Crystalline Silicon Substrates Research Articles

III-Nitride/Si Tandem Solar Cell for High Spectral Response: Key Attributes of Auto-tunneling Mechanisms

The key attributes of double hetero junction tandem solar cell based on III-Nitride alloys and silicon is investigated thoroughly. GaN/InGaN/GaN based tandem solar cells are predicting impressive efficiency, however due to its high cost; it is far from immediate implementation. Hence, an attempt is made to realize GaN/InGaN on crystalline silicon(c-Si) substrate that results in high spectral efficiency and cost effectiveness. The proposed multi-junction tandem solar cell consists of a GaN layer, intrinsic-InxGa1−xN (i-InGaN), tandem InxGa1−xN (t-InGaN) upon crystalline p-silicon and n-silicon layers. Energy band diagrams, current-voltage curve, power graph, electric field and potential graphs are explored using TCAD tool. Additionally, key parameters such as ’In’ content, thickness of layers, absorption coefficients, polarization charges are optimized. A remarkable conversion efficiency of 25.6% and 26.1% are achieved with & without polarization effect, respectively and became a potential candidate for next-generation photovoltaics applications.

Caracterización en frecuencia de microondas de películas de titanato de bario obtenidas vía Sol-Gel

El presente trabajo se centra en la caracterización estructural, morfológica y dieléctrica de películas de titanato de bario (BTO o BaTiO3 por su fórmula química) depositados mediante la técnica que proporciona recubrimiento por medio de un sistema de rotación (spin coating) sobre substratos de silicio cristalino (Si) y resonadores CPW mediante la técnica Sol-Gel, utilizando una relación molar Ba/Ti de 0.5/0.5. Las guías de ondas se fabricaron sobre substratos de alúmina (Al2O3) con 3 mm de metalización en oro (Au) empleando la técnica de ablación láser. La microscopia electrónica de barrido (SEM) con espectrometría de dispersión de energía de rayos X (EDS) permitió evidenciar la existencia de una película de BTO con una composición elemental de 14.62 % de bario y 5.65 % de titanio, además de un espesor de 0.77 mm medido utilizando la modalidad perfilométrica de la microscopia de fuerza atómica (AFM). La caracterización dieléctrica se llevó a cabo mediante la comparación de la respuesta en frecuencia (parámetro S21) de un resonador CPW con película de BTO depositada y otro resonador de referencia (sin película) usando un analizador vectorial de red (VNA). Estas medidas se comparan a su vez con simulaciones computacionales para obtener las propiedades dieléctricas. Para la película de BTO se determinó una constante dieléctrica relativa (er) de 160 con tangente de pérdida (Tand) de 0.012 para una frecuencia de 3.60 GHz. La constante dieléctrica y la propiedad ferroeléctrica del material elaborado son características bastante promisorias para aplicaciones en circuitos de microondas, tales como miniaturización y sintonizabilidad.

Mechanism of Diffusion of Carbon and Silicon Monooxides in a Cubic Silicon Carbide Crystal

The main processes that occur during diffusion of gaseous carbon CO and silicon SiO monoxides through a layer of a single-crystal silicon carbide SiC of the cubic polytype are described. This problem arises as a single-crystal SiC layer is grown by the method of matched atomic substitution due to the chemical reaction of a crystalline silicon substrate with CO gas. The reaction products are an epitaxial SiC layer and SiO gas. CO and SiO molecules are shown to decompose in the SiC crystal into individual atoms. The oxygen atoms diffuse over interstitial sites only in the [110] direction with the activation energy 2.6 eV. The Si and C atoms displace by the vacancy mechanism in the corresponding SiC sublattices with activation energies 3.6 and 3.9 eV, respectively, and only in the [110] direction.

Effect of post-deposition annealing on electrical properties and structures of aluminum oxide passivation film on a crystalline silicon substrate

We studied the effect of post-deposition annealing (PDA) on the electrical property and the structure of aluminum oxide (AlOx) passivation films prepared by atomic layer deposition with various temperatures. Surface recombination velocity (Smax), interface trap density (Dit), and fixed charge density (Qeff/q) before and after the PDA were evaluated employing lifetime and capacitance–voltage measurements. The structural change by the PDA was investigated by a Stokes ellipsometer and X-ray reflectivity (XRR) measurements at SPring-8. The Smax of all samples was improved by the PDA. The improvement of Smax in the samples deposited at the temperature of 200 °C and 300 °C was due to the Dit decrease, but that in the sample deposited at the temperature of 25 °C was due to both the Dit decrease and the Qeff/q increase. From the XRR measurements, it revealed that the formation of the interfacial thin layer is essential for the appearance of negative fixed charges.

Thermophysical properties of refractory W-50.4%Re and Mo-39.5%Re thin alloy layers deposited on silicon and silica substrates

The examined samples were W-Re and Mo-Re thin alloy layers with high content of Rhenium, applied in industry as protective coatings. The 550 nm of W-50.4%Re and 580 nm of Mo-39.5%Re alloys were deposited on crystalline silicon and amorphous silica substrates by magnetron sputtering method. For thermal characterization of investigated layers the scanning thermal microscopy (SThM) and high frequency photothermal radiometry (HF-PTR) measurements were carried out. The thermal methods were supported by the microstructural studies performed by the atomic force microscopy (AFM) and X-ray diffraction (XRD). The SThM method allowed determining the thermal conductivity (κ) of the alloy layers. From the HF-PTR the effective thermal conductivity (κeff) was determined directly. Estimation of the thermal boundary resistance (Rth) between particular alloy layer and its substrate enabled determination of the real κ of the layer with its thermal diffusivity (α) and effusivity (ε) from the HF-PTR fitting. The results showed, that W-Re and Mo-Re layers deposited on Si are characterized by higher κ, α, and ε values, and lower Rth in comparison to those deposited on SiO2. The κ values for W-Re and Mo-Re layers deposited on Si and SiO2 substrates were estimated in the range from 7 W·m−1 K−1 to 12 W·m−1 K−1, and 1.6 W·m−1 K−1 to 4 W·m−1 K−1, respectively. The correlation between the alloy layer structure, it's thermophysical properties and substrate structure was observed. The AFM and XRD measurements confirmed the short range order formation in Mo-Re layers deposited on Si.

Acceleration of the Decay of Excitons in an Organometallic Perovskite Film on the Crystalline Silicon Surface

It has been found that the optical properties and characteristics of exciton photoluminescence in thin organometallic perovskite layers, which are promising for application in high-efficiency solar cells, change when these layers are deposited on a crystalline silicon (c-Si) substrate. The observed shift of the photoluminescence band toward higher photon energies and a decrease in the lifetime of photoluminescence compared to layers deposited on a glass substrate with conducting metal oxide coating have been explained by the effect of an electric field that is formed in an organometallic perovskite/c-Si heterostructure and leads to the field ionization and the decay of excitons in the organometallic perovskite layer.

Preparation and characterization of copper zinc tin sulfide-selenide thin films using a single target RF sputtering method

Copper zinc tin sulfide-selenide (CZTSSe) thin films have been prepared from a single alloyed CZTSSe target using one-step RF plasma magnetron sputtering technique. The films morphology, stoichiometry and crystalline properties have been examined as a function of the target to substrate distance, the deposition power and the substrate type. It was found that; within the range of the investigated target to substrate distance; better film crystallization was achieved when this distance equals to the target diameter, namely 5 cm in this work. An appropriate film thickness of 1.1 μm along with a more adequate compositional ratio equals to 14% Cu, 14% Zn, 16% Sn and 56% (S+Se) were obtained at low deposition power of 30 W with gradually decreasing the power during the deposition process. In this case, the low deposition rate resulted in proper compositional ratio, but the film crystallinity was found to be affected by the substrate type. As such, it was found that the use of a crystalline silicon substrate instead of the amorphous Soda Lime Glass substrate enhanced the film crystallinity.

Impact of phosphorus diffusion on n-type poly-Si based passivated contact silicon solar cells

This paper describes the impact of phosphorus dopant concentrations in n-type passivated contact structures. Free carrier absorption (FCA) of the phosphorus doped poly-Si layers was studied by using different phosphorus dopant concentrations, with a range of from 9 × 1019 to 2.3 × 1020 cm−3, and different poly-Si layer thicknesses, with a range of from 30 to 200 nm. In the worst case, the effect of FCA reduce the short circuit current density by 0.89 mA/cm2. The impacts of tunnel SiO2 thicknesses, poly-Si thicknesses and diffusion temperatures on the performances of the poly-Si passivated contacts were studied. Phosphorus concentrations induced silicon surface field passivation play an important role in passivated contact structure. On the planar n-type mono crystalline-silicon substrates, excellent J0 value of 6.5 fA/cm2 was achieved by optimizing phosphorus doping in poly-Si films and silicon substrate. Different poly-Si thickness and diffusion temperature were studied simultaneously to optimize the phosphorous dopants in the poly-Si passivated contacts for the specified poly-Si thickness. N-type silicon solar cell have been fabricated by using the optimized poly-Si passivated contacts, as addressed above. Average efficiency of 22.52%, and best cell efficiency of 23.04% were demonstrated.

Effect of Polymer Capping Layers on Initial Fracture Mechanism of Silicon Anodes

Using silicon nanomaterials is a widely accepted strategy for mitigating the extreme volume expansion associated with the lithiation of silicon and the accompanying capacity fade. However, the high surface area of silicon nanomaterials provides more opportunity for electrolyte decomposition which leads to high irreversible capacity loss and low Coulombic efficiency. Silicon microparticles area available in large scale at a low cost and offer an alternative with lower surface area that have been shown to have high initial Coulombic efficiency. However, to make silicon microparticles viable, the drastic volume change and high stress of these larger particles must be mitigated. In order to develop a more thorough understanding of the initial lithiation mechanics of the silicon crystalline microparticles, this work studies the initial lithiation mechanism through model crystalline electrodes. We have discovered that the thickness of the crystalline silicon wafer itself affected the initial crack formation mechanism. The next step for this study was to modify the mechanical properties of the top surface layer of the crystalline silicon substrates by adding a polymer capping layer and observe how these polymer layers affect the electrochemically induced fractures in crystalline silicon anodes through TEM, SEM and ellipsometry analysis. Polymer films of typical binder materials such as PVDF, PAA and CMC as well as novel modified PAA polymer binders were deposited on crystalline silicon substrates and lithiated to the same extent as an uncoated silicon anode to directly compare crack formation under the same level of silicon lithiation. The results of this work provide important analysis targeted at the initial crack formation of silicon and how polymer capping layers affect the lithiation depth and cracking formation of crystalline silicon. These findings may be applied to create a viable capping layer to reduce cracking in larger, more economical, silicon particles. Figure 1

Valence and conduction band offsets at beryllium oxide interfaces with silicon carbide and III-V nitrides

Beryllium oxide (BeO) is a large bandgap material with extreme properties that make it an ideal gate dielectric for pairing with other wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN). In this regard, the authors have utilized x-ray photoemission spectroscopy to determine the valence band offset (VBO) between atomic layer deposited (ALD) BeO and epilayers of the cubic form of silicon carbide (3C-SiC) grown on crystalline silicon (Si) substrates. The BeO VBO with 3C-SiC epilayers grown on both Si (111) and (001) substrates was determined to be 1.6 ± 0.1 and 1.5 ± 0.1 eV, respectively. Applying the band alignment rules of transitivity and commutativity, the authors additionally determine the VBO for BeO with GaN, aluminum nitride, and hexagonal boron nitride to be 0.9 ± 0.2, 0.7 ± 0.3, and 1.0 ± 0.2 eV, respectively. Utilizing the reported bandgap for ALD BeO (8.0 ± 0.1 eV) and literature values for SiC and the group III-nitrides (III-N), the authors find a type I band alignment with conduction band offsets >1 eV in all cases. These results indicate that BeO is a promising dielectric for wide bandgap SiC and III-N high-power, high-temperature, and high-frequency device applications.

Silicon Encapsulated All Solid-State Li-ion Microbatteries

The demand for safe, all solid-state energy storage for microelectronic devices is sharply increasing with the evolution of micro-electronics, namely Internet of Things (IoT). Microelectronics applications in IoT and health care industries progressively demand higher all-solid state volumetric, gravimetric and areal capacity packed in smaller volumes and areas – driving competitive exploration of next generation materials and designs especially via the solid state microbattery model. Conventional all-solid-state Li-ion batteries maintain control of performance via standard thin film encapsulation and packaging techniques (2.5D packaging), where theoretically high capacity 3D thin film microbatteries continue to fail the commercial sector due to leakage, dielectric breakdown, 3D fabrication, and parasitic cell degradation. 3D microbattery milestone failures, combined with cost, time of assembly and large active/packaging areas (>1mm2) of 2.5D form factors, limit the commercial practicality of current microbattery demand in an ever-shrinking foot print market. The work presented herein is a novel approach in addressing the above issues through silicon-based encapsulation and packaging in conjunction with composite silicon-based electrode material. Methods were developed to fabricate conformally deposited all-solid-state Li-ion materials into 3D trench patterned silicon substrates using advanced solid polymer electrolyte (SPE), interfacial additives (e.g. LiTFSI containing Polyaniline (PANI)) and commercial electrode materials (e.g., graphite & LFP). 3D features (≤1mm2) in crystalline silicon substrates were created via standard microfabrication methods (e.g. through silicon via (TSV) reactive ion etching (RIE))— where 16 trenches (1mm2 area, 350mm depth, 2mm pitch) enabled 35mm x 35mm chiplets on a 200mm silicon wafer (Figure 1a). The field, sidewalls and base of the 3D trenches were conformally patterned with electron/ion insulating materials (e.g., SiO2 &/or Si3N4) (Figure 1b). Insulation was partially etched away at trench bases to create an electrical connection between the active battery material and silicon substrate. Active battery material slurries (graphite, solid polymer electrolyte (SPE), interfacial additives) filled the insulated trenches, were pressed, heated, and dried—yielding low impedance functioning composite cells (Figure 1c). The top of the trench was subsequently planarized with a metal contact laminated cathode material (LFP) via conductive epoxy. Finished In-silicon microbattery cell(s) were encapsulated with coin cells as a second-generation (Gen 2) test model. By adjusting the formulation of an interfacial additive, a thinner interphase was achieved with superior interlayer adhesion of an electrochemically tailored (in-situ formed) silicon/additive/anode composite. Composite cells with Li-containing PANI compared with non-Li-containing PANI interfacial additive resulted in a charge transfer resistance 5 orders of magnitude lower and 2.8x greater areal discharge capacity (1.74uAh/mm2), lasting 60 rechargeable cycles with an average working voltage range of 2.5V to 1.0V (Figure 1d). Gen 2+ test modules consisted of single, stand-alone, ~2.6mm2 packaging area In-silicon microbatteries with full cell charge transfer interfacial impedance less than 120W at the pre-cycle stage with the lowest interfacial impedance observed after more than 80 cycles (<50W). EIS measurements illustrated reduction in cell impedance due to in-situ formation of a composite anode containing crystalline silicon, a silicon/lithium bilayer, interfacial additive and graphite (Figure 1e). The Gen 2+ stand-alone module yielded top areal capacity greater than 1.50uAh/mm2, with more than 100 rechargeable cycles obtained over an average voltage range of 3.5V to 1.0V. Minimum rechargeable capacities of Gen 2+ test modules (1mB) were double that of Gen 2 (4mB-parallel), as enabled via an 18x reduction in packaging area, resulting in nearly 3x reduction in composite cell impedance and consequently, a 1.2 volt increase of onset discharge voltage (Figure 1f). Active Battery to Packaging Area Ratios for the Gen 2+ In-silicon microbattery module (0.51) have already begun to rival industry standard ratios (e.g., 0.59 with ~25mm x 25mm thin film microbattery footprint). The next generation design for In-silicon microbatteries is predicted to advance active/packaging ratios higher than the thin film standard @ a ratio of 0.64 as the optimization of silicon encapsulation thickness to active battery area is realized. It is projected that with the In-silicon microbattery technology presented, combined with current state of the art solid-state materials, In-silicon microbatteries can exceed performance of commercially available microbattery products (e.g., >2.5uAh/mm2, >200mAh/g). The In-silicon microbattery design provides superior ease of integration with any Si or non-Si based integrated circuit (IC) technology obtained via common microfabrication infrastructure, at low tool cost & production steps. Future efforts will demonstrate that In-silicon microbattery technology is scalable not only to (IoT) applications, yet with Gen 3 form factors and composite cells, such all-solid-state Lithium based capability is scalable to established mobile applications (smart phones) and extremely high energy applications including renewables, grid storage and electric vehicles (EV). Figure 1

Determination of Refractive Index and Thickness of Nanosized Amorphous Carbon Films Via Visible Range Reflectance Spectra

The values of thickness and refractive index (1.92 < nf < 2.19) of amorphous nanosized carbon films obtained on a crystalline silicon substrate by a pulsed laser deposition were experimentally determined via an analysis of visible range of reflection spectra. Manufactured films can be used as single-layer anti-reflective coatings for Si and GaAs semiconductors.

Infrared Diagnostics of Free Charge Carriers in Silicon Nanowires

Free charge carrier concentration in arrays of silicon nanowires (SiNWs) with cross-sectional size of the order of 100[Formula: see text]nm was quantitatively studied by means of the infrared spectroscopy in an attenuated total reflection mode. SiNWs were formed on lightly-doped [Formula: see text]-type crystalline silicon substrates by metal-assisted chemical etching followed by additional doping through thermoactivated diffusion of boron at 900–1000∘C. The latter process was found to increase the concentration of free holes in SiNWs up to [Formula: see text][Formula: see text]cm[Formula: see text]. Potential applications of highly doped SiNWs in thermoelectric energy converters and infrared plasmonic devices are discussed.

Effect of Seed Layer and Thermal Annealing on Structural and Optical Properties of Silicon Layers Deposited by PECVD

Hydrogenated silicon (Si:H) layers have been deposited on crystalline silicon substrate by radiofrequency plasma-enhanced chemical vapor deposition technique (rf-PECVD) from SiH4/H2 gas mixture using different deposition times and after a seed layer with thickness of 70 nm (to improve the nucleation of nanocrystallites). The effect of the deposition time on the as-deposited and annealed layers was investigated. Ultraviolet–visible–infrared (UV–Vis–IR) spectroscopy was used to determine the thickness of the layers. Before annealing, the layer thickness showed a linear variation with deposition time in the range from 450 s to 1500 s. On the other hand, for deposition times of 450 s, 600 s, and 1500 s, the layers showed an x-ray diffraction (XRD) peak corresponding to the (111) crystal plane of Si. Raman spectroscopy confirmed the appearance of the crystalline phase in these layers. Raman scattering studies showed that, when using the short deposition time for the top layer, the crystalline peak dominated. We deduce that insertion of a seed layer improves the crystallinity of the top layer. In addition, the crystallinity increased slightly with the deposition time. The structural properties of the layers annealed at 900°C were studied by Raman spectroscopy and XRD analysis. We noted an increase in the crystalline volume fraction and the appearance of (111) crystal plane of silicon, confirming the transition from amorphous to nanocrystalline phase for all the annealed films.

Annealing effects on elemental composition and morphological properties of Pd thin films grown on crystalline silicon substrate

Silicon (Si) has been the most widely used semiconductor for decades, playing an important role in the field of electronics, energy conversion and energy storage. Because of their unique morphological energy band characteristics, Si nanostructures exhibit superior performance in many applications in comparison with their bulk counterparts. In this study, the effects of thermal annealing on elemental composition and morphological properties of palladium metal thin films grown on c-Si substrates were investigated. Palladium (Pd) thin films of different thicknesses were deposited on Si (1 0 0) with and without native oxide layers by electron beam evaporation and annealed in vacuum at 600 °C for two hours. Scanning electron microscopy (SEM) studies have shown that the surface morphology showed an effective dewetting in individual droplets and islands which further coalesce into bigger islands. Rutherford backscattering spectrometry (RBS) and electrical measurements analyses revealed the diffusion of the Si substrate into the Pd layer during annealing. This contribution will discuss the effects of the metal layer thickness as well as the native oxide on the metal thin films.

Aerosol-Assisted Chemical Vapor Deposition of ZnS from Thioureide Single Source Precursors

A family of 12 zinc(II) thoureide complexes, of the general form [{L}ZnMe], [{L}Zn{N(SiMe3)2}], and [{L}2Zn], have been synthesized by direct reaction of the thiourea pro-ligands iPrN(H)CS(NMe2) H[L1], CyN(H)CS(NMe2) H[L3], tBuN(H)CS(NMe2) H[L2], and MesN(H)CS(NMe2) H[L4] with either ZnMe2 (1:1) or Zn{N(SiMe3)2}2 (1:1 and 2:1) and characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis (TGA). The molecular structures of complexes [{L1}ZnMe]2 (1), [{L2}ZnMe]2] (2), [{L3}ZnMe]∞ (3), [{L4}ZnMe]2] (4), [{L1}Zn{N(SiMe3)2}]2 (5), [{L2}Zn{N(SiMe3)2}]2 (6), [{L3}Zn{N(SiMe3)2}]2] (7), [{L4}Zn{N(SiMe3)2}]2] (8), [{L1}2Zn]2 (9), and [{L4}2Zn]2 (12) have been unambiguously determined using single crystal X-ray diffraction studies. Thermogravimetric analysis has been used to assess the viability of complexes 1-12 as single source precursors for the formation of ZnS. On the basis of TGA data compound 9 was investigated for its utility as a single source precursor to deposit ZnS films on silica-coated glass and crystalline silicon substrates at 150, 200, 250, and 300 °C using an aerosol assisted chemical vapor deposition (AACVD) method. The resultant films were confirmed to be hexagonal-ZnS by Raman spectroscopy and PXRD, and the surface morphologies were examined by SEM and AFM analysis. Thin films deposited from (9) at 250 and 300 °C were found to be comprised of more densely packed and more highly crystalline ZnS than films deposited at lower temperatures. The electronic properties of the ZnS thin films were deduced by UV-Vis spectroscopy to be very similar and displayed absorption behavior and band gap (Eg = 3.711-3.772 eV) values between those expected for bulk cubic-ZnS (Eg = 3.54 eV) and hexagonal-ZnS (Eg = 3.91 eV).

Research on the Gas Effect of Octafluorocyclobutane Plasma Jet at Atmospheric Pressure for Silicon Etching

The capacitively coupled radio frequency double-pipe plasma discharge jet is used for the etching process. An argon carrier gas is fed through the atmospheric-pressure plasma source; octafluorocyclobutane (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> ) etch gas is injected into the plasma. Etchings were carried out on a crystalline silicon substrate. The etching characteristics are discussed and the etch rate tendency shows the reliance of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> gas flow rate and oxygen addition. The optimum etching rate of 7.2 μm/min was obtained at a plasma power level of 100 W and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> gas flow rate was 250 sccm. From surface profile detection, it displays the etch profile under this atmospheric-pressure plasma jet treatment. This plasma technique could offer a breakthrough for chamber-free dry etching processing.

Structural and Optical Properties of Silicon Nanowire Arrays Fabricated by Metal Assisted Chemical Etching With Ammonium Fluoride.

Here we report on the metal assisted chemical etching method of silicon nanowires (SiNWs) manufacturing, where the commonly used hydrofluoric acid (HF) has been successfully replaced with ammonium fluoride (NH4F). The mechanism of the etching process and the effect of the pH values of H2O2: NH4F solutions on the structural and optical properties of nanowires were studied in detail. By an impedance and Mott-Schottky measurements it was shown that silver-assisted chemical etching of silicon can be attributed to a facilitated charge carriers transport through Si/SiOx/Ag interface. It was shown that the shape of nanowires changes from pyramidal to vertical with pH decreasing. Also it was established that the length of SiNW arrays non-linearly depends on the pH for the etching time of 10 min. A strong decrease of the total reflectance to 5–10% was shown for all the studied samples at the wavelength <800 nm, in comparison with crystalline silicon substrate (c-Si). At the same time, the intensities of the interband photoluminescence and the Raman scattering of SiNWs are increased strongly in compare to c-Si value, and also they were depended on both the length and the shape of SiNW: the biggest values were for the long pyramidal nanowires. That can be explained by a strong light scattering and partial light localization in SiNWs. Hereby, arrays of SiNWs, obtained by using weakly toxic ammonium fluoride, have great potential for usage in photovoltaics, photonics, and sensorics.

Enhanced green luminescence from ZnO nanorods

Preferentially c-axis oriented ZnO nanorods were grown on a ZnO seed layer spin coated on a crystalline silicon substrate. A low-temperature aqueous chemical growth method using the chemical bath deposition technique was used to grow the ZnO nanorods. The samples were annealed at 700 °C in a reducing atmosphere (H2/Ar) with a relative ratio of 5%:95% for different times (20, 30, and 50 min). X-ray diffraction analysis revealed that the crystallite sizes increased with an increasing annealing time up to 30 min and then decreased for longer annealing time. Scanning electron microscope images showed a successful growth of the vertically aligned ZnO nanorods which were approximately 500 nm in length and 50 nm in diameter. The diameter of the nanorods increased with an increasing annealing time up to 30 min and then decreased when the annealing time was increased further. Photoluminescence (PL) measurements confirmed that the unannealed sample exhibited two distinct emissions, namely, the band to band emission around 378 nm and a broad orange emission centered at 600 nm which was due to the oxygen related defects. The annealed samples exhibited only a broad green emission centered at 500 nm and their intensities increased with annealing time. The highest intensity was recorded for the sample annealed for 30 min and the intensity decreased for further annealing time. The deconvoluted PL peak of the green emission indicated that three different kinds of defects were responsible for the emission at 500 nm. The decay measurements indicated that the green emission (500 nm) had an average lifetime of 11.58 μs. The quantum yield of the sample annealed for 30 min was measured using an integrating sphere at a wavelength of 325 nm, and it was found to be 43%. These ZnO nanorods can be very useful in optoelectronic applications, such as green light emitting diodes and field emission displays.

Механизм диффузии монооксидов углерода и кремния в кристалле кубического карбида кремния

The basic processes are described occurring in the case of the diffusion of carbon monoxide CO and silicon monoxide SiO through a layer of single-crystal silicon carbide SiC. This problem arises when a single-crystal SiC layer is grown by the method of atom substitution due to the chemical reaction of a crystalline silicon substrate with CO gas. The reaction products are the epitaxial layer of SiC and the gas SiO. It has been shown that CO and SiO molecules decompose in SiC crystals. Oxygen atoms migrate through interstitials in the [110] direction only with an activation energy of 2.6 eV. The migration of Si and C atoms occurs by the vacancy mechanism in the corresponding sublattices with activation energies of 3.6 eV and 3.9 eV, respectively, and also in the [110] direction only.