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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 23 — Nov. 9, 2009
  • pp: 21098–21107
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Room-temperature photoluminescence in erbium-doped deuterated amorphous carbon prepared by low-temperature MO-PECVD

Raymond Y. C. Tsai, Li Qian, Hossein Alizadeh, and Nazir P. Kherani  »View Author Affiliations


Optics Express, Vol. 17, Issue 23, pp. 21098-21107 (2009)
http://dx.doi.org/10.1364/OE.17.021098


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Abstract

We report on a novel optical thin film material, erbium-doped deuterated amorphous carbon, fabricated directly on silicon substrate at room-temperature via controlled thermal evaporation of a Metal-Organic compound in a Plasma-Enhanced Chemical Vapour Deposition (MO-PECVD) system. High erbium concentrations (up to 2.3 at.%) and room-temperature photoluminescence at 1.54 μm are successfully demonstrated. Concentration quenching due to erbium clustering is reduced by adopting an appropriate MO precursor—Er(tmhd)3. Another quenching mechanism, caused by non-radiative C-H and O-H vibrational transitions, is shown for the first time to be significantly reduced by deuteration instead of hydrogenation of amorphous carbon. Our results suggest that erbium-doped deuterated amorphous carbon is a promising new class of photonic material for silicon-compatible optoelectronics applications in the technologically important 1.5μm wavelength region.

© 2009 OSA

1. Introduction

Integration of electronic and optical communication devices on a single silicon chip is challenged by silicon’s inability to readily emit or amplify light on the one hand, and its incompatibility with predominately III-V high speed photonic devices on the other. Realization of electrical and optical functions co-existing on a single chip requires the development of silicon-compatible light emitting materials. Due to Er3+ emission in the 1.5 μm region, the wavelength preferred by the majority of optical communication devices, erbium doping in a variety of silicon-based materials has been investigated [1

1. A. Polman, “Erbium implanted thin film photonic materials,” J. Appl. Phys. 82(1), 1–39 ( 1997). [CrossRef]

] for their potential application in integrated optoelectronics. Most recent breakthroughs include the demonstration of electroluminescence in erbium-doped silicon-rich silicon oxide (SRSO(Er)) light-emitting diodes [2

2. M. E. Castagna, A. Muscara, S. Leonardi, S. Coffa, L. Caristia, C. Tringali, and S. Lorenti, “Si-based erbium-doped light-emitting devices,” J. Lumin. 121(2), 187–192 ( 2006). [CrossRef]

], the observation of optically pumped gain and amplifier characteristic in SRSO(Er) waveguides [3

3. J. Lee, J. H. Shin, and N. Park, “Optical gain at 1.5 μm in nanocrystal Si-sensitized Er-doped silica waveguide using top-pumping 470 nm LEDs,” J. Lightwave Technol. 23(1), 19–25 ( 2005). [CrossRef]

,4

4. V. Toccafondo, F. Di Pasquale, S. Faralli, N. Daldosso, L. Pavesi, and H. E. Hernandez-Figueroa, “Study of an efficient longitudinal multimode pumping scheme for Si-nc sensitized EDWAs,” Opt. Express 15(22), 14907–14913 ( 2007). [CrossRef] [PubMed]

], and the realization of an ultra-low threshold in optically pumped micro-laser based on erbium-implanted SiO2 [5

5. A. Polman, B. Min, J. Kalkman, T. J. Kippenberg, and K. J. Vahala, “Ultralow-threshold erbium-implanted toroidal microlaser on silicon,” Appl. Phys. Lett. 84(7), 1037–1039 ( 2004). [CrossRef]

]. Extensive efforts in seeking promising host candidates are still going strong. Other than crystalline silicon and silica, it was shown that photo- or electro-luminescence at 1.54μm also exists in hydrogenated amorphous silicon [2

2. M. E. Castagna, A. Muscara, S. Leonardi, S. Coffa, L. Caristia, C. Tringali, and S. Lorenti, “Si-based erbium-doped light-emitting devices,” J. Lumin. 121(2), 187–192 ( 2006). [CrossRef]

], in silicon carbide [6

6. R. A. Babunts, V. A. Vetrov, I. V. Ilin, E. N. Mokhov, N. G. Romanov, V. A. Khramtsov, and P. G. Baranov, “Properties of erbium luminescence in bulk crystals of silicon carbide,” Phys. Solid State 42(5), 829–835 ( 2000). [CrossRef]

,7

7. M. Markmann, E. Neufeld, A. Sticht, K. Brunner, and G. Abstreiter, “Excitation efficiency of electrons and holes in forward and reverse biased epitaxially grown Er-doped Si diodes,” Appl. Phys. Lett. 78(2), 210–212 ( 2001). [CrossRef]

], and in Er silicate [8

8. M. Miritello, R. L. Savio, F. Iacona, G. Franzò, A. Irrera, A. M. Piro, C. Bongiorno, and F. Priolo, “Efficient Luminescence and Energy Transfer in Erbium Silicate Thin Films,” Adv. Mater. 19(12), 1582–1588 ( 2007). [CrossRef]

], and more recently, optical gain was observed in Yb3+-sensitized Er-doped porous silicon [9

9. A. Najar, J. Charrier, H. Ajlani, N. Lorrain, S. Haesaert, M. Oueslati, and L. Haji, “Optical gain at 1.53 μm in Er3+–Yb3+ co-doped porous silicon waveguides,” Mater. Sci. Eng. B 146(1-3), 260–263 ( 2008). [CrossRef]

].

Notwithstanding the extensive research on Er-doped silicon-based materials, Er-doping in carbon materials has received little scrutiny, despite the fact that carbon-based materials are compatible with silicon substrates and offer a number of advantages as a host. Take hydrogenated amorphous carbon (a-C:H) as an example, which can be readily prepared using a low-temperature plasma enhanced chemical vapour deposition (PECVD) process. (Here, hydrogenation of amorphous carbon stabilizes the structure by terminating the π dangling bonds.) This material is promising because of its high film quality, its easy integration with current metal-oxide-semiconductor (CMOS) technology, and its low cost and reproducibility. Moreover, it is feasible to obtain a-C:H films with a wide range of opto-electronic properties by adjusting the deposition parameters in the growth process. In particular, a-C:H offers the following desirable properties [10

10. R. Clergereaux, D. Escaich, S. Martin, P. Raynaud, and F. Gaillard, “Carbon Layer as a New Material for Optics,” in New Materials for Microphotonics, edited by J. H. Shin, M. Brongersma, C. Buchal, and F. Priolo (Mater. Res. Soc. Symp. Proc. 817, Warrendale, PA, 2004), paper L6.23.

]: (i) it can be directly deposited on silicon substrate and easily etched by an oxygen plasma, allowing easy integration; (ii) it has large tailorable optical band gap (0.9 – 4.3 eV) covering from IR to visible; (iii) its conductivity can be altered by two orders of magnitude (5×103 – 5×105 S m−1) through p- or n-doping; (iv) its refractive index can be altered from 1.47 – 2.76, providing more flexibility in waveguide design and mode confinement. These flexible opto-electronic properties of a-C:H allows one to tailor the host material for specific optoelectronic applications.

Major difficulties with obtaining light emission near 1.54 μm in Er-doped a-C:H films is due to the severe quenching of radiative emission by the C-H and O-H vibrational modes [11

11. L. Winkless, R. H. C. Tan, Y. Zheng, M. Motevalli, P. B. Wyatt, and W. P. Gillin, “Quenching of Er(III) luminescence by ligand C–H vibrations: Implications for the use of erbium complexes in telecommunications,” Appl. Phys. Lett. 89(11), 111115 ( 2006). [CrossRef]

,12

12. Y. Yan, A. J. Faber, and H. de Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 ( 1995). [CrossRef]

]. Herein we report, for the first time, that deuteration, instead of hydrogenation, can effectively overcome the quenching of ErP3+P luminescence caused C-H and O-H bonds. Erbium-doped deuterated amorphous carbon (a-C:D(Er)) films are fabricated directly on silicon substrate at room-temperature via an MO-PECVD system. We show that high erbium concentrations and significantly enhanced room-temperature photoluminescence (PL) at 1.54 μm can be obtained in a-C:D(Er). Our results suggest that a-C:D(Er) is a promising photonic material for silicon-compatible optoelectronics applications.

2. Amorphous carbon as a host material

2.1 The metal-organic precursor

One important concern regarding the host material for erbium is its ability to reduce concentration quenching effects associated with erbium ion clustering at high concentrations. Such quenching effects limit the optical gain that can be obtained from Er-doped hosts, as a result of co-operative upconversion and energy migration [13

13. J.-M. P. Delavaux, S. Granlund, O. Mizuhara, L. D. Tzeng, D. Barbier, M. Rattay, F. Saint André, and A. Kevorkian, “Integrated optics erbium-ytterbium amplifier system in 10-Gb/s fiber transmission experiment,” IEEE Photon. Technol. Lett. 9, 247–249 ( 1997). [CrossRef]

,14

14. G. N. van den Hoven, E. Snoeks, A. Polman, C. van Dam, J. W. M. van Uffelen, and M. K. Smit, “Upconversion in Er-implanted Al2O3 waveguides,” J. Appl. Phys. 79(3), 1258–1266 ( 1996). [CrossRef]

]. At high erbium concentrations, an Er ion in the excited state is more likely to release its energy non-radiatively to cause an upward transition in a nearby Er ion, a process known as co-operative upconversion, than to de-excite radiatively. The upconversion process is then likely to repeat through a chain of ion-ion interactions, resulting in energy migration in a host until a quenching centre is encountered, where the energy is dissipated non-radiatively. This quenching process causes a decrease in luminescence efficiency [15

15. F. Priolo, G. Franzò, D. Pacific, V. Vinciguerra, F. Iacona, and A. Irrera, “Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals,” J. Appl. Phys. 89(1), 264–272 ( 2001). [CrossRef]

].

To reduce concentration quenching, we selected tris(2,2,6,6-tetramethy1-3-5-heptanedionato) Erbium(III), abbreviated Er(tmhd)3, as the metal-organic precursor in our MO-PECVD process. Its chemical composition is Er(C11H19O2)3, which is illustrated in Fig. 1
Fig. 1 Illustration of the erbium metal organic precursor, tris(2,2,6,6-tetramethy1-3-5-heptanedionato) Erbium(III), abbreviated Er(tmhd)3. The large central atom (purple) represents Er, the immediately surrounding 6 atoms (red) represent O, the larger atoms (dark grey) attached to the oxygen atoms are C atoms, while the smaller atoms (light grey) attached to carbon atoms represent H atoms. Note, the hydro-carbon ligands provide the framework for seamless integration into a hydrogenated/deuterated amorphous carbon network.
. Under appropriate deposition conditions, the Er(tmhd)3 molecule can be incorporated into the host material while preserving the Er-O bonds, as well as the long carbon chains (ligands). Thus, large separation between erbium ions is ensured, and accordingly, Er-Er co-operative upconversion is reduced. Moreover, the hydro-carbon ligands provide the framework for seamless integration into a hydrogenated (or deuterated) amorphous carbon network, allowing high solubility of erbium. Erbium concentration as high as 8.74 at.% in carbon films was reported [16

16. V. Prajzlera, I. Huttel, P. Nekvindova, J. Schrfel, A. Mackova, and J. Gurovic, “Erbium doping into thin carbon optical layers,” Thin Solid Films 433(1-2), 363–366 ( 2003). [CrossRef]

]. Furthermore, the ligands in Er(tmhd)3 act as sensitizers, which absorb optical excitation energy and transfer it to the encapsulated Er ion [17

17. G. A. Crosby and M. Kasha, “Intramolecular energy transfer in ytterbium organic chelates,” Spectrochim. Acta [A] 10, 377–382 ( 1958).

20

20. O. H. Park, S. Y. Seo, B. S. Bae, and J. H. Shin, “Indirect excitation of Er3+ in sol-gel hybrid films doped with an erbium complex,” Appl. Phys. Lett. 82(17), 2787–2789 ( 2003). [CrossRef]

]. Thus, the effective absorption cross-section of Er3+ is increased, making it more amenable to optical pumping.

Other advantages of using Er(tmhd)3 as a precursor include: (i) Er(tmhd)3 has a high vapour pressure of 0.1 mm Hg at 160 °C [21

21. J. E. Sicre, J. T. Dubois, K. J. Eisentraut, and R. E. Sievers, “Volatile lanthanide chelates. II. Vapor pressures, heats of vaporization, and heats of sublimation,” J. Am. Chem. Soc. 91(13), 3476–3481 ( 1969). [CrossRef]

], allowing us to deliver a controlled evaporant using a low-temperature deposition technique; (ii) unlike ion-implantation, which is expensive and creates film damage during the implantation process, our low-temperature MO-PECVD technique does not require subsequent high-temperature annealing to repair film damage; (iii) each Er(tmhd)3 molecule contains an erbium ion in the Er3+ form (which emits at 1.54mm) surrounded by six oxygen atoms [22

22. N. I. Giricheva, N. V. Belova, S. A. Shlykov, G. V. Girichev, N. Vogt, N. V. Tverdova, and J. Vogt, “Molecular structure of tris(dipivaloylmethanato)lanthanum(III) studied by gas electron diffraction,” J. Mol. Struct. 605(2-3), 171–176 ( 2002). [CrossRef]

], which can be directly incorporated in the host material without needing a post-growth process to activate erbium; and, (iv) Er(tmhd)3 does not give rise to contamination problems often associated with using other metal-organic sources for Er [23

23. D. B. Beach, R. T. Collions, F. K. Legoues, and J. O. Chu, “Erbium-Doped Silicon Prepared by UHV/CVD,” in Chemical Perspectives of Microelectronic Materials III, edited by C.R. Abernathy, C.W. Bates, Jr., D.A. Bohling, and W.S. Hobson (Mater. Res. Soc. Symp. Proc. 282, Pittsburgh, PA, 1993) 397–402.

].

2.2 Hydrogenation versus deuteration

Another important issue concerning a host for Er is the existence of non-radiative deactivation channels intrinsically within the host material. For amorphous carbon, it is well known that C-H vibrations in the vicinity of Er3+ play an important role in quenching the luminescence lifetime of Er3+ [11

11. L. Winkless, R. H. C. Tan, Y. Zheng, M. Motevalli, P. B. Wyatt, and W. P. Gillin, “Quenching of Er(III) luminescence by ligand C–H vibrations: Implications for the use of erbium complexes in telecommunications,” Appl. Phys. Lett. 89(11), 111115 ( 2006). [CrossRef]

], and hydroxyl groups (O-H) was also shown to resonate with the Er3+ 1.5 μm emission in silicate glass [12

12. Y. Yan, A. J. Faber, and H. de Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 ( 1995). [CrossRef]

]. A systematic comparison between Er-implanted silicate glasses with different O-H impurity contents showed a correlation between O-H content and luminescence lifetime [24

24. E. Snoeks, P. G. Kik, and A. Polman, “Concentration quenching in erbium implanted alkali silicate glasses,” Opt. Mater. 5(3), 159–167 ( 1996). [CrossRef]

]. In Fig. 2
Fig. 2 Illustration of energy levels of vibrational modes in organic media and the broadened 4I13/24I15/2 transition of Er3+; ν represents the harmonic numbers. The data concerning the C-H, C-D, O-H, and O-D vibrational modes are taken from [26]. The arrows indicate the energy transfer from excited Er3+ to the matching vibrational modes. The different styles of the arrows (bold compared to dashed) indicate the transition probability, which is higher for C-H and O-H at ν = 2 (bold) than for C-D and O-D at ν = 3 (dashed).
, it can be clearly seen that the radiative transition in Er3+ (~6500 cm−1), between the ground state 4I15/2 and the first excited state 4I13/2, approximately matches the second harmonics of C-H and O-H bond vibrations (5900 and 6900 cm−1, respectively) of the host material. Hence, excited Er ions can efficiently perturb the nearby C-H or O-H oscillators, resulting in a non-radiative transition. It is therefore not surprising that so far only one publication, by Speranza et al. [25

25. G. Speranza, L. Calliari, M. Ferrari, A. Chiasera, K. Tran Ngoc, A. M. Baranov, V. V. Sleptsov, A. A. Nefedov, A. E. Varfolomeev, and S. S. Fanchenko, “Erbium-doped thin amorphous carbon films prepared by mixed CVD sputtering,” Appl. Surf. Sci. 238(1-4), 117–120 ( 2004). [CrossRef]

], reported a study of Er luminescence in a a-C:H host, observing very weak Er photoluminescence (PL) despite applying a high optical excitation power on a sample of high Er concentration (~1.2 at.%).

To effectively suppress this inherent quenching of Er emission by C-H and O-H vibration modes, in this study, we remove the C-H bonds in the host by substituting hydrogen atoms with heavier deuterium atoms (H → D), consequently presenting a first demonstration of significantly enhanced room-temperature photoluminescence in erbium-doped deuterated amorphous carbon (a-C:D(Er)) films.

As can be seen from Fig. 2, deuteration modifies the harmonic number, ν, of the transitions that overlap with the radiative transition of Er, from ν = 2 (for C-H and O-H) to ν = 3 (for C-D and O-D). The interaction strength between Er3+ and the third harmonic of C-D vibrations, is much weaker than that between Er3+ and the second harmonic of C-H vibrations [26

26. Y. Haas, G. Stein, and E. Wurzberg, “Radiationless transitions in solutions: Isotope and proximity effects on Dy3+ by C-H and C-N bonds,” J. Chem. Phys. 60, 258–263 ( 1974). [CrossRef]

]. Therefore transition probability between Er3+ and the vibration modes of the host material is reduced through deuteration. The transition probabilities of ν = 2 and ν = 3 can be quantitatively compared by adopting the Franck-Condon factor, F, with an approximation of the undistorted oscillator model [27

27. W. Siebrand, “Radiationless Transitions in Polyatomic Molecules. I. Calculation of Franck—Condon Factors,” J. Chem. Phys. 46(2), 440–448 ( 1967). [CrossRef]

]:
F(E)=eγγνν!,   γ=12k(q¯q¯0)2ω
(1)
where k is force constant, q¯and q¯0are equilibrium positions of the oscillators, ħ is Planck’s constant, and ω is frequency. Equation (1) suggests that the factor F decrease as ν increases. As an example, F are 0.076 and 0.012 for ν = 2 and ν = 3, respectively, assuming γ = 0.5.

3. Sample fabrication

Four a-C:D(Er) samples with varying Er concentrations were prepared by dc saddle-field PECVD (DCSF-PECVD) [28

28. R. V. Kruzelecky, S. Zukotynski, C. I. Ukah, F. Gaspari, and J. M. Perz, “The preparation of amorphous Si:H thin films for optoelectronic applications by glow discharge dissociation of SiH4 using a direct-current saddle-field plasma chamber,” J. Vac. Sci. Technol. A 7(4), 2632 ( 1989). [CrossRef]

30

30. J. Franks, “Atom beam source,” Vacuum 34(1-2), 259–261 ( 1984). [CrossRef]

] at room temperature using deuterated methane (CD4) as the precursor gas. The films were deposited on a 0.6-mm-thick 10-20 Ωcm crystalline silicon 〈100〉 and 1-mm-thick fused silica substrates. Erbium incorporation was achieved through thermal evaporation of metal-organic precursor Er(tmhd)3, inside the deposition chamber as illustrated in Fig. 4
Fig. 4 A schematic diagram of metal organic – dc saddle-field plasma enhanced chemical vapour deposition system used for the preparation of erbium doped deuterated amorphous carbon. The grey region surrounding the semi-transparent electrodes (mesh) represents the deuterated methane plasma.
.

The semi-transparent mesh anode is situated symmetrically between two parallel electrically grounded semi-transparent mesh cathodes. The resulting symmetric electric field serves to significantly extend the electron mean free path, thus permitting lower pressure dc discharges ordinarily not attainable with dc diode electrode configuration.

The evaporator containing the metal-organic precursor is placed ~8 cm away from the edge of the substrate holder. The Er doping concentration was controlled by modulating the evaporator temperature, and accordingly, the evaporant flux.

4. Sample characterization techniques

Three characterization tools were applied to study the material and the optical properties of our thin-film samples: X-ray photoelectron spectroscopy (XPS) was used to determine the composition of the film; Photoluminescence (PL) spectra were used to compare the relative photo emission intensities from different samples in the 1.5μm region; and the binding energy (BE) spectra were used to study the oxidation state of Er. Below we provide details on the tools and procedures of the film characterizations.

XPS spectra were recorded on a K-Alpha monochromated XPS spectrometer (Thermo scientific, East Grinstead, UK) which included a monochromatic Al K-Alpha (1486.6 eV) x-ray source used for excitation and an ultra high vacuum chamber (operating pressure ~7.5 × 10−8 Torr) with the vast majority of the residual pressure due to argon from the operation of the surface charge compensation flood gun. The elemental composition and depth distribution was determined by dividing the individual peak area, after background subtraction [31

31. D. Shirley, “High-Resolution X-Ray Photoemission Spectrum of the Valence Bands of Gold,” Phys. Rev. B 5(12), 4709–4714 ( 1972). [CrossRef]

], by their respective atomic sensitivity factor (ASF) provided by the manufacturer.

The BE used to study the oxidation state of Er was calibrated by using the peak of adventitious carbon, setting it to 285 eV. High resolution spectra were fitted using Gaussian-Lorentzian curves in order to more accurately determine the BE of Er 4d core level. Prior to curve fitting, a background was subtracted.

PL measurements were performed on the samples to verify the optical activity of Er in a-C:D films. The optical pumping source for the PL measurement was the 514 nm line of an Ar+ laser, operating at 600mW. It is focused down to 1mm spot size on the surface of the sample. The energy from the laser is near resonant with 2H11/2 excited level of Er ions. The excited Er ions decay to the 4I13/2 level through fast non-radiative transition and then emit at 1.54 μm through the 4I13/24I15/2 transition. The emission spectrum from Er ions is dispersed by double-grating monochromator, with a 70-μm input/output slit size, and detected by a thermoelectric-cooled InGaAs photodetector using a standard lock-in technique.

5. Results and discussion

Erbium concentrations of 0.47, 0.75, 1.4, and 2.3 at.% in a-C:D film samples were measured using XPS, and the atomic concentrations in the films are summarized in Table 1

Table 1. Atomic concentrations of a-C:D(Er) samples computed from XPS spectra

table-icon
View This Table
. Figure 5
Fig. 5 C, Si, O, Er and O concentrations as function of the distance from the film surface as determined by XPS for sample #4.
depicts Er, O, and C concentrations for Sample #4 (the one with the highest Er content) as a function of the distance from the film surface, showing uniform erbium concentration across the thickness of the sample, which is 2 μm. The drop in the Er concentration near the surface is associated with the depletion of the Er MO reservoir; on the other hand, the increase of the O concentration near the surface could be caused by surface contamination. The analysis also suggests some C and O penetration into the Si substrate, likely an effect of the sputtering process during the XPS. The O/Er ratio is observed to be approximately 6 in the film region, suggesting that the source of O is mainly from the metal-organic ligands, as intended.

As seen in Fig. 6 (a)
Fig. 6 (a) Room-temperature PL spectra of a-C:D(Er) samples with different Er concentrations and film thicknesses. The peak is centered at 1540 nm with FWHM of ~70 nm. (b) The peak PL intensity normalized to film thickness as a function of Er concentration in a-C:D(Er) films. The symbols are actual data points, the line is a guide to the eye. The linear region suggests no concentration quenching for Er concentrations up to at least 1.4 at.%.
, room-temperature PL spectra peaked at 1540 nm, corresponding to the 4I13/24I15/2 transition of Er3+ and its full width at half-maximum (FWHM) is about 70 nm. This FWHM is wider than those of other Er-doped silicate glasses, suggesting that Er3+ have different local environments in the amorphous carbon matrix. The wider emission bandwidth indicates the potential of enabling a wide gain bandwidth for optical amplification.

To study the concentration dependence of the Er luminescence efficiency in more detail, the peak PL intensity is normalized to film thickness, denoted by Inor, and then plotted as a function of Er concentration NEr. Under cw laser excitation, Inor is proportional to σφNτ/τrad, where σ is the excitation cross section, φ is the photon flux, N is the optically active Er concentration, τ is the lifetime, and τrad is the radiative lifetime. If all incorporated Er atoms are optically active, i.e., N ≈ NEr, and if there are no quenching effects that would affect σ and τ/τrad, an increase in NEr should be accompanied by a linear increase in Inor. In Fig. 6(b), Inor increases linearly up to 1.4 at.% of Er and then begins to drop, suggesting a reduction in τ as NEr increases beyond this point; this indicates that concentration quenching is beginning to become significant only after the Er concentration has reached 1.4 at.% and beyond.

In order to verify that the majority of the incorporated erbium is in the optically active form of Er3+, surrounded by oxygen atoms (as illustrated in Fig. 1), binding energy (BE) analysis using XPS was carried out. The shape of the BE spectrum is indicative of the oxidation state of Er in the material, and the BE spectra of the Er(tmhd)3 powder, the evaporated film of Er(tmhd)3, and all a-C:D(Er) samples were compared. The normalized 4d spectra of Er are given in Fig. 7
Fig. 7 Er 4d XPS spectra of the four a-C:D(Er) film samples, an Er(tmhd)R3R film (prepared by evaporating the powder) and the Er(tmhd)R3R powder. Each spectrum is normalized to its maximum intensity after a background subtraction and offset vertically for clarity of presentation.
, showing a characteristic spectral feature near 169 eV. Such feature is attributed to the 4d levels in Er3+ forming a multiplet through an interaction with the unfilled shell [32

32. J. F. Moulder, W. F. Stickle, P. E. Sobol, and K. D. Bomben, Handbook of X-ray Photoemission Spectroscopy, Physical Electronics Division (Perkin-Elmer, Eden Prairie, 1995).

]. Spectral multiplets at ~169 eV with essentially the same features as shown in Fig. 6 were observed in the 4d photoemission spectra obtained from the erbium state of 4f11/Er3+ [32

32. J. F. Moulder, W. F. Stickle, P. E. Sobol, and K. D. Bomben, Handbook of X-ray Photoemission Spectroscopy, Physical Electronics Division (Perkin-Elmer, Eden Prairie, 1995).

], as well as from Er2O3 [33

33. N. Guerfi, T. A. Nguyen Tan, J. Y. Veuillen, and D. B. Lollman, “Oxidation of thin ErSi1.7 overlayers on Si(111),” Appl. Surf. Sci. 56, 501–506 ( 1992). [CrossRef]

]. The existence of the multiplet near 169 eV for all the cases we measured suggests that the oxidation state of Er in Er(tmhd)3 powder did not change markedly during evaporation and the deposition of the Er(tmhd)3 film, nor did it change significantly during the MO-PECVD process. We therefore conclude that the incorporation of Er into the a-C:D(Er) samples essentially preserves the Er3+ state, forming efficient emission centers.

6. Conclusion

We have demonstrated significantly enhanced room-temperature Er photoluminescence in a-C:D(Er) thin films deposited by metal-organic PECVD. Our simple fabrication technique offers four essential advantages of the a-C:D(Er) material: (i) controllable and uniform Er concentration as large as 2.3 at.%, the highest reported in amorphous carbon as a host material; (ii) the possibility of obtaining a wide range of tailorable optoelectronic properties; (iii) the elimination of the annealing step (a required step in many Er-doped materials); and, (iv) deuteration for suppressing quenching. All these concur in an easy one-step film growth procedure. Film thicknesses up to 2000 nm have been achieved using this technique. No concentration quenching effects have been observed up to 1.4 at.% Er3+. Binding energy analysis confirmed that the Er ions in a-C:D(Er) having the optically active oxidation state of Er+3 can be incorporated at room-temperature. It has also been shown that deuteration of amorphous carbon has effectively removed the non-radiative second order C-H and O-H vibrational modes, resulting in a significant enhancement in PL at 1.5 μm in a-C:D(Er) in contrast to that in a-C:H(Er). The efficient Er emission in a-C:D(Er) films, along with its wide range of tailorable conductivity, optical bandgap and refractive index, suggests a-C:D(Er) is a promising material for realizing integrated light-emitting and light-amplifying devices using CMOS technology.

Acknowledgements

We thank the following researchers who assisted with this work: G. Weiser for technical discussion on the selection of metal-organic Er compounds, V. Sukvatkin for assistance with the PL measurements, P. Broderson for performing XPS analysis, D. Yeghikyan and T. Kosteski for assistance with the fabrication facility, and A. Chutinan with the illustration of the metal-organic Er precursor. This work was supported through grants from the Natural Sciences and Engineering Research Council of Canada, Ontario Centres of Excellence, and Ontario Research Fund – Research Excellence program.

References and links

1.

A. Polman, “Erbium implanted thin film photonic materials,” J. Appl. Phys. 82(1), 1–39 ( 1997). [CrossRef]

2.

M. E. Castagna, A. Muscara, S. Leonardi, S. Coffa, L. Caristia, C. Tringali, and S. Lorenti, “Si-based erbium-doped light-emitting devices,” J. Lumin. 121(2), 187–192 ( 2006). [CrossRef]

3.

J. Lee, J. H. Shin, and N. Park, “Optical gain at 1.5 μm in nanocrystal Si-sensitized Er-doped silica waveguide using top-pumping 470 nm LEDs,” J. Lightwave Technol. 23(1), 19–25 ( 2005). [CrossRef]

4.

V. Toccafondo, F. Di Pasquale, S. Faralli, N. Daldosso, L. Pavesi, and H. E. Hernandez-Figueroa, “Study of an efficient longitudinal multimode pumping scheme for Si-nc sensitized EDWAs,” Opt. Express 15(22), 14907–14913 ( 2007). [CrossRef] [PubMed]

5.

A. Polman, B. Min, J. Kalkman, T. J. Kippenberg, and K. J. Vahala, “Ultralow-threshold erbium-implanted toroidal microlaser on silicon,” Appl. Phys. Lett. 84(7), 1037–1039 ( 2004). [CrossRef]

6.

R. A. Babunts, V. A. Vetrov, I. V. Ilin, E. N. Mokhov, N. G. Romanov, V. A. Khramtsov, and P. G. Baranov, “Properties of erbium luminescence in bulk crystals of silicon carbide,” Phys. Solid State 42(5), 829–835 ( 2000). [CrossRef]

7.

M. Markmann, E. Neufeld, A. Sticht, K. Brunner, and G. Abstreiter, “Excitation efficiency of electrons and holes in forward and reverse biased epitaxially grown Er-doped Si diodes,” Appl. Phys. Lett. 78(2), 210–212 ( 2001). [CrossRef]

8.

M. Miritello, R. L. Savio, F. Iacona, G. Franzò, A. Irrera, A. M. Piro, C. Bongiorno, and F. Priolo, “Efficient Luminescence and Energy Transfer in Erbium Silicate Thin Films,” Adv. Mater. 19(12), 1582–1588 ( 2007). [CrossRef]

9.

A. Najar, J. Charrier, H. Ajlani, N. Lorrain, S. Haesaert, M. Oueslati, and L. Haji, “Optical gain at 1.53 μm in Er3+–Yb3+ co-doped porous silicon waveguides,” Mater. Sci. Eng. B 146(1-3), 260–263 ( 2008). [CrossRef]

10.

R. Clergereaux, D. Escaich, S. Martin, P. Raynaud, and F. Gaillard, “Carbon Layer as a New Material for Optics,” in New Materials for Microphotonics, edited by J. H. Shin, M. Brongersma, C. Buchal, and F. Priolo (Mater. Res. Soc. Symp. Proc. 817, Warrendale, PA, 2004), paper L6.23.

11.

L. Winkless, R. H. C. Tan, Y. Zheng, M. Motevalli, P. B. Wyatt, and W. P. Gillin, “Quenching of Er(III) luminescence by ligand C–H vibrations: Implications for the use of erbium complexes in telecommunications,” Appl. Phys. Lett. 89(11), 111115 ( 2006). [CrossRef]

12.

Y. Yan, A. J. Faber, and H. de Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 ( 1995). [CrossRef]

13.

J.-M. P. Delavaux, S. Granlund, O. Mizuhara, L. D. Tzeng, D. Barbier, M. Rattay, F. Saint André, and A. Kevorkian, “Integrated optics erbium-ytterbium amplifier system in 10-Gb/s fiber transmission experiment,” IEEE Photon. Technol. Lett. 9, 247–249 ( 1997). [CrossRef]

14.

G. N. van den Hoven, E. Snoeks, A. Polman, C. van Dam, J. W. M. van Uffelen, and M. K. Smit, “Upconversion in Er-implanted Al2O3 waveguides,” J. Appl. Phys. 79(3), 1258–1266 ( 1996). [CrossRef]

15.

F. Priolo, G. Franzò, D. Pacific, V. Vinciguerra, F. Iacona, and A. Irrera, “Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals,” J. Appl. Phys. 89(1), 264–272 ( 2001). [CrossRef]

16.

V. Prajzlera, I. Huttel, P. Nekvindova, J. Schrfel, A. Mackova, and J. Gurovic, “Erbium doping into thin carbon optical layers,” Thin Solid Films 433(1-2), 363–366 ( 2003). [CrossRef]

17.

G. A. Crosby and M. Kasha, “Intramolecular energy transfer in ytterbium organic chelates,” Spectrochim. Acta [A] 10, 377–382 ( 1958).

18.

R. E. Whan and G. A. Crosby, “Luminescence studies of rare earth complexes: Benzoylacetonate and dibenzoylmethide chelates,” J. Mol. Spectrosc. 8(1-6), 315–327 ( 1962). [CrossRef]

19.

M. Kleinerman, “Energy Migration in Lanthanide Chelates,” Bull. Am. Phys. Sot. 9, 265 (1964), J. Chem. Phys. 51(6), 2370 ( 1969). [CrossRef]

20.

O. H. Park, S. Y. Seo, B. S. Bae, and J. H. Shin, “Indirect excitation of Er3+ in sol-gel hybrid films doped with an erbium complex,” Appl. Phys. Lett. 82(17), 2787–2789 ( 2003). [CrossRef]

21.

J. E. Sicre, J. T. Dubois, K. J. Eisentraut, and R. E. Sievers, “Volatile lanthanide chelates. II. Vapor pressures, heats of vaporization, and heats of sublimation,” J. Am. Chem. Soc. 91(13), 3476–3481 ( 1969). [CrossRef]

22.

N. I. Giricheva, N. V. Belova, S. A. Shlykov, G. V. Girichev, N. Vogt, N. V. Tverdova, and J. Vogt, “Molecular structure of tris(dipivaloylmethanato)lanthanum(III) studied by gas electron diffraction,” J. Mol. Struct. 605(2-3), 171–176 ( 2002). [CrossRef]

23.

D. B. Beach, R. T. Collions, F. K. Legoues, and J. O. Chu, “Erbium-Doped Silicon Prepared by UHV/CVD,” in Chemical Perspectives of Microelectronic Materials III, edited by C.R. Abernathy, C.W. Bates, Jr., D.A. Bohling, and W.S. Hobson (Mater. Res. Soc. Symp. Proc. 282, Pittsburgh, PA, 1993) 397–402.

24.

E. Snoeks, P. G. Kik, and A. Polman, “Concentration quenching in erbium implanted alkali silicate glasses,” Opt. Mater. 5(3), 159–167 ( 1996). [CrossRef]

25.

G. Speranza, L. Calliari, M. Ferrari, A. Chiasera, K. Tran Ngoc, A. M. Baranov, V. V. Sleptsov, A. A. Nefedov, A. E. Varfolomeev, and S. S. Fanchenko, “Erbium-doped thin amorphous carbon films prepared by mixed CVD sputtering,” Appl. Surf. Sci. 238(1-4), 117–120 ( 2004). [CrossRef]

26.

Y. Haas, G. Stein, and E. Wurzberg, “Radiationless transitions in solutions: Isotope and proximity effects on Dy3+ by C-H and C-N bonds,” J. Chem. Phys. 60, 258–263 ( 1974). [CrossRef]

27.

W. Siebrand, “Radiationless Transitions in Polyatomic Molecules. I. Calculation of Franck—Condon Factors,” J. Chem. Phys. 46(2), 440–448 ( 1967). [CrossRef]

28.

R. V. Kruzelecky, S. Zukotynski, C. I. Ukah, F. Gaspari, and J. M. Perz, “The preparation of amorphous Si:H thin films for optoelectronic applications by glow discharge dissociation of SiH4 using a direct-current saddle-field plasma chamber,” J. Vac. Sci. Technol. A 7(4), 2632 ( 1989). [CrossRef]

29.

P. K. Lim, F. Gaspari, and S. Zukotynski, “Structural properties of a-C:H deposited using saddle-field glow-discharge decomposition of methane,” J. Appl. Phys. 78(9), 5307 ( 1995). [CrossRef]

30.

J. Franks, “Atom beam source,” Vacuum 34(1-2), 259–261 ( 1984). [CrossRef]

31.

D. Shirley, “High-Resolution X-Ray Photoemission Spectrum of the Valence Bands of Gold,” Phys. Rev. B 5(12), 4709–4714 ( 1972). [CrossRef]

32.

J. F. Moulder, W. F. Stickle, P. E. Sobol, and K. D. Bomben, Handbook of X-ray Photoemission Spectroscopy, Physical Electronics Division (Perkin-Elmer, Eden Prairie, 1995).

33.

N. Guerfi, T. A. Nguyen Tan, J. Y. Veuillen, and D. B. Lollman, “Oxidation of thin ErSi1.7 overlayers on Si(111),” Appl. Surf. Sci. 56, 501–506 ( 1992). [CrossRef]

OCIS Codes
(130.3130) Integrated optics : Integrated optics materials
(160.5690) Materials : Rare-earth-doped materials

ToC Category:
Materials

History
Original Manuscript: August 24, 2009
Revised Manuscript: October 16, 2009
Manuscript Accepted: October 19, 2009
Published: November 4, 2009

Citation
Raymond Y. C. Tsai, Li Qian, Hossein Alizadeh, and Nazir P. Kherani, "Room-temperature photoluminescence in erbium-doped deuterated amorphous carbon prepared by low-temperature MO-PECVD," Opt. Express 17, 21098-21107 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-23-21098


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References

  1. A. Polman, “Erbium implanted thin film photonic materials,” J. Appl. Phys. 82(1), 1–39 (1997). [CrossRef]
  2. M. E. Castagna, A. Muscara, S. Leonardi, S. Coffa, L. Caristia, C. Tringali, and S. Lorenti, “Si-based erbium-doped light-emitting devices,” J. Lumin. 121(2), 187–192 (2006). [CrossRef]
  3. J. Lee, J. H. Shin, and N. Park, “Optical gain at 1.5 μm in nanocrystal Si-sensitized Er-doped silica waveguide using top-pumping 470 nm LEDs,” J. Lightwave Technol. 23(1), 19–25 (2005). [CrossRef]
  4. V. Toccafondo, F. Di Pasquale, S. Faralli, N. Daldosso, L. Pavesi, and H. E. Hernandez-Figueroa, “Study of an efficient longitudinal multimode pumping scheme for Si-nc sensitized EDWAs,” Opt. Express 15(22), 14907–14913 (2007). [CrossRef] [PubMed]
  5. A. Polman, B. Min, J. Kalkman, T. J. Kippenberg, and K. J. Vahala, “Ultralow-threshold erbium-implanted toroidal microlaser on silicon,” Appl. Phys. Lett. 84(7), 1037–1039 (2004). [CrossRef]
  6. R. A. Babunts, V. A. Vetrov, I. V. Ilin, E. N. Mokhov, N. G. Romanov, V. A. Khramtsov, and P. G. Baranov, “Properties of erbium luminescence in bulk crystals of silicon carbide,” Phys. Solid State 42(5), 829–835 (2000). [CrossRef]
  7. M. Markmann, E. Neufeld, A. Sticht, K. Brunner, and G. Abstreiter, “Excitation efficiency of electrons and holes in forward and reverse biased epitaxially grown Er-doped Si diodes,” Appl. Phys. Lett. 78(2), 210–212 (2001). [CrossRef]
  8. M. Miritello, R. L. Savio, F. Iacona, G. Franzò, A. Irrera, A. M. Piro, C. Bongiorno, and F. Priolo, “Efficient Luminescence and Energy Transfer in Erbium Silicate Thin Films,” Adv. Mater. 19(12), 1582–1588 (2007). [CrossRef]
  9. A. Najar, J. Charrier, H. Ajlani, N. Lorrain, S. Haesaert, M. Oueslati, and L. Haji, “Optical gain at 1.53 μm in Er3+–Yb3+ co-doped porous silicon waveguides,” Mater. Sci. Eng. B 146(1-3), 260–263 (2008). [CrossRef]
  10. R. Clergereaux, D. Escaich, S. Martin, P. Raynaud, and F. Gaillard, “Carbon Layer as a New Material for Optics,” in New Materials for Microphotonics, edited by J. H. Shin, M. Brongersma, C. Buchal, and F. Priolo (Mater. Res. Soc. Symp. Proc. 817, Warrendale, PA, 2004), paper L6.23.
  11. L. Winkless, R. H. C. Tan, Y. Zheng, M. Motevalli, P. B. Wyatt, and W. P. Gillin, “Quenching of Er(III) luminescence by ligand C–H vibrations: Implications for the use of erbium complexes in telecommunications,” Appl. Phys. Lett. 89(11), 111115 (2006). [CrossRef]
  12. Y. Yan, A. J. Faber, and H. de Waal, “Luminescence quenching by OH groups in highly Er-doped phosphate glasses,” J. Non-Cryst. Solids 181(3), 283–290 (1995). [CrossRef]
  13. J.-M. P. Delavaux, S. Granlund, O. Mizuhara, L. D. Tzeng, D. Barbier, M. Rattay, F. Saint André, and A. Kevorkian, “Integrated optics erbium-ytterbium amplifier system in 10-Gb/s fiber transmission experiment,” IEEE Photon. Technol. Lett. 9, 247–249 (1997). [CrossRef]
  14. G. N. van den Hoven, E. Snoeks, A. Polman, C. van Dam, J. W. M. van Uffelen, and M. K. Smit, “Upconversion in Er-implanted Al2O3 waveguides,” J. Appl. Phys. 79(3), 1258–1266 (1996). [CrossRef]
  15. F. Priolo, G. Franzò, D. Pacific, V. Vinciguerra, F. Iacona, and A. Irrera, “Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals,” J. Appl. Phys. 89(1), 264–272 (2001). [CrossRef]
  16. V. Prajzlera, I. Huttel, P. Nekvindova, J. Schrfel, A. Mackova, and J. Gurovic, “Erbium doping into thin carbon optical layers,” Thin Solid Films 433(1-2), 363–366 (2003). [CrossRef]
  17. G. A. Crosby and M. Kasha, “Intramolecular energy transfer in ytterbium organic chelates,” Spectrochim. Acta [A] 10, 377–382 (1958).
  18. R. E. Whan and G. A. Crosby, “Luminescence studies of rare earth complexes: Benzoylacetonate and dibenzoylmethide chelates,” J. Mol. Spectrosc. 8(1-6), 315–327 (1962). [CrossRef]
  19. M. Kleinerman, “Energy Migration in Lanthanide Chelates,” Bull. Am. Phys. Sot. 9, 265 (1964), J. Chem. Phys. 51(6), 2370 (1969). [CrossRef]
  20. O. H. Park, S. Y. Seo, B. S. Bae, and J. H. Shin, “Indirect excitation of Er3+ in sol-gel hybrid films doped with an erbium complex,” Appl. Phys. Lett. 82(17), 2787–2789 (2003). [CrossRef]
  21. J. E. Sicre, J. T. Dubois, K. J. Eisentraut, and R. E. Sievers, “Volatile lanthanide chelates. II. Vapor pressures, heats of vaporization, and heats of sublimation,” J. Am. Chem. Soc. 91(13), 3476–3481 (1969). [CrossRef]
  22. N. I. Giricheva, N. V. Belova, S. A. Shlykov, G. V. Girichev, N. Vogt, N. V. Tverdova, and J. Vogt, “Molecular structure of tris(dipivaloylmethanato)lanthanum(III) studied by gas electron diffraction,” J. Mol. Struct. 605(2-3), 171–176 (2002). [CrossRef]
  23. D. B. Beach, R. T. Collions, F. K. Legoues, and J. O. Chu, “Erbium-Doped Silicon Prepared by UHV/CVD,” in Chemical Perspectives of Microelectronic Materials III, edited by C.R. Abernathy, C.W. Bates, Jr., D.A. Bohling, and W.S. Hobson (Mater. Res. Soc. Symp. Proc. 282, Pittsburgh, PA, 1993) 397–402.
  24. E. Snoeks, P. G. Kik, and A. Polman, “Concentration quenching in erbium implanted alkali silicate glasses,” Opt. Mater. 5(3), 159–167 (1996). [CrossRef]
  25. G. Speranza, L. Calliari, M. Ferrari, A. Chiasera, K. Tran Ngoc, A. M. Baranov, V. V. Sleptsov, A. A. Nefedov, A. E. Varfolomeev, and S. S. Fanchenko, “Erbium-doped thin amorphous carbon films prepared by mixed CVD sputtering,” Appl. Surf. Sci. 238(1-4), 117–120 (2004). [CrossRef]
  26. Y. Haas, G. Stein, and E. Wurzberg, “Radiationless transitions in solutions: Isotope and proximity effects on Dy3+ by C-H and C-N bonds,” J. Chem. Phys. 60, 258–263 (1974). [CrossRef]
  27. W. Siebrand, “Radiationless Transitions in Polyatomic Molecules. I. Calculation of Franck—Condon Factors,” J. Chem. Phys. 46(2), 440–448 (1967). [CrossRef]
  28. R. V. Kruzelecky, S. Zukotynski, C. I. Ukah, F. Gaspari, and J. M. Perz, “The preparation of amorphous Si:H thin films for optoelectronic applications by glow discharge dissociation of SiH4 using a direct-current saddle-field plasma chamber,” J. Vac. Sci. Technol. A 7(4), 2632 (1989). [CrossRef]
  29. P. K. Lim, F. Gaspari, and S. Zukotynski, “Structural properties of a-C:H deposited using saddle-field glow-discharge decomposition of methane,” J. Appl. Phys. 78(9), 5307 (1995). [CrossRef]
  30. J. Franks, “Atom beam source,” Vacuum 34(1-2), 259–261 (1984). [CrossRef]
  31. D. Shirley, “High-Resolution X-Ray Photoemission Spectrum of the Valence Bands of Gold,” Phys. Rev. B 5(12), 4709–4714 (1972). [CrossRef]
  32. J. F. Moulder, W. F. Stickle, P. E. Sobol, and K. D. Bomben, Handbook of X-ray Photoemission Spectroscopy, Physical Electronics Division (Perkin-Elmer, Eden Prairie, 1995).
  33. N. Guerfi, T. A. Nguyen Tan, J. Y. Veuillen, and D. B. Lollman, “Oxidation of thin ErSi1.7 overlayers on Si(111),” Appl. Surf. Sci. 56, 501–506 (1992). [CrossRef]

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