Plasma-enhanced Chemical Vapor Deposition Technique Research Articles

A-SiC:H anti-resonant layer ARROW waveguides

Over the last decades, anti-resonant reflecting optical waveguides (ARROW) have been used in different integrated optics applications. In this type of waveguide, light confinement is partially achieved through an anti-resonant reflection. In this work, the simulation, fabrication and characterization of ARROW waveguides using dielectric films deposited by a plasma-enhanced chemical vapor deposition (PECVD) technique, at low temperatures ( ∼ 300 °C), are presented. Silicon oxynitride (SiO x N y ) films were used as core and second cladding layers and amorphous hydrogenated silicon carbide (a-SiC:H) films as first cladding layer. Furthermore, numerical simulations were performed using homemade routines based on two computational methods: the transfer matrix method (TMM) for the determination of the optimum thickness of the Fabry-Perot layers; and the non-uniform finite difference method (NU-FDM) for 2D design and determination of the maximum width that yields single-mode operation. The utilization of a silicon carbide anti-resonant layer resulted in low optical attenuations, which is due to the high refractive index difference between the core and this layer. Finally, for comparison purposes, optical waveguides using titanium oxide (TiO 2 ) as the first ARROW layer were also fabricated and characterized.

Ultrafast dynamics of photoexcited charge carriers in nanocrystalline diamond

We report on ultrafast charge carrier dynamics in sub-band-gap energy states in nanocrystalline diamond self-supporting membranes prepared by plasma-enhanced chemical vapor deposition technique. The obtained data are hence not influenced by the substrate effects. Results of the femtosecond transient transmission and photoluminescence laser spectroscopy indicate relaxation of photoexcited carriers with the time constants of the order of 1 ps. This is attributed to an ultrafast spatial separation of holes and electrons at the surface of nanocrystals. Only the carrier population photoexcited in energy levels of 1.68 eV silicon related center decays on a much longer time scale with the time constant of 2.4 ns.

Two-photon absorption in Si-nanocrystals deposited by plasma-enhanced chemical-vapor deposition

We present a systematic z-scan study of the nonlinear absorption coefficient β of Si-nanocrystals embedded in SiO 2 (Si-nc/SiO 2) excited in the nanosecond regime. Two different wavelengths of a Nd:YAG laser have been used, λ = 1064 and 532 nm. The samples under study were deposited on silica substrates by plasma-enhanced chemical-vapor deposition technique and subsequently annealed up to 1250 ∘ C . We have observed an increase in β as the Si content in the Si-nc/SiO 2 films rises, indicating that the nonlinear behavior strongly depends on the amount of Si. Typical values of β around 1 cm/MW were obtained at 1064 nm, while they are one order of magnitude higher exciting at 532 nm, following the same trend as bulk Si with respect to the excitation energy. Large Si-nc present an energy of high-symmetry transitions ( E og , E 2 ) that approaches the system to a resonant condition with the excitation energy. On the other hand, we observed an increase of β with the annealing temperature that can be associated to an additional absorption from free carriers, as the crystalline degree scales with the thermal budget.

Improved Density Of States and Effective Charge Density in Si/Pecvd Sioxny Interface

SiOxNy films deposited by the PECVD (Plasma Enhanced Chemical Vapor Deposition) technique at low temperatures from silane (SiH4) nitrous oxide (N2O) and helium (He) as precursor gases at different RF power and R = N2O/SiH4, in order to produce films with good SiOxNy/Si interface quality and low effective charge density were deposited and characterized. In order to compare the film structural properties with the interface (SiOxNy/Si) quality and interface charge density MOS capacitors were fabricated using these films as dielectric layer. The structure of the films was investigated by Fourier Transform Infrared Spectroscopy (FTIR). The MOS capacitors were characterized by low and high frequency capacitance (C-V) measurements, from where the interface state density, the effective charge density and the electrical breakdown were extracted. The better interface properties and a relatively low effective charge density were obtained for a film deposited with R=10 and RF power of 125 mW/cm2.

Enhancing optical properties of nanocrystalline silicon films with air exposure

We report the effect of air exposure and deposition temperatures, T d, on the optical property of nanocrystalline silicon (nc-Si). The nc-Si thin films were investigated by photoluminescence (PL), optical absorption, X-ray diffraction (XRD), Fourier-transform infrared (FTIR) absorption and Raman scattering. Experimental results show the structural change from an amorphous to a nanocrystalline phase at T d=80 °C. In addition, it suggests that T d low condition leads to the increase in the density of SiH-related bonds and a decrease in the average grain size, 〈 δ〉. The oxygen absorption peak increases with the air-exposure time. The PL exhibited two peaks at around 1.75–1.78 and 2.1–2.3 eV. The PL increases and blue shifts consistently with the decrease of 〈 δ〉 and increase of oxygen content. The first peak may be related to nanocrystallites in nc-Si films and the origin of another one may be due to defect-related oxygen. Thus, by the plasma-enhanced chemical vapor deposition (PECVD) technique at low T d, we can produce the nc-Si films with different grain sizes, causing the corresponding luminescent properties. The new method processes advantages of low deposition temperature and effective oxidation of nc-Si on inexpensive substrates, thus making it more suitable for developing low-cost array or flexible nc-Si optoelectronic devices.

Growth of transition‐metal‐doped ZnO films by plasma‐enhanced CVD combined with RF sputtering

AbstractTransition‐metal (TM) doped zinc oxide (ZnO) films were grown by a developed plasma‐enhanced chemical vapor deposition (PECVD) technique combined with RF sputtering. In the developed system, TMs such as Fe, Cr and Ni were doped into the ZnO films by RF sputtering with a stainless‐steel electrode connected to a RF generator. X‐ray diffraction (XRD) measurements revealed that the TM‐doped ZnO films were successfully grown with c‐axis orientation at 400 °C with RF power of 25 W. The doped TMs were segregated to the surface when the films were annealed at 700 °C in O2 ambient. After higher‐temperature annealing at 800 °C, ZnO nanostructures with wire and tube shapes were formed by a catalytic influence of the segregated TMs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanostructures in silicon investigated by atomic force microscopy and surface photovoltage spectroscopy

Surface photovoltage spectroscopy (SPS) and conductive atomic force microscopy (C-AFM) have been used for the characterization of nanocrystalline hydrogenated Si (nc-Si:H). This is a promising material both for silicon-based opto-electronics as well as for photovoltaic applications. Notwithstanding its interesting properties many issues regarding the material electronic and optical properties are not completely understood. The present contribution reports microscopic and spectroscopic analyses of nc-Si:H films grown for photovoltaic applications by low-energy plasma-enhanced chemical vapor deposition technique. Electronic levels associated with defect states were investigated by SPS, whereas the conduction mechanism at a microscopic level was investigated by C-AFM.

Electrochemical investigation of the influence of thin SiO x films deposited on gold on charge transfer characteristics

The paper reports on the investigation of the electrochemical behavior of a thin gold film electrode coated with silicon dioxide (SiO x ) layers of increasing thickness. Stable thin films of amorphous silica (SiO x ) were deposited on glass slides coated with a 5 nm adhesion layer of titanium and 50 nm of gold, using plasma-enhanced chemical vapor deposition (PECVD) technique. Scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of the interfaces. In the case of SECM, the influence of the SiO x thicknesses on the electron transfer kinetics of three redox mediators was investigated. Normalized current–distance curves (approach curves) were fitted to the theoretical model in order to find the effective heterogeneous first order rate constant ( k eff) at the sample. EIS was in addition used to confirm the diffusion barrier character of the SiO x interlayer.

Functional Metal Oxide Coatings by Molecule-Based Thermal and Plasma Chemical Vapor Deposition Techniques

Deposition of thin films through vaccum processes plays an important role in industrial processing of decorative and functional coatings. Many metal oxides have been prepared as thin films using different techniques, however obtaining compositionally uniform phases with a control over grain size and distribution remains an enduring challenge. The difficulties are largely related to complex compositions of functional oxide materials, which makes a control over kinetics of nucleation and growth processes rather difficult to control thus resulting in non-uniform material and inhomogeneous grain size distribution. Application of tailor-made molecular precursors in low pressure or plasma-enhanced chemical vapor deposition (CVD) techniques offers a viable solution for overcoming thermodynamic impediments involved in thin film growth. In this paper molecule-based CVD of functional coatings is demonstrated for iron oxide (Fe2O3, Fe3O4), vanadium oxide (V2O5, VO2) and hafnium oxide (HfO2) phases followed by the characterization of their microstructural, compositional and functional properties which support the advantages of chemical design in simplifying deposition processes and optimizing functional behavior.

Luminescence Tuning of Amorphous Si Quantum Dots Prepared by Plasma-Enhanced Chemical Vapor Deposition

Amorphous Si (a-Si) quantum dots (QDs) embedded in a silicon nitride film were prepared by a plasma-enhanced chemical vapor deposition (PECVD) technique using gaseous mixtures of silane, hydrogen and nitrogen. We observed that the Si QDs had an amorphous structure from the Raman spectroscopy measurement. The Fourier transform infrared (FTIR) spectra showed that the relative transmittance of the SiH bands decreased, but that of the NH bands increased, with increasing nitrogen flow rate. During the deposition of SiNx, the number of dangling bonds of silicon acting as nucleation sites increased. As the hydrogen flow rate increased the growth rate decreased, due to the reduction in the hydrogen partial pressure. The hydrogen and nitrogen gas flow rates were found to be important parameters for determining the size of the a-Si QDs. In addition, we observed that the PL peak shifted toward a higher energy with increasing hydrogen and nitrogen gas flow rates, which was attributed to the increase in the quantum confinement effect in the a-Si QDs.

Regrowth of Carbon Nanotube Array by Microwave Plasma-Enhanced Thermal Chemical Vapor Deposition

A repeated growth process (regrowth process) has been carried out to fabricate a carbon nanotube (CNT) array without additional catalyst by a custom-made plasma-enhanced thermal chemical vapor deposition (PE-thermal CVD) technique. An Fe film with a thickness of 3 nm is coated as a catalyst before the first growth on the SiO2/Si by arc plasma deposition. Two types of treatments, lift-off and thermal annealing, are used to remove the CNTs away for the next growth. Thermal annealing is also used to remove amorphous carbon, which covers the catalytic nanoparticles and to activate the catalyst. The CNT array is regrown without coating additional catalyst through the regrowth process. After certain cycles, high-purity single-walled carbon nanotubes (SWNTs) are synthesized and the ID/IG ratio of the Raman spectrum reaches a low value of 0.41. The crystallization of CNTs is improved after each growth cycle of thermal annealing treatment.

Investigation of hydrocarbon coated porous silicon using PECVD technique to detect CO2 gas

In the present work, we investigate the influence of hydrocarbon (CHx) thin film coating on porous silicon (PS) by plasma enhanced chemical vapor deposition (PECVD) technique to detect CO2 gas. The fabricated CHx/PS heterojunction device shows up to one and two orders of magnitude enhancement in current under CO2 gas exposure. FTIR spectroscopy measurements reveal a remarkable structural modification of the CHx/PS device during CO2 gas exposure. Further, the enhancement of CHx related absorbance bands by a factor 6.2 for the CHx/PS specimen in comparison with PS confirm the good quality of the deposited CHx thin films.

Silicon-based thin-film solar cells fabricated near the phase boundary by VHF PECVD technique

The light-soaked and annealing behaviors for silicon (Si)-based thin-film single-junction solar cells fabricated near the phase boundary using a very-high-frequency plasma-enhanced chemical vapor deposition (VHF PECVD) technique are investigated. The hydrogen dilution ratio is changed in order to achieve wide band gap hydrogenated amorphous Si (a-Si:H) and narrow band gap hydrogenated microcrystalline Si (μc-Si:H) absorbers. Just below the a-Si:H-to-μc-Si:H transition, highly hydrogen-diluted a-Si:H solar cells with a good stability against light-soaking and fast annealing behavior are obtained. In contrast, the solar cell fabricated at the onset of the μc-Si:H growth is very unstable and its annealing behavior is slow. In the case of μc-Si:H solar cells with the crystal volume fraction of 43–53%, they show the lowest light-induced degradation among the fabricated solar cells. However, it is very difficult to recover the degraded μc-Si:H solar cells via thermal annealing.

Crystalline SiN x Ultrathin Films Grown on AlGaN/GaN Using In Situ Metalorganic Chemical Vapor Deposition

Surface passivation by SiN x films is indispensable for high-power operation of AlGaN/GaN heterojunction field-effect transistors (HFETs) since it can effectively suppress collapse in the drain current. So far, the plasma-enhanced chemical vapor deposition technique has been used for the SiN x deposition; however, possible damage induced by the plasma processing may affect direct-current performance or reliability. In this paper, we present subsequent deposition of SiN x ultrathin films on AlGaN/GaN in the same metalorganic chemical vapor deposition reactor. It is experimentally found that this in situ SiN x passivation doubles the sheet carrier density at the AlGaN/GaN interface from that of the unpassivated sample. High-resolution cross-sectional transmission electron microscopy reveals that in situ SiN x is crystallized on the AlGaN layer as island-like structures via the Stranski-Krastanov growth mode. The lattice constants of in situ SiN x are estimated to be a ≈ 3.2 A and c ≈ 2.4 A, which are quite different from those of well-known Si3N4 crystal structures. First-principles calculation predicts that the crystal structure of in situ SiN x is the defect wurtzite structure, which well explains the experimental results. The passivation technique using crystalline SiN x films would be promising for high-power and high-frequency applications of AlGaN/GaN HFETs.

Cone Kinetics Model: Insights into the Morphologies of Mixed-phase Silicon Film Growth

ABSTRACTThe ‘cone kinetics’ model, which explains development of cone-shaped inclusions during nanocrystalline silicon film growth and during low-temperature silicon epitaxy breakdown, is extended to protocrystalline (‘edge’) amorphous silicon, Si heterojunctions and other Si film morpholologies. We generalize the physics underlying cone formation and present diagrams that delineate the deposition regimes giving rise to the different film morphologies; these regimes are determined by the nucleation rate of the second phase and the relative growth rate of the phases present. The model predicts cone growth during thin-film deposition by plasma-enhanced and other chemical vapor deposition techniques when isotropic growth is coupled with the isolated nucleation of a second phase with a higher growth rate. Protocrystalline amorphous silicon and other embedded crystallite phases are formed when a second phase successfully nucleates but has a smaller growth rate than the surrounding amorphous film. The cone kinetics phase diagram provides a simple explanation of the various nanocrystalline film morphologies observed when silane precursors are diluted with different concentrations of hydrogen gas.

Electrical conduction in undoped ultrananocrystalline diamond thin films and its dependence on chemical composition and crystalline structure

The electrical conduction behavior of undoped ultrananocrystalline diamond (UNCD) and its dependence on deposition temperature and chemical structure are presented. UNCD films were grown using a microwave plasma-enhanced chemical vapor deposition technique at deposition temperatures of 400 °C and 800 °C. The chemical structure of the UNCD films is characterized with several tools including: Elastic recoil detection analysis, Fourier transform infrared spectroscopy, electron energy loss spectroscopy, Raman spectroscopy, and environmental scanning electron microscope. The results show a higher content of sp2-bonded carbon for the 800 °C deposition samples (∼65%) in comparison with the 400 °C samples (∼38%). In both kinds of films, the hydrocarbon bonds have the saturated sp3 structures, while there is lower hydrogen content in the 800 °C samples (∼8%) than in the 400 °C samples (∼10%). For conduction properties, experiments are conducted using a probe station and conductive-atomic force microscopy. Experimental data show that the samples deposited at 800 °C are several orders of magnitude more conductive than the 400 °C samples. The conduction occurs primarily along the grain boundary for both types of samples. The conductivity of both types of films also shows field dependent nonlinear behavior. Both the Poole–Frenkel models and single and overlapping Coulombic potential models show that the conduction is directly correlated with the sp2 bond carbon density, and the role of the hydrocarbon bonds in the conduction path is formed by the network of the sp2 bonded carbon.

Preparation and characterization of thin organosilicon films deposited on SPR chip

The paper reports on the preparation and characterization of organosilicon thin polymer films deposited on glass slides coated with 5 nm adhesion layer of titanium and 50 nm of gold. The polymer was obtained by the decomposition of 1,1,3,3-tetramethyldisiloxane precursor (TMDSO) premixed with oxygen induced in a N 2 plasma afterglow using remote plasma-enhanced chemical vapor deposition (PECVD) technique. The film thickness was controlled by laser interferometry and was 9 nm. The chemical stability of the gold substrate coated with the organosilicon polymer film (p-TMDSO) was studied in different acidic and basic solutions (pH 1–14). While the gold/polymer interface showed a high stability in acidic media, the film was almost completely removed in basic solutions. The resulting surfaces were characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), water contact angle measurements, cyclic voltammetry, and surface plasmon resonance (SPR).

Effect of argon and substrate bias on diamond thin film surface morphology

Nanocrystalline materials are of high interest, because mechanical and physical properties of such materials are different from those or coarse-grained type. Continuous and smooth nanocrystalline diamond (NCD) thin films were successfully grown on mirror polished silicon substrates, using double bias plasma-enhanced hot filament chemical vapour deposition technique. A gas mixture of Ar:CH 4:H 2 and CH 4:H 2 was used as the precursor gas. The effect of the gas composition, flow rate and substrate bias during deposition on diamond crystallite size was investigated. Changing the growth parameters facilitates control of grain size of polycrystalline diamond thin films from microcrystalline to nanocrystalline. The structure of fine-grained NCD films has been studied with scanning electron microscopy and Raman spectroscopy.

Carbon nanotube tip melting with vacuum breakdown in cold cathode

Failure of patterned multiwalled carbon nanotubes during field emission (FE) was systematically studied at different fields using an indigenous FE setup. Here, the findings are reported from the experimental observation of the degradation of carbon nanotube (CNT) based field emitters over a silicon substrate. The CNTs were grown on the patterned silicon substrate using chemical vapor deposition (CVD) and plasma-enhanced CVD (PECVD) techniques. Scanning electron microscopy (SEM) was employed to observe the effect of different fields over CNTs. The observed current density of 28mA∕cm2 at a field of 5V∕μm from CNTs grown via CVD before giving a high-field treatment remained almost the same until the substrate started melting. Similar observations were made in CNTs grown via PECVD. SEM images clearly reveal that the high-field treatment resulted in melting of silicon substrate at a certain point; at some other points, etching of silicon substrate was also observed. The authors attribute these observations to arcing because the base vacuum was not sufficiently adequate for the applied field. Due to arcing, the localized temperature became so high that the substrate started to melt. The SEM images give an insight into understanding the degradation mechanism of CNT-based field emitters.

Effect of rapid thermal treatment on photoluminescence of surface passivated porous silicon

The photoluminescence of porous silicon with and without carbon deposition fabricated by plasma-enhanced chemical vapor deposition technique has been investigated. After the deposition, the rapid thermal processes in the temperature ranging from 500 to 1100 °C have been carried out. It was found that after the carbon deposition a new intense blue emission appeared. The rapid thermal processes at 800and 900 °C could enhance the blue emission, while the other rapid thermal processes quenched it. Finally, the mechanism for the effect of carbon deposition and rapid thermal processes on photoluminescence properties of porous silicon was discussed.