High blue emission in impurified (Er-doped) SiOC films obtained by the HWCVD technique using SBA-15 and TEOS

doi:10.21203/rs.3.rs-5168059/v1

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High blue emission in impurified (Er-doped) SiOC films obtained by the HWCVD technique using SBA-15 and TEOS

https://doi.org/10.21203/rs.3.rs-5168059/v1

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SiOC is widely investigated due to its different applications and uses and is currently being studied due to its ability to produce stable and intense photoluminescence. This work presents a study of the changes in the optical, morphological and compositional properties of SiOC:Er thin films obtained by the hot wire chemical vapor deposition (HWCVD) technique using tetraorthosilicate (TEOS), erbium oxide and mesoporous silicon oxides (SBA-15) as new precursors. According to the FTIR absorption spectrum and EDS analysis of the films, all the films were composed of carbon, oxygen and silicon atoms. Moreover, in the photoluminescence spectrum, high emission in the blue region was observed, indicating the presence of Si-nc in the samples. We suggest that the distance between the erbium atoms and Si-nc in SiOC films is responsible for the high-intensity photoluminescence emission.

SiOC

HWCVD

SBA-15

Silicon oxycarbide (SiOC) is currently being studied because of its ability to produce stable and intense photoluminescence. In addition, it has been shown that light emission can be modulated over a wide range of wavelengths with high quantum efficiency, from wavelengths in the infrared to the near ultraviolet region.

SiOC is widely investigated for its various applications, and it can be employed as a diffusion barrier and low-k dielectric. In addition, it has been shown that SiOC can be used as a host for optically active impurities, such as rare earth ions.

SiOC has been reported to have advantages over other silicas, where partial substitution of oxygen by carbon species within an amorphous silicon oxide matrix improves the thermal, chemical and mechanical properties of the material. [1, 2, 3] On the other hand, many SiOCs have been used as hosts for other silicas.

On the other hand, many techniques, including low-pressure chemical vapor deposition (LPCVD), plasma-assisted chemical vapor deposition (PECVD), and hot wire-assisted chemical vapor deposition (HWCVD), have been employed to obtain SiOC films.

In addition, the HWCVD technique allows the use of low substrate temperatures and fast deposition rates to obtain films composed of an amorphous matrix with small crystalline silicon grains embedded within it.

It has been reported that the impurification of SiOC with erbium atoms can be used for modulated light emission. The ⁴I_13/2-⁴I_15/2 intraf transition of Er^+ 3 leads to light emission at approximately 1540 nm, the standard wavelength for telecommunications. On the other hand, much progress has been made in the fabrication of Er-doped devices from Si-based materials, such as lasing in an Er-doped silica toroidal microcavity and the use of Si nanocrystals as sensitizers for Er in SiO₂ materials. [4]

Although SiOC does not exhibit good optical and electrical properties, it has been reported that an increase in the number of defects present in the material, as well as the incorporation of impurities, could increase its conduction and emission properties. In addition, the quantum confinement phenomenon present in the material at the moment of introducing Si-nc inside the amorphous SiOC matrix would cause a large increase in these two properties. [5, 6, 7]

In this work, the use of tetraorthosilicate (TEOS) and mesoporous silicon oxide (SBA-15), which are new precursors for the deposition of SiOC films containing erbium atoms, was reported.

SiOC and SiOC films containing Er atoms were obtained by the HWCVD technique. SBA-15 (previously reported) and TEOS (99.999% Sigma‒Aldrich trace metal base) [8] were used as solid sources of oxygen and silicon, respectively. The tungsten filament was heated to 2000°C, supplying 82 V while maintaining a constant H₂ flow of 100 sccm in the reactor. For all the samples, the substrate temperature was maintained at approximately 300°C, and a deposition time of 10 minutes was used; the source-filament distance was 3 mm, and the substrate-source distance was 3.5 cm, maintaining a constant total system pressure of 1 atm.

The incorporation of erbium atoms in the SBA-15 matrix for use as a source in SiOC films containing Er atoms was performed following the method reported by "Gómez-Cazalilla M., Mérida-Robles J.M., Gurbani A., Rodríguez-Castellón E., and Jiménez-López A." [9], where erbium oxide (Er₂O₃) powder (99.9% Sigma‒Aldrich trace metal base) was used as the host material.

SiOC and SiOC films containing Er atoms were deposited on p-type silicon (100) substrates with a resistivity of 2–3 Ω. The substrates were cleaned by conventional RCA I and RCA II techniques [10] prior to deposition. The solid sources of silicon and erbium were obtained by grinding 100 mg of SBA-15 or Er-SBA-15 powders and compacting them under a pressure of 5 tons to obtain 10 mm diameter and 2 mm thick granules.

Figure 1a) shows the asymmetric stress vibration of the Si-O-Si bond (1068 cm^− 1) in all the samples, which is characteristic of SiOC species. From this figure, it is possible to see a broad band located at 750–850 cm^− 1 in the Si-C, CO and Si-O regions with a binding energy of 406 kJ/mol for Si-O and 358 kJ/mol for C-O.

These energy values are indicative of the three-dimensional nature of SiOC, which is chemically and mechanically stable and increases the adhesion of the obtained film to the substrate [11, 12, 13, 14]. On the other hand, the high intensity, width and position of the band at 1068 cm^− 1 (Fig. 1 (b)) of the Si-O-Si species are related to the stoichiometry of SiOx. A value less than 1080 cm-1 corresponds to a silicon-rich silicon oxide species; for this reason, all our films are composed of silicon-rich silicon oxide with a high silicon content. Figure 1a) and b) show the contribution of the O-Si-O bond located at 460 cm^− 1. The band located at 1278 cm^− 1 observed in all the samples is due to the SiMe₂ species, a product of the redistribution reactions of the Si-O and Si-C bonds.

Figure 2a) and b) show SEM images of the SiOC and SiOC films containing Er atoms at a nominal Si/Er molar ratio of 10. Figure 2a) shows that the film is composed of quasi spherical grains that are uniformly distributed over the substrate surface. In addition, Fig. 2b) shows an irregular morphology that is composed of quasi-spherical clusters of smaller size than the sample shown in Fig. 2a). The presence of silicon and oxygen species in the samples could be responsible for the formation of these quasi-spherical clusters, which were observed at 1.75 keV and 0.5 keV (Fig. 3 (a)).

Figure 3a) and b) show a predominant signal at approximately 0.5 KeV, which is due to oxygen atoms, and a lower intensity signal at approximately 1.75 KeV is assigned to silicon atoms. From the same figures, it is possible to observe a small signal at lower energies that is consistent with carbon atoms.

The low intensity of the carbon signals shown in Fig. 3a) and b) may be due to the high contribution of oxygen and silicon atoms to the film; however, the contribution of the substrate must be excluded since the thickness of these samples was ~ 420 nm and because the electron beam energy for the analysis was 5 keV, which was sufficient energy to pass through the sample and reach the substrate. No contribution from erbium atoms was detected in the SiOC films (Fig. 3(b)).

Figure 4 shows the photoluminescence (PL) spectra of the SiOC and SiOC films containing Er atoms. A broad PL spectrum is observed for all the films. The maximum peaks are observed at 380 nm for SiOC films, at 407 nm for SiOC films containing 5% molar Er, and at 425 nm for SiOC films containing 10% molar and 15% molar Er. It is also evident from this figure that the higher the Er content in the film is, the greater the emission intensity [15, 16, 17]. At lower Er concentrations, the PL of the film has the weakest intensity and shows a slight shift toward smaller wavelengths, which could be due to the presence of silicon nanocrystals in the films or to oxygen-associated defects such as neutral oxygen vacancies (NOVs) (Si-Si bonds), nonbonded oxygen hole centers (NBOHC), positively charged oxygen vacancies (\(\:{E}_{\delta\:}^{{\prime\:}}\) centers) and weak oxygen bonds (WOB) [18, 19, 20].

Figure 4 shows that when the amount of Er in the film increases, the PL emission intensity increases dramatically. The change in the PL intensity is related to the increase in the Er content.

Figure 5 shows a proposed mechanism for the energy transfer process, where an exciton inside a silicon nanocrystal can transfer its energy to an intrinsic luminescent center or to an erbium ion, in both cases competing for the exciton energy. From this figure, it is clear that the excitons are confined within the silicon crystal. When excitons are excited by photons from an external source, they can transfer their energy to the intrinsic luminescent centers within the material.

The presence of silicon nanocrystals provides an alternative route for energy transfer, and when the concentration of erbium increases, this becomes the primary route for energy transfer. The small emission observed in the ~ 800 nm region is due to transitions from the ⁴I_11/2 level to the ⁴I_15/2 base energy level, which are characteristic transitions of Er^+ 3

In this work, SiOC and SiOC films with erbium atoms were obtained using two new precursors, SBA-15 and TEOS. From the FTIR spectral absorption data, it was possible to observe the contributions of Si-O, Si-C, Si-Si, and Si-Me species, which are indicative of the composition of the SiOC films. The contents of silicon, oxygen, and carbon were also observed by EDS; however, it was not possible to detect the content of erbium atoms in the films. The high intensity observed in the photoluminescence spectra was indicative of the presence of erbium atoms in the samples.

The distance between the silicon nanocrystals and the erbium ions plays a key role. In this sense, the energy transfer process from silicon nanocrystals to an intrinsic luminescent center or erbium ion is enhanced. On the other hand, the presence of silicon and oxygen species in the samples could be responsible for the formation of the quasi-spherical clusters that were observed in all the samples.

Author Contributions

William Gómez Salazar, M.D. (Investigation: Lead; Software: Lead; Writing – review & editing: Lead)

Crisoforo Ruíz Morales, PhD (Investigation: Supporting; Methodology: Supporting; Writing – review & editing: Supporting)

Enrique Andres Rosendo, PhD (Resources: Supporting; Supervision: Supporting)

Erick Hernandez Gastellou, PhD (Investigation: Supporting; Methodology: Supporting)

Ivan Balderas García, PhD (Investigation: Equal; Methodology: Equal; Resources: Equal)

Godofredo Salgado García, PhD (Methodology: Supporting; Resources: Supporting)

Reina Isasmendi Galeazzi, PhD (Resources: Supporting)

Antonio Solis Coyopolt, PhD (Investigation: Supporting; Resources: Supporting)

Roman Trujillo Romano, PhD (Resources: Supporting)

Kevin Enrique Peña García, Lic. (Investigation: Supporting; Writing – review & editing: Supporting)

Funding

CONACyT grant funding for the program 001877 - MASTER'S DEGREE IN SEMICONDUCTOR DEVICES

Competing interests

We declare that there are no conflicts of interest associated with the authors of this document.

Data availability

The data are available upon request to the corresponding author.

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The authors declare no competing interests.

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High blue emission in impurified (Er-doped) SiOC films obtained by the HWCVD technique using SBA-15 and TEOS

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1. Introduction

2. Experimental procedure

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