Sudha Kartha,C(American Institute of Physics., January 13, 2007)
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Abstract:
Poly(methyl)methacrylate was made photoconducting by molecular doping and the
photoconductivity was investigated using modulated photocurrent technique . Low-temperature
current-voltage measurements showed that the transport mechanism was thermally activated
hopping. An experimental investigation of the photoconductivity action spectrum along with
theoretical calculation enabled an estimation of the diffusion coefficient of the material. The
presence of states with a distribution of lifetimes could be understood from the frequency response
of the photocurrent . The photocurrent was due to the field-assisted dissociation of these states.
Jayaraj, M K(Institute of Materials Engineering Australasia Ltd, 2005)
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Abstract:
ZnGa2O4 spinel is a promising new UV transparent electronic conductor. Enhancing the electrical conductivity of this
potential oxide phosphor can make it a promising transparent conducting oxide. In this paper, we have investigated the
effects of processing and doping on the conductivity of semiconducting ZnGa2O4, particularly thin films. Crystalline
zinc gallate thin films have been deposited on fused quartz substrates employing the pulsed laser deposition (PLD)
technique at room temperature for an oxygen partial pressure of 0.1 Pa (0.001mbar). The films were found to be UV
transparent, the band gap of which shifted to 4.75eV on hydrogen annealing. The band gap of the oxygen stoichiometric
bulk powder samples (4.55eV) determined from diffuse reflection spectrum (DRS) shifted to 4.81eV on reduction in a
hydrogen atmosphere. The electrical conductivity improved when Sn was incorporated into the ZnGa2O4 spinel. The
conductivity of ZnGa2O4:Sn thin films was further improved on reduction.
Jayaraj, M K(Electrochemical Society, February 18, 2008)
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Abstract:
The optical and carrier transport properties of amorphous transparent zinc indium tin oxide (ZITO)(a-ZITO) thin films and the
characteristics of the thin-film transistors TFTs were examined as a function of chemical composition. The as-deposited films
were very conductive and showed clear free carrier absorption FCA . The analysis of the FCA gave the effective mass value of
0.53 me and a momentum relaxation time of 3.9 fs for an a-ZITO film with Zn:In:Sn = 0.35:0.35:0.3. TFTs with the as-deposited
channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at 300°C decreased
the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages VT when Zn
contents were 25 atom % or larger. VT shifted to larger negative values, and subthreshold voltage swing increased with decreasing
the Zn content, while large on–off current ratios 107–108 were kept for all the Zn contents. The field effect mobilities ranged
from 12.4 to 3.4 cm2 V−1 s−1 for the TFTs with Zn contents varying from 5 to 48 atom %. The role of Zn content is also
discussed in relation to the carrier transport properties and amorphous structures.
Jayaraj, M K(American Vacuum Society, January 8, 2008)
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Abstract:
Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films
deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical
compositions of Zn:Sn=1:1 and 2:1 as a function of oxygen partial pressure PO2 used for the film
deposition and annealing temperature. Different from a previous report on sputter-deposited films
Chiang et al., Appl. Phys. Lett. 86, 013503 2005 , the PLD-deposited films crystallized at a lower
temperature 450 °C to give crystalline ZnO and SnO2 phases. The optical band gaps Tauc gaps
were 2.80−2.85 eV and almost independent of oxygen PO2
, which are smaller than those of the
corresponding crystals 3.35−3.89 eV . Films deposited at low PO2
showed significant subgap
absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases
when carrier concentration exceeded threshold values and the threshold value depended on the film
chemical composition. The films deposited at low PO2
2 Pa had low carrier concentrations. It is
thought that the low PO2
produced high-density oxygen deficiencies and generated electrons, but
these electrons were trapped in localized states, which would be observed as the subgap absorptions.
Similar effects were observed for 600 °C crystallized films and their resistivities were increased by
formation of subgap states due to the reducing high-temperature condition. High carrier
concentrations and large mobilities were obtained in an intermediate PO2
region for the as-deposited films.
Optical emission spectroscopic studies were carried out on the plasma produced by ablation of zinc
oxide target using the third harmonic 355 nm of Q-switched Nd:YAG laser, in vacuum and at three
different ambient gas oxygen pressures. The spatial variations of electron density Ne and electron
temperature Te were studied up to a distance of 20 mm from the target surface. The kinematics of
the emitted particles and the expansion of the plume edge are discussed. The optimum conditions
favorable for the formation of high quality zinc oxide thin films are thereby suggested.
Jayaraj, M K(Electrochemical Society, July 18, 2007)
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Abstract:
ZnGa2O4:Dy3+ phosphor thin films were deposited on quartz substrates by radio frequency rf magnetron sputtering and the effect
of substrate temperature on its structural and luminescent properties was investigated. Polycrystalline film could be deposited even
at room temperature. The crystalline behavior, Zn/Ga ratio, and surface morphology of the films were found to be highly sensitive
to substrate temperature. Under UV illumination, the as-deposited films at and above 300°C gave white luminescence even
without any postdeposition treatments. The photoluminescent PL emission can be attributed to the combined effect of multicolor
emissions from the single luminescence center Dy3+ via host-sensitization. Maximum PL emission intensity was observed for the
film deposited at 600°C, and the CIE chromaticity coordinates of the emission were determined to be x,y = 0.34, 0.31 .
Zinc oxide (ZnO) thin films were deposited on quartz, silicon, and polymer substrates by pulsed laser deposition (PLD)
technique at different oxygen partial pressures (0.007 mbar to 0.003 mbar). Polycrystalline ZnO films were obtained at
room temperature when the oxygen pressure was between 0.003 mbar and .007 mbar, above and below this pressure the
films were amorphous as indicated by the X-ray diffraction (XRD). ZnO films were deposited on Al2O3 (0001) at
different substrate temperatures varying from 400oC to 600oC and full width half maximum (FWHM) of XRD peak is
observed to decrease as substrate temperature increases. The optical band gaps of these films were nearly 3.3 eV. A
cylindrical Langmuir probe is used for the investigation of plasma plume arising from the ZnO target. The spatial and
temporal variations in electron density and electron temperature are studied. Optical emission spectroscopy is used to
identify the different ionic species in the plume. Strong emission lines of neutral Zn, Zn+ and neutral oxygen are
observed. No electronically excited O+ cations are identified, which is in agreement with previous studies of ZnO plasma
plume.
Jayaraj, M K(American Institute of Physics, January 4, 2006)
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Abstract:
The radio frequency plasma generated during the sputtering of Indium Tin Oxide target using Argon
was analyzed by Langmuir probe and optical-emission spectroscopy. The basic plasma parameters
such as electron temperature and ion density were evaluated. These studies were carried out by
varying the RF power from 20 to 50 W. A linear increase in ion density and an exponential decrease
in electron temperature with rf power were observed. The measured plasma parameters were then
correlated with the properties of ITO thin films deposited under similar plasma conditions.