Doped Zinc Oxide Films Research Articles

In situ aluminum doped zinc oxide thin films by pulse electrodeposition for the all-electrodeposited cadmium-free copper indium diselenide solar cells

Pulse electrodeposition was used to produce aluminum doped zinc oxide (AZO) films, which were then used to construct an all-electrodeposited cadmium-free (Cd-free) Copper Indium Diselenide (CISe) solar cell. Aluminum was added into the films during the deposition process by positioning an Aluminum (Al) metal foil into the electrolyte. Energy Dispersive Spectrometry (EDS) elemental mapping confirmed the incorporation of Al into the films. According to X-Ray Diffraction (XRD) patterns, the aluminum doped zinc oxide films have a wurtzite hexagonal crystal structure, only with (002) planes indicating phase purity. The impedance analysis of the annealed device with electrodeposited aluminum doped zinc oxide revealed that it had better charge transfer resistance than the as-deposited device.

P-Type ZnO Films Made by Atomic Layer Deposition and Ion Implantation.

Zinc oxide (ZnO) is a wide bandgap semiconductor that holds significant potential for various applications. However, most of the native point defects in ZnO like Zn interstitials typically cause an n-type conductivity. Consequently, achieving p-type doping in ZnO is challenging but crucial for comprehensive applications in the field of optoelectronics. In this work, we investigated the electrical and optical properties of ex situ doped p-type ZnO films. The p-type conductivity has been realized by ion implantation of group V elements followed by rapid thermal annealing (RTA) for 60 s or flash lamp annealing (FLA) on the millisecond time scale in nitrogen or oxygen ambience. The phosphorus (P)-doped ZnO films exhibit stable p-type doping with a hole concentration in the range of 1014 to 1018 cm-3, while antimony (Sb) implantation produces only n-type layers independently of the annealing procedure. Microstructural studies of Sb-doped ZnO show the formation of metallic clusters after ms range annealing and SbZn-oxides after RTA.

Effect of process parameters on microstructure and Raman characteristics of magnesium doped ZnO thin films

MgxZn1-xO thin films were prepared on glass substrates by radio frequency magnetron sputtering under different sputtering processes. The surface morphology, microstructure, and Raman characteristics of the films were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman Spectrometer. The results show that an increase in the O/Ar ratio decreases the surface smoothness of the thin film and worsens the particle uniformity. The particles of undoped Magnesium doped Zinc Oxide (ZnO) films are small and uniform, and the uniformity of the particles in the films becomes worse after doping. Moreover, there are multiple diffraction peaks in the magnesium doped Zinc Oxide films, presenting a polycrystalline state, but the diffraction peak positions do not significantly change with the concentration and intensity of magnesium doped. The Raman characteristic peak undergoes a blue shift with the increase of magnesium doping concentration, and the peak position shifts from 573 cm−1 to 607 cm−1.

Wide-range ethanol sensor based on a spray-deposited nanostructured ZnO and Sn–doped ZnO films

This study compares the performance of a highly sensitive ethanol sensor incorporating a zinc oxide (ZnO) nanostructured film with that of (1–3) % tin-doped zinc oxide (Sn–ZnO) nanostructured films across a wide range of ethanol concentrations from 0.5 to 400 ppm. X-ray diffraction analysis confirms the polycrystalline structure of Sn–ZnO films, with a significant (002) plane orientation. Notably, Sn doping reduces the optical bandgap from 3.28 eV (ZnO) to 2.41 eV (3% Sn–ZnO). Ethanol vapor sensing experiments reveal that the 2% Sn–ZnO film operates at a lower temperature of 220 °C compared to the ZnO film (290 °C). Particularly, the 2% Sn–ZnO film exhibits rapid and strong responses to low ethanol concentrations (0.5–100 ppm) at this temperature. Response values of 2.22 ± 0.01 and 17.66 ± 0.08 with response times of 11 ± 1 and 15 ± 1 s are achieved at ethanol concentrations of 0.5 and 400 ppm, respectively. Conversely, the ZnO film performs better at higher ethanol concentrations (150–400 ppm). These findings advance gas sensing mechanisms in ZnO and Sn–ZnO films, with implications for future advancements in gas sensor technology.

Modification in structural, electrical and defect luminescence properties of ZnO nanorod films with Cu, Al and double-doping

Zinc oxide nanorods have broad application prospects in the field of photoelectric devices. However, the application as photodetectors in the visible light band is limited by their narrow luminescent spectrum and poor electrical conductivity. In this work, three different zinc oxide nanorod films respectively with Cu, Al and double-doping have been prepared for investigating the modifying effect of their defect luminescence and electric performance. In this paper, Cu doped zinc oxide with rod structure and Al doped zinc oxide with flaky structure are fabricated by hydrothermal method and sol-gel method, respectively. As for the double-doping, Al doped zinc oxide films are grown on the surface of Si by sol-gel method, and Cu doped zinc oxide nanorods are grown on the surface of Al doped zinc oxide films by hydrothermal method. The results show that the Cu doping can improve the number of defects, leading to the electrons transport from VZn to Zni and then releasing the photons. Alternatively, the trivalent aluminum ions exist in zinc oxide nanorods in the form of replacement or gap, increasing the carrier concentration, turn-on voltage and rectification ratio of zinc oxides. As for the Cu–Al double-doping, Al doped zinc oxide films are located between Cu doped zinc oxide nanorods and Si substrate and work as an intermediate layer of current. Trivalent aluminum ions can change the semiconductor properties of zinc oxide and make it have the performance of p-type semiconductor which can improve the electrical properties of zinc oxide semiconductor. Besides, the carrier concentration of Cu–Al double-doping zinc oxide is nearly 3 times higher than that of pure one. Increasing the carrier concentration can increase the current of ZnO–Si heterojunction in the dark, thus improving the photoelectric properties of ZnO nanorods.

Influence of Annealing Temperature on the Optical Properties of Cu Doped Zinc Oxide Films

Influence of Annealing Temperature on the Optical Properties of Cu Doped Zinc Oxide Films

Preparation, optimization and electrochromic properties of dual-band device with four modes

A dual-band electrochromic device with four modes was fabricated to selective modulate the transmittance from visible to near-infrared bands for the energy-saving field. The new LiClO4 + TBACl + AgNO3 electrolyte was prepared to respectively regulate the redox reactions of silver ion and lithium ion to prove the four modes of the device. The dual-band device with a sandwich structure was fabricated by the titanium dioxide electrochromic film, the gallium doped zinc oxide ion storage film and the LiClO4 + TBACl + AgNO3 electrolyte. The titanium dioxide and gallium doped zinc oxide films were prepared by a nanoparticle deposition system, which is an environmentally friendly dry deposition technique. By controlling the supplied potential, the redox reactions of silver ion and lithium ion present four modes, including transparent mode, warm mode, cold mode and full block mode. For warm mode, the localized surface plasmon resonance effect was excited by generating silver nanoparticles using two-stage potential. Moreover, the titanium dioxide film with high surface roughness shown the large light scattering effect, the transmittance of ∼0% at whole wavelengths was obtained in full block mode. The electrochromic device shown the large transmittance modulation (71%) and excellent cyclic stability (600 cycles). Therefore, it is proved that the transmittance can be adjusted at a specific wavelength by the electrochromic device, which provides an effective way for developing dual-band smart devices to reduce energy consumption.

Microstructural, Optical, and Work Function Tuning of Fullerene (C60) Modified Zinc Oxide Films for Optoelectronic Devices

Here, we report the synthesis of pristine and fullerene (C60) modified zinc oxide (ZnO) films by the sol-gel method. Various compositions of C60 ranging from pristine to 0.25 wt%, 0.50 wt%, and 1.00 wt% have been chosen for the modification of ZnO film. The incorporation of C60 in pristine ZnO films modifies its structural, surface morphological, optical, and electrical properties. Structural characterization suggests that pristine and C60 modified ZnO films exhibit Wurtize crystal structure. Surface morphological characterization demonstrates that incorporation of C60 into ZnO leads to the formation of spherical nano-particles which varies on the doping of C60. The properties of C60 doped ZnO films show a reduction in the bandgap values from 3.11 eV to 2.73 eV with enhanced optical absorption and photoluminescence properties. Further, the surface potential and work function of pristine and C60 incorporated ZnO films, as investigated by Kelvin probe force microscopy (KPFM) show tuning of Fermi level in pristine and C60 modified ZnO films. The work function of the ZnO films changes from −4.38 eV to −4.46 eV on the incorporation of C60. The variations in work function may be due to reduced microstructural and localized defects offered during the incorporation of C60. Also, C60 modified ZnO Schottky diodes exhibited enhanced carrier mobility with better charge transport properties.

Comparative Study of Aluminum-Doped Zinc Oxide, Gallium-Doped Zinc Oxide and Indium-Doped Tin Oxide Thin Films Deposited by Radio Frequency Magnetron Sputtering.

A timely replacement of the rather expensive indium-doped tin oxide with aluminum-doped zinc oxide is hindered by the poor uniformity of electronic properties when deposited by magnetron sputtering. Recent results demonstrated the ability to improve the uniformity and to decrease the resistivity of aluminum-doped zinc oxide thin films by decreasing the energy of the oxygen-negative ions assisting in thin film growth by using a tuning electrode. In this context, a comparative study was designed to elucidate if the same phenomenology holds for gallium-doped zinc oxide and indium-doped tin oxide as well. The metal oxide thin films have been deposited in the same setup for similar discharge parameters, and their properties were measured with high spatial resolution and correlated with the erosion track on the target’s surface. Furthermore, the films were also subject to post annealing and degradation tests by wet etching. While the tuning electrode was able to reduce the self-bias for all three materials, only the doped zinc oxide films exhibited properties correlating with the erosion track.

Photophysical investigation of the formation of defect levels in P doped ZnO thin films

Zinc oxide (ZnO) offers a major disadvantage of asymmetry doping in terms of reliability, stability, and reproducibility of p-type doping, which is the main hindrance in realization of optoelectronic devices. The problem is even more complicated due to formation of various native defects in unintentionally doped n-type ZnO. The realization of p-type conductivity in doped ZnO requires an in-depth understanding of the formation of an effective shallow acceptor, as well as donor-acceptor compensation. Photophysical properties such as photoconductivity along with photoluminescence (PL) studies have unprecedentedly and effectively been utilized in this work to monitor the evolution of various in-gap defects. Phosphorus (P) doped ZnO thin films have been grown by RF magnetron sputtering under various Ar to O2 gas ratios to investigate the effect of O2 on the donor-acceptor compensation by comprehensive photoconductivity measurements supported by the PL studies. Initial elemental analyses indicate presence of abundant zinc vacancies (VZn) in O-rich ambience. The results predict that P sits in the zinc (Zn) site rather than the oxygen (O) site causing the formation of PZn–2VZn acceptor-like defects, which compensates the donor defects in P doped ZnO films. Photocurrent spectra uniquely reveal presence of more oxygen vacancies (VO) defects states in lower O2 flow, which gets compensated with an increase in the O2 flow. Successive photocurrent transients indicate probable presence of more VO in the films grown with lower O2 flow and more VZn in higher O2 flow. Overall the photosensitivity measurements clearly present that O-rich ambience expedites the formation of acceptor defects which are compensated, thereby lowering the dark current and enhancing the ultraviolet photosensitivity.

Designing Low-Cost Arduino Powered Spin Coater for Thin Film Deposition

In the present work, we have designed a low-cost spin coater using the Arduino Uno board. The advantage of selecting Ardunio is, it has pulse width modulation (PWM) based pins. Depending on the width of the pulse, the output voltage changes which will intern changes the speed of the DC motor connected to the PWM pin. The thickness of deposited film using spin coater depends on RPM and duration of rotation. The rotation of the substrate during deposition has three stages a gradual increase in RPM, maintaining constant RPM over a while, and a gradual decrease in RPM. All these parameters can be controlled by an Arduino board. An Aluminum doped Zinc Oxide film was deposited on glass substrate using Arduino based spin coater. X-ray diffraction, UV – VIS spectroscopy, and FTIR methods were used as characterization techniques. Hexagonal crystal structure of deposited AZO layer was confirmed by XRD and optical band gap, transparency were calculated by UV-VIS spectroscopy.

Structural, optical and electrical properties of sol-gel spin-coated Ga and F Co-doped ZnO films

Zinc oxide (ZnO) film is a promising transparent conductive material suitable for various applications including transparent electrode, piezoelectric transducers, solar radiation protection and sensors. Ga doped ZnO film has excellent electrical properties but has inferiority in terms of optical transmittance, which has prompted investigations and researches on co-doped ZnO film in order to ameliorate its optical and electrical properties. In this study, Ga and F co-doped ZnO (GFZO) film has been prepared on quartz substrates with different F doping concentrations by sol-gel spin-coating method. The structural, optical and electrical properties of GFZO films were investigated using X-ray diffraction, scanning electron microscopy, optical spectroscopy, photoluminescence, and Hall Effect measurement system. Highly c-axis oriented GFZO films were obtained. The crystallinity of GFZO became better with increased of F content. The transmittance and conductivity were improved with increased F doping concentrations. GFZO films with 2 at.% F showed the lowest resistivity and superior transmittance.

Deterministic modeling of hybrid nonlinear effects in epsilon-near-zero thin films

In nonlinear optics, significant effort is concentrated on improving the strength and efficiency of interactions; however, experimentally investigating nonlinear materials is a complex, time-consuming, and costly investment. Moreover, it is often challenging to isolate, study, and optimize material parameters in an experiment due to complexities in the growth process. Recently, epsilon-near-zero materials have received a great deal of attention as promising nonlinear optical materials, but like many up-and-coming materials, the ability to explore and optimize their properties has been challenging. Here, we establish a framework to rapidly evaluate the performance of nonlinear epsilon-near-zero materials for both inter- and intraband effects in silico, requiring only an energy–momentum (E–k) diagram, linear optical properties, and experimental conditions. Measured nonlinear reflection and transmission in gallium-doped zinc oxide films are compared to the numerical framework for both intra- and interband excitation to verify accuracy across wavelength and irradiance while two figures of merit (FoMs) are introduced to quickly evaluate the performance of films without a full numerical framework. This capability is used to predict the performance of highly doped gallium nitride, cadmium oxide, zinc oxide, and indium tin oxide films, and efficient intra- and interband operation conditions are identified. Through this numerical framework and the FoMs, the exploration of unstudied epsilon-near-zero materials is enabled without the need for a nonlinear experiment, thereby accelerating the search for more efficient nonlinear materials and excitation conditions.

Analysis of the effect of copper concentration on the structural, spectroscopic, and electrical properties of Cu:ZnO thin films

A detailed report on the investigation of structural, spectroscopic, and electrical properties of copper doped zinc oxide (CZO) thin films on the glass substrate is presented here. The spray pyrolysis technique was employed to prepare optimized ZnO thin films and copper (Cu) was added as the dopant with different concentrations. Structural properties of all samples were studied by analyzing the x-ray diffractogram (XRD) that showed a crystallite size around 40 nm. Zinc oxide (ZnO) films deposited at various Cu concentrations possess hexagonal crystal structure with (002) preferential orientation. At high copper concentrations, impurity peaks corresponding to copper were observed. Scanning electron micrographs (SEM) revealed good connectivity between the grains, along with the dense and uniform texturing on the surface. Absorbance spectra showed a red shift in absorption edge. A second band gap was observed at higher copper concentrations corresponding to the copper oxide (CuO) phase. Raman analysis with spatial imaging, x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) studies were carried out for all the samples, that showed the presence of copper secondary phase at high copper concentration. CZO films showed higher resistivity than pristine ZnO. However, resistivity decreased at a higher Cu level. Photosensitivity measurements showed a sensitivity of about 32.64 for 5 at% Cu doped ZnO films under white light. Photosensitivity of the material is attributed to the copper-related defect levels.

Enhancement of performance of Ga incorporated ZnO UV photodetectors prepared by simplified two step chemical solution process

The present study establishes the UV photodetector capability of Zinc Oxide (ZnO) and Gallium incorporated ZnO (GZO) thin films prepared by a simplified two-step chemical bath deposition technique. The prepared UV detectors were characterized by tools such as XRD, SEM, UV, PL and Photoresponse to investigate their properties. The structural study revealed the enhancement of film crystallinity with respect to Ga doping level. The optical studies confirm the higher absorption at UV range for 3% Ga doped ZnO film. From PL study, the green emission observed at 522 nm is associated with the defects from oxygen vacancies (Vo+). Once the UV light is irradiated on the GZO film surface, electrons and holes are generated as the illumination energy is larger than the ZnO bandgap energy, known as above-band energy illumination. The photo-generated holes then neutralize the chemisorbed ions causing the release of electrons in the conduction band of ZnO, this could increase the photocurrent. In this study, the calculated photo-detectivity (D*), responsivity (R) and external quantum efficiency (EQE) of the prepared UV detectors are 1.24 ×1010 jones, 0.38 AW-1, and 125.10% respectively for 3% Ga doped ZnO film. These parameters are noticeable and this study proves that GZO films in fact work as good sensitive UV detectors.

Extraordinarily high ultraviolet photodetection by defect tuned phosphorus doped ZnO thin film on flexible substrate

Phosphorus (P) doped zinc oxide (ZnO) thin film has skillfully been deposited on flexible substrate using radio frequency sputtering technique at room temperature under controlled oxygen ambient to tune its point defects. P doped ZnO film shows a very high ultraviolet (UV) photosensitivity with responsivity and detectivity values of 23.5 mA/W and 1.86×1013 Jones respectively as compared to the values of 0.073 mA/W and 2.56×1010 Jones respectively for pristine ZnO. Incorporation of P dopant under controlled oxygen ambient results in a very low dark current value due to acceptor-donor compensation leading to an unprecedentedly ultra-high photo-to-dark current ratio of 2.15×105 under 350 nm illumination. A photosensitivity under repetitive flat and bending conditions has been attained. Further, photoresponse towards a low intensity UV illumination of power 29 μW/cm2 has been noted with a photo-to-dark current ratio of 3.88×103 indicating an excellent photodetection efficiency of the P doped ZnO film.

Investigation of Flexible Arrayed Lactate Biosensor Based on Copper Doped Zinc Oxide Films Modified by Iron-Platinum Nanoparticles.

Potentiometric biosensors based on flexible arrayed silver paste electrode and copper-doped zinc oxide sensing film modified by iron-platinum nanoparticles (FePt NPs) are designed and manufactured to detect lactate in human. The sensing film is made of copper-doped zinc oxide (CZO) by a radio frequency (RF) sputtering system, and then modified by iron-platinum nanoparticles (FePt NPs). The surface morphology of copper-doped zinc oxide (CZO) is analyzed by scanning electron microscope (SEM). FePt NPs are analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The average sensitivity, response time, and interference effect of the lactate biosensors are analyzed by voltage-time (V-T) measurement system. The electrochemical impedance is analyzed by electrochemical impedance spectroscopy (EIS). The average sensitivity and linearity over the concentration range 0.2–5 mM are 25.32 mV/mM and 0.977 mV/mM, respectively. The response time of the lactate biosensor is 16 s, with excellent selectivity.

Highly sensitive zinc oxide ultraviolet photodetector by titanium incorporation

In this study, zinc oxide (ZnO) thin films were prepared on glass substrates by the sol-gel chemical method with different Ti/Zn molar ratios. The electrical, optical, and structural properties of titanium doped ZnO thin films have been studied in detail. Interestingly, according to the electrical measurement results, there is a significant increase in resistivity and a decrease in carrier concentration of ZnO thin films with the addition of titanium. Ultraviolet-Visible (UV-Vis) spectrophotometer results show an increase in optical transmittance by 10 % in the visible region with the addition of titanium. Photoluminescence studies indicate that titanium addition causes a notable decrease in green and red emission peaks caused by structural defects of ZnO by showing a passivation effect. Moreover, the sensitivity to ultraviolet (UV) light was increased as high as 775 times in 3 % Ti-doped ZnO thin films. The specific detectivity of the samples increased by two orders of magnitude. Titanium doped ZnO films exhibit superior properties for UV sensors.

Twisted-motion substrate with sustained azimuthal rotation effect on the growth of AZO thin films by rf-sputtering

Nanorods of aluminum doped zinc oxide films (AZO) were grown on borosilicate glass substrates using an rf-sputtering technique combining simultaneously substrate twisting motion frequency with sustained rotation. Twist-motion frequency of 0.35, 0.5, and, 0.75 Hz between 40° to -40° taking the horizontal plane as reference was adjusted. Effects of this twist-motion frequency as a function of the sustained azimuth rotation of the substrate at 15, 30, and 45 rpm were observed. The morphological, optical, and structural properties were compared between films. Well defined vertical nanorods shapes were observed. The thickness of the films is affected by both twist motion and rotation speed, and the average optical transmittance was greater than 80 % which shows that all samples have high transparencies in the visible range. The combination of these growth parameters of twist and rotation of the substrate allowed us to obtain refractive index values between 1.77 and 2.11 at a wavelength of 700 nm and an energy bandgap in the range of 3.47 and 3.63 eV. The crystallite size of the nanorods obtained was between 29 and 40 nm and the films showed a preferential orientation normal at the surface film to direction of the c-crystallographic plane (002). We report compressive stress in our samples.

Effect of annealing processing on morphology, spectroscopy studies, Urbach disordering energy, and WDD dispersion parameters in Cu-Al doped zinc oxide films

In this article, a mosaic target made of ZnO and Al-Cu atoms were used for fabricating of the Cu-Al doped zinc oxide films (CAZO films) using RF magnetron co-sputtering. The CAZO films were deposited in room temperature on glass substrates with the sputtering gases O2 and Ar in proportion of 30%. Then, films were annealed at different temperatures of 400, 500, and 600 °C in a electrical furnace with Ar atmosphere. Atomic Force Microscopy images showed that the size of nanoparticles in films annealed at 600 °C have maximum value about of 18.8 nm. Atomic Force Microscopy data shown that the films annealed at 600 °C were rougher and they were about of 4.68 nm. Transmittance T(λ) and reflectance R(λ) measurements in the wavelength range (300–2500 nm) were used to calculate the absorption coefficient α (λ), the refractive index n(λ), the optical dispersion parameters according to Wemple and Didomenico, and the optical band gap of films. The optical band gap has been estimated and confirmed by five different methods. It can be seen that with increasing annealing temperature the optical band gap of films were decreased. Films annealed at 400°C have more disordered. It is found that the as films annealed at 500°C have minimum values of the dispersion energy E d and the oscillator strength fin about of 0.57 eV and 2.42 (eV)2, respectively. The as deposited films have minimum values of oscillator length strength S 0 in about of 5.5 μm−2.