Optical and structural features of silicon-rich hydrogenated amorphous silicon nitride thin films

A systematic study of fabrication and effect of post-deposition processing on the optical and structural features of silicon-rich hydrogenated amorphous silicon nitride thin films deposited by Hg-sensitized Photo-Chemical Vapour Deposition technique is presented. Both deposition parameters and post-deposition thermal treatment resulted into substantial change in the refractive index associated with the densification of the film. Our studies reveal that the presence of hydrogen and its out-diffusion upon thermal treatment play a crucial role in the overall structural evolution, specially the stabilization of individual phases such as Si and Si3N4. We further report the room-temperature photoluminescence from as-deposited films, which is due to formation of silicon nanostructures in crystalline and amorphous forms. These studies are of great interest from the prospective of commercially viable Si-based technology.     

Photoanodic properties of sol-gel-derived iron oxide thin films with embedded gold nanoparticles: effects of polyvinylpyrrolidone in coating solutions

Fe₂O₃ thin films containing dispersed Au nanoparticles were prepared on nesa silica glass substrates, using Fe(NO)₃·9H₂O-HAuCl₄·4H₂O-CH₃COCH₂COCH₃-CH₃OC₂H₄OH solutions containing polyvinylpyrrolidone (PVP). The photoanodic properties were studied in a three-electrode cell with the film sample as the working electrode and an aqueous buffer solution of pH=7 as the supporting electrolyte. The Au particles increased photoanodic quantum efficiency at wavelengths <500-600 nm. Quantum efficiency was further increased by modifying the microstructure of the film electrodes through the addition of PVP. The maximum incident photon to current efficiency (IPCE) of about 20% was achieved in an Au-dispersed film prepared from a solution containing PVP. PVP in coating solutions provided the fired films with an increase in size of the grains and voids between them and in donor density, either of which could contribute to the increased IPCE.     

Visible electroluminescence from silicon nanoclusters embedded in chlorinated silicon nitride thin films

Visible electroluminescence (EL) has been obtained from devices with active layers of silicon nanocrystals embedded in chlorinated silicon nitride (Si-nc/SiN_x:Cl) thin films, deposited by remote plasma enhanced chemical vapour deposition, using SiCl₄/NH₃/H₂/Ar. The active nc-Si/SiN_x:Cl film was sandwiched between Al contacts and a transparent conductive contact of ZnO_x:Al deposited by the pyrosol process. White EL centred at around 600 nm was observed, with a turn-on voltage of 5 V, and the intensity increasing as a function of voltage. Recombination between electron-hole pairs generated in the Si-nc by electron impact ionization is proposed as the EL mechanism.     

Comparison of silicon nanocrystals embedded silicon oxide films by sputtering and PECVD

The material and optical properties of the silicon rich oxide (SRO) films prepared by PECVD and sputtering were comprehensively studied. The optical properties were found strongly depend on the material properties of the SRO films. The photocurrent of the photodiodes using PECVD deposited SRO was ~ 3 order higher than that prepared by the sputtering, while the leakage current of the later was much lower than the former, leading the light/dark current ratio of the sputtered photodiodes was higher than the PECVD prepared ones when the bias voltage exceeded ~ 1.6 V. The transmission electron microscopy and the X-ray photoelectron spectroscopy were used to investigate the variations of the constitutive Si nanocrystals and the oxidation states. After annealing, size of the nanocrystals decreased and the oxidation states changed, changing the optical properties of the photodiodes.     

High concentration erbium doping of silicon-rich SiO2 thin films on silicon

In this work, high concentration erbium doping in silicon-rich SiO₂ thin films is demonstrated. Si plus Er dual-implanted thermal SiO₂ thin films on Si substrates have been fabricated by using a new method, the metal vapor vacuum arc ion source implantation with relatively low ion energy, strong flux and very high dose. X-Ray photoelectron spectroscopy measurement shows that very high Er concentrations on the surfaces of the samples, corresponding to 10 at.% or the doping level of 10²¹ atoms cm⁻³, are achieved. This value is much higher than that obtained by using other fabrication methods such as the high-energy ion implantation and molecular beam epitaxy. Reflective high-energy electron diffraction, atomic force microscopy and cross-section high-resolution transmission electron microscopy observations show that the excess Si atoms in SiO₂ matrix accumulate to form Si clusters and then crystallize gradually into Si nanoparticles embedded in SiO₂ films during dual-ion implantation followed by rapid thermal annealing. Er segregation and precipitates are not formed. Photoluminescence at the wavelength of 1.54 μm exhibits very weak temperature dependence due to the introduction of Si nanocrystals into the SiO₂ matrix. The 1.54-μm light emission signals from annealed samples decrease by less than a factor of 2 when the measuring temperature increases from 77 K to room temperature.     

Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

Synthesis and characterization of amorphous silicon oxide nanowires embedded with Ni nanoparticles

The growth of silicon oxide nanowires (SiOxNWs) was obtained by thermal process of nickel (Ni) nanoparticles (NPs) deposited on silicon (Si) wafer in mixed gases of nitrogen (N₂) and hydrogen (H₂). TEM analysis showed that SiOxNWs had diameters ranging from 100 to 200 nm with lengths extending up to a few μm and their structure was amorphous. SiOxNWs were grown by the reaction between Ni NPs and Si wafer and Ni NPs acted as catalysts. Ni silicides (NixSi) were also formed inside the wafer by Ni diffusion into Si wafer.     

Preparation and optical properties of gold nanoparticles embedded in barium titanate thin films

High amount of gold nanoparticles was successfully incorporated into amorphous BaTiO₃ thin films by sol-gel process. Thiourea was applied to prevent Au ions from being reduced and aggregating as the effective stabilization agents. These films exhibited unique surface plasma resonance red-shifting and particular changes of surface plasma resonance intensity with the increase of heat-treating temperature, which could be attributed to the influence of BaTiO₃ ferroelectric domains. The films also exhibited superfast nonlinear optical response and larger third-order nonlinear susceptibility ⁽³⁾, which was attributed to hot electron contribution.     

Microstructure and optical properties of plasmapolymer thin films with embedded silver nanoparticles

Plasmapolymer thin films with embedded silver nanoparticles were deposited by simultaneous plasma polymerization and metal evaporation. The particle size and shape were determined by transmission electron microscopy (TEM) and analysed by optical image processing. The optical properties in the UV/ VIS/NIR spectral region were determined by the plasma resonance absorption of the silver particles. Transmittance spectra were calculated with the Bergman effective medium theory and compared with experimental spectra.     

Current transfer processes in thin lutecium and terbium oxide films on silicon

The results of the experimental study of the current transfer processes in thin Lu₂O₃ and Tb₂O₃ films on silicon substrates are presented. It is shown that, depending on the experimental conditions, the process of either the thermionic-field or the over-barrier emission prevails. Illumination of the structure does not change the effective surface barrier height. The results presented may be important for the practical applications of rare earth oxide-based thin-film systems.     

Comparison between silicon thin films with and without incorporating crystalline silicon nanoparticles into the film

We have deposited Si thin films using a multi-hollow discharge plasma CVD method to compare properties of the films with and without incorporating crystalline Si nanoparticles into the films. After the deposition of the films, we have evaluated crystallization of the films by irradiating laser. We have found that a laser power at which crystalline Si nanoparticles embedded a-Si:H films start to be crystallized is lower than that for a-Si:H films without the nanoparticles. The incorporation of the nanoparticles has no effect on the defect density of the films. These results suggest incorporation of crystalline Si nanoparticles into the films play a role of crystallization of Si films during the deposition.     

Dielectric functions of PECVD-grown silicon nanoscale inclusions within rapid thermal annealed silicon-rich silicon nitride films

Spectroscopic ellipsometry (SE) measurements were carried out in order to characterize the optical properties of silicon nanoscale inclusions (Si-ni) contained in silicon-rich silicon nitride (SRSN) films. These films were deposited using the plasma enhanced chemical vapor deposition (PECVD) technique followed by rapid thermal annealing (RTA) during 1 min. We focus our study on the influence of the deposition and annealing conditions - such as the ammonia to silane flow ratio R, the annealing atmosphere and temperature - on the optical responses of the SRSN layers and the behavior of the Si-ni dielectric functions. Our results suggest that the variation of R affects in a more significant way the structure and optical properties of the SRSN films than the change of the annealing gas or temperature.     

Erbium implanted silicon rich oxide thin films suitable for slot waveguides applications

Thin (50 nm) erbium implanted silicon rich oxide films suitable for slot waveguides applications have been produced and studied by means of optical spectroscopy and structural characterisation techniques. Comparison between different deposition techniques in terms of light emitting properties of erbium ions is presented. Special attention is given to the efficiency improvement of the energy transfer from silicon nanoclusters to erbium ions where the type of annealing treatment is proven to be of crucial importance.     

Nanoindentation stress-strain curves of plasma-enhanced chemical vapor deposited silicon oxide thin films

Plasma-enhanced chemical vapor deposited (PECVD) silicon oxide (SiO_x) thin films have been widely used in Micro/Nano Electro Mechanical Systems to form electrical and mechanical components. In this paper, we explore the use of nanoindentation techniques as a method of measuring equivalent stress-strain curves of the PECVD SiO_x thin films. Four indenter tips with different geometries were adopted in our experiments, enabling us to probe the elastic, elasto-plastic, and fully plastic deformation regimes of the PECVD SiO_x thin films. The initial yielding point (σ_I) and stationary yielding point (σ_II) are separately identified for the as-deposited and annealed PECVD SiO_x thin films, as well as a standard fused quartz sample. Based on the experimental results, a shear transformation zone based amorphous plasticity theory is applied to depict the plastic deformation mechanism in the PECVD SiO_x.     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Tensile testing of silicon thin films

The tensile strength of silicon thin films was investigated using a specimen chucking system dedicated for microscale specimens. The system uses electrostatic force to fix and hold the free end of the cantilever‐shaped specimens. The thin film tensile tester was built using this system. The accuracy and reliability of this method were assured by comparing it with other tensile‐testing methods using single‐crystal silicon specimens. The result shows good agreement between the testing methods. The strength properties of polysilicon thin films, such as the effect of the testing environment and the specimen size and the film fabrication conditions, were investigated.     

Electroreflectance spectra of thin silicon films

Electroreflectance spectra for thin silicon films have been investigated in the photon energy region 2.8–5.0 eV. The critical point energy E₁(E′'₀) and the broadening parameter Γ were determined for unexposed and ion-bombarded surfaces. Definite correlation between Γ^-1 and the Hall mobility was found. It is concluded that the variations in E₁(E_'0) for the films are caused by the emergence of density “tails” and the existence of inward mechanical microtensions.