CdO Films Research Articles

Laterally Modulating Carrier Concentration by Ion Irradiation in CdO Thin Films for Mid‐IR Plasmonics

AbstractThis report demonstrates tunable carrier densities in CdO thin films through local ion irradiation, providing lateral control of mid‐IR optical properties. Ion‐solid interactions produce donor‐like defects that boost electron concentrations from the practical minimum of 2.5 × 1019 cm−3 to a maximum of 2.5 × 1020 cm−3 by metered ion exposure. This range is achieved using He, N, Ar, or Au ions at 1–2.8 MeV; when normalized by displacements per atom, all ion species produce comparable results. Since CdO is well‐described by the Drude model, irradiation‐tuned carrier densities directly alter the infrared dielectric function, and in turn, mid‐infrared optical properties. Further, it is demonstrated that by combining irradiation with traditional lithography, CdO films expose to ions in the presence of 3‐µm thick, patterned photoresist exhibit lateral carrier density profiles with ≈400‐nm resolution. Scanning near‐field optical microscopy reveals sharp optical interfaces with almost no companion contrast in surface morphology, microstructure, or crystallinity. Finally, CdO lateral homostructures supporting surface plasmon polaritons (SPPs) are demonstrated whose dispersion relation can be tuned through periodic patterning in a monolithic platform by simple nanofabrication. Numerical simulations show these polaritons result from strong coupling between excitations at CdO plasma frequencies and SPPs supported by the platinum substrate.

Large Mid‐Infrared Magneto‐Optic Response from Doped Cadmium Oxide at Its Epsilon‐Near‐Zero Frequency

AbstractThe epsilon‐near‐zero (ENZ) frequency regime of transparent conducting oxide materials is known to yield large enhancements in their optical nonlinearity and electro‐optic response. Here, Faraday rotation is investigated in Gd and In‐doped CdO films and it is found that the Verdet constant peaks at values >3 105 deg T−1 m−1 near the ENZ frequency, which is tunable in the wavelength range 2 < λ< 10 µm by varying the doping concentration. These results are among the highest reported to date in the mid‐infrared spectral range and are in good agreement with the Drude model, which confirms that the magneto‐optic response of doped CdO derives from its free carriers. The combination of a tunable Verdet constant, low optical loss compared to other plasmonic materials, and the ability to deposit CdO on Si with no loss in performance make this material a promising platform for integrated magneto‐optic and magnetoplasmonic devices that operate across the mid‐infrared.

Advanced Photovoltaic Applications of CdO Films Prepared by Pulsed Laser Ablation on Porous Silicon

Advanced Photovoltaic Applications of CdO Films Prepared by Pulsed Laser Ablation on Porous Silicon

Studying of cadmium oxide/ Aluminium films for optoelectronics: structural, optical and electrical characteristics

In the results of this research, thin films of CdO-Al were produced using the spray pyrolysis (SP) technique. The primary aim was to explore how varying concentrations of aluminum (Al) influence the physical properties of the films. The X-ray diffraction (XRD) analysis confirmed the presence of a cubic crystal structure in the pure CdO films. Additionally, it revealed that the introduction of increased Al doping led to lattice shrinkage and a reduction in lattice parameters. Elevated levels of aluminum (Al) content were correlated with a decrease in crystallite size and an augmentation in lattice strain, as indicated by both scanning electron microscopy (SEM) and X-ray diffraction (XRD) data. Additionally, an X-ray photoelectron spectroscopy (XPS) examination revealed the presence of Al3+ ions within the films. The optical energy gap of CdO-Al films exhibited a slight increase, reaching up to 3% aluminum doping. The analysis of the refractive index dispersion and non-linear refractive index revealed a decreasing trend up to 3% aluminum content, with subsequent fluctuations at higher concentrations. The measurements of sheet resistance demonstrated a noticeable decrease with an increase in aluminum content, specifically up to 3%.

Analysis and characterization of molybdenum-doped cadmium oxide

Molybdenum-doped cadmium oxide films were prepared by a spray pyrolysis technique at substrate temperature of 300 °C. The effect of doping on structural, electrical and optical properties were studied. X-ray analysis shows that the undoped CdO films are preferentially oriented along the (111) crystallographic direction. Molybdenum doping concentration increases the films’ packing density and reorients the crystallites along the (200) plane. A minimum resistivity of 4.68 10−4 Q cm with a maxi- mum mobility of 75 cm2 V−1 s−1 is achieved when the CdO film is doped with 0.5 wt.% Mo. The band-gap value is found to increase with doping and reaches a maximum of 2.56 eV for 0.75 wt.% as compared to undoped films of 2.2 eV.

Investigations into the structural, morphology and optoelectronics properties of the CdO:Cu films produced by spray pyrolysis

This study used spray pyrolysis to create CdO films that were undoped and doped with Cu at varied concentrations (0, 1, 2, 3, 4 and 5%). The materials' polycrystalline cubic nature is confirmed by XRD examination. Rietveld refinement was used to get the lattice constant. In terms of energy dispersive more about the chemical makeup of materials. The structure, morphological, optical, and electrical properties of the film were investigated using the (XRD), (SEM), UV- spectrophotometer, and Hall arrangement. The band optical gaps, opt E g , of the CdO:Cu films were observed to decrease as the quantity of Cu doping increased. Also, effective Cu doping enhances the electrical characteristics of CdO, as shown by the film's 3 % resistivity. The carrier concentration is approximately 5x1020 of that 2.25x1020 of the undoped film, whereas the amount of Cu doping is approximately ten of that of the CdO film. To increase both optical and electrical properties in a variety of optoelectronic device applications, Cu-CdO films can be used as Transparent Conducting Oxide (TCO) materials.

Structural, Optical, and Electrical Properties of SnO2–CdO–In2O3 Films Prepared by Magnetron Co‐sputtering

SnO2–CdO (SCO) films and SnO2–CdO–In2O3 (SCIO) films are successfully deposited on Si (100) and glass substrates by radio frequency and direct current magnetron co‐sputtering. The films are characterized by X‐ray diffraction, scanning electron microscope, energy‐dispersive X‐ray spectroscopy, ultraviolet visible near‐infrared spectroscopy, and four‐point probes. SCO films exhibit Cd2SnO4 (011) preferred orientation, and the SCO film deposited at the sputtering power of 80W exhibits excellent crystalline quality and transmittance. The arrangement of clusters changes from sparse to dense when the indium element concentration increases. The resistivities of SCIO films are of two orders of magnitude lower than those of the SCO films. However, the visible light transmittances decrease slightly and the optical bandgap values decrease from 5.00 to 4.85 eV. The results indicate that the indium element plays an important role in improving the electrical properties of SCO films. SCIO films are expected to be a good candidate for transparent conductive films.

Long‐term stable and high responsivity visible-ultraviolet photodetector of Se-doped CdO film on Si by spin coating

Se-doped CdO thin films were prepared on p-Si substrates via spin coating. Morphological, structural and absorption measurements of CdO:Se film was performed. Then, a CdS:Se/p-Si heterojunction was produced by coating CdO:Se film on a p-Si substrate using spin coating method. From the I–V measurements, it has been seen that the device has a very good rectification feature in the dark, at room temperature. In order to investigate the performance of the device under light, a detailed analysis was performed by performing I–V measurements under ultraviolet (UV) light (365 and 395 nm, 10 mW cm−2) and different intensities of visible light (between 10 and 125 mW cm−2) as well as ambient light. It was observed that the CdO:Se/p-Si heterojunction performed well under both illumination conditions. The maximum responsivity and specific detectivity values were obtained as 0.72 and 4.47 A W−1 and 3.31 × 109 and 2.05 × 1010 Jones for visible and UV regions, respectively. It was also seen that the device exhibited very high performance and stability even after 160 days.

Characterization of Zn-Doped CdO Nanoparticles Thin Films Synthesized by Pulsed Laser Deposition

In this investigation, thin films of CdO:Zn were synthesized by using the technology of pulsed lasers. Additionally, the effect of different concentrations of Zn doping on the material's physical properties was investigated. According to XRD research, the films have a polycrystalline structure, and it was discovered that the size of the crystallites changes depending on the amount of Zn doping. The morphology of the produced films reveals that there are spherical nanoparticles distributed evenly all over the surface of the films and ranging in size from nanometer to nanometer. The increase in Zn doping concentrations resulted in an improvement of the material's optical characteristics. The results of the Hall effect observations show that each of the films possesses n-type conductivity. This property, combined with the films' low resistivity, enables them to be utilized in a wide variety of contexts. In addition to this, each of the films has a large concentration of carrier molecules.

Fast and broadband photoresponse in CdO thin film

Thermal annealing is recognized as an effective tool to manage the structural and electronic properties of oxide thin films. Combined with the atmospheric environment control, additional issues concerning surface effects act to change the performance of oxides for photodetectors purposes. The present investigation systematically studies morphological and optical properties and electrical transport of CdO thin films using an as-grown reference and annealed samples at 500 °C under O2 and N2 atmospheres. As-grown CdO presents fast and high photoresponses in a wide range of the visible spectrum, with an amplitude that reaches nearly 3000%. Also, a transition from negative to positive photoresistance was observed for temperatures below 230 K. From the analysis of the photoluminescence spectra, we noted two activation energies for as-grown CdO, whereas annealed samples presented only one. Therefore, the additional defect level, reduced after annealing, is responsible for the huge amplitude as well as the negative to positive transition in the photoresistance of as-grown CdO film.

Chemically sprayed CdO: Cr thin films for formaldehyde gas detection and optoelectronic applications

Chromium (Cr) doped CdO films are chemically sprayed and are characterized by their optical, electrical, structural, and microstructural characteristics. The thickness of the films is determined by spectroscopic ellipsometry. The cubic crystal structure with a superior growth along (111) plane of the spray-deposited films is confirmed from the powder X-ray diffraction (XRD) analysis. XRD studies also suggested that some of the Cd2+ ions were substituted by Cr3+ ions, and the solubility of Cr in CdO is minimal, to be around ∼0.75 wt%. The analysis by atomic force microscopy shows uniform distribution of grains throughout the surface, whose roughness is varied from 33 to 13.9 nm concerning Cr-doping concentration. The microstructures from the field emission scanning electron microscope reveal a smooth surface. The elemental composition is examined using an energy dispersive spectroscope. The micro-Raman studies carried out in room temperature endorse the presence of metal oxide (Cd–O) bond vibrations. Transmittance spectra are obtained using UV–vis–NIR spectrophotometer, and the band gap values are estimated from the absorption coefficient. The films show high optical transmittance (>75%) in vis-NIR region. A maximum optical band gap of 2.35 eV is obtained from 1.0 wt% Cr-doping. The electrical measurement (Hall analysis) confirmed the degeneracy nature and n-type semi-conductivity. The carrier density, carrier mobility, and dc-conductivity are increased for higher Cr-dopant percentage. High mobility (85 cm2V−1s−1) is observed for 0.75 wt% Cr-doping. The 0.75 wt% Cr-doping show a remarkable response to formaldehyde gas (74.39%).

Piezoelectric generator based on centrosymmetric CdO film with (111) orientation and its atomic mechanism

Piezoelectric generator based on centrosymmetric CdO film with (111) orientation and its atomic mechanism

Investigating the influence of Eu-doping on the structural and optical characterization of cadmium oxide thin films

In the present investigation, a low-cost and high-operational sol-gel spin coating technique for preparing undoped and various Europium (Er)-doped CdO films of molar percentages of 1%, 5%, 10%, and 15% were considered. Using X-ray diffraction, the polycrystalline nature reveals two preferred orientations of (111) and (200). The mean crystallite size was evaluated and increased from 20.95 to 49.37 nm using the well-known Scherer’s formula by increasing the Eu- dopant content. The atomic force microscopy images indicate a homogeneity of a granular distribution deteriorated with Eu-content. The root means square roughness value was evaluated and increased from 4.1 nm to 284 nm with Eu-doping. High transmission of approximately 80% in the visible region spectrum was recorded. The optical band gaps are increased from 2.2 to 2.46 eV from the undoped and various Eu-content %. A relationship between the Eu- content % for CdO films and the optical parameters was discussed to support the availability of the device for optoelectronic applications.

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 was determined and its value lies between (2.4-2.5) eV.

Synthesis and Characterization of Sol–Gel Screen Printed Zn:CdO (ZCO) Film for Optoelectronic Technologies

In present report on Zn doped (5%) CdO thick film is synthesized on to the glass substrate (pre-cleaned) via sol–gel screen printing process. The synthesized sintered Zn:CdO film are then characterized via XRD, SEM, EDX, UV–vis spectroscopy, PL spectroscopy, and dark conductivity measurement examinations. The XRD examination of sintered film informs the polycrystalline nature and authenticates that Zn:CdO film holds the cubic crystalline structure. SEM examination dispenses the information on morphology of Zn:CdO film. The EDX examination supports the existence of Cd, O, and Zn in the sintered film. The UV–vis spectroscopy via reflectance mode substantiates the direct transition of band gap with a value of 2.60 eV. PL spectra of the sintered film manifest a strong near band edge emission located around 500 nm. The Arrhenius plot (log σDC vs 1000/T) attests the semiconducting nature for the sintered film.

Characterization and physical property studies of Sn, Al doped and co-doped CdO thin films

TM (TM = Sn, Al) doped and co-doped CdO thin films were deposited by spray pyrolysis technique on glass substrate at temperature 350 ˚C. The effect of TM doping and co-doping on the structural, morphological, optical, and electrical properties of CdO thin films was investigated. The obtained films are crystallized in the cubic structure and oriented along the preferential (111) crystallographic plane. The average optical transmittance reaches 79% in the visible range for Sn doped CdO films and 74% for Al-Sn co-doped films. The gap values of the obtained samples are between 2.29 and 2.49 eV. All the deposited films exhibit n-type conductivity with a low electrical resistivity of 7.85.10-4 Ω.cm obtained for Al doped CdO films.

Preparation and investigation of the structural and optical characteristics of manganese- doped cadmium oxide films

In this paper, undoped and Mn-doped CdO thin films deposited on the glass substrates by the chemical spray pyrolysis method (CSP) technique. The prepared thin films characterized by XRD, AFM, FESEM and UV visible. The results of the X-ray diffraction patterns revealed that the prepared films have a polycrystalline structure and a cubic structure. The crystallite size (D) value for all prepared films was calculated using Scherrer's method, Williamson-Hall method and size strain plot (SSP) method, from the results, it was observed that, the crystallite size decreases with increase in doping ratio of Manganese. The optical propertis show that with an increase in Mn concentration, the CdO films' transparency and the energy gap of the films increases. The Hall effect measurement revealed that all prepared films have negatives type (n-type) charge carriers, the value of the doping ratio rises, the Hall coefficient decreases.

Role of Cobalt Doping on the Physical Properties of CdO Nanocrystalline Thin Films for Optoelectronic Applications

In the current work, the authors aim to present an insight on the role of cobalt (Co) doping for the structural, morphological, and linear and nonlinear optical (NLO) properties of CdO thin films. The films were prepared using the spray pyrolysis (SP) technique, and the weight % of Co (x) was varied from 0–10. The structural properties of the films were confirmed by the powder X-ray diffraction (P-XRD) studies and are polycrystalline with a cubic structure and a lattice parameter of 0.4658 nm. As Co content in CdO films increases, cluster grain size and porosity decrease significantly, as seen in surface topographic and nanostructural analysis. Through the Burstein–Moss shift, the optical band gap “Eg” in Co: CdO film decreases from 2.52 to 2.05 eV with the increase in Co-doping. To study the NLO parameters, open aperture (OA) and closed aperture (CA) Z-scan measurements were performed using the diode-pumped solid-state continuous wave laser excitation (532 nm), and with the increased Co-content, the NLO parameters—nonlinear absorption coefficient (β∼10−3 cm/W), nonlinear refractive index n 2 ∼ 10−8 cm2/W), and the 3rd-order NLO susceptibility χ 3 ∼ 10−7 to 10−6 e.s.u.) values were determined and found to be enhanced. The maximum NLO parameters achieved in the present study with increasing Co concentration on CdO nanostructures prepared by the SP method are found to be the highest among the reported values and suggest that processed films are a capable material for optoelectronic sensor applications.

Electrolyte-gate-driven carrier density modulation and metal–insulator transition in semiconducting epitaxial CdO films

CdO has drawn much recent interest as a high-room-temperature-mobility oxide semiconductor with exciting potential for mid-infrared photonics and plasmonics. Wide-range modulation of carrier density in CdO is of interest both for fundamental reasons (to explore transport mechanisms in single samples) and for applications (in tunable photonic devices). Here, we thus apply ion-gel-based electrolyte gating to ultrathin epitaxial CdO(001) films, using transport, x-ray diffraction, and atomic force microscopy to deduce a reversible electrostatic gate response from −4 to +2 V, followed by rapid film degradation at higher gate voltage. Further advancing the mechanistic understanding of electrolyte gating, these observations are explained in terms of low oxygen vacancy diffusivity and high acid etchability in CdO. Most importantly, the 6-V-wide reversible electrostatic gating window is shown to enable ten-fold modulation of the Hall electron density, a striking voltage-induced metal–insulator transition, and 15-fold variation of the electron mobility. Such modulations, which are limited only by unintentional doping levels in ultrathin films, are of exceptional interest for voltage-tunable devices.

Synthesis Optimization of Cadmium Carbonate Films as Potential Precursor to Produce CdSe, CdTe, and CdO Films

Cadmium-derived materials are highly demanded for optoelectronics applications, and the scientific community has widely worked in different ways to develop them. In this research, the optimization of CdCO3 films using a chemical bath deposition (CBD) method at different deposition times (10, 11, and 12 h) is reported. The intention to optimize CdCO3 films is in order to propose it as a precursor to produce different types of cadmium-derived semiconductors such as CdSe, CdTe, and CdO. The obtained films were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, optical absorption by diffuse reflectance, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results provide evidence that CdCO3 films were effectively synthesized, featuring a rhombohedral crystalline structure with a preferential plane (104), and crystallite sizes were 65, 69, and 87 nm for the deposited samples at 10, 11, and 12 h, respectively. Surface morphology analysis revealed microstructures around 3–5 μm, with a deltoid shape, agglomerated and distributed randomly for all samples. The bandgap obtained was 3.78 eV for all samples.