Non-stoichiometric Silicon Carbide Research Articles

Carbon-rich amorphous silicon carbide and silicon carbonitride films for silicon-based photoelectric devices and optical elements: Application from UV to mid-IR spectral range

In the work we demonstrated the possibility to apply amorphous non-stoichiometric silicon carbide (a-SixC1-x:H) and silicon carbonitride (a-SixC1-x-yNy:H) films for improvement of exploitation characteristics of silicon-based photoelectric devices and optical elements in very wide spectral range - from UV to mid-IR. The a-SixC1-x:H films possessing optical properties required for effective antireflection (AR) effects for silicon (refractive index (n) at λ = 632 nm from 1.86 to 1.98, optical bandgap (Eopt) from 2.7 to 3.1 eV, and extinction coefficient (k) is close to zero practically in all spectral range) were obtained by PE-CVD from methane, silane, hydrogen, and argon gas mixture. To deposit silicon carbonitride films some amount of nitrogen was added to the gas mixture. For the a-SixC1-x-yNy:H films the following optical parameters were obtained: n = 1.76–1.93, Eopt = 3.1–3.4 eV, k~0. It has been shown that the proposed films possess unique mechanical properties and ratio of the films hardness to their Young modulus is very high (H/E > 0.13). It is evidence of the films high wear resistance that is of great importance when the films are used for protection of silicon optical elements in IR spectral range. It is established that the films of both types are very suitable as excellent AR coatings for silicon in the spectral range of Si-based solar cell photosensitivity, telecommunication windows, and mid-IR. Deposition of even single layer AR film allowed us to reduce reflection losses significantly (reflection coefficient (R) at minimum of reflection becomes close to zero). As a result, efficiency of etched multicrystalline Si-based solar cell (SC) was significantly improved. Transmittance of Si-based optical elements with front and rear AR films reached practically 100% in the telecommunication windows spectral range.

Crystal structures and the electronic properties of silicon-rich silicon carbide materials by first principle calculations

Silicon carbide has been used in a variety of applications including solar cells due to its high stability. The high bandgap of pristine SiC, necessitates nonstoichiometric silicon carbide materials to be considered to tune the band gap for efficient solar light absorptions. In this regards, thermodynamically stable Si-rich SixC1-x materials can be used in solar cell applications without requiring the expensive pure grade silicon or pure grade silicon carbide. In this work, we have used density functional theory (DFT) to examine the stability of various polymorphs of silicon carbide such as 2H–SiC, 4H–SiC, 6H–SiC, 8H–SiC, 10H–SiC, wurtzite, naquite, and diamond structures to produce stable structures of Si-rich SixC1-x. We have systematically replaced the carbon atoms by silicon to lower the band gap and found that the configurations of these excess silicon atoms play a significant role in the stability of Si-rich SixC1-x. Hence, we have investigated different configurations of silicon and carbon atoms in these silicon carbide structures to obtain suitable SixC1-x materials with tailored band gaps. The results indicate that 6H-SixC1-x is thermodynamically the most favorable structure within the scope of this study. In addition, Si substitution for C sites in 6H–SiC enhances the solar absorption, as well as shifts the absorption spectra toward the lower photon energy region. In addition, in the visible range the absorption coefficients are much higher than the pristine SiC.

Two‐Photon Absorption‐Free Ultrafast Optical Switching in Carbon‐Rich SixC1−x Microring

Ultrafast Kerr effect switching in near‐infrared two‐photon absorption (TPA)‐free and free‐carrier‐absorption (FCA)‐free nonstoichiometric silicon carbide (SixC1−x) microring waveguides is performed and investigated. With pulsed return‐to‐zero on–off‐keying (PRZ‐OOK) stream for the Si‐rich SixC1−x‐based all‐optical switches, the inversely modulated probe reveals an asymmetric bit shape data extinction ratio (ER) of only 8.7 dB owing to the TPA + FCA effect. By eliminating the FCA effects in nearly stoichiometric SixC1−x microring waveguide, the high‐speed wavelength conversion of a data stream with an ER of 14 dB can be observed when coinciding the probe wavelength with the transmission dip. Slightly deviating the probe wavelength from the transmission dip, most probe power still remains in bus waveguide to cause a strong FCA effect to degrade the ER down to 7.4 dB. A symmetrically converted and inverted data stream with high on/off extinction can be observed in the C‐rich SixC1−x‐based microring waveguide with completely suppressed trailing‐edge response. To further approach the upper limitation on bandwidth, the wavelength‐converted and sign‐reversible PRZ‐OOK data switching at a bit rate up to 12 Gbit s−1 can be obtained with similar ER of better than 20 dB, as contributed mainly by the enhanced Kerr nonlinearity in the C‐rich SixC1−x.

Особливості структуроутворення вторинного карбіду кремнію, синтезованого в умовах взаємодії нанорозмірного нестехіометричного карбіду кремнію з оксидом заліза

Особливості структуроутворення вторинного карбіду кремнію, синтезованого в умовах взаємодії нанорозмірного нестехіометричного карбіду кремнію з оксидом заліза

Nonstoichiometric SiC Bus/Ring Waveguide Based All-Optical Data Format Follower and Inverter

Nonstoichiometric silicon carbide (SiC) bus/ring waveguide resonator based all-optical data-format follower and inverter is demonstrated to perform ultrafast dual-functional wavelength and data-format conversion. The buried Si quantum dots (Si-QDs) with strong quantum confinement effect effectively result in a significant change on the nonlinear refractive index of 3.14 × 10–13 cm2/W, which induces a red-shift of 0.07 nm on the resonant wavelength comb of the nonstoichiometric SiC ring waveguide resonator. By injecting the 12 Gbit/s optical pulsed return-to-zero on–off keying (PRZ-OOK) data stream into the ring waveguide at a notched wavelength of 1551.08 nm, the induced red-shift on resonant wavelengths allows versatile all-optical data processing functions, including data wavelength conversion and data format following/inversion, on the data patterns transferred to the probe. The eye-opening diagram analysis at 12 Gbit/s reveals that the data transferred to the probe can provide a signal-to-noise ratio ...

(Invited) Thermal Carbonization of Porous Silicon: The Current Status and Recent Applications

Porous silicon (PSi) is a versatile material for a wide range of applications. Its large surface area combined with easily adjustable pore morphology and surface chemistry offers an excellent platform for many different applications. For example, the refractive index of PSi is strictly depending on the porosity and can be controlled by the current density of electrochemical etching. This enables precise control of the refractive index and allows the fabrication of highly complex optical structures for many interesting applications. However, for decades, the biggest stumbling block for PSi applications has been the chemical instability of PSi. As-anodized PSi is hydrogen terminated and it slowly oxidizes even at room temperature. This instability of as-anodized PSi is unacceptable in most applications. On the other hand, intentional oxidation of PSi, in order to improve the stability, usually leads to too high resistivity for electrical applications and changes the optical properties of PSi too drastically. Moreover, the oxidized PSi is not chemically stable enough for certain type of applications, especially in aqueous conditions. It may react adversely with drugs and its functionalization needs to be done through silanization chemistry which shares the silicon oxide bonding related instability, e.g., for targeted drug delivery applications. Thermal carbonization by acetylene to stabilize PSi was introduced in 2000 [1]. It produces a non-stoichiometric silicon carbide layer on the PSi, which is very stable in harsh environments, like in NaOH, KOH, HF etc. solutions with extreme pH values. It also increases the conductivity of the PSi, which is beneficial for electrical sensor and energy storage applications and it has been found to be nontoxic both in in vitro and in vivo applications. Therefore, the thermally carbonized PSi (TCPSi) has been used in various different applications ranging from gas sensors and biosensors to targeted drug delivery, bioimaging and electrochemical supercapacitors since its introduction [2–9]. In the presentation, the current status and novel applications, in which thermally carbonized PSi has been used, will be discussed. In addition, some new information about the physical and chemical properties of TCPSi will be introduced. REFERENCES: [1] J. Salonen, V.-P. Lehto, M. Björkqvist, E. Laine, L. Niinistö, Studies of Thermally-Carbonized Porous Silicon Surfaces, Physica Status Solidi (a), 182 (2000) 123-126. [2] V. Torres-Costa, R.J. Martin-Palma, J.M. Martinez-Duart, J. Salonen, V.P. Lehto, Effective passivation of porous silicon optical devices by thermal carbonization, Journal of Applied Physics, 103 (2008) 4. [3] J. Tuura, M. Bjorkqvist, J. Salonen, V.P. Lehto, Electrically isolated thermally carbonized porous silicon layer for humidity sensing purposes, Sensors and Actuators B - Chemical, 131 (2008) 627-632. [4] T. Jalkanen, E. Mäkilä, Y.I. Suzuki, T. Urata, K. Fukami, K. Sakka, J. Salonen, Y.H. Ogata, Studies on Chemical Modification of Porous Silicon-Based Graded-Index Optical Microcavities for Improved Stability Under Alkaline Conditions, Advanced Functional Materials, 22 (2012) 3890-3898. [5] B. Sciacca, S.D. Alvarez, F. Geobaldo, M.J. Sailor, Bioconjugate functionalization of thermally carbonized porous silicon using a radical coupling reaction, Dalton Transactions, 39 (2010) 10847–10853. [6] P.J. Kinnari, M.L.K. Hyvönen, E.M. Mäkilä, M.H. Kaasalainen, A. Rivinoja, J.J. Salonen, J.T. Hirvonen, P.M. Laakkonen, H.A. Santos, Tumour homing peptide-functionalized porous silicon nanovectors for cancer therapy, Biomaterials. 34 (2013) 9134–9141. [7] L.M. Bimbo, M. Sarparanta, H.A. Santos, A.J. Airaksinen, E. Mäkilä, T. Laaksonen, L. Peltonen, V.-P. Lehto, J. Hirvonen, J. Salonen, Biocompatibility of thermally hydrocarbonized porous silicon nanoparticles and their biodistribution in rats, ACS Nano. 4 (2010) 3023–3032. [8] J. Salonen, Drug Delivery with Porous Silicon, in: L. Canham (Ed.) Handbook of Porous Silicon, Springer International Publishing, 2014, Ch. 91, pp. 909-919. [9] S. Chatterjee, R. Carter, L. Oakes, W.R. Erwin, R. Bardhan, C.L. Pint, Electrochemical and Corrosion Stability of Nanostructured Silicon by Graphene Coatings: Toward High Power Porous Silicon Supercapacitors, Journal of Physical Chemistry C. 118 (2014) 10893–10902.

The Structurization of Aluminum Oxide Composite Ceramics Involving Products of Iron Oxide Reduction by Nanosized Nonstoichiometric Silicon Carbide

The paper studies the structurization of aluminum oxide ceramics sintered with additions of a synthesized fine SiC–Fe 2 O 3 powder alloy. The fine-grained powder alloy particles promote the densification of the alumina matrix. The mechanical properties of the composites are examined. The material obtained is tested as a cutting tool.

Strong optical nonlinearity of the nonstoichiometric silicon carbide

The optical nonlinearity of the nonstoichiometric silicon carbide with a variable C/Si composition ratio is studied. The significantly enhanced optical nonlinearity and the mechanism related to the bonding structures and the composition ratio in the nonstoichiometric silicon carbide are elucidated.

Study on the Correlation between Film Composition and Piezoresistive Properties of PECVD Si<sub>x</sub>C<sub>y</sub> Thin Films

The effects of carbon content on the piezoresistive properties of non-stoichiometric silicon carbide (SixCy) films deposited on thermally oxidized (100) Si substrates by Plasma Enhanced Chemical Vapor Deposition (PECVD) from silane (SiH4) and methane (CH4) gas mixtures have been investigated. Four different film compositions have been obtained by varying SiH4 flow ratios from 1.0 to 4.0 sccm, while the other parameters were kept constant. In order to evaluate the piezoresistive properties of the SixCy films, we have developed test structures consisting of SixCy thin-film resistors defined by reactive ion etching (RIE) with Ti/Au pads formed by lift-off process. The gauge factor (GF) and temperature coefficient of resistance (TCR) of each SixCy film were measured.

Phase formation and interaction between nanosized nonstoichiometric silicon carbide and iron oxide

The interaction between nanosized powder of a solid solution of carbon in silicon carbide and iron oxide (as iron oxide pigment and disperse sintered iron ore concentrate) in high-temperature heating is studied. The quantitative phase composition of the products is analyzed. The potential reactions between silicon carbide and iron oxide are examined. It is established that the (SiC–C)–Fe2O3 powder mixtures interact to produce a heterophase structure through the reduction of iron and the formation of silicides (e-FeSi, Fe2Si, Fe3Si, Fe5Si3), carbides (Fe3C, Fe7C3), and iron (α-Fe) as fine particles with homogenous microstructure.

Si<sub>x</sub>C<sub>y</sub> Thin Films Deposited at Low Temperature by DC Dual Magnetron Sputtering: Effect of Power Supplied to Si and C Cathode Targets on Film Physicochemical Properties

A DC dual magnetron sputtering system with graphite (C) and silicon (Si) targets was used to grow stoichiometric and non-stoichiometric silicon carbide (SixCy) thin films at low temperature. Two independently DC power sources were used to enable the total discharge power be shared, under certain proportions, between the Si and C magnetron cathodes. The motivation was to control the sputtering rate of each target so as to vary the stoichiometric ratio x/y of the deposited films. The species content, thickness and chemical bonds of as-deposited SixCy films were studied by Rutherford backscattering spectroscopy (RBS), profilometry analysis and Fourier transform infrared absorption (FTIR), respectively. Overall, the present work reveals a new reliable plasma sputtering technique for low temperature growth of amorphous SixCy thin films with the capability of tuning the degree of formation of a-SiC, a-Si and a-C bonds in the film bulk.