the sudden abrupt decrease in the Er PL at 700 °C for both nonresonant 476 nm and resonant 980 nm excitation lines, suggests some agglomeration of the Er ions at this deposition temperature 700 °C , which reduces the number of optically active Er ions,29 and consequently the PL intensity. 

Q13. How much of the Er-PL efficiency is derived from the temperature of the annea?

the improvement of the Er-PL up to a maximum for Td=600 °C corresponds to a moderate value of Si excess and almost the lowest NEr. 

Q14. What is the reason for the 35% decrease in thickness?

the expected improvement of the compactness, combined to the reduction in the structural disorder, is not sufficient to explain the 35% decrease in the thickness. 

Q15. How does the Er-PL efficiency compare to the annealed samples?

By comparison, the volume diffusion of the elements occurring during the postdeposition annealing requires higher activation energy and result apparently in the formation of much less Si-based sensitizers and optically active Er3+ ions.