M.G. Takwale

Characterization of silicon oxynitride thin films deposited by electron beam physical vapor deposition technique

Abstract Thin films of silicon oxynitride (SiO x N y ) were deposited successfully on silicon wafer substrates using electron beam physical vapor deposition (EB-PVD) technique by varying the substrate temperature ( T =100–450 °C) and deposition time ( t =0.5–2.5 min). The films were characterized by UV–Visible and X-ray photoelectron spectroscopy (XPS), Tally step measurement and Ellipsometry. The minimum reflectivity R =1.72% is obtained for the films deposited under the conditions of T =350 °C, t =1.5 min at λ =548 nm. Further, the characterization results revealed that the refractive index (RI) of the films increases with increase in the substrate temperature due to increase in silicon nitride content. The refractive index and the thickness of the films were found to be in the range of n =1.72–1.90 and d =40–138 nm, respectively. The values n =1.88 and d =79 nm observed corresponding to the minimum reflectivity R =1.72% satisfy the condition of near quarter wavelength single layer antireflection coating. Thus, the above films might have the tremendous potential for antireflective coating applications.

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.%).

Dependence of structural and electrical properties of undoped spray-deposited indium oxide thin films on deposition temperature

Abstract Thin films of undoped In 2 O 3 have been deposited at different substrate temperatures using the spray pyrolysis technique. These films show a preferred orientation which depends upon the deposition temperature of the substrate. The number of charge carriers and their mobility for the films have been measured and attempts have been made to explain these results. The results of optical transmission and energy band gap measurements are also included.

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.

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.

Synthesis and Optical Properties of Cobalt Oxide (Co3O4) Nanoclustered Films Produced by Pulsed DC Electrochemical Deposition Process

The Co3O4 films were prepared using two steps method. Initially, the films were deposited on thoroughly cleaned copper substrates by using pulsed DC electrochemical deposition method from a solution containing Co(NO3)2:6H2O and H3BO3. The films were deposited at different molar concentrations: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7 M of Co(NO3)2 in deposition bath. These as‐deposited films were transformed into Co3O4 phase by heating them at 400 °C/2 hr. These as‐heated films were characterized by using X‐ray diffraction, X‐ray photoelectron spectroscopy, UV‐Visible spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. From the characterization studies, the as‐heated films were found to be containing single cubic spinel Co3O4 phase with high purity. The variation in molar concentration of Co(NO3)2 in deposition bath showed the intense effect on optical properties of Co3O4 films. The better optical properties, absorptance (α) = 0.950, emittance (e) = 0.070 were obtained for ...

Interelectrode separation effects on a-SiGe:H films prepared by plasma chemical vapor deposition

Abstract The properties of a-SiGe:H films prepared by the glow discharge plasma CVD method at various interelectrode separation were studied systematically. This study was done at two different rf power densities. It has been found that interelectrode separation plays an important role in determining film properties. It shows a more marked effect on photosensitivity at lower rf power density than at higher rf power density. Photosensitivity, in general, decreased, whereas growth rate increased with the increase in interelectrode separation. High photosensitivity (1.3×105) was obtained even at higher growth rate (245 A/min) just by controlling the interelectrode separation. Bandgap of the films was about 1.4 eV. Structural properties of the films were studied by positron life time spectroscopy (PLTS).