Goh Boon Tong

Influence of Hydrogen Dilution of Silane on the Properties of nc-Si:H films grown by Layer-by- Layer deposition technique

Hydrogenated nanocrystalline silicon (nc-Si:H) films produced by layer-by-layer (LBL) deposition technique were studied. The films were grown at different hydrogen to silane flow-rate ratio on crystal silicon (111) substrate. The properties of films were investigated by X-ray diffraction (XRD), micro-Raman scattering spectroscopy, Fourier transform infrared (FTIR) spectroscopy, optical transmission spectroscopy, atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). These properties showed dependence on the hydrogen dilution of silane. Appearance of XRD peaks at diffraction angles of 28.4 o and 56.1 o which correspond to silicon orientation of (111) and (311) respectively, were observed in all films indicating evidence of crystallinity in the films. Raman scattering results indicated that crystallinity in the films was due to the presence of nanocrystallites embedded in an amorphous matrix. The energy gap of the films showed dependence on the hydrogen content in the films. Increase in nanocrystallite size resulted in increase in disorder at low hydrogen dilution films but films remain homogenous with increase in nanocrystallite size for the high hydrogen dilution films.

Effects of Substrate Temperature on the Properties of Hydrogenated Nanocrystalline Silicon Thin Film Grown by Layer-by-Layer Technique

Nanocrystalline silicon (nc-Si) thin films prepared by layer-by-layer (LBL) technique were studied. The LBL technique involves periodic interruption of the deposition process whereby the silane diluted in hydrogen plasma discharge is stopped for a fixed period of time during which the growth surface is treated with hydrogen plasma discharge. This technique controls the crystallite size in the film structure. The films are grown at different substrate temperatures ranging from room temperature to 400degC. The dependence of the optical and structural properties of the films on the substrate temperature is investigated using optical transmission, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy technique. The effects of substrate temperature were studied and these properties showed strong dependence on the substrate temperature. Initial increase in the substrate temperature to 200degC resulted in a blue shift in the absorption edge but higher substrate temperature shifted it back towards lower energy. Higher substrate temperatures also lowered the hydrogen content in the film and increased the concentration of monohydride bonds in the film structure. Increase in crystallinity was observed with increase in substrate temperature.

Dependence of Radio Frequency Power on Optical, Chemical Bonding and Photoluminescence Properties of Hydrogenated Amorphous Carbon Nitride Films

Hydrogenated amorphous carbon nitride films (a-CNx:H) were prepared in a radio-frequency plasma enhanced chemical vapour deposition (r.f. PECVD) system with a parallel-plate configuration. The gas sources of CH4 and N2 were fixed at CH4:N2 ratio of 1:3. The films were grown on glass and Si substrates on the grounded electrode at 100degC. The effect of r.f. power (varied between 0.71 - 3.54 W/cm2) on the optical, infrared (IR) absorption spectra and photoluminescence (PL) spectra of the a- CNx:H films were studied. It was observed that the deposition rate increases linearly up to the r.f. power of 2.83 W/cm2 , while the optical band gap (E04) decrease exponentially in the whole range. This is proposed to be the effect of an increase in nitrogen incorporation into the sp2 carbon clusters, as indicated by FTIR. The PL spectra consist of a band in the region of 2.10-2.40 eV, with peaks at approximately 2.23, 2.27 and 2.33 eV. The PL intensity of the films increases as the r.f. deposition power increases and is related to the increase of the sp2 clusters with increasing nitrogen incorporation.

Fabrication and characterization of co-sputtering Au/SiO 2 thin films prepared by RF magnetron sputtering

An amorphous silicon suboxide was synthesized by co-sputtering of Au and SiO2 using RF magnetron sputtering. The extracted data from XRD, SEM as well as EDX were utilized to characterize the surface of the thin film samples.

The Effects of Deposition Pressure on the Optical and Structural Properties of d.c. PECVD Hydrogenated Amorphous Carbon Films

A direct-current plasma enhanced chemical vapour deposition (PECVD) system was designed and built in-house for the deposition of hydrogenated amorphous carbon(a-C:H) thin films. In this work, a-C:H thin films prepared using this system at different deposition pressures were studied. The influence of deposition pressure on the deposition rate, energy gap, bonded hydrogen content and structure of the film has been investigated. The characterization techniques were determined from optical transmission spectroscopy, Fourier transform infrared spectroscopy and Xray diffraction measurements. The results demonstrated that the deposition pressure had strong influence on the deposition rate, optical energy gap and the bonded H content in the film. Evidence of crystallinity was observed in films prepared at low deposition pressure.

Effect of varying nitrogen flow rates on the optical properties of amorphous-SiCN thin films

Series of amorphous silicon carbon nitride (a-SiCN) films are synthesized using RF-PECVD technique on glass and silicon substrates from precursor gas of silane, methane and nitrogen. In this work, the change in nitrogen flow rate from 0 sccm to 50 sccm is a mean used to vary the elemental composition and bonding properties which lead to change in optical properties. The films thickness varies between 327 nm to 944 nm. The changes for the stated properties are discussed against the change in the stated nitrogen flow rate. The optical properties are investigated by means of UV-VIS spectroscopy in the wavelength range of 190 nm to 2500 nm. The transmittance of the films at ultra-violet wavelength is found to increases with increase in nitrogen flow rate. The index of refraction, n obtained for SiCN films from transmittance and reflectance measurements is lower compared to SiC films. The films optical band gap increases from 1.74 eV to 2.08 eV before it decreases to 1.89 eV as nitrogen flow rate increases fro...

Spectroscopic (UV/VIS, Raman) and Electrophoresis Study of Cytosine-Guanine Oligonucleotide DNA Influenced by Magnetic Field.

Studying the effect of a magnetic field on oligonucleotide DNA can provide a novel DNA manipulation technique for potential application in bioengineering and medicine. In this work, the optical and electrochemical response of a 100 bases oligonucleotides DNA, cytosine-guanine (CG100), is investigated via exposure to different magnetic fields (250, 500, 750, and 1000 mT). As a result of the optical response of CG100 to the magnetic field, the ultra-violet-visible spectrum indicated a slight variation in the band gap of CG100 of about 0.3 eV. Raman spectroscopy showed a significant deviation in hydrogen and phosphate bonds’ vibration after exposure to the magnetic field. Oligonucleotide DNA mobility was investigated in the external electric field using the gel electrophoresis technique, which revealed a small decrease in the migration of CG100 after exposure to the magnetic field.

Effects of RF Power on the Hydrogen Bonding And Structural Order in Si:H Thin Films Deposited from Hydrogen Diluted Silane

The effects of rf power on the hydrogen bonding and structural order in hydrogenated silicon (Si:H) thin films prepared by plasma enhanced chemical vapor deposition (PECVD) from silane highly diluted with hydrogen have been studied. The radio‐frequency, rf power was varied from 20 to 100 W representing power densities of 0.7 to 3.5 mW/cm2 for our home‐built rf PECVD system. The structure and hydrogen bonding properties of the films were studied using Fourier transform infrared and micro‐Raman scattering spectroscopy. The hydrogenated silicon films showed dominant presence of monohydride bonds indicating homogeneity of the amorphous component of the films. Rf powers of 40 and 60 W produced films with the low hydrogen content and increased concentration of polyhydrides bonds. The crystalline volume fraction decreased with increase in rf power and structural order was enhanced for the films prepared at rf power of 40 and 60 W.

High Temperature Post-Deposition Annealing Studies of Layer-by-layer (LBL) Deposited Hydrogenated Amorphous Silicon Films

High temperature post-deposition annealing studies were done on hydrogenated amorphous silicon thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) using the layer-by-layer (LBL) deposition technique. The films were annealed at temperatures of 400 o C, 600 o C, 800 o C and 1000 o C in ambient nitrogen for one hour. Auger electron spectroscopy (AES) depth profiling results showed that high concentration of O atoms were present at the substrate/film interface and at film surface. Very low concentration of O atoms was present separating silicon layers at regular intervals from the film surface and the substrate due to the nature of the LBL deposition and these silicon oxide layers were stable to high annealing temperature. Reflectance spectroscopy measurements showed that the onset of transformation from amorphous to crystalline phase in the LBL a-Si:H film structure started when annealed at temperature of 600 o C but the X-ray diffraction (XRD) and Raman scattering spectroscopy showed that this transition only started at 800 o C. The films were polycrystalline with very small grains when annealed at 800 o C and 1000 o C. Fourier transform infrared spectroscopy (FTIR), measurements showed that hydrogen was completely evolved from the film at the on-set of crystallization when annealed at 800 o C. The edge of the reflectance fringes shifted to longer wavelength decrease in hydrogen content but shifted to shorter wavelength with increase in crystallinity.

Influence of Hydrogen Plasma Treatment Time to Si:H Layer Deposition Time Ratio on the Properties of Layer‐by‐Layer Deposited Hydrogenated Silicon (Si:H) Thin Films

Hydrogenated silicon (Si‐H) thin films were deposited from a mixture of pure silane (SiH4) and hydrogen (H2) gases in a home‐built plasma enhanced chemical vapour deposition (PECVD) system using the layer‐by‐layer (LBL) deposition technique. In the LBL process, the deposition was performed by periodically alternating the deposition of Si:H layer with the hydrogen treatment process of the growth surface. In this work, the effects of the H pasma treatment time to Si‐H layer growth time ratio on the film properties were studied. The LBL deposited Si‐H films studied in this work were deposited using different Si‐H layer growth times ranging from 2 minutes to 7 minutes with the hydrogen plasma treatment time on the growth surface fixed at 3 minutes. Optical transmission spectroscopy, X‐ray diffraction (XRD), micro‐Raman scattering spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) measurements were done on these films to investigate the optical, structural and morphological properties of the films. The films deposited by this technique produced the highest deposition rate of 6.3 A/s when the growth time of the Si‐H layer was fixed at 5 minutes. These films were amorphous in structure and had large optical energy gaps irrespective of the Si‐H layer deposition time. High concentration of cone‐like structures was observed in the AFM images for the films deposited using the higher Si‐H layer deposition times.Hydrogenated silicon (Si‐H) thin films were deposited from a mixture of pure silane (SiH4) and hydrogen (H2) gases in a home‐built plasma enhanced chemical vapour deposition (PECVD) system using the layer‐by‐layer (LBL) deposition technique. In the LBL process, the deposition was performed by periodically alternating the deposition of Si:H layer with the hydrogen treatment process of the growth surface. In this work, the effects of the H pasma treatment time to Si‐H layer growth time ratio on the film properties were studied. The LBL deposited Si‐H films studied in this work were deposited using different Si‐H layer growth times ranging from 2 minutes to 7 minutes with the hydrogen plasma treatment time on the growth surface fixed at 3 minutes. Optical transmission spectroscopy, X‐ray diffraction (XRD), micro‐Raman scattering spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) measurements were done on these films to investigate the optical, structural and morpho...