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The Properties of photoconductive ultraviolet detector fabricated on CdO nanofilms were presented. The Cadmium Oxide (CdO) semiconducting transparent nanostructure film is deposited on glass and porous silicon substrates by spray pyrolysis. The structural and optical properties of the grown films are presented. The crystalline structure was studied by X-ray diffraction. The direct band gap of CdO nanofilm was found to be 3.4eV, comparing with that of the bulk CdO. The deposited CdO film was coated by nanosheet of polyamind polymer to improve the photoresponsivity of the detector.
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Asama N. Naje, Lamia K. abbas, Ghaida Salman and Estabraq T. Abdullah
Physics department, college of science, University of Baghdad
E-mail: ,
Abstract: The Properties of photoconductive ultraviolet detector fabricated on CdO
nanofilms were presented. The Cadmium Oxide (CdO) semiconducting transparent
nanostructure film is deposited on glass and porous silicon substrates by spray pyrolysis. The
structural and optical properties of the grown films are presented. The crystalline structure
was studied by X-ray diffraction. The direct band gap of CdO nanofilm was found to be
3.4eV, comparing with that of the bulk CdO. The deposited CdO film was coated by
nanosheet of polyamind polymer to improve the photoresponsivity of the detector.
Keywords: CdO nanostructure, Spray pyrolysis, XRD, Optical properties.
1. Introduction
Cadmium oxide (CdO) attracts a great attention due to its electrical and optical
properties. CdO is an n-type semiconductor with a ranging direct band gap at approximately
2.2-2.7 eV [1-5]. CdO has many attractive properties such large energy bandgap, high
transmission coefficient in visible spectral domain, remarkable luminescence characteristics
Thin films of CdO have been prepared by employing various physical and chemical
deposition techniques, such as evaporation, spray pyrolysis, solution growth, Langmuir-
Boldgett deposition, sputtering, etc [6-10].
This materials have been widely studied for optoelectronic applications in transparent
conducting oxides (TCO) [11], solar cells[12], photovoltaic device [13], photodiodes [14] as
well as other types of applications like IR heat mirror, gas sensors [15], low-emissive
windows, thin-film resistors, etc [16-17].
In the present study, synthesis and characterization of CdO nanostructure ultraviolet detector
has been studied by depositing the CdO nanofilm on nanospikes silicon layer.
International Journal of Science, Environment ISSN 2278-3687 (O)
and Technology, Vol. 3, No 2, 2014, 684 – 691
Received Mar 4, 2014 * Published April 2, 2014 *
Asama N. Naje, Lamia K. abbas, Ghaida Salman and Estabraq T. Abdullah
2. Experimental Works
N-type Si wafer of 0.05 .cm resistivity was used as a starting material in the
photochemical etching. The samples of 2 x 2 cm
dimensions were cut from the wafer and
rinsed with acetone and methanol to remove dirt. In order to remove the native oxide layer on
the samples, they were etched in diluted (10 %) HF acid. After cleaning the samples they
were immersed in HF acid of 50 % concentration in a Teflon beaker. The samples were
mounted in the beaker on two Teflon tablets in such a way that the current required for the
etching process could complete the circuit between the irradiated surface and the bottom
surface of the Si sample.
Tungsten halogen lamp of 250 Watts integrated with diacnamic ellipsoidal mirror was used
as the photon beam source. The photoetching irradiation time was chosen to be 10 minutes.
At the end of the photochemical etching process, the samples were rinsed with ethanol and
stored in a glass containers filled with methanol to avoid the formation of oxide layer above
the nanospikes film.
The CdO nanofilms were prepared by chemical spray pyrolysis technique. The films were
deposited on porous silicon layer heated to (250ºC). A 0.1M Spray solution is prepared by
dissolving cadmium acetate (Cd(CH
O )
of molecular weight equal to
266.527gm / mole in
a mixture of methanol and deionized water (1:1).
The above mixture
solution was placed in the flask of the atomizer and spread by controllable pressurized
nitrogen gas flow on the heated substrates. The spraying time was 4 seconds, which is
controlled by adjustable solenoid valve. The heated substrate was left for 12 sec after each
spraying run to give time for the deposited (CdO) layer to be dry. The optimum
experimental conditions for obtaining homogeneous CdO thin film at (250 ºC) were
determined by the spraying time, the drying time and the flashing gas pressure.
The thickness of the prepared films was measured by laser interferometer technique. The
thickness of the films
was found to be in the range between (800-1000m). The micro
sk of (0.4mm) electrode spacing was used to deposit the Aluminum (Al) electrical
electrodes on the film surface.
The variation of photoresponsivity of CdO Photoconductive UV detector with the bias
voltage was carried out under the illumination with UV diode of 2.5 mWatt power and of 385
nm wavelength.
Current-Voltage Characteristics of CdO Nanostructure Ultraviolet...
3. Result and Discussion
3.1 Structural Characteristics
The X-ray diffraction (XRD) pattern of the CdO nanofilm deposited on nanospike layer
of n–type silicon substrate is illustrated in Figure 1.
The figure shows the (111), (200), and (220) peaks occurred at 2
values of 33
, 38
respectively, with full width at half maximum (FWHM) of (200) peak of about
0.658°. The CdO nanofilm are strongly crystallized with a preferred (200) orientation,
which has been observed by other authors [5,7,18]. Particle size was determined from
the width of XRD peaks using Scherer's formula [19]:
D is the grain size, K is the shape factor, being equal to 0.9, is the wavelength of X-
ray, is the full-width at half maximum FWHM (degree), and is the diffraction angle in
. Figure 1 shows the grain size of CdO sample (24.4nm) obtained from the
FWHM of peak corresponding to 2=38.60
3.2 Optical properties
The absorption spectrum of the CdO nanofilms deposited on glass substrate is shown in
Fig 2.
The figure shows high absorption coefficient in the UV region, whereas it is transparent in
the visible region. Assuming direct transition, the dependence of (h)
on the photon energy
h is plotted following Taue relation [20] and the graph is illustrated in Fig.3.
 
                 
2 theta
Figure 1. XRD of CdO nanofilm.
Asama N. Naje, Lamia K. abbas, Ghaida Salman and Estabraq T. Abdullah
The extrapolation of the linear part of the above plot to ( h )
= 0 give the energy gap value
of the CdO nanofilm, which was found to be about 2.5eV, and 3.46 eV. The above two
values may be related to the nanostructured CdO film and to bulk CdO material.
This value
is in a good agreement with the values presented by other workers [3-21].
The photoluminescence spectrum of CdO nanofilm on glass substrate is plotted using SL 174
spectrofluorometer supplied by ELICO Company covering the 300–900 nm wavelength
range. The room temperature photoluminescence spectrum of CdO film deposited on glass
substrate excited by 300nm line is shown in figure 4.
Figure 2. The absorpance spectrum of CdO
on glass
       
versus E
plot of CdO nanofilm
200 300 400 500 600 700
Current-Voltage Characteristics of CdO Nanostructure Ultraviolet...
The spectrum shows two peaks: the first peak at 386 nm which can be referred to the strong
direct band transition (or band to band transition). The second peak at 520nm is due to the
exciton emission.
The energy band gap from photoluminescence spectrum of the CdO film is calculated by
using the following equation
( )
For the PL wavelength 386nm and 520nm the energy band gap found are to be
(3.2 and 2.38eV).
Similar peaks in spectrum of CdO have been reported by [22].
3.3 Electrical Properties
The variation of the photoconductive response of the fabricated photoconductive detector as
a function of the bias voltage at dark and under illumination with UV source of 2.50 mw
radiation power for etching time (10min) are illustrated in Fig .
Figure 4: The Photoluminescence spectrum of CdO film on glass
      
Asama N. Naje, Lamia K. abbas, Ghaida Salman and Estabraq T. Abdullah
I (mA)
Bias Voltage (volt)
   
        
Figure.5. I-V characteristics of CdO nanofilm with and
without polymer
It can be noticed from the figure that the dark current was about 68mA at 5 v bias whereas
the photoconductive current was 161mA. This result reflects a good UV radiation sensitivity
with photoconductive gain
of 2.36.
The functionalization of the CdO film surface by polyamide nylon improved the
photoconductive gain as shown in Fig.5.
The CdO UV detectors prepared by chemical spray pyrolysis technique were fabricated on
photochemical etched silicon substrates. The direct band gap of CdO nanofilm was found to
2.5eV, and 3.46 eV. The above two values may be related to the nanostructured CdO film
and to bulk CdO. The variation of the photoconductive response of the fabricated detector
was 161mA
photoconductive gain
was 2.36.
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... A rare combination of high conductivity and transparency makes it promising to use CdO in heterostructured CdO/CdTe and CdO/Cu 2 O solar cells, phototransistors and diodes, etc. [6,7]. For this reason, in recent years there were many studies on the synthesis CdO using a variety of methods of chemical deposition, including sonochemical and hydrothermal ones and physical-chemical methods (reactive magnetron sputtering, electrochemical deposition, MO CVD, pyrolysis of gas jet, sol-gel, etc.) [6,[8][9][10][11][12][13][14][15][16][17][18][19]. The main drawback of the above methods is that they either require a large number of reagents that by the nature of things contaminate the final product, or they are practically and technically sophisticated. ...
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A new plasma-solution method of the CdO ultradisperse powders synthesis was described. The atmospheric pressure direct current discharge was excited in the ambient air by applying a high direct voltage to two pointed titanium electrodes placed above liquid anode and liquid cathode in the H-shaped cell. The discharge current was 40 mA and the total input power was about 40 W. The action of the DC glow discharge on the cadmium nitrate water solution in the absence of additional reagents and without electrodes-solution contact was shown to result in the production of the solids in the liquid phase. The kinetics of particles formation was studied using turbidimetry and nephelometry methods. Powders’ chemical composition and morphology was obtained using X-ray diffraction spectroscopy (XRD), electron-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), differential-scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was found that as-synthesized powders are not the pure cadmium hydroxide but the mixture of the cadmium nitrate, hydroxy nitrate and hydroxide. Some assumptions regarding the mechanisms and pathway of the chemical processes both under the plasma action on the solution and during the calcination of as-synthesized powders were discussed.
... The highest energy band gap values in the black dotted lines can be attributed to nanostructured CdO thin films, whereas the lowest values in the black solid lines represent bulk CdO materials. These observations are in good agreement with the reported results by Naje et al. [41]. SEM Analysis. ...
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Recently, researchers have developed a great interest in the synthesis of metal oxide nanoparticles due to their potential applications in various fields of science and industry, especially in catalysis, due to their high activity. Bis (2-hydroxy-1-naphthaldehydato)cadmium(II) complexes were prepared and used as precursors for the synthesis of cadmium oxide nanoparticles via thermal decomposition method using HDA as a stabilizing agent. The prepared complexes were also used as single source precursors to prepare CdO thin films onto the glass substrates by spin coating and were annealed at 250, 300, and 350°C, respectively. The precursors were characterized by Fourier transform infrared (FTIR) spectroscopy, elemental analysis, nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). The synthesized CdO nanoparticles and CdO thin films were characterized by ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM).
... admium oxide (CdO) has attracted a great attention due to its high electrical conductivity and high transmittance with a suitable refractive index in the visible domain of the solar spectrum [1] . This material could be used for different applications such as solar cells [2] , temperature controlled in satellites [3] , gas sensors [4] , photo transistors [5] because of its low electrical resistivity [2] , large energy band gap approximately of (2.2 eV) and great luminescence characteristics [5] . Many methods were adopted to grow CdO thin films like vacuum evaporation thermal technique [6] , sol-gel spin coating [7,8] , spray pyrolysis [9] . ...
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CdO thin films have been deposited by Spray Pyrolysis Technique (SPT) on a glass substrate. The structural and optical properties of thin films were studied at different annealing temperatures 100, 200 and 300 Co. By using X-Ray Diffraction, XRD patterns indicated that films are polycrystalline in nature and cubic phase with preferred orientation along the plane (111). The optical properties using UV-VIS spectroscopy show that the direct band gaps decreased from (3 to 2.75) eV with increasing the annealing temperature from(100-300)Co, this decreasing could be ascribed to increase of the localized states available in band gap which referred by Urbach, energy value.
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Cadmium oxide (CdO) nanoparticles have been prepared by precipitation method using cadmium acetate and ammonia solution. The electrical resistivity (ρ) has been measured at low temperature using four-probe method which is found to be 0.351 ω-cm at 7 K and 0.264 ω-cm at 300 K, respectively. The decrease of resistivity with increasing temperature indicates the semiconducting behaviour. The activation energy values are found to be 0.06 meV in temperature range 7-15 K and 0.6 meV in 39-152 K from temperature dependent resistivity. Photoluminescence (PL) spectrum shows band edge emission at 395 nm and green emission at 550 nm. Green emission arises from the oxygen vacancy of CdO materials because of recombination of a photo generated hole in valence band with an electron in conduction band.
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Cadmium oxide and cadmium sulphide particles in the nanometer size regime have been synthesized using chemical routes. CdO nanoparticles are prepared by using ethylene glycol as a capping agent and CdS nanoparticles were prepared with H2S gas. Variety of techniques like X-ray diffraction (XRD), UV-Vis absorption spectroscopy and Scanning Electron Microscopy (SEM) are used to carry out structural characterization of the nanoparticles. The optical band gap of these materials has been determined in order to establish a relationship between energy band gap of bulk and nanomaterials.
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Undoped and Al–doped CdO films have been prepared by sol–gel spin–coating method. Effects of Al dopant on the structural and optical properties of CdO film have been investigated. The films were prepared for Al/Cd ratios of 1% and 3%. The crystal structure and orientation of the films have been investigated by X–ray diffraction method. CdO and CdO:Al films have polycrystalline structure with (111) preferential orientation. Al dopant increases the optical transparency of the films in the visible region. The optical absorption study reveals that the direct optical transitions occur in the optical band gap and the films have a direct optical band gap. The optical band gaps of undoped, 1% Al–doped and 3% Al–doped CdO films were found to be 2.476, 2.591 and 2.682 eV, respectively. The optical constants, refractive index, extinction coefficient and optical dielectric constants of these films were determined using transmittance and reflectance spectra. Al doping concentration affects strongly the optical constants of the thin films. The optical constants and optical absorption edge of the CdO thin film can be controlled by Al dopant.
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CdO nanowires were produced by calcination process using Cd(OH)2nanowires as precursors. The Cd(OH)2 nanowires were synthesized via arc discharge method submerged in de-ionized water. Transmission electron microscopy (TEM) analysis of the as-synthesized Cd(OH)2 nanowires revealed that nanowire morphology was abundant form with the diameters range from 5 to 40 nm. In addition to the nanowire morphology, Cd(OH)2 nanospheres and hexagonal shaped nanoparticles were also displayed. The Cd(OH)2 nanostructures were used as precursors to produce CdO nanowires and calcinated in air at 400 °C for four hours. After calcination, the structural, morphological and optical properties of the as-synthesized CdO nanowires were characterized by means of TEM, selected area electron diffraction (SAED), X-ray diffraction (XRD) and UV-vis spectroscopy. The XRD and SAED techniques showed that the as-synthesized Cd(OH)2 nanostructures could be transformed into CdO nanostructures after the calcination process. TEM results revealed that the as-synthesized CdO nanowires were 5–30 nm in diameter and shorter than corresponding Cd(OH)2 nanowires. In addition, the diameters of the spherical or irregular CdO nanoparticles ranged from 20 nm to 50 nm. UV-vis spectroscopy analysis was showed that the direct gap of the CdO nanowires were found to be 2.60 eV which is slightly higher than the earlier reported values of the bulk CdO for direct band gaps (2.3 eV) due to quantum size effect.
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The aim of this work is to determine mean diameter of polycrystalline samples using Scherrer equation. These represent direct connection between mean diameter and crystal structure and morphology by including the Bragg angle and shape factor. Two samples are investigated, first a nano-sized particles of MgO and second a CVD (Chemical Vacuum Deposition) obtained polycrystalline aluminum film. First, shape factor and mean diameter are evaluates using direct measurement of particle morphology from BF-TEM (Bright Field - Transmission Electron Microscopy) images. The value of mean diameter is determined by assuming a lognormal distribution. Than, mean diameter values are evaluated using Scherrer equation applied to SAED (Selected Area Electron Diffraction) images. We obtain for MgO nano-sized a mean diameter about 48 nm from direct measurement, and 70 nm respectively using Scherrer equation, and for Al film 77 nm, and 70 nm respectively.
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We report the formation of a thin layer of CdO on chemically deposited CdS thin films during air anneal at 370°C to 500°C for 5 min to 120 min. During a 5 min anneal, the sheet resistance of the CdS thin films drops from about 1013 □/9 to 3.5 k□/□(370°C) and 470 □/□(500°C). X-ray diffraction studies showed that this is associated with the formation of a thin layer of CdO layer, which occurs at temperatures above 370°C. The CdS, which remains under the conductive CdO top layer, is photosensitive - with photo-to-dark current ratio of 103 - 104. Essentially the air annealing converts the highly resistive and highly photosensitive intrinsic (i) CdS thin film into a (i)CdS-(n+)CdO layer. The technique offers prospects to convert the top part of a chemically deposited CdS thin film window layer of high photosensitivity, deposited on an absorber layer, to a conductive layer. This is of interest in thin film solar cell technology.
Cadmium oxide (CdO) thin films were grown on glass substrates by the successive ionic layer adsorption and reaction (SILAR) technique. The effect of solution concentration on the structural, morphological, optical and electrical properties of the as deposited samples was analyzed. The structural studies reveal that the films are polycrystalline with preferred orientation along the (2 0 0) plane. The lattice parameter was found to be equal to 4.690 Ǻ. Grain size increases from 15.96 nm to 21 nm as the solution concentration increases. Optical absorption measurements showed that films coated with 0.05 M showed a maximum transmittance of 84 %. Band gap energy of the coated films decreases with the increase in solution concentration. The sheet resistance increases from 14 x 10 2 Ω/□ to 17.5 x 10 2 Ω/□ as the solution concentration increases from 0.05 M to 0.2 M. Films coated with 0.1 M has low temperature coefficient of resistance (-1.75 x 10 -3 / K).
The heterostructure n-CdO/a-C/p-Si is proposed for use as a solar cell device. The heterostructure consists of two semiconductor layers having different optical band gaps. An ultrathin layer of a-C with a narrow optical band gap is located between these layers. The photovoltaic effect in this device has been investigated. It is shown that the short-circuit current Isc=46mA/cm2 for heterostructure n-CdO/a-C/p-Si corresponds to the values obtained in the best solar cells based on crystalline silicon. It is also shown that the heterostructure n-CdO/p-Si (without a-C) has a short circuit current which is much weaker.
High speed photodiodes with semitransparent film-semiconductor junctions, which behave as Schottky barriers, are designed and prepared. The optimized width of the depletion layer of the photodiode is calculated for the selected cut-off frequency. The relations between transmittance and sheet resistivity are studied with some films of semiconducting compounds, which affect the gain and response time of photodiodes. The photodiodes, fabricated by the deposition of the semitransparent films of CdS or CU2Se on Si, have high frequency response and the cut-off frequency of Cu2Se-n.Si photodiodes is higher than 4 GHz.
CdO thin films were prepared by a conventional pneumatic spray deposition technique on glass substrates from a solution of cadmium acetate diluted with methanol and water. During post thermal treatment CdO exhibits low spreading resistance of 15 Ω per square for 350 nm films. Four point dc - conductivities measured from samples prepared by varyind the post thermal treatment. Optical measurements show that the films are highly transparent, above 90% transmission, for wavelengths ≥ 600 nm. During the last few years thin films of cadmium oxide (CdO) has revealed itself as a very promising material for use in the photovoltaic industry. Because of its high electrical conductivity high optical transparency in the spectral region of sun radiation, a refractive CdTe and a good match with the CdTe lattice, it may be used as a substitute of CdS, In2O3 and SnO2 in photovoltaic hetero structure. In a previous paper we reported the improvement of the electro-optical properties of CdO thin films deposited after laser treatment. Various techniques have been employed to prepare CdO thin films such as sputtering solution growth, activated reactive evaporation pulsed laser sputtering , sol-gel method and direct laser treatment on CdS layers (1,2,3) . In this paper CdO thin films was prepared by spray pyrolysis technique and post thermal treatment. In this article we present characterization properties CdO films such as the structural, optical and electrical properties. The influence of annealing temperature on the films characteristic properties is investigated. 2. EXPERIMENTAL