An investigation into second harmonic generation by Si-rich SiN<sub><i>x</i></sub>thin films deposited by RF sputtering over a wide range of Si concentrations

Kitao, Akihiro; Imakita, Kenji; Kawamura, Ibuki; Fujii, Minoru

doi:10.1088/0022-3727/47/21/215101

Cited by 35 publications

(20 citation statements)

References 34 publications

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“…1). As the Si content increases (with the lower flow rate of NH 3 ), the transmittance threshold shifts towards shorter wavelengths in good agreement with previous studies [9]. The oscillatory behavior of the transmittance at longer wavelengths can be ascribed to interference between beams reflected at the interfaces of the SiN film.…”

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confidence: 90%

“…The problem can be overcome by poling [4,5], straining the material [3] or by using multilayer composites [6][7][8]. Unexpectedly, CMOS-compatible amorphous silicon nitride films (SiN) have been shown to possess a bulk second-order nonlinearity by measuring strong second-harmonic generation (SHG) from thin films [9][10][11]. Although the exact reason for this strong SHG response remains unclear, it is believed that the complicated composition, crystalline phase, and defects in the film during the deposition may be responsible [10,[12][13][14][15][16].…”

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confidence: 99%

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Enhancement of bulk second-harmonic generation from silicon nitride films by material composition

et al. 2017

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We present a comprehensive tensorial characterization of second-harmonic generation from silicon nitride films with varying compositions. The samples were fabricated using plasma-enhanced chemical vapor deposition, and the material composition was varied by the reactive gas mixture in the process. We found a six-fold enhancement between the lowest and highest second-order susceptibility, with the highest value of approximately 5 pm/V from the most silicon-rich sample. Moreover, the optical losses were found to be sufficiently small (below 6 dB/cm) for applications. The tensorial results show that all samples retain in-plane isotropy independent of the silicon content, highlighting the controllability of the fabrication process. High-performance complementary metal oxide semiconductor (CMOS) compatible materials are essential elements for advanced on-chip photonic devices to realize the future progress in all-optical processing. The ultra-fast speed and high bandwidth of integrated photonic networks continuously require new materials possessing excellent linear and nonlinear optical properties [1,2]. Although silicon (Si) is still the most commonly used CMOS material, the intrinsic drawbacks of Si, such as its narrow bandgap and centrosymmetric structure, highly limit its future applications especially in the visible and ultraviolet spectral regimes [2,3]. Thus, exploring novel CMOScompatible materials with wide bandgap and strong optical nonlinearities is very important for future integrated devices.Many photonic applications rely on nonlinear optical effects. One of the limitations of many nonlinear materials for CMOS-compatible platforms is the lack of second-order nonlinearity due to centrosymmetry. The problem can be overcome by poling [4,5], straining the material [3] or by using multilayer composites [6][7][8]. Unexpectedly, CMOS-compatible amorphous silicon nitride films (SiN) have been shown to possess a bulk second-order nonlinearity by measuring strong second-harmonic generation (SHG) from thin films [9][10][11]. Although the exact reason for this strong SHG response remains unclear, it is believed that the complicated composition, crystalline phase, and defects in the film during the deposition may be responsible [10,[12][13][14][15][16].In this Letter, we show that the strong second-harmonic signal from SiN films can be further enhanced by varying the composition of the films prepared with plasma-enhanced chemical vapor deposition (PECVD). Furthermore, we demonstrate that such composition tuning does not compromise the linear optical properties or optical losses of the material for applications. Our results are crucial for the comprehensive understanding of the linear and nonlinear optical properties in SiN films with different structures, opening the path for further optimization of SiN for on-chip devices.We recognize that there have been previous studies yielding different values for the SHG susceptibility of SiN [9,10,11,17,18]. Samples prepared by sputtering can yield very high values of the su...

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Enhancement of bulk second-harmonic generation from silicon nitride films by material composition

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“…The measured conversion efficiency corresponds to a high equivalent second-order susceptibility, χ ( eq 2) = 3.7±0.2 pm/V. Although highly Si-rich SiN thin films might be expected to yield a somewhat larger value as concluded from photoelectron spectroscopy ( χ ( eff 2) = 11.8 pm/V [25]), the second order susceptibility that we find is larger than in SiN thin films ( χ ( eff 2) = 2.5 pm/V [24]), is one order of magnitude larger than in stress-released Si 3 N 4 waveguides ( χ ( eff 2) = 0.3 pm/V [27]) and more than two orders of magnitude larger than in Si 3 N 4 ring resonators ( χ ( eff 2) < 0.04 pm/V) [26].…”

Section: Discussionmentioning

confidence: 90%

“…On the other hand, there have been four reports on second-order response in related amorphous SiN-type materials. Specifically, second-harmonic generation has been observed in SiN films (fabricated using plasma enhanced chemical vapor deposition [24] or fabricated with RF sputtering [25]), in Si 3 N 4 ring resonators (fabricated with plasma enhanced chemical vapor deposition at lower temperatures [26]) where the nanoscale structure of the waveguide breaks the inversion symmetry and modal phase matching is employed, and in Si 3 N 4 waveguides fabricated using stress release patterns [27] where, similar to our work, the coherent photogalvanic effect breaks the inversion symmetry. However, we find an equivalent secondorder response that is an order of magnitude larger.…”

Section: Introductionmentioning

confidence: 99%

Photo-induced second-order nonlinearity in stoichiometric silicon nitride waveguides

et al. 2017

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Abstract:We report the observation of second-harmonic generation (SHG) in stoichiometric silicon nitride waveguides grown via low-pressure chemical vapor deposition (LPCVD). Quasirectangular waveguides with a large cross section were used, with a height of 1 µm and various different widths, from 0.6 to 1.2 µm, and with various lengths from 22 to 74 mm. Using a mode-locked laser delivering 6-ps pulses at 1064 nm wavelength with a repetition rate of 20 MHz, 15% of the incoming power was coupled through the waveguide, making maximum average powers of up to 15 mW available in the waveguide depending on the waveguide cross section. Second-harmonic output was observed with a delay of minutes to several hours after the initial turn-on of pump radiation, showing a fast growth rate between 10 −4 to 10 −2 s −1 , with the shortest delay and highest growth rate at the highest input power. After this first, initial build-up (observed delay and growth), the second-harmonic became generated instantly with each new turn-on of the pump laser power. Phase matching was found to be present independent of the used waveguide width, although the latter changes the fundamental and second-harmonic phase velocities. We address the presence of a second-order nonlinearity and phase matching, involving an initial, power-dependent build-up, to the coherent photogalvanic effect. The effect, via the third-order nonlinearity and multiphoton absorption leads to a spatially patterned charge separation, which generates a spatially periodic, semi-permanent, DC-field-induced second-order susceptibility with a period that is appropriate for quasi-phase matching. The maximum measured second-harmonic conversion efficiency amounts to 0.4% in a waveguide with 0.9 × 1 µm 2 cross section and 36 mm length, corresponding to 53 µW at 532 nm with 13 mW of IR input coupled into the waveguide. The maximum equivalent χ (2) -susceptibility amounts to 3.7 pm/V, as retrieved from the measured conversion efficiency.

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“…At quasi-phase matching, we report a SHG efficiency comparable to that reported in SiN resonant structures [7], with the benefit of a wider bandwidth. Even higher conversion efficiencies are expected using Si-rich SiN, which exhibits χ (2) values ten times larger than the stoichiometric compound [13]. Phase matched SHG in SiN waveguides can then compete with conventional χ (2) materials, but with fairly easier onchip integration, and with the capability of dynamically and all-optically reconfigure the phase matching configuration.…”

Section: Resultsmentioning

confidence: 99%

All-optically induced quasi phase matching in SiN waveguides for second harmonic generation enhancement

Grassani

Billat

Pfeiffer

et al. 2017

Conference on Lasers and Electro-Optics

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Abstract:We report more than 30dB second harmonic generation enhancement in SiN waveguide by all-optical writing of a persistent χ (2) grating. Phase matching peaks are observed for different writing wavelengths. IntroductionThanks to tight light confinement and fabrication flexibility, CMOS compatible materials like silicon (Si) and silicon nitride (SiN) allowed the integration of various χ (2) theoretically vanishes in the dipole approximation both for Si and SiN. On the one hand, attempts were reported to integrate well performing χ (2) materials, such as lithium niobate [6], on CMOS waveguides. On the other hand, photonic confinement leading to resonant structures with limited bandwidth [7], or symmetry breaking in strained Si waveguides [8] were employed to enhance the efficiency of second order processes. SiN, in particular, is a very promising material as it features a very a large transparency window (from visible to mid-infrared), and already exhibited interesting bulk second order nonlinearity [9]. However, the conversion efficiency is often limited by the modal phase matching condition, which imposes stringent constraint on the waveguide design. Here we show the enhancement by more than 30 dB of the second harmonic of a narrow linewidth telecom pulsed laser. We observe a similar SHG enhancement changing the pump laser wavelength within the erbium window. Finally, probing the waveguide in continuous-wave (CW), the SHG peak shifts accordingly to the employed pump wavelength. We report a maximum SHG efficiency of 1.23ˑ10 -6 W -1 cm

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An investigation into second harmonic generation by Si-rich SiN_xthin films deposited by RF sputtering over a wide range of Si concentrations

Cited by 35 publications

References 34 publications

Enhancement of bulk second-harmonic generation from silicon nitride films by material composition

Enhancement of bulk second-harmonic generation from silicon nitride films by material composition

Photo-induced second-order nonlinearity in stoichiometric silicon nitride waveguides

All-optically induced quasi phase matching in SiN waveguides for second harmonic generation enhancement

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An investigation into second harmonic generation by Si-rich SiNxthin films deposited by RF sputtering over a wide range of Si concentrations

Cited by 35 publications

References 34 publications

Enhancement of bulk second-harmonic generation from silicon nitride films by material composition

Enhancement of bulk second-harmonic generation from silicon nitride films by material composition

Photo-induced second-order nonlinearity in stoichiometric silicon nitride waveguides

All-optically induced quasi phase matching in SiN waveguides for second harmonic generation enhancement

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An investigation into second harmonic generation by Si-rich SiN_xthin films deposited by RF sputtering over a wide range of Si concentrations