CdO Films Research Articles

Effect of Substrate Temperature on Structural and Optical Properties of CdO Thin Films

Thin films of CdO have been prepared by spray pyrolysis technique. XRD analysis reveals that all the prepared samples were polycrystalline and have preferred orientation along [111] orientation. The surface topography was determined by AFM which indicate that surface roughness and rms roughness were increased by the increasing of substrate temperature. The optical energy gap were determined and its value lies between (2.4-2.5) eV.

Bandgap variation of nanostructure tin doped CdO films via SILAR processing

Five series of pure and tin-doped CdO films have been grown on amorphous glass substrates by the successive ionic layer adsorption and reaction (SILAR) method. The film׳s structural, morphological and optical properties have been investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and UV–vis spectrophotometer. XRD results showed that all of the films are polycrystalline cubic CdO. Doping of tin enhances the film׳s (111) preferred orientation and causes slight shift in the (111) Bragg angle towards higher value. From the FESEM images, it was seen that tin-doping concentration affects the shapes of the nanostructures. It was found that the tin-doping concentration modify the microstructures. With UV–vis analysis at the room temperature it was seen that the optical band gap and transmission properties of the films change with increasing tin concentration in the growth bath.

A Study of the Optical Conductivity, Extinction Coefficient and Dielectric Function of CdO by Sucessive Ionic Layer Adsorption and Reaction (SILAR) Techniques

Aims: The research is to study the Optical Conductivity, Extinction Coefficient and Dielectric function using deposited CdO films Place and Duration of Study: The research place is at the Material Science and Nanotechnology Unit, Department of Physics and Astronomy, University of Nigeria Nsukka, between of August 2012 to June 2013. Methodology: The approach used in the deposition of CdO is the Solution Method, known as the Successive Ionic Layer Adsorption and Reaction techniques (SILAR) Technique and the UV-VIS-NIR spectroscopy was used for film characterization. Results: The deposited CdO thin film has a low and high transmittance in the UV and visible region respectively. The band gap of the deposited CdO decreases with an increase in No. of cycles films and ranges from 1.45eV – 2.35eV, this was attributed to the increase in the thickness of films. Also studied is the variation of the film optical conductivity with the band gap, which was observed to decrease with an increase in band gap. Lastly, the Original Research Article American Chemical Science Journal, 4(6): 736-744, 2014 737 relationship between the film band gap and the dielectric function of the materials was consider, the dielectric constant varies exponentially with the band gap and also increases with the number of cycles (film thickness).

Optical properties of CdO films prepared by DC planar magnetron sputtering

CdOfilms have been produced on glass substrates by DC planar magnetron sputtering technique in Ar and O2 gases 1:4 and distance 6cm between cathode and anode and thickness 174 nm. It is observed from optical properties that the films possess transmittance 80% in visible and near infrared region of spectrum and direct band gap values in the rang 2.31-2.4 e V

Temperature Dependent Structural and Optical Properties of Nanostructured Cr Doped CdO Thin Films Prepared by DC Reactive Magnetron Sputtering

Nanostructured Cr doped CdO thin films were deposited by DC reactive magnetron sputtering technique on glass substrates at different substrate temperatures. The structural, electrical and optical properties of Cr doped CdO films were investigated. From XRD data, all the films are highly oriented in the (2 0 0) direction. Surface morphology of the samples has been studied using FESEM and the elemental composition of the films is determined from EDS spectra. The minimum resistivity of 1.92 × 10-4Ω.cm is obtained for the thin film deposited at substrate temperature of 350°C. The optical transmittance of Cr doped CdO thin films increases with the increase of substrate temperature from room temperature to 350°C. The optical absorption edge of the films is shifted towards lower wavelengths with increase in the substrate temperature. The optical direct band gap values of Cr doped CdO films increased with the increase of substrate temperature. The increase in optical band gap may be due to improvement in crystallinity of the films and Burstein-Moss shift.

Liquefied petroleum gas sensing properties of sprayed nanocrystalline Ga-doped CdO thin films

Undoped and Ga-doped cadmium oxide thin films were prepared by chemical spray pyrolysis technique using (CH3COO)2Cd·2H2O as a precursor solution without or with (Ga (NO3)3−x·H2O) as a doping solution, respectively. The dopant concentration (at% Ga to Cd) was varied from 0 to 2.5at%. X-ray diffraction (XRD) analyses reveals all the films are of polycrystalline cadmium oxide, possessing cubic structure. The film shows the (200) preferential orientation for undoped CdO and Ga-doped CdO films. The crystallite size for the 1.5at% Ga-doped film is found to be minimum (15nm) among all the films. At a higher doping concentration of 2.5at%, the disorder produced in the lattice causes an increase in the resistivity of the film. It is found that compared to the undoped CdO film, Ga-doped films show high response to LPG. Among all the doped films studied, the 1.5at% Ga-doped CdO film shows the maximum response (63%) to 1040ppm of LPG in air at 673K. Further, the response and recovery times of the films to LPG become shorter at higher operating temperatures. A possible mechanism of LPG sensing has been explained. The photoluminiscence (PL) studies reveal UV emission in pure CdO which shifts to green emission on doping of Ga.

Effect of coumarin concentration on the physical properties of CdO nanostructures

In this work, nanostructured CdO films with different coumarin contents in the growth solution were fabricated on glass substrates by the SILAR method. The effects of coumarin content in the bath on optical, structural and morphological properties were studied by means of (UV–vis) spectrophotometer, SEM and XRD analysis. The analysis showed that the band gaps, surface morphologies and XRD peak intensities of the CdO films were found to change with coumarin content. A change in the band gap energy can be attributed to the improvement in crystallinity of the samples. XRD analysis showed that, the films have poly-crystalline structures with decent crystallinity levels.

Improving carriers mobility in copper and iron-codoped CdO

Thin films of Fe and Cu-codoped CdO (CdO:Cu:Fe) with different Fe content and fixed Cu content were deposited in a high vacuum on glass and Si wafer substrates. These films were studied by X-ray fluorescence (XRF), X-ray diffraction (XED), optical spectroscopy, and dc-electrical measurements. The structural results show enhancement of film [111] orientation with Fe doping especially with 1.3%Fe film. Also, light doping with Fe improves the dc-conduction parameters of the CdO:Cu:Fe films so that the utmost enhancement of mobility (90.5cm2/Vs) and conductivity (1470.6S/cm) was found with 1.3wt% Fe doping level. It was found that the variation in the bandgap is related to the variation in electron concentration that caused by Fe doping. For low Fe ion concentration (<1.3wt% ), the bandgap varies according to the Moss–Burstein model.

Structural and optical properties of Ba-doped CdO films prepared by SILAR method

Nanostructure materials have opened a new discussion in the field of semiconductor device technology because material properties could be changed by changing the crystal morphology and size. In this article, Ba doped CdO films were prepared by SILAR method. The crystal morphology, structure and optical properties of the films were characterized by scanning electron microscopy, X-ray diffraction and ultraviolet–visible spectroscopy, respectively. From the SEM analysis it is seen that Ba-doping concentration affects the shapes of the nanostructures. XRD analysis showed that the films have poly-crystalline structures. The room temperature UV–vis analysis showed that the optical band gap of the CdO films was firstly decreased then increased with the increasing barium doping concentration.

The structural, electrical, and optical properties of hydrogenated chromium-doped CdO films

Cadmium oxide thin films doped with different amounts of chromium and annealed in hydrogen atmosphere have been grown on glass substrates by means of physical vapour deposition (PVD) method. The structural, electrical, and optical properties of the prepared Cr-doped CdO (CdO:Cr–H) films were systematically studied. The structural investigations show that the incorporated Cr ions mainly occupied locations in interstitial positions of CdO lattice. The bandgap engineer by Cr incorporation and hydrogenation were studied. The variations of the electrical parameters of CdO:Cr–H films with Cr incorporation and hydrogenation were investigated. It was established that among the investigated samples, the largest mobility and conductivity were measured with 1.5%:Cr–H film. Therefore, hydrogenated CdO:Cr films can be effectively used in different applications of near infrared-transparent-conducting-oxide (NIR-TCO).

Optical properties of Al-CdO nano-clusters thin films

The aluminum doped cadmium oxide (CdO:Al) thin films were grown onto glass substrates by sol–gel spin-coating method. The structural properties of undoped and Al-doped CdO thin films were studied by atomic force microscopy. AFM results reveal that the studied CdO films were formed from the nano-clusters. The optical transmittance of undoped and Al-doped CdO is decreased with increasing Al contents. The optical band gaps of the CdO films were varied from 2.54eV to 2.32eV with increasing Al dopants. The width of localized states in the optical band gap of the films is increased with increasing Al content. The improvement of the optical constant of Al-doped CdO has potential applications as transparent conducting oxide for different optoelectronic device applications.

Effect of Gamma Irradiation on the Optical Properties of Mg Doped CdO Thin Films Deposited by Spray Pyrolysis

Thin films of CdO and 9% Mg doped CdO doped have been prepared using spray pyrolysis technique. Transmission and absorption spectra were recorded in order to estimate these films. The deposited thin films were exposed to γ - rays. We have studied the transmission, absorptions and absorption coefficient as a function of photon energy before and after irradiation. The optical constants such as: reflectance, extinction coefficient, refractive index, real and imaginary parts of the dielectric constant and the electrical conductivity were calculated also.

Effect of Gamma Irradiation on the Optical Properties of Mg Doped CdO Thin Films Deposited by Spray Pyrolysis

Thin films of CdO and 9% Mg doped CdO doped have been prepared using spray pyrolysis technique. Transmission and absorption spectra were recorded in order to estimate these films. The deposited thin films were exposed to γ - rays. We have studied the transmission, absorptions and absorption coefficient as a function of photon energy before and after irradiation. The optical constants such as: reflectance, extinction coefficient, refractive index, real and imaginary parts of the dielectric constant and the electrical conductivity were calculated also.

Effects of La Dopant on Nanocluster Size and Optical Band Gap of CdO Films Prepared by Sol-Gel Method

The undoped and lanthanum doped cadmium oxide thin lms were prepared by sol gel method. The CdO lms were doped with various percentages of La, 0.1, 0.5, 1, and 2 at.%. We have investigated the structural properties of the CdO lms by atomic force microscopy. The obtained results show that both the grain size and the surface roughness of CdO lms reduce with increase of La doping content. Additionally, the result shows a signi cant decrease of the transmittance in the range of 300 to 500 nm with increase of La doping level. The optical band gap of CdO lms increases with La doped CdO lms. It was found that the band gaps to be 2.25, 2.36, 2.4, 2.28, and 2.31 eV for La contents with 0.1, 0.5, 1, and 2 at.% doped CdO, respectively.

Morphological, electrical and optical properties of highly oriented undoped and doped zinc oxide and cadmium oxide films grown by atmospheric-pressure chemical vapor deposition

Morphological, electrical and optical properties of undoped and Ga-doped ZnO and undoped CdO films grown on sapphire (Al2O3) substrates by the atmospheric-pressure CVD method using Zn, Cd, H2O and GaCl3 as source materials were investigated. The influences of the deviation from the stoichiometric composition were clearly observed on photoluminescence (PL), photoluminescence excitation (PLE) and photoacoustic (PA) spectra of the undoped ZnO films. The carrier concentration n in the undoped ZnO film was found to be dominated by the hydrogen related donors rather than native defects. The Ga doping in ZnO film led to the degradation of surface flatness, the increase in carrier concentration n and the decrease in Hall mobility μ. With increasing carrier concentration n, the Ga-related neutral donor bound exciton line of the Ga-doped ZnO film shifted towards shorter wavelengths, accompanied by asymmetric broadening. This is probably due to the screening of the Coulomb potential by heavily introduced donors and free-electrons. Highly oriented CdO films with smooth surfaces were successfully grown on r-Al2O3 substrates. Transmittance values for the CdO/r-Al2O3 films were higher than 70% in the range of 700–2500nm. Under the assumption that the reflectance is neglected, the direct and indirect optical gap energies of the CdO films determined from the transmittance spectra were 2.34–2.38eV and 1.98–2.06eV, respectively. PA measurements for the CdO films revealed that the tail states associated with the residual impurities and/or the structural defects reduce the direct optical gap energy. A maximum Hall mobility μ of 178cm2/Vs was achieved on the CdO/r-Al2O3 film with the carrier concentration n of 4.2×1019cm−3.

Influence of substrate temperature on the structural and properties of In-doped CdO films prepared by PLD

Transparent indium-doped cadmium oxide (In—CdO) thin films were deposited on quartz glass substrates by pulsed laser deposition (PLD) from an ablating Cd—In metallic target. The effect of substrate temperature on the structural, optical and electrical properties of In-doped CdO thin films were studied in detail. The optical transmittance of In doped CdO films are obviously influenced by the substrate temperature. All films exhibit a transmittance higher than 75% in the visible region. More significantly, In-doping leads to an evident widening of optical band gap from 2.56 to 2.91 eV; and the increase in optical band gap is found to depend on the deposition temperature. It is also seen that the electrical properties of these films strongly depend on the substrate temperature. The In—CdO thin film grown at 300 °C has low resistivity (1.15 × 10−4 Ω·cm), high carrier concentration (5.35 × 1020 cm−3), and high mobility (101.43 cm2/(V·s)).

Influence of annealing temperature on properties of nanocrystalline CdO thin films synthesized via thermal oxidation process

Chemical bath deposited CdS thin films have been annealed in air at different temperatures to obtain CdO films via thermal oxidation route. The obtained nanostructured and highly transparent thin films of CdO have wide range of applications in solar cells, smart windows, optoelectronic devices, gas sensors; etc.The influences of annealing temperature on structural, morphological, optical and solid state properties of prepared CdO films have been investigated. The techniques used for the investigation includes x-ray diffractometry, scanning electron microscopy, UV-VIS spectroscopy. The optical energy band gap and other optical constants were evaluated

Dopant-induced band filling and bandgap renormalization in CdO : In films

The effect of carrier concentration on the Fermi level and bandgap renormalization in over 30 indium-doped cadmium oxide (CdO : In) films with carrier concentrations ranging from 1 to 15 × 1020 cm−3 was studied using the two-band k · p model with electron–electron and electron–ion interactions. It is shown that the Tauc relation, which is based on parabolic valence and conduction bands, overestimates the optical bandgap in the CdO films. Theoretical calculations of the optical bandgap give good agreement with experiments by taking into account the Burstein–Moss effect for a nonparabolic conduction band and bandgap renormalization effects. The band filling and bandgap renormalization in these CdO : In films are about 0.5–1.2 eV and 0.1–0.3 eV, respectively.

Germanium Doping to Improve Carrier Mobility in CdO Films

This investigation addresses the structural, optical, and electrical properties of germanium incorporated cadmium oxide (CdO : Ge) thin films. The focus was on the improvement in carrier mobility to achieve high transparency for near-infrared light and low resistivity at the same time. The properties were studied using X-ray diffraction, SEM, spectral photometry, and Hall measurements. All CdO : Ge films were polycrystalline with high texture orientation along [111] direction. It was observed that it is possible to control the carrier concentration () and mobility () with Ge-incorporation level. The mobility could be improved to a highest value of cm2/V·s with Ge doping of 0.25 wt% while maintaining the electrical resistivity as low as Ω·cm and good transparency % in the NIR spectral region. The results of the present work proved to select Ge as dopant to achieve high carrier mobility with low resistivity for application in transparent conducting oxide (TCO) field. Generally, the properties found make CdO : Ge films particularly interesting for the application in optoelectronic devices like thin-film solar cells.

FABRICATION AND STUDY CHARACTERISTICS OF CDO/SI HETEROJUNCTIONDETECTOR BY CBD TECHNIQUE

In this work CdO/Si heterojunction detector were fabricated by depositing CdO thin film on p-type single crystal silicon wafers by chemical bath deposition technique(CBD) . The effect of cadmium ion concentration on the structural properties of deposited film and optoelectronic characteristics of fabricated detector has been considered in this work . From the x-ray diffraction result, it is shown that the CdO film has a single crystalline in cubic structure with preferential orientation along the (311) crystal plane. The -voltage characteristics under dark result, it is shown that ideality factor of heterojunction has higher value(n˃1).From current-voltage characteristics under illuminations result, it is shown that photocurrent increase with increasing cadmium ion concentration in solution. The capacitance–voltage characteristic shows a typical abrupt heterojunction. The optoelectronic characteristics shows the CdO/Si detector has good spectral responsivity in visible and NIR with higher peak responsivity at 900 nm were found 0.38 A/W.