Doped Thin Films Research Articles

N-type CdTe:In for photovoltaics: in situ doping, type verification and compensation effects

We explored the in-situ doping of cadmium telluride thin films with indium to produce n-type absorbers as an alternative to the near-universal choice of p-type for photovoltaic devices. The films were grown by close space sublimation from melt-synthesised feedstock. Transfer of the indium during film growth was limited to 0.0014%–0.014%—unless reducing conditions were used which yielded 14%–28% efficient transport. While chunks of bulk feedstock were verified as n-type by the hot probe method, carrier type of thin film material was only able to be verified by using hard x-ray photoelectron spectroscopy to determine the Fermi level position within the band gap. The assignment of n-type conductivity was consistent with the rectification behaviour of a p-InP/CdTe:In junction. However, chloride treatment had the effect of compensating n-CdTe:In to near-intrinsic levels. Without chloride, the highest dopant activation was 20% of the chemical concentration of indium, this being for a film having a carrier concentration of n = 2 × 1015 cm−3. However, the activation was often much lower, and compensation due to over-doping with indium and native defects (stoichiometry) are discussed. Results from preliminary bifacial devices comprising Au/P3HT/ZnTe/CdTe:In/CdS/FTO/glass are presented.

Flexoelectricity-stabilized ferroelectric phase with enhanced reliability in ultrathin La:HfO2 films

Doped HfO2 thin films exhibit robust ferroelectric properties even for nanometric thicknesses, are compatible with current Si technology, and thus have great potential for the revival of integrated ferroelectrics. Phase control and reliability are core issues for their applications. Here, we show that, in (111)-oriented 5%La:HfO2 (HLO) epitaxial thin films deposited on (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates, the flexoelectric effect, arising from the strain gradient along the film's normal, induces a rhombohedral distortion in the otherwise Pca21 orthorhombic structure. Density functional calculations reveal that the distorted structure is indeed more stable than the pure Pca21 structure, when applying an electric field mimicking the flexoelectric field. This rhombohedral distortion greatly improves the fatigue endurance of HLO thin films by further stabilizing the metastable ferroelectric phase against the transition to the thermodynamically stable non-polar monoclinic phase during repetitive cycling. Our results demonstrate that the flexoelectric effect, though negligibly weak in bulk, is crucial to optimize the structure and properties of doped HfO2 thin films with nanometric thicknesses for integrated ferroelectric applications.

Influence of Effective Surface Area on Gas Sensing Properties and Surface Morphology of Ag Doped Cu2O Thin Films by Cost Effective Method of M-SILAR Technique

Influence of Effective Surface Area on Gas Sensing Properties and Surface Morphology of Ag Doped Cu2O Thin Films by Cost Effective Method of M-SILAR Technique

Nanostructured cauliflowers patterning in Zr doped tungsten oxide thin films grown by AACVD

The effort is made to grow the cellular segmentation patterning of undoped and Zr doped Tungsten Oxide (ZWO) coatings engineered by aerosol assisted Chemical Vapor Deposition (AACVD) onto silica glass at 400 °C. Nanostructured cauliflowers were successfully grown without using any particular template via the chemical route of AACVD for undoped and Zr doped Tungsten Oxide. The tailored coatings of nano cauliflowers were explored by employing FE-Scanning electron microscopy/Energy Dispersive X-ray spectroscopy (FE-SEM/EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), Fourier transformation Infrared spectroscopy (FTIR), UV-VIS spectroscopy (UV-VIS) and four-point probe method to study surface morphological, chemical composition, optical and electrical properties systematically. Morphological features present fractal-type cauliflower patterning because of Zr incorporation. XRD spectra revealed a monoclinic (WO3) phase in undoped Tungsten Oxide with preferential orientation (0 2 0) whereas Zr doping triggered the growth of Magneli suboxide W5O14 with tetragonal (0 0 1) preferred reflection. Adding Zr dopant caused a slight expansion of lattice with a decrease in crystallite size (54–18) nm. Vibrational information exhibits shoulder at around 854.30 cm−1, attributed to O–W–O bond shifting. Undoped and Zr doped Tungsten oxide thin film signatures positioned at 446.65 cm-1, 692 cm-1, and 854.30 cm-1 are witnessed with a red and blue shift in all rest of the Zr doped thin films. The mismatch of W and Zr ions in ionic radii, electronegativity, and thermal coefficients promote stresses leading to the variation in lattice parameters, bond length, and crystallite size with stretching of IR modes attributed to the incorporation of Zr into the host lattice sites of Tungsten oxide. XPS deconvoluted peaks yield the analysis for bond energy of O1s electrons located around 505.19 eV and 510.85 eV characterized as metallic oxide of Tungsten (WO3). UV-VIS spectroscopy presented a highly absorptive nature of coatings in the spectral range between (300–900) nm with the widening of both direct (1.9–3.2) eV and indirect (1.9–2.6) eV band gap which is of absolute interest for both fundamental and applied aspects. Transport properties unveiled the decrease of electrical resistivity of order from 106 Ω-cm (undoped) to 105 Ω-cm (Zr doped), attributed to grown high angle nanoparticles boundaries of tungsten oxide contribute to governing of nano cauliflowers and, as a result, the volume of the grain boundaries increases. The interplay between crystalline quality, tuned architecture, and oxygen vacancies can contribute to the understanding of morphological, optical, and transport properties.

Influence of doping concentration and annealing temperature on the structure, particle morphology, and luminescent properties of powders and pulsed laser deposited thin films of bismuth-doped lanthanum gallate

Bi3+ doped LaGaO3 powders and thin films were grown via citric acid sol-gel combustion method and pulsed laser deposition (PLD) technique, respectively. X-ray diffraction data confirmed crystallization of the orthorhombic LaGaO3 phase. Inductive coupled plasma spectroscopy data indicated that some Bi3+ ions evaporated at temperatures exceeding 800 °C during thermal treatment. The highest photoluminescence (PL) and cathodoluminescence (CL) emissions with a peak stabilized at 370 nm were observed from La1-x GaO3:Bi3+x=0.003 powders annealed at 1200 °C. The PL and CL emission spectra of La1-x GaO3:Bi3+x=0.003 PLD thin films were similar to those of the powder samples. The effect of Bi3+ concentration and annealing temperature on the properties of powders and thin films is discussed.

In-depth opto-electrical analysis of Ni:CdS film towards the performance as Ag/Ni:CdS/FTO Schottky diode

Nickel doped cadmium sulfide (Ni:CdS) thin films are deposited onto glass and FTO substrate using spray pyrolysis technique. The effect of annealing temperature on the thin films and its morphological, microstructural, optical dispersion, linear-nonlinear and electrical, properties are extensively investigated by using various techniques such as field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM), X-ray diffraction (XRD) and ultraviolet visible (UV-VIS) diffuse reflectance spectroscopy. Morphological studies revealed that doped thin films surface is almost homogeneous and well-covered. Peaks associated with Ni, Cd and S elements are present in EDS analysis, which confirm the composition of the films. The energy band calculation using the Tauc plot from the recorded absorption spectra reveals the decrement in the energy gap from 3.75 eV to 3.61 eV and the refractive index is in the range of 2.57–2.62. The effect of annealing temperature on complex dielectric constant are also analyzed. Moreover, the dispersion of refractive index is calculated in terms of Wemple-DiDomenico approach. Third order susceptibility and nonlinear refractive index are calculated of Ni:CdS films. The designed Ag/Ni:CdS/FTO Schottky diode is tested under illumination conditions, and the empirical diode parameters, viz. ideality factor, barrier height, series resistance etc. are influenced by annealing temperature.

Development of fluorochromic polymer doped materials as platforms for temperature sensing using three dansyl derivatives bearing a sulfur bridge

Three novel bis-dansyl derivatives bearing a sulfur bridge have been synthesized, fully characterized, and their photophysical characterization studied in solution, as well as, in the solid state. All compounds exhibit fluorescence emission with quantum yields up to 60%, which vary significantly depending on the solvent used, and the inherent molecular structure. Moreover, these compounds demonstrate positive solvatofluorochromic behaviour emitting from bluish-green to yellow. Kamlet-Taft studies were performed to better understand the solute–solvent interactions. Due to the intrinsic characteristics of the compounds, efforts were made to understand their potential usefulness for environmental remediation and thus metal ion sensing studies were investigated. Compounds L1 and L2 showed high sensitivity to Cu2+ and Hg2+ ions and were found to modulate their emission extensively, with L2 capable of detecting and quantifying up to 4 µM of Hg2+. Considering the solid-state emission of these compounds, the application towards temperature sensing was put forth. L3 was found to quench its emission in a linear relation with temperature up to 170 °C. Several doped polymer thin films were fabricated, which served as a platform to establish a linear relation with temperature beyond their melting point. Polymethylmetacrylate (PMMA) films emitted up to temperatures of 218 °C, which could be fully restored at room temperature. These results suggest the potential application of these bis-chromophoric compounds as molecular thermometers.

Impact of copper doping on optical, UV induced wettability and photo-catalytic properties of sol-gel synthesized ZnO thin films

Self-cleaning properties concerning with photo-catalytic activity of thin films are important to develop pollutant-free functional surfaces for various applications. In this work, enhanced self-cleaning properties (photo-catalytic properties) as well as UV induced wettability of ZnO thin films were achieved by the doping of copper through sol-gel spin coating method. X-ray diffraction pattern revealed c-axis and a-axis plane dominance for ZnO and Cu doped ZnO (CuZnO) films, respectively. Scanning electron microscopy images showed nano-grain surface for CuZnO films. Optical transmittance was found in the range 90–79%. Optical band gap values were estimated between 3.34 and 3.39 eV. CuZnO films were found to exhibit hydrophilic state having water contact angle (WCA) in the range of 35° to 57°. Irradiance with UV light produced super-hydrophilic state in all prepared films. Contact angle reduction rate was found best in case of 6% doped CuZnO thin film. The recovery time of contact angle was between 20 and 22 h for all the films. Photo-catalytic effect was evaluated with methylene blue (MB) and methyl orange (MO) dyes and better reduction rate of 38.4% and 40% respectively was attained with 6% Cu doped film. Moreover, MB & MO stain removal was observed.

The effect of thickness on the optical and electrical properties of Hf doped indium oxide thin films

The doping of Hf has great potential to adjust the optical and electrical properties of In2O3 films, which has rarely been reported. In this paper, Hf-doped indium oxide films (IHFO) with excellent optical (average transmittance: 95.81%) and electrical properties (resistivity: 7.1 × 10−4 Ω cm) were deposited by RF sputtering on the glass substrate. X-ray photoelectronic spectra (XPS) showed that Hf4+ substituted In3+, resulting in an increase in carrier concentration and thus decreased resistivity. The X-ray diffraction (XRD) and Scanning electron microscopy (SEM) indicated that the change in the preferred orientation of IHFO film from (400) to (222) leads to different shape grains, which are associated with nuclei merging due to thickness increase. As the optical path of the visible light in film increase with film thickness, the film's visible light absorption is enhanced, resulting in the average transmittance of the films decreasing from 95.81% to 87.68%. Considering the effect of thickness on optical and electrical properties, the IHFO film at a thickness of 893 nm exhibits the highest FOM value of 2.85 × 10−2 Ω−1 with high average transmittance (89.84%) and low sheet resistance(12 Ω/sq). This result indicates that the IHFO film deposited with optimal thickness can be an alternative for high-performance TCO in various optoelectronic fields.

Linear-in-temperature resistivity for optimally superconducting (Nd,Sr)NiO2.

The occurrence of superconductivity in proximity to various strongly correlated phases of matter has drawn extensive focus on their normal state properties, to develop an understanding of the state from which superconductivity emerges1-4. The recent finding of superconductivity in layered nickelates raises similar interests5-8. However, transport measurements of doped infinite-layer nickelate thin films have been hampered by materials limitations of these metastable compounds: in particular, a high density of extended defects9-11. Here, by moving to a substrate (LaAlO3)0.3(Sr2TaAlO6)0.7 that better stabilizes the growth and reduction conditions, we can synthesize the doping series of Nd1-xSrxNiO2 essentially free from extended defects. In their absence, the normal state resistivity shows a low-temperature upturn in the underdoped regime, linear behaviour near optimal doping and quadratic temperature dependence for overdoping. This is phenomenologically similar to the copper oxides2,12 despite key distinctions-namely, the absence of an insulating parent compound5,6,9,10, multiband electronic structure13,14 and a Mott-Hubbard orbital alignment rather than the charge-transfer insulator of the copper oxides15,16. We further observe an enhancement of superconductivity, both in terms of transition temperature and range of doping. These results indicate a convergence in the electronic properties of both superconducting families as the scale of disorder in the nickelates is reduced.

In‐Plane AlN‐based Actuator: Toward a New Generation of Piezoelectric MEMS

AbstractA novel design that utilizes aluminum nitride (AlN) piezoelectric thin films deposited on vertical surfaces for lateral motion and sensing is a step toward emerging multi‐axial microelectromechanical systems (MEMS). This work demonstrates the fabrication process and potential applications of an in‐plane moving piezoactuator. The actuator is excited using the inverse piezoelectric effect of the AlN thin film grown on the vertical surfaces of a Si cantilever. Lateral motion of the actuator is enabled when a voltage is applied between the top and bottom electrodes of the device, which are highly doped Si and titanium nitride thin film. The motion of the actuator is captured using scanning electron microscope.

Graphene Oxide Doped Alginate Coated Optical Fiber Sensor for the Detection of Perfluorooctanoic Acid in Water

A novel and easy to fabricate graphene doped alginate thin film (Alg /GO) capable of binding with perfluorooctanoic acid (PFOA) and working on the principle of a Fabry-Perot interferometry (FPI) type optical fiber sensor is presented here. Utilizing a simple dip coating technique, the Alg/GO coating was deposited on the freshly cleaved fiber end-face followed by cross-linking in calcium chloride. The experimental results from two independent data analysis techniques, including Fourier-transform infrared (FTIR) spectroscopy and analytical adsorption tests were used to confirm that the developed graphene doped alginates can adsorb PFOA. It was also found that GO doped alginate coating adsorbs twice as much PFOA compared to alginate alone. Similarly, experimental results of the developed FPI sensor demonstrate the sensitivity to PFOA in aqueous solutions with a limit of detection (LOD) of 0.4 ppb and a non-linear correlation between 0 to 2 ppb with increasing concentration of PFOA in water. The response time at this concentration was estimated to be 17 s, considering a thin film coating thickness of approximately 30 μm as determined via imaging with the aid of differential interference contrast (DIC) microscopy. The relatively high sensitivity and ease of formation of the coating offers the potential for future development of portable optical sensors for emerging environmental contaminants.

Improvement of carrier transport properties of CsPbBr3 thin films by moisture absorption and TbCl3 doping technique

Moisture absorption and TbCl3 doping of CsPbBr3 thin films were investigated to improve the carrier transport properties. We found that post-deposition moisture-absorbing treatment improved the carrier diffusion length of CsPbBr3 thin films. The moisture-absorbing treatments under a relative humidity of about 20%–40% were effective to improve the carrier diffusion length. TbCl3 doping during the thermal evaporation of CsPbBr3 affected the structure of the deposited films. An excessive amount of TbCl3 doping leads to the formation of CsPb2Br5 additional phase, but a small amount of TbCl3 doping (1%) can improve the carrier diffusion length. The moisture-absorbing treatment and TbCl3 doping are promising techniques to improve the optoelectronic properties of CsPbBr3.

Investigation on structural, optical and electrical behaviours of Sn doped copper oxide thin films and fabrication of diode

Investigation on structural, optical and electrical behaviours of Sn doped copper oxide thin films and fabrication of diode

A nuanced understanding of the doping of poly(3,4-ethylenedioxythiophene) with tosylate

The conducting polymer poly(3,4-ethylenedioxythiophene) (known as PEDOT) is routinely fabricated into doped thin films for investigation of its inherent properties as well as for a range of applications. Fabrication of PEDOT is often achieved via oxidative polymerisation, where the conducting polymer is polymerised and doped (oxidised) to yield a conductive polymer thin film. The oxidiser and the polymerisation temperature are two parameters that may influence the properties and performance of the resultant PEDOT thin film. In this study, the role of temperature for the chemical polymerisation of PEDOT using the oxidiser iron tosylate is investigated from a computational and experimental viewpoint. While computations of the doping energetics suggest increasing doping with increasing temperature, x-ray photoelectron spectroscopy of fabricated PEDOT thin films indicate doping is much more complicated. With the aid of computations of the spatial distribution functions for tosylate in PEDOT, experiments indicate that two different populations of tosylate anions exist in the PEDOT matrix. Their relative populations change as a function of the polymerisation temperature. Therefore, polymerisation temperature plays a critical role in tailoring the properties of PEDOT in pursuit of being fit-for-purpose for the desired application.

Ce-Pr-Nd]:CsPbI1.8Br1.2: Stability enhanced light harvester in perovskite solar cells, energy storage material for batteries, and an OER/HER electro-catalyst

Current work for the first time investigates the impact of the lanthanide co-doping strategy on the fully inorganic cesium lead halide (CsPbI1.8Br1.2) perovskite by using oxides of cerium, praseodymium, and neodymium forming [Ce-Pr-Nd]:CsPbI1.8Br1.2. The doped perovskite material expressed an enhancement in the opto-electronic, crystalline, and morphological aspects upon lanthanide addition besides gaining an impressive stability at the ambient conditions. The dark brown doped thin films heated at 200 °C succeeded in acquiring a bandgap energy of between 1.66 and 1.73 eV showing stable response for 28 days revealed by ultra-violet spectrophotometry. Furthermore, the desired black phase cubic crystalline geometry was exposed by x-ray diffraction with an average crystallite size of 62.61 nm. In terms of morphology, the doping treatment not only enhanced the performance of CsPbI1.8Br1.2 but also it acted as a passivator for curing the surficial defects. The performance of the pristine and doped perovskite material was assessed by utilizing it as the light trapping material inside perovskite solar cells where highly improved performance was obtained for the doped absorber layer with 15.53 % efficiency, 68 % fill factor, 15.01 mA cm−2 short circuit current, and an excellent open circuit voltage of 1.14 V. Furthermore, the perovskite undoped and doped materials were fabricated in the form of an electrode for assessment of charge storage potential for battery application. With the electro-active behavior signifying surficial faradic redox process, there was an augmentation in the battery capacity with doping which boosted from 228 to 311.3 mAh g−1. With the series resistance as lows as 0.62 Ω, faster reaction kinetics were revealed for doped electrode. The oxygen and hydrogen evolution potential of the developed pristine and doped materials as bifunctional catalysts was assessed by estimation of the overpotential values and Tafel slope values. The Tafel slope values of the doped electro-catalysts were lower in comparison to the pristine material suggestive of the synergism between perovskite and dopants giving rise to an excellent energy generation capacity. The Tafel slope for oxygen and hydrogen generation of the doped electrode were 256.4 and 120.6 mV dec−1 indicating excellent hydrogen evolution. The stability and endurance of the developed material reflected from their original characteristics retention makes them excellent materials for use in energy application, specifically, [Ce-Pr-Nd]:CsPbI1.8Br1.2 excelled over pristine material showing the profound impact of doping on host lattice.

Super Flexible and High Mobility Inorganic/Organic Composite Semiconductors for Printed Electronics on Polymer Substrates

AbstractIn solution‐processed flexible electronics, it is challenging to obtain superior electrical and mechanical performance simultaneously. Attempts have been made to fabricate polymer doped oxide thin film transistors (TFTs), where, polymer doping frustrates the crystal structure of the parent oxide and causes amorphization. However, it also degrades the device mobility rapidly, thereby, limiting the allowable polymer content to only small values, which may not be sufficient for decisive enhancement in mechanical performance. In contrast, here an approach is proposed, where a set of water‐insoluble and chemically inert polymers are chosen to form inorganic/organic composite semiconductors. Herein, these selected polymers oppose a large degree of intermixing with the parent oxide lattice at the atomic scale, promote its crystallization, and help to maintain the electrical properties of the oxide semiconductors intact, even when they're in near‐equal amounts. Consequently, unaltered linear mobility of 40–45 cm2 V−1 s−1 can be obtained in In2O3‐based inorganic/organic composite semiconductor TFTs with a near‐equal weight of polymeric additives. Owing to the large polymer content, the TFTs are found to survive rigorous bending fatigue tests down to 1.5 mm bending radius without any deterioration in their electrical performance and without the formation of micro‐cracks in the composite semiconductor material.

Impact of Nd doping in Bi2S3 thin films coated by nebulizer spray pyrolysis technique for photodetector applications

In this study, cost effective & scalable nebulizer spray pyrolysis approach was used to produce varying concentrations of Bi2S3:Nd (0, 1, 3, 5 wt%) thin films on glass substrates and the effect of Nd dopants on the crystalline, morphological, optical and photo sensing properties of the Bi2S3 thin films were studied. From the XRD results, the diffraction pattern of the prepared Bi2S3:Nd thin films exhibits an orthorhombic structure for all concentrations of Nd dopants with a predominant peak along (130) plane. Upon increasing the concentration of Nd dopants up to 3 wt% the predominant peak intensity increases with an increase in crystallite size of 25 nm and decreases with a further increase in the incorporation of Nd dopant. The surface morphological studies showed uniform nanocrystalline morphology for all the Bi2S3 thin films. The UV–Vis absorption studies revealed higher absorption of the prepared thin films over UV region and narrowing of the energy gap from 2.18 to1.63 eV with the incorporation of Nd dopant from 0 to 3%, repectievely. The photo sensing properties of the fabricated devices showed higher responsivity (R), detectivity (D*), EQE, and rapid rise/fall time of 1.36 × 10−1 A/W, 3.05 × 1010 Jones, 43%, and 0.1/0.2 s for Bi2S3:Nd 3 wt% thin film photodetector confirming the suitability of the device for commercial photodetector applications.

Investigation of phosphorus-doping of MgZnO thin films using efficient spin-on dopant process

Phosphorus doped MgZnO thin films were prepared using the RF sputtering technique on a Si wafer, followed by spin-on doping (SOD) and annealing. The SOD is a cheap and non-destructive process in which the dopant film is spun on a Si wafer and placed in the vicinity of deposited undoped MgZnO thin film at a high temperature to perform doping. After doping, the MgZnO thin films were annealed at temperatures such as 700, 800, and 900 °C, which significantly improved morphological, structural, and optical properties. The atomic force microscopy and scanning electron microscopy measurements revealed that phosphorus-doped MgZnO thin films annealed at 800–900 °C have good morphology and large grains. X-ray diffraction spectra demonstrated the (002) orientation of MgZnO thin films. The photoluminescence spectra measured at 20 K demonstrated the acceptor bound exciton peak at 3.47 eV and acceptor binding energy of around 64.34 meV, indicating the formation of shallow acceptor levels by phosphorus doping of MgZnO thin films using the SOD process. In Raman spectroscopy measurement, the peak of E2high phonons mode of MgZnO wurtzite structure was observed around 436 cm−1. The FWHM value of this peak reduces with augmentation annealing temperature, demonstrating improvement in crystallinity. X-ray photoelectron spectroscopy measurement demonstrated the presence of phosphorus atoms in the SOD processed MgZnO thin films, which is again verified by Fourier-transform infrared spectroscopy measurement showing vibration modes of P–O bonds. It was observed that the different properties of SOD-prepared phosphorus-doped MgZnO films were superior to the film prepared using the alternate costly and destructive ion-implantation technique. These findings have revealed that high-quality phosphorus-doped p-type MgZnO thin films by the SOD process are very suitable for UV optoelectronic device applications.

Improvement of optoelectronic properties of in doped CeO2 thin films for photodiode applications

Improvement of optoelectronic properties of in doped CeO2 thin films for photodiode applications