Nanocrystalline SiC films prepared by direct deposition of carbon and silicon ions

The method of direct deposition of carbon and silicon ions was used for preparation of nanocrystalline silicon carbide films. The deposition energy of carbon and silicon ions was 90 eV. The effect of substrate temperature in the range of 500-1150 °C on the structure of SiC films was studied by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD). According to XPS data, the films contained heterobonded Si-C atoms and homobonded Si-Si and C-C atoms, the relation between which varied as the function of substrate temperature. The data of XRD showed a noticeable growth of a nanocrystalline phase of cubic silicon carbide in the films at a temperature of about 700 °C. The content of 3C-SiC nanocrystalline phase reached 80 at.% at 950 °C. There was an established change from cubic polytype to rhombohedral polytype of silicon carbide α-SiC-21R at a substrate temperature higher than 1000 °C. The size of SiC crystal grains depended on the substrate temperature and changed from 4-5 up to 8-10 nm over the range of 700-950 °C. Besides, silicon unbonded with carbon also crystallized in nanocrystalline form with similar sizes of crystal grains. A possible model of the change of the polytypic composition of SiC film under the conditions of direct ion deposition was discussed.     

Electrical characterization of amorphous silicon carbide thin films deposited via polymeric source chemical vapor deposition

Polymeric source chemical vapor deposition (PS-CVD) was used to synthesize amorphous silicon carbide (a-SiC) thin films. The PS-CVD process was conducted at temperatures between 750 and 1000 °C. The substrates used were silicon single crystal wafers of p-type and n-type, and thermally grown silicon dioxide substrates. The chemical and electrical properties of the films were studied by various techniques, including Fourier transform infrared spectroscopy, elastic recoil detection (ERD), and capacitance-voltage technique. A correlation was observed between the average concentration of oxygen in the films and the deposition temperature, linking a low oxygen concentration to a high deposition temperature. However, the concentration of oxygen in the films deposited at the same temperature is independent of the substrate. The thin films deposited at low temperature showed insulating behaviour, while the semiconducting behaviour is obtained at high deposition temperatures. Ohmic contacts were obtained on the deposited semiconductor thin film by evaporating nickel contacts, followed by annealing of the sample at 800 °C for 2 min.     

Properties of plasma enhanced chemical vapor deposited silicon nitride for the application in multicrystalline silicon solar cells

Hydrogenated films of silicon nitride (SiNx:H) were investigated by varying the deposition condition in plasma enhanced chemical vapor deposition (PECVD) reactor and annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in multicrystalline silicon solar cells. By varying the gas ratio (ammonia to silane), the silicon nitride films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, silicon wafer with the film deposited at 450 °C showed the best minority carrier lifetime. The film deposited with the gases ratio of 0.57 showed the best peak of carrier lifetime at the annealing temperature of 800 °C. The performance parameters of cells fabricated by varying co-firing peak temperature also showed the best values at 800 °C. The multicrystalline silicon (mc-Si) solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrate (125 mm × 125 mm) was found to have the conversion efficiency of 15%.     

Surface nano-structured silicon carbide thin film produced using hot filament decomposition of ethylene at low temperature on silicon wafer

The structure and spectroscopic properties of nano-structured silicon carbide (SiC) thin films were studied for films obtained through deposition of decomposed ethylene (C₂H₄) on silicon wafers via hot filament chemical vapor deposition method at low temperature followed by annealing at various temperatures in the range 300-700 °C. The prepared films were analyzed with focus on the early deposition stage and the initial growth layers. The analysis of the film's physics and structural characteristics was performed with Fourier transform infrared spectroscopy and Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, and X-ray diffraction. The conditions for forming thin layer of cubic SiC phase (3C-SiC) are found. X-ray diffraction and Raman spectroscopy confirmed the presence of 3C-SiC phase in the sample. The formation conditions and structure of intermediate SiC layer, which reduces the crystal lattice mismatch between Si and diamond, are essential for the alignment of diamond growth. This finding provides an easy way of forming SiC intermediate layer using the Si from the substrate.     

Annealing optimization of silicon nitride film for solar cell application

Hydrogenated films of silicon nitride (SiNx:H) is commonly used as an antireflection coating as well as passivation layer in crystalline silicon solar cell. SiNx:H films deposited at different conditions in Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor were investigated by varying annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in silicon solar cells. By varying the gases ratio (R = NH₃/SiH₄ + NH₃) during deposition, the SiNx:H films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, the silicon wafer with SiNx:H film deposited at 450 °C showed the best effective minority carrier lifetime. The film deposited with the gases ratio of 0.57 shows the best peak of carrier lifetime at the annealing temperature of 800 °C. The single crystalline silicon solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrates (125 mm × 125 mm) were found to have the conversion efficiencies as high as 17.05 %. Low cost and high efficiency single crystalline silicon solar cells fabrication sequence employed in this study has also been reported in this paper.     

Influence of growth parameters on the microstructures of erbium films deposited on Si(111) substrates

Erbium films were grown on single crystal Si(111) substrates by electron beam vapor deposition. The microstructures of the erbium films were systematically investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Results indicate that the surface morphologies and microstructures of the erbium films with Si as substrates are susceptible to the substrate temperatures when the deposition rates are fixed. The pure erbium films with columnar grains were obtained at temperatures below 200 °C, but in the films grown at temperatures higher than 350 °C, some pinholes that are composed of erbium silicides were found. The pinholes have triangular shapes which is in accordance with the geometry of the underlying Si(111) substrate. The films grown at a substrate temperature equal or greater than 450 °C have cracks which would be formed due to the different shrinkage degree of erbium and silicon when the substrate temperature was cooled down to room temperature. The films grown at 200 °C show the (002) preferred orientation, which is consistent to the prediction by the theory of surface energy minimization. The deposition rate and deposition time are considered as factors to affect the reaction of the erbium film and the silicon substrate.     

Characterisation of silicon carbide films deposited by plasma-enhanced chemical vapour deposition

The paper presents a characterisation of amorphous silicon carbide films deposited in plasma-enhanced chemical vapour deposition (PECVD) reactors for MEMS applications. The main parameter was optimised in order to achieve a low stress and high deposition rate. We noticed that the high frequency mode (13.56 MHz) gives a low stress value which can be tuned from tensile to compressive by selecting the correct power. The low frequency mode (380 kHz) generates high compressive stress (around 500 MPa) due to ion bombardment and, as a result, densification of the layer achieved. Temperature can decrease the compressive value of the stress (due to annealing effect). A low etching rate of the amorphous silicon carbide layer was noticed for wet etching in KOH 30% at 80 °C (around 13 A/min) while in HF 49% the layer is practically inert. A very slow etching rate of amorphous silicon carbide layer in XeF₂ -7 A/min- was observed. The paper presents an example of this application: PECVD-amorphous silicon carbide cantilevers fabricated using surface micromachining by dry-released technique in XeF₂.     

Fabrication of nanocrystalline silicon carbide thin film by helicon wave plasma enhanced chemical vapour deposition

Nanocrystalline cubic silicon carbide thin films have been fabricated by helicon wave plasma enhanced chemical vapour deposition on Si substrates using the mixture of SiH₄, CH₄, and H₂ at a low substrate temperature of 300 °C. The infrared absorption spectroscopy analyses and microstructural characteristics of the samples deposited at various magnetic fields indicate that the high plasma intensity in helicon wave mode is a key factor to the success of growing nanocrystalline silicon carbide thin films at a relative low substrate temperature. Transmission electron microscopy measurements reveal that the films consist of silicon carbide nanoparticles with an average grain size of several nanometers, and the light emission measurements show a strong blue photoluminescence at room temperature, which is considered to be caused by the quantum confine effect of small size silicon carbide nanoparticles.     

Non-uniform deposition in the early stage of hot-wire chemical vapor deposition of silicon: The charge effect approach

The deposition behavior in hot-wire chemical vapor deposition (HWCVD) of silicon was investigated, focusing on the thickness uniformity of films deposited on silicon and glass substrates, and based on the previous suggestion that a major depositing flux in HWCVD should be negatively charged nanoparticles. The deposition was performed using a 20%-SiH₄-80%-H₂ gas mixture at a 450 °C substrate temperature under a working pressure of 66.7 Pa (0.5 Torr). Non-uniform depositions for three hot-wire temperatures, 1590 °C, 1670 °C, and 1800 °C, and on the silicon and glass substrates were compared. The non-uniformity was most pronounced at 1800 °C and more pronounced on the glass substrate. On the glass substrate, the deposition rate was highest at the corner and lowest at the center, which was attributed to the fastest charge removal, to a conducting stainless steel substrate holder, at the corner. Once the entire glass substrate was deposited with silicon, the growth rate tended to become uniform, possibly due to the high charge removal rate of silicon. The observed deposition behavior indicated that the major depositing flux is negatively charged.     

Mechanical properties of amorphous and microcrystalline silicon films

Hydrogen-free amorphous silicon (a-Si) films with thickness of 4.5-6.5 μm were prepared by magnetron sputtering of pure silicon. Mechanical properties (hardness, intrinsic stress, elastic modulus), and film structure (Raman spectra, electron diffraction) were investigated in dependence on the substrate bias and temperature. The increasing negative substrate bias or Ar pressure results in simultaneous reducing compressive stress, the film hardness and elastic modulus. Vacuum annealing or deposition of a-Si films at temperatures up to 600 °C saving amorphous character of the films, results in reducing compressive stress and increasing the hardness and elastic modulus. The latter value was always lower than that for monocrystalline Si(111). The crystalline structure (c-Si) starts to be formed at deposition temperature of ∼ 700 °C. The hardness and elastic modulus of c-Si films were very close to monocrystalline Si(111). Phase transformations observed in the samples at indentation depend not only on the load and loading rate but also on the initial phase of silicon. However, the film hardness is not too sensitive to the presence of phase transformations.     

Microwave synthesis of phase-pure, fine silicon carbide powder

Fine, monophasic silicon carbide powder has been synthesized by direct solid-state reaction of its constituents namely silicon and carbon in a 2.45 GHz microwave field. Optimum parameters for the silicon carbide phase formation have been determined by varying reaction time and reaction temperature. The powders have been characterized for their particle size, surface area, phase composition (X-ray diffraction) and morphology (scanning electron microscope). Formation of phase-pure silicon carbide can be achieved at 1300 °C in less than 5 min of microwave exposure, resulting in sub-micron-sized particles. The free energy values for Si + C → SiC reaction were calculated for different temperatures and by comparing them with the experimental results, it was determined that phase-pure silicon carbide can be achieved at around 1135 °C.     

Enhanced deposition of cubic boron nitride films on roughened silicon and tungsten carbide-cobalt surfaces

We report the influence of substrate surface roughness on cubic boron nitride (cBN) film deposition under low-energy ion bombardment in an inductively coupled plasma. Silicon and cemented tungsten carbide-cobalt (WC-Co) surfaces are roughened by low-energy ion-assisted etching in a hydrogen plasma, followed by deposition in a fluorine-containing plasma. Infrared absorption coefficients are measured to be 22,000 cm⁻¹ and 17,000 cm⁻¹ for sp²-bonded BN and cBN phases, respectively, for our films. For the silicon substrates, the film growth rate and the cBN content in the film increase with increasing the surface roughness, while the amount of sp²BN phase in the film shows only a small increase. A larger surface roughness of the substrate results in a smaller contact angle of water, indicating that a higher surface free energy of the substrate contributes to enhancing growth of the cBN film. For the WC-Co substrates, the film growth rate and the cBN content in the film increase similarly by roughening the surface.     

Growth of poly-crystalline silicon-germanium on silicon by aluminum-induced crystallization

The formation of poly-crystalline silicon-germanium films on single-crystalline silicon substrates by the method of aluminum-induced crystallization was investigated. The aluminum and germanium films were evaporated onto the single-crystalline silicon substrate to form an amorphous-germanium/aluminum/single-crystalline silicon structure that was annealed at 450 °C-550 °C for 0-3 h. The structural properties of the films were examined using x-ray diffraction, Raman spectroscopy and Auger electron spectroscopy. The x-ray diffraction patterns confirmed that the initial transition from an amorphous to a poly-crystalline structure occurs after 20 min of aluminum-induced crystallization annealing process at 450 °C. The micro-Raman spectral analysis showed that the aluminum-induced crystallization process yields a better poly-crystalline SiGe film when the film is annealed at 450 °C for 40 min. The growth mechanism of the poly-crystalline silicon-germanium by aluminum-induced crystallization was also studied and is discussed.     

Properties of nanocrystalline SiC:Ge:H alloy deposited by hot-wire chemical vapor deposition using Organosilane and Organogermane

Nanocrystalline hydrogenated silicon carbide: germanium alloy (nc-SiC:Ge:H) films have been deposited by hot-wire chemical vapor deposition at a low substrate temperature of about 300 °C. Germanium incorporation into the films and film structure based on cubic silicon carbide were confirmed by X-ray photoelectron spectroscopy and X-ray diffraction. Optical absorption spectra of the films with a germanium mole fraction of about 2% shifted to lower energies by about 0.2 eV compared with that of nanocrystalline cubic silicon carbide films.     

Simplified modulated evaporation process for the production of CuInS2 films with reduced substrate temperatures

CuInS₂ films with sub-micrometer thickness have been grown onto soda-lime glass substrates from the elemental constituents by a modulated flux deposition procedure. A reduced substrate temperature of about 350 °C was used during the process. Morphological characterization of the films suggests the formation of an In-rich layer in a first step of the deposition process. Adequate modulation of the In and Cu evaporation fluxes during a second stage makes the film evolving to the ternary CuInS₂ compound. The absence of any copper sulfur phases on the film surface would make unnecessary the use of any etching treatment after deposition of the film.     

Fabrication of hydrophobic inorganic coatings on natural lotus leaves for nanoimprint stamps

Hydrophobic inorganic films were obtained by direct deposition of copper or silicon onto natural lotus leaves by ion beam sputtering deposition technique. Scanning electron microscopy observations showed a lotus-leaf-like surface structure of the deposited inorganic films. Hydrophobic nature of the inorganic films on lotus leaves had been improved compared to the inorganic films deposited on flat silicon substrates. Water contact angles measured on the lotus-leaf-like copper and silicon films were 136.3 ± 8° and 117.8 ± 4.4°, respectively. The hydrophobic lotus-leaf-like inorganic films had been repeated used as nanoimprint stamps. Negative structures of lotus-leaf-like inorganic films were obtained on the polystyrene resist layers.     

Characterization of activated non-evaporable porous Ti and Ti-Zr-V getter films by synchrotron radiation photoemission spectroscopy

Highly porous Ti and TiZrV film getters on (100) silicon substrates, grown by the glancing angle deposition of dc magnetron sputtering method, were used to study the activation process. The effect of activation temperature on the reducing degree of the porous Ti and TiZrV films were investigated by synchrotron radiation photoemission spectroscopy (SRPES). Elemental carbon absorbed on the surface of the Ti film, exposed in air, will be transformed to a Ti carbide phase, however, that which is on the surface of the TiZrV film will be completely removed by heat at 250 °C or above. The oxidized Ti in a porous TiZrV film is more easily reduced than that in the porous Ti films. The breakdown of V-O and Ti-O bonds on the TiZrV film surface is easier than that of the Zr-O bond. We suggest that the decrease of reducing temperature of oxidized TiZrV, comparing with that of oxidized Ti, is caused by the displacement reaction of Zr on oxidized Ti or oxidized V.     

Initial stages of the ion-beam assisted epitaxial GaN film growth on 6H-SiC(0001)

Ultra-thin gallium nitride (GaN) films were deposited using the ion-beam assisted molecular-beam epitaxy technique. The influence of the nitrogen ion to gallium atom flux ratio (I/A ratio) during the early stages of GaN nucleation and thin film growth directly, without a buffer layer on super-polished 6H-SiC(0001) substrates was studied. The deposition process was performed at a constant substrate temperature of 700 °C by evaporation of Ga and irradiation with hyperthermal nitrogen ions from a constricted glow-discharge ion source. The hyperthermal nitrogen ion flux was kept constant and the kinetic energy of the ions did not exceed 25 eV. The selection of different I/A ratios in the range from 0.8 to 3.2 was done by varying the Ga deposition rate between 5 × 10¹³ and 2 × 10¹⁴ at. cm^− 2 s^− 1. The crystalline surface structure during the GaN growth was monitored in situ by reflection high-energy electron diffraction. The surface topography of the films as well as the morphology of separated GaN islands on the substrate surface was examined after film growth using a scanning tunneling microscope without interruption of ultra-high vacuum. The results show, that the I/A ratio has a major impact on the properties of the resulting ultra-thin GaN films. The growth mode, the surface roughness, the degree of GaN coverage of the substrate and the polytype mixture depend notably on the I/A ratio.     

Efficiency improvement of multicrystalline silicon solar cells after surface and grain boundaries passivation using vanadium oxide

The aim of this work is to investigate the effect of vanadium oxide deposition onto the front surface of multicrystalline silicon (mc-Si) substrat, without any additional cost in the fabrication process and leading to an efficient surface and grain boundaries (GBs) passivation that have not been reported before. The lowest reflectance of mc-Si coated with vanadium oxide film of 9% was achieved by annealing the deposited film at 600 °C. Vanadium pentoxide (V₂O₅) were thermally evaporated onto the surface of mc-Si substrates, followed by a short annealing duration at a temperature ranging between 600 °C and 800 °C, under O₂ atmosphere. The chemical composition of the films was analyzed by means of Fourier transform infrared spectroscopy (FTIR). Surface and cross-section morphology were determined by atomic force microscope (AFM) and a scanning electron microscope (SEM), respectively. The deposited vanadium oxide thin films make the possibility of combining in one processing step an antireflection coating deposition along with efficient surface state passivation, as compared to a reference wafer. Silicon solar cells based on untreated and treated mc-Si wafers were achieved. We showed that mc-silicon solar cells, subjected to the above treatment, have better short circuit currents and open-circuit voltages than those made from untreated wafers. Thus, the efficiency of obtained solar cells has been improved.     

Synthesis of silicon carbide nanowires by solid phase source chemical vapor deposition

In this paper, we report a simple approach to synthesize silicon carbide (SiC) nanowires by solid phase source chemical vapor deposition (CVD) at relatively low temperatures. 3C-SiC nanowires covered by an amorphous shell were obtained on a thin film which was first deposited on silicon substrates, and the nanowires are 20–80 nm in diameter and several μm in length, with a growth direction of [200]. The growth of the nanowires agrees well on vapor-liquid-solid (VLS) process and the film deposited on the substrates plays an important role in the formation of nanowires.