RF Magnetron Sputtering Technique Research Articles

Performance optimization of AlN ultrasonic thin-film sensors deposited by RF magnetron sputtering

The AlN thin-film ultrasonic transducers were deposited by reactive RF magnetron sputtering technique. The effects of deposition parameters: target-substrate distance, argon-nitrogen flow ratio, deposition time, substrate temperature and radial distance from the deposition center on the ultrasonic performance of AlN thin films were studied. A metal electrode layer was deposited on the AlN film transducer to fabricate an ultrasonic temperature sensor, and the effects of the size and thickness of the electrode layer on the performance of the sensor were studied. Piezoelectric response measurements were performed in air over a temperature range of −60 °C–900 °C, and the dependence of ultrasonic response (time-of-flight and pulse echo amplitude) on temperature was analyzed. Long-term heat treatment in air at 750 °C for 128 h showed that the high-entropy alloy oxide protective layer could effectively delay oxidation of the AlN layer and improve the service life of the sensor.

In vitro assessment of corrosion, antibacterial properties, and degradation behavior of zirconia-coated polyetheretherketone (PEEK)

The medical industry often uses ceramic and polymeric coatings to safeguard metal substrates. However, more investigation is required to explore the implementation of ceramic coatings on polymer substrates and to determine their degradation and in vitro characteristics. This work involves applying zirconia coating onto the 3D-printed PEEK polymer substrate using the RF magnetron sputtering technique. With varying layer thickness and printing speed parameters, PEEK samples (S1, S2, S3, and S4) were 3D printed and coated with zirconia. The coated and uncoated samples were immersed in Fusayama artificial saliva solution for 30 days. Following immersion in artificial saliva, this study examined the corrosion of 3D-printed PEEK samples with and without coatings. Elemental mapping, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy were employed to evaluate sample morphology and estimate the binding energy of possible compounds generated in the artificial saliva solution. In vitro assessments such as antibacterial studies were performed against E. coli and S. aureus, and cytotoxic analysis was performed using Human Wharton’s jelly-derived mesenchymal stem cells (WJ-MSCs) to determine cell proliferation. The results indicated that sample S3, printed with 0.15 mm layer thickness and 20 mm/s print speed coated with zirconia showed a better degradation rate of 9.01% whereas the other three samples S1, S2, and S4 coated with zirconia showed deterioration rates of 36.4%, 33% and 16% respectively. Sample S3 showed a better antibacterial activity as biofilm formation was absent and also showed cell viability of about 79% and hence can be considered as a viable option for dental applications.

Improvement in bioactivity, hardness and friction resistance of 3 % manganese-doped hydroxyapatite coated on alumina using radio frequency magnetron sputtering

Hydroxyapatite (HAP) is a common hard tissue implant material known for its superior biocompatibility and osteoconductivity. However, its poor mechanical strength, brittleness and slow degradation limit the applications. This study explores the enhancement of HAP mechanical properties and bioactivity by coating 3 wt% manganese-doped HAP (Mn-HAP) on another inert biomaterial alumina (Mn-HAP/Al2O3) substrates using the RF magnetron sputtering technique. Characterization of these samples was performed using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), Grazing Incidence X-ray Diffraction (GIXRD), Fourier Transform Infrared Spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) techniques. Mechanical property was assessed through Vicker's hardness and adhesion of the film was studied by scratch testing. Corrosion resistance was evaluated using Tafel plots in Ringer's solution by Electrochemical analyser (ECA), and dielectric properties were measured using Impedance analyser. Biocompatibility was examined by wettability tests, thrombogenicity, antioxidant test, antimicrobial investigation and MTT [3-(4, 5-dimethythiazol-2-yl)-2, 5-diphenyl tetrazolium bromide] assay. The results show that Mn-HAP/Al2O3 coatings exhibit superior properties as compared to pure HAP, alumina, and HAP/Al2O3. Mn-HAP showed enhanced crystallinity and grain refinement, leading to improved hardness of 1198 HV for Mn-HAP/Al2O3 as compared to 39.84 HV for pure HAP and 1028 HV for HAP/Al2O3. The friction coefficient was found to be best in the Mn-HAP/Al2O3 sample. Corrosion rate significantly decreases in Mn-HAP/Al2O3 (1.63 ± 0.28) mmpy after coating on alumina. In vitro studies demonstrated enhanced cell attachment, proliferation, and differentiation after Mn-HAP coating on alumina. Antimicrobial tests revealed improved resistance against E. coli and S. aureus, with Mn-HAP/Al2O3 showing a larger zone of inhibition. The study concludes that 3 wt% Mn-HAP coatings deposited by RF magnetron sputtering hold great promise for enhancing the performance and longevity of hard tissue implants, paving the way for advanced biomedical applications.

Dual-Wave ZnO Film Ultrasonic Transducers for Temperature and Stress Measurements.

ZnO film ultrasonic transducers for temperature and stress measurements with dual-mode wave excitation (longitudinal and shear) were deposited using the reactive RF magnetron sputtering technique on Si and stainless steel substrates and construction steel bolts. It was found that the position in the substrate plane had a significant effect on the structure and ultrasonic performance of the transducers. The transducers deposited at the center of the deposition zone demonstrated a straight columnar structure with a c-axis parallel to the substrate normal and the generation of longitudinal waves. The transducers deposited at the edge of the deposition zone demonstrated inclined columnar structures and the generation of dominant shear or longitudinal shear waves. Transducers deposited on the bolts with dual-wave excitation were used to study the effects of high temperatures in the range from 25 to 525 °C and tensile stress in the range from 0 to 268 MPa on ultrasonic response. Dependencies between changes in the relative time of flight and temperature or axial stress were obtained. The dependencies can be described by second-order functions of temperature and stress. An analysis of the contributions of thermal expansion, strain, and the speed of sound to changes in the time of flight was performed. At high temperatures, a decrease in the signal amplitude was observed due to the decreasing resistivity of the transducer. The ZnO ultrasonic transducers can be used up to temperatures of ~500 °C.

Influence of power ramps on the physical properties of AZO thin films deposited at room temperature by RF magnetron sputtering technique

Abstract Aluminum-doped zinc oxide (AZO) thin films were deposited on glass substrates at room temperature by RF sputtering technique. Power ramps between 125 and 105 W were applied with a step of 4 W by intervals of 15, 7.5 and 1.8 min, for 180 min at 1.60 Pa. In this study, we investigated the structural, morphological, electrical, and optical properties of AZO films. X-ray Diffraction analysis showed that the films have a wurtzite-type hexagonal crystalline structure with a preferential crystallographic orientation (002) normal to the c axis. The average transmittance is greater than 76% for the wavelength range in the visible spectrum. The bandgap values were found between 3.32 and 4.01 eV, and refractive index was 1.79–2.60. Atomic force microscope measurements show homogeneous films with a roughness between 17–22 nm. A minimum resistivity value of 2.0 × 10−3 Ω cm was obtained for the film by using a power ramp of 4 W/1.8 min.

Studies on Dual Sputtered CuGaO2 Thin Films

There has been extensive research conducted on n-type transparent conducting oxide (TCO) films like Sn-doped In2O3 (ITO) [1], Al-doped ZnO (AZO) [2], etc. P-type transparent conducting oxides are yet to be researched extensively. Active devices such as p-n junction devices and transistors are required to make progress in the development of transparent electronics. In this effort, research in p-Type TCOs is important. Most of the p-Type TCOs are copper-based ternary oxides [3].In this work, CuGaO2 thin films were prepared using the dual-target RF magnetron sputtering technique. Cu2O and Ga2O3 targets were simultaneously sputtered on quartz substrates. The sputtering power of Cu2O was kept constant at 50 W and the sputtering power of Ga2O3 was varied. The films were deposited at room temperature and were subsequently annealed in nitrogen ambiance at 900 °C. The X-ray diffraction and optical studies were performed to analyze the films to optimize their properties.[1] Fallah, H.; Ghasemi, M.; Hassanzadeh, A.; Steki, H. The effect of annealing on structural, electrical and optical properties of nanostructured ITO films prepared by e-beam evaporation. Mater. Res. Bull. 2007, 42, 487–496[2] Shantheyanda, B.P.; Todi, V.O.; Sundaram, K.B.; Vijayakumar, A.; Oladeji, I. Compositional study of vacuum annealed Al doped ZnO thin films obtained by RF magnetron sputtering. J. Vac. Sci. Technol. A 2011, 29, 051514.[3] Sundaresh, S.; Bharath, A.H.; Sundaram, K.B. Effect of Cu2O Sputtering Power Variation on the Characteristics of Radio Frequency Sputtered p-Type Delafossite CuCrO2 Thin Films. Coatings 2023, 13, 395.

Structural, morphological, optical and electrical characterization of MgO thin films grown by sputtering technique on different substrates

Magnesium Oxide (MgO) thin film structures were deposited on glass and n-Si substrates by means of RF magnetron sputtering technique. Structural, morphological, optical characteristics of MgO thin film were determined by XRD, AFM and UV–Vis spectrometer techniques. The optical properties like absorption coefficient and optical band gap were extracted using optical transmittance and absorption spectra. The band-gap of MgO thin film was determined for direct electronic transition. Additionally, electric parameters like ideality factor, saturation current and barrier height of the Au/MgO/n-Si device were computed from the forward I–V data in dark state. The ideality factor was found to be greater than one. This indicates that the I–V characteristics of the device exhibits non-ideal attitude. The results show that the MgO thin film can be applied to both optical and electronic device applications.

Design, fabrication, and physical properties analysis of laminated Low-E coated glass for retrofit window solutions

The ever-growing demand for improved energy efficiency in buildings has stimulated a stream of research focused on innovative retrofit energy solutions. Laminated low emissivity (Low-E) type coated glass components can be used in retrofitting window systems for enhancing energy savings provided by the insulating properties of glass laminates containing these heat-mirror-type coatings. In particular, custom-designed double-silver low-E coatings embedded into the laminate structure (directly facing the polymer interlayers during and after the lamination) are of interest due to being protected from environmental exposure, enabling easy component transportation, storage, and window retrofits. In this study, we provide some details on the design of several reflector-type solar control low-E coatings of high environmental stability and demonstrate the feasibility of their fabrication on 3 mm thick glass substrates, followed by the lamination. We describe the optical properties of laminated structural glass components of potential usefulness for retrofitting window applications in new and existing buildings. Several thin-film coatings of a low-E type are deposited by using the RF magnetron sputtering technique and then subjected to lamination by using transparent epoxy and PVB materials, to be protected by a clear glass cover layer. The optical performance characteristics of these coatings (measured before and after lamination) elucidate the effects these lamination materials and cover glass thickness have on the final optical properties (leading to a slight reduction in the optical transmission in the visible spectral range, by around 8–10 % while retaining low thermal emissivity across the infrared spectral range). The outcomes of this research, if industrialized could contribute significantly to the development of sustainable building components and practices, and to acheiving a reduction in building energy consumption by way of enabling window retrofit operations at potentially reduced costs.

Structural analysis of NbN thin films grown through rf magnetron sputtering

In this work NbN thin films have been grown through rf magnetron sputtering technique from an 8-NbN (99.99%) target. In particular, we have studied the influence of the additional N2 flux in the preparation chamber on crystallization and microstructure of the deposited films. The films have been characterized by X-Ray diffraction (XRD) in 0-20 configuration and at a grazing angle, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD results show that the films grown at different fluxes of N2 have high textured coefficients along the [200] direction. SEM results indicate the films have columnar growth with high homogeneity and an average thickness of 0.7 μm. TEM results reveal that the films have grown from crystalline nanoparticles of NbN with high texture along the (200) plane.

Deposition and Optical Characterization of Sputter Deposited p-Type Delafossite CuGaO2 Thin Films Using Cu2O and Ga2O3 Targets.

CuGaO2 thin films were deposited using the RF magnetron sputtering technique using Cu2O and Ga2O3 targets. The films were deposited at room temperature onto a quartz slide. The sputtering power of Cu2O remained constant at 50 W, while the sputtering power of Ga2O3 was systematically varied from 150 W to 200 W. The films were subsequently subjected to annealing at temperatures of 850 °C and 900 °C in a nitrogen atmosphere for a duration of 5 h. XRD analysis on films deposited with a Ga2O3 sputtering power of 175 W annealed at 900 °C revealed the development of nearly single-phase delafossite CuGaO2 thin films. SEM images of films annealed at 900 °C showed an increasing trend in grain size with a change in sputtering power level. Optical studies performed on the film revealed a transmission of 84.97% and indicated a band gap of approximately 3.27 eV. The film exhibited a refractive index of 2.5 within the wavelength range of 300 to 450 nm.

Room temperature gas sensors for NH3 detection based on SnO2 films and lamellar-structured Ti3C2Tx MXene heterojunction nanocomposites

Efficient and accurate detection of ammonia (NH3) by gas sensors at room temperature holds great practical value and significance in industrial production and environmental protection. In this work, we designed SnO2/Ti3C2Tx heterojunction nanocomposites via a facile RF magnetron sputtering technique. Benefitting from the surface porosity and few lamellar-structured of the composites, as well as the construction of heterojunctions between SnO2 and Ti3C2Tx, the SnO2/Ti3C2Tx sensor demonstrated a response of up to 13.35 % towards 50 ppm NH3 at room temperature, which was 3.5 times higher than the Ti3C2Tx-based sensor. Meanwhile, the response/recovery time was reduced to 24.9/86.5 s. In addition, the SnO2/Ti3C2Tx sensor exhibited good selectivity, repeatability, and long-term stability. This work should provide an effective strategy for the design of high-performance NH3 gas sensors at room temperature.

Effect of Ag incorporation on the microstructure and properties of ZnS thin films

In this study, ZnS thin films doped with different content of Ag were deposited on quartz glass substrates by RF magnetron sputtering technique and were annealed at 600 °C in sulfur vapor. The crystal structure, grain size, surface morphology, composition, optical properties and defects of the doped ZnS thin films were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), UV–Vis spectroscopy and positron annihilation doppler broadening spectroscopy (DBS). The results showed that all films exhibited the cubic sphalerite structure with a preferred orientation along the (111) crystal plane, and the composition of the doped films were more consistent with the stoichiometric ratio compared to the undoped film. The grain size gradually increased as the Ag content grew, indicating the improvement of crystallinity of the ZnS thin films. Besides, the bandgap values of these ZnS films with good optical transparency in the visible region were decreased from 3.87eV to 3.53eV as the Ag content grew. DBS results also showed that the defect concentration of ZnS films gradually decreased from the surface to the inner layer, and the film defects decreased with the increase of Ag content. However, the types of defects changed when the Ag content increased. Furthermore, the results showed Ag also has an effect on the porosity of ZnS thin films.

Charge-carrier engineering of staggered-gap p-CuAlO2/β-Ga2O3 bipolar heterojunction for self-powered photodetector with exceptional linear dynamic range and stability

Beta-gallium oxide (β-Ga2O3)-based heterojunction photodetectors (HJPDs) based on p-n heterojunction have drawn a lot of attention since p-type doping of β-Ga2O3 is challenging to perform. Thus, choosing affordable and effective inorganic hole transport layers (HTLs) is a crucial first step in commercializing PDs. Copper aluminum oxide (p-CuAlO2) is a very likely candidate material for heterojunction with β-Ga2O3, because of its large hole mobility for use in solar-blind photodetectors and high-power electronics. In this study, we propose employing a p-CuAlO2 interlayer for built a β-Ga2O3-based SBUV HJPDs by regulating the oxygen flow rate (OFR) from 0 % to 30 % using the RF magnetron sputtering (RFMS) technique. Prior to building the p-CuAlO2/β-Ga2O3 HJPDs, the heterojunction band alignment was established and displayed staggered-gap band alignment with a valence band (ΔEV) offset of 1.1 eV and conduction band offset (ΔEC) of 0.65 eV with OFR of 30 %. In response to the UV-C (255 nm) wavelength, the good optoelectronic device properties such as low dark current of ∼10−12 A, large photo-to-dark current (Ilight/Idark) ratio (∼104), responsivity (R) (26.36 mA/W), detectivity (D*) (2.87 × 1010 cmHz1/2W−1), external quantum efficiency (EQE) (1.28 × 104 %), noise-equivalent power (NEP) (0.03 pWHz−1/2), linear dynamic range (LDR) (99.13 dB), and comparable rise (τr) and decay times (τd) of 0.25 s and 0.15 s respectively, were demonstrated for p-CuAlO2/β-Ga2O3 HJPDs with OFR of 30 % and also compared with pristine Pt/β-Ga2O3 Schottky barrier diode photodetector (SBDPD). The band offset at the p-CuAlO2/β-Ga2O3 interface is employed to explain the improvement of p-CuAlO2/β-Ga2O3 HJPDs. The incorporation of p-CuAlO2 into Pt/β-Ga2O3 SBDPD lead to an improved extraction efficiency of the generated free hole carriers under illumination. The Silvaco TCAD simulator was employed to get insight into the function of the p-CuAlO2 layer. The investigation focused on analyzing the variation profile of the recombination rate and electric field in Pt/β-Ga2O3 SBDPD and p-CuAlO2/β-Ga2O3 HJPD with OFR of 30 %. The outcomes demonstrate the stability and electron transfer impact of staggered gap p-CuAlO2/β-Ga2O3 HJPDs. Our findings show that the p-CuAlO2/β-Ga2O3 HJPDs have a great deal of potential as a candidate structure for the Ga2O3-based modern optoelectronic technologies.

Investigation of Antibacterial Efficacy of CuCrO2 Delafossite Thin Films Against E. coli

Terminals used in hospitals, information systems displaying patient information, and smartphones use touch panels that incorporate n and p transparent conducting oxide (TCO) layers [1]. There are a lot of pre-existing research present on n-type TCO while at the same time similar research interest related to p-type TCOs has been lacking. This is due to the inherently high electrical resistivity or low optical transparency of p-type TCOs. Recently, there has been a spike in research related to p-type delafossite thin films, owing to their excellent electrical and optical properties as compared to the other p-type counterparts. Cu-based p-type delafossite materials exhibit low resistivity and at the same time good optical transparency in the visible region. Among the Cu-based delafossites, copper chromium oxide (CuCrO2) exhibits the lowest electrical resistivity reported yet. Use of CuCrO2 as the p-type TCO along with a suitable n-type TCO might demonstrates significant potential to be used for optoelectronic applications.In this work, CuCrO2 thin films have been deposited on quartz substrates using dual target RF magnetron sputtering technique. This involved dual sputtering of 3- inch Cu2O and Cr2O3 targets. The substrate temperature was maintained at 400 °C during the deposition with Ar used as the sputtering gas. This was followed by post deposition annealing. Previous research carried out by our group has indicated that single-phase CuCrO2 was obtained at an annealing temperature of 650 °C in N2 ambiance for 4 hours [2, 3]. Successful synthesis of single-phase CuCrO2 has been confirmed using XPS and XRD study. The resistivity of CuCrO2 was obtained as 0.652 Ω-cm, which is the lowest reported so far. The optical study denoted an average optical transmission of > 60% in the visible wavelength spectrum and a high optical bandgap of 3.2 eV. The antibacterial efficacy of different thickness of CuCrO2 thin films was tested against E. coli bacterial strain and compared against the efficacy of plain quartz in this research work. Results showed that with an increase in the thickness of CuCrO2 thin films, the efficacy against E. coli increases. The highest antibacterial efficacy of 78.07 % was shown by 2000 A° CuCrO2 thin film.[1] Chiu T-W, Yang Y-C, Yeh A-C, Wang Y-P, Feng Y-W. Antibacterial property of CuCrO2 thin films prepared by RF magnetron sputtering deposition. Vacuum. 2013;87:174-177.[2] Sundaresh S, Bharath AH, Sundaram KB. Effect of Annealing Temperature on Radio Frequency Sputtered p-Type Delafossite Copper Chromium Oxide (CuCrO2) Thin Films and Investigation of Diode Characteristics Forming Transparent pn-Heterojunction. Coatings2023.[3] Sundaresh S, Bharath AH, Sundaram KB. Effect of Cu2O Sputtering Power Variation on the Characteristics of Radio Frequency Sputtered p-Type Delafossite CuCrO2 Thin Films. Coatings2023.

High temperature AlN thin film ultrasonic transducers with dual mode wave excitation

AlN thin film ultrasonic transducers with dual mode wave (transverse and longitudinal) excitation were deposited by reactive RF magnetron sputtering technique. The transducers deposited at radial distances of 0 and 50 mm in the sample plane exhibited well-developed straight and inclined columnar structures with dominating (002) and (103) X-ray diffraction peaks, respectively. The transducers deposited at radial distances of 0, 30, and 50 mm demonstrated excitation of longitudinal, transverse, and longitudinal-transverse waves, respectively. Short term heat treatment was conducted in air within a temperature range of 20–900 °C to investigate the high temperature ultrasonic response. Temperature dependencies of the time-of-flight and pulse-echo amplitude were analyzed. Long term heat treatment in air at 700 °C for 192 h revealed a degradation of ultrasonic response due to the oxidation of the AlN layer.

High-performance of laser annealed ITO/Cr-Ag/ITO multilayered thin film for transparent conducting application.

A novel laser annealing treatment was used to enhance the optoelectronics, and the morphological properties of ITO/Cr-Ag/ITO (ICAI) thin film are presented. The multilayer thin film was deposited using the RF magnetron sputtering technique and annealed using an Nd:Yag laser. The ICAI properties were characterized using X-ray diffraction, an atomic force microscope, field emission scanning electron microscope, energy dispersive X-ray, UV–visible spectroscopy, four and two-probe point probe. These techniques show the high quality of the thin film and the improvement of the properties caused by the laser annealing. The XRD shows that laser annealing improves the crystalline quality of the film. The AFM and FESEM exhibit uniform and high surface quality, where the roughness was decreased, and the grain size was enlarged. The optical transmittance was increased from 80 to 90 %, similar to the bandgap from 3.35 to 3.79 eV The electrical measurements show a significant decrease in the resistivity, and an Ohmic contact improved with laser annealing. The annealed structure has recorded a high figure of merit of 174 × 10−3 Ω−1. These results demonstrate that laser annealing treatment significantly enhances the thin film's properties. Therefore. The ICAI structure can replace the other transparent conducting material with a low annealing temperature and low energy.

Studies on photovoltaic properties of BFO/WO3 bilayer thin films for solar energy harvesting applications

BFO possess high remnant polarization (∼100 μC/cm2) and low direct band gap (∼2.7 eV) having potential for photovoltaic (PV) applications. In the present work, WO3 insulating layer is utilized with BFO and BFO/WO3 bilayer thin film structure is fabricated for reducing the leakage current along with possessing the low band gap and high ferroelectric polarization. In BFO/WO3 bilayer structure, the WO3 nanostructured thin film layer was fabricated utilizing rf-magnetron sputtering technique under the optimized parameters while BFO thin film layer was fabricated by altering the incident energy of excimer laser (150 mJ − 250 mJ) in Pulsed Laser deposition technique. BFO/WO3 bilayer structure prepared at 200 mJ laser energy demonstrated the superior ferroelectric properties (Ps = 63.24 µC/cm2 and Pr = 25.94 µC/cm2) with high values of short circuit photocurrent density (Jsc = ∼18 mA/cm2) and open-circuit voltage (Voc = ∼320 mV) under the UV illumination of Intensity = 160 mW/cm2 and λ = 355 nm. Obtained results suggest the utilization of prepared BFO/WO3 bilayer thin film structures on future novel energy harvesting purposes.

Al doping and defect regulation of sputtered CdZnTe films based on Al–AlN transition layers

CdZnTe films with less defects and high quality were fabricated on aluminum-rich AlN (Al–AlN) transition layers by RF magnetron sputtering technique. The Al doping and regulation effect on defect states, structure and photoelectrical performance of CdZnTe films were minutely investigated by XRD, HRTEM, SEM, XPS, Photoluminescence and Photoelectric characteristics. Results strongly suggested the self-doping process of Al from Al–AlN transition layers, which helped to compensate the defect density of Cd vacancy in CdZnTe films, thus improving crystallization, response performances and resistivity of Al-doped CdZnTe films. Electrical characterization implied the formation of good ohmic contact between electrodes and Al-doped CdZnTe films. Under 254 nm UV light illumination, the surface dark current of optimal Al-doped CdZnTe film was 25 times smaller than that of non-doped film, and rise and decay times were 3.4 and 2.8 times faster, indicating the feasibility of high quality film detectors for solar-blind UV detection.

Enhanced photovoltaic performance of silicon-based solar cell through optimization of Ga-doped ZnO layer

In the present study, the impact of deposition pressure and substrate temperature of Ga-doped Zinc Oxide (GZO) thin film and the photovoltaic performance of this structure as a transparent conductive oxide (TCE) layer in silicon-based solar cell were investigated. Implementing a single target of GZO, the structural, optical, and electrical properties of 350 nm thick GZO thin films with various deposition pressure (5 mTorr, 10 mTorr, 15 mTorr and 20 mTorr) at room temperature (RT) and substrate temperature (RT, 150 °C, 200 °C, 250 °C) at 15 mTorr deposition pressure were fabricated using RF magnetron sputtering technique. The aim here was to find out the GZO films with the optimum pressure and substrate temperature to incorporate them into solar cell as a TCE layer. The X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques were used to determine the structural properties of all samples. The optical transmission measurements were performed using spectroscopic Ellipsometer and the band gap values were calculated by Tauc plot using optical transmission data. In addition, the electrical characterization of the GZO samples were analyzed by the Van der Pauw method and Hall measurements. Finally, the most promising GZO thin film was determined based on the structural and optoelectrical characterization. The findings indicated that the XRD pattern of all the prepared films was dominated by (002) preferential orientation irrespective of the deposition pressure and substrate temperature. The AFM measurements showed that all the samples had a dense surface morphology regardless of the deposition pressures, but the surface morphology of the samples was clearly changed upon increasing substrate temperatures. The transmission values of the film did not significantly alter (∼82%) when the deposition pressures except for the substrate temperature of 200 °C (86%) were changed. The band gap values were calculated between 3.30 eV and 3.36 eV, which can be associated with enhancement of crystalline quality of the films. The lowest resistivity and the highest carrier concentration values belonged to the film fabricated at 15 mTorr@200 °C by 2.0 × 10−3 Ω.cm and 1.6 × 1020 cm−3, respectively. Both increasing the deposition pressure (up to 15 mTorr) and substrate temperature (up to 200 °C) contributes to improving the crystallite size, widening the optical band gap, lowering the resistivity, and increasing the carrier concentration. In order to evaluate and compare the effect of both deposition pressure and substrate temperature, Silicon-based solar cells were fabricated using the most promising layers (15 mTorr@RT, 15 mTorr@200 °C). The cell performance with the GZO thin film as a TCE layer showed that varying both the pressure and substrate temperature of the GZO film contributed to enhancing the solar cell parameters. Thus, the conversion efficiency increased from 9.24% to 12.6% with the sequential optimization of pressure and temperature. It can be concluded that the pressure applied during the deposition and substrate temperature had a significant impact on the properties of GZO thin films and its photovoltaic performance of solar cell used as TCE layer.

The barriers for electron and hole injection from Si substrate into the RF magnetron-deposited In2O3 : Er films

The In2O3 : Er films were deposited on Si substrates by the RF magnetron sputtering technique. For the Si substrates of both n- and p-type the current through the MOS-structure (Si/In2O3 : Er/In-contact) was described by the thermionic emission of the main currents over the barrier, with the correction of the applied voltage into the partial voltage drop in silicon. By the temperature dependence measurements of the forward currents at small under-barrier biases the barriers for the current injection from Si into the films were found equal to the 0.14 eV and 0.3 eV for the electrons and holes accordingly. The obtained small barrier for the holes is described by the presence of the defect state density. It tails from the valence band maximum into the In2O3 : Er band gap and provides there the conduction channel for holes. The defect state density in the In2O3 : Er band gap is proved by the PL data in the respective energy range 1.55–3 eV. The band analysis for the hetero-structure Si/In2O3 : Er is performed. It gives the energy gap between the electrons in the In2O3 : Er conduction band and the holes in the band gap channel equal to the 1.56 eV.