Abhai Mansingh

Influence of postdeposition annealing on the structural and optical properties of sputtered zinc oxide film

The influence of postdeposition annealing on the structural and optical properties of rf sputtered insulating zinc oxide films has been investigated. The as‐grown films deposited on quartz substrates were highly c‐axis oriented and in a state of stress. These films become almost stress free after a postdeposition annealing treatment at 673 K for 1 h in air. Above 673 K, a process of coalescence was observed which causes major grain growth resulting in microcrack formation and surface roughness. The refractive index shows a strong frequency dispersion below the interband absorption edge. The optical dispersion data have been fitted to (1) a single oscillator model and (2) the Pikhtin–Yas’kov model. The origin of optical dispersion at different annealing temperatures has been discussed in the light of these models. A packing density of more than 99% is estimated in the film annealed at 673 K, indicating that these films are almost void free.

Growth and characterization of tin oxide films prepared by chemical vapour deposition

Abstract Undoped tin oxide films have been prepared by a chemical vapour deposition technique. The effect of different deposition parameters on the sheet resistance of the films has been studied. Films are highly transparent (about 90%) in the visible region, have a quite low sheet resistance (25 Ω/□) and have reproducible properties. X-ray diffraction shows the structure to be polycrystalline with a grain size of about 570 A. The preferred orientation is (101) for the films deposited at substrate temperatures up to 350 °C, after which the preferred orientation changes to (200). The electrical properties of the films also exhibit a change at this deposition temperature. Direct and indirect band gaps are calculated to be 3.93 eV and 2.53 eV respectively. Degradation of the films with time has also been studied. The figure of merit ϕ = T 10 /R sh (9.45 × 10 -3 Ω -1 at 0.66 μm) obtained is the highest amongst the values reported for undoped tin oxide films.

DC conduvtivity of V2O5TeO2 glasses

The dc conductivity of semiconducting vanadium tellurite glasses of compositions in the range 50 to 80 mol% V2O5 has been measured in the temperature region 77 to 400 K. Measurements have been made on annealed samples at different annealing temperatures. Annealing the samples at temperature of about 250°C causes the appearance of a complex crystalline phase resulting in an increase of conductivity. Results are reported for amorphous samples of different compositions. The conductivity of tellurite glasses is slightly higher than the corresponding composition of phosphate glasses, but the general trend of the increase of conductivity and decrease of high temperature activation energy with increasing V2O5 content is similar in the two systems. The data have been analysed in the light of existing models of polaronic hopping conduction. A definite conclusion about the mechanics of conduction (adiabatic or nonadiabatic) is difficult in the absence of a precise knowledge of the characteristic phonon frequency v0. Adiabatic hopping is indicated for v0∼1011 Hz, however this value leads to unreasonably low value for the Debye temperature θD, and higher values for v0∼1013 hz satifiies the conditions for nonadiabatic hopping which appears to be the likely mechanism of conduction in V2O5TeO2 glasses. The low temperature data (< 100 K) can be fitted to Motts variable range hopping, which when combined with ac conductivity data gives reasonable values of α, but a high value for the disorder energy.

Preparation and characterization of rf sputtered indium tin oxide films

Indium tin oxide films have been grown by rf sputtering at various Ar‐O2 mixtures, at low substrate temperatures (200 °C), and deposition rates (25 A/min), followed by post deposition annealing (at 350 °C) in different ambients (O2, N2, and cracked ammonia). Influence of a reactive gas (oxygen) on the sputtering rate of a metallic (indium/tin) alloy target has been investigated. Growth parameters and annealing conditions have been optimized. The films were characterized by electron and x‐ray diffraction, scanning electron microscopy, and transmittance as a function of wavelength. The effect of heat treatment in various environments on the structural, electrical, and optical properties has been investigated. Effect of a new annealing ambient, cracked ammonia (reducing atmosphere), on the reactively sputtered oxide films is being reported for the first time. Cracked ammonia was found to be very effective and cheap and resulted in films of high quality (electrical and optical) with good structural properties...

Effect of target‐substrate distance on the growth and properties of rf‐sputtered indium tin oxide films

Indium tin oxide films have been deposited by rf sputtering an oxide target (90% In2O3+10% SnO2). Transparent conducting films have been obtained on room‐temperature substrates without any post‐deposition annealing. The effects of target‐substrate separation on the growth characteristics and film properties have been studied. The virtual‐source formation of the sputtered neutrals in the gap between the target and substrate has been observed. The effect of sputtering parameters on the position of the virtual source has been studied. It has been observed that the films deposited onto substrates kept below and above the virtual source have different properties. The films on substrates kept above the virtual source have (222) preferred orientations, with a direct optical band gap of 3.7 eV, an electron effective mass of 0.51 m, and a figure of merit ∼14×10−3 Ω−1. The films on substrates below the virtual source have preferred orientations along (440) and (400), with a band gap of 3.5 eV, an effective mass of ...

Structural and electrical properties of rf‐sputtered amorphous barium titanate thin films

Structural and electrical properties of rf‐sputtered amorphous BaTiO3 thin films grown on water‐cooled substrates have been investigated. The dielectric and electrical properties have been studied for films grown under varying sputtering gas composition (Ar+O2 gas mixtures) as a function of film thickness, frequency, and temperature. As‐grown films were amorphous in nature and highly transparent. Post‐deposition annealing had no discernible effect either on film structure or dielectric properties, and there was no evidence of ferroelectricity. Films sputtered in pure argon showed a dielectric constant e’∼12 with little dependence on frequency (0.1–100 kHz) over the temperature range 0–75 °C. The dielectric properties were a function of film thickness and the percentage of oxygen in the sputtering gas during growth. The thickness‐dependent dielectric properties of amorphous BaTiO3 thin films on conducting glass substrates could be satisfactorily explained by a model based on the existence of electrode barr...

Structural and optical properties of sol‐gel‐processed BaTiO3 ferroelectric thin films

BaTiO3 thin films having a perovskite structure were deposited onto stainless steel and fused quartz substrates by sol‐gel processing. Crystalline, transparent, and crack‐free films of 5000 A thickness were fabricated by spinning and post‐deposition annealing at a temperature of 600 °C. Ferroelectric properties were confirmed by P‐E hysteresis loops. The dielectric constant and optical transmission were also measured.

Optical properties of reduced lithium niobate single crystals

The optical transmission of LiNbO3 single crystals has been measured in the wavelength range 200–900 nm, for different degrees of reduction, to study the effect of reduction on the optical characteristics of LiNbO3 near the fundamental absorption edge. The optical transitions in LiNbO3 were found to be indirect and the band gap decreased with increasing degree of reduction. The band observed at 2.48 eV in the absorption spectrum in heavily reduced samples has been attributed to the formation of polarons, and the theoretical model of Reik and Heese [J. Chem. Solids 28, 581 (1967)] for small polarons is used to correlate the optical and electrical properties.

Rapid thermally processed ferroelectric Bi4Ti3O12 thin films

Polycrystalline Bi4Ti3O12 thin films having perovskite structure were successfully produced on platinum coated silicon substrates by the sol‐gel technique. Crack‐free and crystalline films of 5000 A thickness were fabricated by spinning and post‐deposition rapid thermal annealing treatment at 500 °C for 20 s. The films exhibited good structural, dielectric, and ferroelectric properties. The measured dielectric constant and loss factor at a frequency of 100 kHz were 180 and 0.014 and remanent polarization and coercive field were 5.4 μC/cm2 and 135 kV/cm, respectively. The films showed good switching endurance under bipolar stressing at least up to 1010 cycles.

Preparation and characterisation of V2O5B2O3 glasses

The binary V2O5B2O3 glasses were prepared. With low V2O5 content the samples were amorphous but very unstable due to their hygroscopic character; these developed crystallinity due to B2O3 content. There was some crystallinity in compositions ranging from 30 mol.% to 50 mol.% V2O5. In higher compositions good amorphous structure was noticed. The structure was also highly dependent on the quenching rate. The physical parameters such as density, glass transition temperature and the X-ray diffraction, infrared absorption spectra are discussed with respect to all compositions. The dc electrical conductivity was measured for only those samples (70 to 90 mol.% of V2O5) which were found to be amorphous in nature. It is observed that in this glass system too, the high temperature conduction phenomenon is due to adiabatic hopping like that in V2O5TeO2 glasses. The electrical properties are highly sensitive to the thermal history of preparation of the samples.