Jaydeep V. Sali

Acetone vapor sensing properties of screen printed WO3 thick films

This paper presents acetone vapor sensing properties of WO(3) thick films. In this work, the WO(3) thick films were prepared by standard screen-printing method. These films were characterized by X-ray diffraction (XRD) measurements, and scanning electron microscopy (SEM). The acetone vapor sensing properties of these thick films were investigated at different operating temperature and acetone vapor concentrations. The WO(3) thick films exhibit excellent acetone vapor sensing properties with the maximum sensitivity approximately 456% at 300 degrees C in air atmosphere with fast response and recovery time.

The role of hydrogen dilution of silane and phosphorus doping on hydrogenated microcrystalline silicon (μc-Si:H) films prepared by hot-wire chemical vapor deposition (HW-CVD) technique

Abstract The electrical, structural and optical properties of undoped and phosphorus doped μc-Si:H films prepared by a HW-CVD technique have been studied. The hydrogen (H 2 ) dilution of silane has been varied carefully to produce undoped μc-Si:H films. The amorphous-to-microcrystalline transition was observed for a hydrogen dilution ratio >0.75. The phosphorus doped μc-Si:H films were deposited by varying the phosphine (PH 3 ) gas flow rate. The structural properties of these films have been investigated by Raman spectroscopy, low angle X-ray diffraction spectroscopy and Fourier transform infrared vibrational spectroscopy. Electrical characterization has been carried out by dark conductivity and charge carrier activation energy measurements. The phosphorus doped μc-Si:H films showed that the addition of PH 3 to the source gases promotes the growth of crystallinity. The increase in crystallite size and crystalline volume fraction with the addition of PH 3 to the source gases indicates that it enhances the crystallization of the μc-Si:H film. Low angle XRD studies shows that the PH 3 doped μc-Si:H does not show any preferential orientation crystallites. For optimized deposition conditions PH 3 doped μc-Si:H films with high dark conductivity (0.4 S/cm), low activation energy (0.03 eV) and high band gap (1.82 eV) were obtained with a high deposition rate (13 A/s). However, for these optimized conditions, the hydrogen content was relatively large (8.3 at.%).

Narrow band gap, high photosensitivity a-SiGe:H films prepared by hot wire chemical vapor deposition (HW-CVD) method

Abstract In this letter, we report narrow band gap (1.39–1.53 eV) a-SiGe:H films with high photosensitivity (∼10 4 –10 5 ) are grown successfully by HW-CVD using a mixture of (GeH 4 +SiH 4 ) at low flow rates and without hydrogen dilution with higher deposition rates (>10 A/s). These films are characterized by Raman spectroscopy, FTIR spectroscopy and UV–Visible spectroscopy. The band gap of a-SiGe:H films can be narrowed by increasing the germane gas fraction without apparent degradation in their electronic properties. The low hydrogen content in a-SiGe:H films indicates that the growth of a-SiGe:H films is mainly from the atomic species (Si, Ge and H) evaporated from the hot filament.

Hot-wire CVD growth simulation for thickness uniformity

Obtaining thickness uniformity over a large substrate area seems to be a bottleneck as far as the industrial applications of the hot-wire CVD (Cat-CVD) process is concerned. In order to address the different issues in this respect, we have simulated the hot-wire CVD growth process and proposed a proper filament geometry for maximum thickness uniformity. The hot filament was assumed as a one-dimensional assembly of point sources. Five types of commonly used filament geometries were considered for their performance to identify the best filament geometry for maximum thickness uniformity. Here, the chamber pressure was assumed to be low enough so that the Knudsen number Kn>1. Based on our results, we propose a parallel filament geometry for maximum thickness uniformity over large substrate areas. By applying the model further to the parallel filament geometry, the relations between substrate–filament distance and minimum filament length, as well as the number of parallel filaments and the separation between them, which are necessary for the required thickness uniformity over the given substrate area, were determined. The validity of the model was checked using the ‘Matched-Pair t-test’. The effect of chamber pressure on thickness uniformity and growth rate, when it is sufficiently high to make the Knudsen number Kn<1, was also simulated. The thickness uniformity was observed to increase with an increase in chamber pressure.

Deposition of hydrogenated amorphous silicon (a-Si:H) films by hot wire chemical vapor deposition: role of filament temperature

Abstract Hydrogenated amorphous silicon (a-Si:H) films were deposited using pure saline (SiH 4 ) without hydrogen dilution by the hot wire chemical vapor deposition (HW-CVD) technique. The electrical, optical and structural properties of these films are systematically studied as a function of filament temperature ( T fil ). The device quality a-Si:H films which were obtained at high deposition rate (3≤ r d ≤85 A/s) using filament temperature (1400≤ T fil ≤1900 °C) without hydrogen dilution show good structural, optical and electrical properties. However, the films deposited at higher filament temperature show an amorphous-to-microcrystalline transition. The FTIR spectroscopic analysis showed that a-Si:H films deposited at low filament temperature contain hydrogen mainly in mono-hydride (Si–H) configuration whereas films deposited at higher filament temperature have hydrogen in di-hydride (Si–H 2 ) or poly-hydride (SiH 2 ) n complexes. The low hydrogen content ( C H ) in the films indicates that the growth of a-Si:H films is mainly from the atomic species (Si and H) evaporated from the hot filament and hydrogen is incorporated in the film via gas phase reactions and substrate–gas interactions. The band gap, however, was found to be ∼1.71 eV or much higher. We suggest high band gap at low hydrogen content may be due to the presence of microvoids. Raman spectroscopic analysis showed the increase in structural disorder and Rayleigh scattering with increase in filament temperature.

The effect of substrate temperature on HW-CVD deposited a-SiGe:H films

Abstract Hydrogenated amorphous silicon germanium (a-SiGe:H) films were deposited using SiH4 and GeH4 mixture without H dilution by hot wire chemical vapor deposition (HW-CVD) technique. The electrical, optical and structural of these films are systematically studied as a function of substrate temperature (Tsub). The FTIR spectroscopic studies showed that a-SiGe:H films deposited at high Tsub contain H mainly the monohydride configuration whereas the films deposited at low Tsub has H in polyhydrides or (Si–H2)n complexes form. The low CH in a-SiGe:H films indicates that the growth of film is mainly from the atomic species evaporated from the hot filament and H gets incorporated in the film via gas phase reactions and substrate–gas interactions. Raman spectroscopic studies showed that the structural order of a-SiGe:H films improve with increase in Tsub. The T sub =300 ° C was found to be the optimized substrate temperature for the synthesis of device quality a-SiGe:H films.

Preparation and Characterization of WO3-Based Liquid Petroleum Gas Sensor

The present investigation deals with the fabrication of liquid petroleum gas (LPG) sensor based on WO3. In this work, WO3 films were prepared by standard screen-printing method. These films were characterized by X-ray diffraction (XRD) measurements, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). These films exhibit high sensitivity, excellent selectivity, fast response and recovery to LPG at 400°C in air atmosphere.

The effect of substrate temperature on P-CVD deposited a-SiGe : H films

Undoped a-SiGe : H films were deposited by the RF plasma chemical vapor deposition method. Films deposited at different substrate temperatures ranging between 100°C and 300°C were studied for their optoelectronic and structural properties. Structural defects like vacancies and microvoids were studied by positron lifetime spectroscopy (PLTS) at room temperature. Optoelectronic properties of the films were correlated with the PLTS measurements. The observations show a decrease in the deposition rate with substrate temperature. Good optoelectronic properties and proper structural relaxation have been obtained with a decrease in microvoid concentration.

SILAR controlled CdSe nanoparticles sensitized ZnO nanorods photoanode for solar cell application: Electrolyte effect

Controlled growth of different sizes of cadmium selenide (CdSe) nanoparticles over well aligned ZnO nanorods have been performed using successive ionic layer adsorption and reaction (SILAR) technique at room temperature (27 °C) in order to form nano heterostructure solar cells. Deposition of compact layer of zinc oxide (ZnO) by SILAR technique on fluorine doped tin oxide (FTO) coated glass substrate followed by growth of vertically aligned ZnO nanorods array using chemical bath deposition (CBD) at low temperature (<100 °C). Different characterization techniques viz. X-ray diffractometer, UV-Vis spectrophotometer, field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy have been used to know the structural, optical, morphological and compositional properties of synthesized nano heterostructure. The photovoltaic performance of the cells with variation in SILAR cycles for CdSe and with use of different electrolytes have been recorded as J-V characteristics and the maximum conversion efficiency of 0.63% have been attained with ferro/ferri cyanide electrolyte for 12 cycles CdSe coating over 1-D ZnO nanorods.

Changes in in-plane electrical conductivity of PEDOT:PSS thin films due to electric field induced dipolar reorientation

Orientation of polar polymer chains can be achieved by direct application of high electric field to the polymer thin films. Changes in morphology due to such electric field treatment can impart changes in electrical conductivity of the thin films. PEDOT:PSS thin films exhibit isotropic in-plane electrical conductivity. We have observed that the electric field treatment at high temperature lead to anisotropic behaviour in in-plane conductivity of thin film of PEDOT:PSS film. In case of films prepared with aqueous solution of PEDOT:PSS, electric field treatment cause rise in electrical in-plane conductivity in orthogonal direction to electric field and it falls in direction of electric field. Thin films prepared with DMSO added aqueous solution of PEDOT:PSS show initial isotropic switching from high conductivity to low conductivity state due to electric field treatment. Prolonged treatment resulted in significant fall in in-plane electrical conductivity specifically in the direction of electric field. A model, based on re-orientation of polymer chains caused by interaction of electric field and electric dipoles of PEDOT:PSS chains, has been proposed to explain this behaviour. The hypothesis is supported by the results of Raman spectroscopy. Co-relating changes are also recorded in absorption spectra of these films. This study may find application in write once read many memory devices based on PEDOT:PSS.