Radio-frequency Sputtering Research Articles

Accurate band alignment of sputtered Sc2O3 on GaN for high electron mobility transistor applications

Abstract Sc2O3 is a promising gate dielectric for surface passivation in GaN-based devices. However, the interface quality and band alignment of sputtered Sc2O3 on GaN is not fully explored. In this work, X-ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry (VASE) wereperformed to extract the discontinuities in the valence and conduction band of Sc2O3/GaN system. Sc2O3 films were deposited on GaN using radio frequency sputtering. The valence band offset of Sc2O3/GaN was deterimened to be 0.76±0.1 eV using Kraut's method. The Sc2O3band gap of 6.03± 0.25 eV has been measured using O 1s energy loss spectroscopy. The electron affinity measurements of GaN and Sc2O3 using XPS secondary electron cut-off spectra provide additional degree of accuracy to derived band line-up for Sc2O3/GaN interface. The band alignment results are compared with literature values of bandoffsets determined experimentally and theoretically for differently grown Sc2O3films on GaN.

Heat-Annealed Zinc Oxide on Flexible Carbon Nanotube Paper and Exposed to Gradient Light to Enhance Its Photoelectric Response.

Buckypaper (BP), a flexible and porous material, exhibits photovoltaic properties when exposed to light. In this study, we employed radio frequency (RF) sputtering of zinc oxide (ZnO) followed by rapid thermal annealing to enhance the photovoltaic response of BP. We investigated the impact of various sputtering parameters, such as the gas flow ratio of argon to oxygen and deposition time, on the morphology, composition, resistivity, and photovoltaic characteristics of ZnO-modified BP. Additionally, the photovoltaic performance of the samples under different illumination modes and wavelengths was compared. It was found that optimal sputtering conditions-argon to oxygen flow ratio of 1:2, deposition time of 20 min, and power of 100 watts-resulted in a ZnO film thickness of approximately 45 nanometers. After annealing at 400 °C for 10 min, the ZnO-modified BP demonstrated a significant increase in photocurrent and photovoltage, along with a reduction in resistivity, compared to unmodified BP. Moreover, under gradient illumination, the ZnO-modified BP exhibited a photovoltage enhancement of 14.70-fold and a photocurrent increase of 13.86-fold, compared to uniform illumination. Under blue light, it showed a higher photovoltaic response than under other colors. The enhancement in photovoltaic response is attributed to the formation of a Schottky junction between ZnO and BP, an increased carrier concentration gradient, and an expanded light absorption spectrum. Our results validate that ZnO sputtering followed by annealing is an effective method for modifying BP for photovoltaic applications such as solar cells and photodetectors.

The impact of post-deposition annealing durations on the formation of Tb4O7 passivation layer on silicon substrate

In this study, we have effectively utilized radio frequency (RF) sputtering to sputter the Tb4O7 passivation layer on an n-type silicon (Si) substrate in an argon (Ar) ambient. Various characterization approaches were used to investigate the impact of varying annealing durations on structural, morphological, compositional, and optical properties. The grazing incidence X-ray diffraction (GIXRD) pattern confirmed that all investigated Tb4O7 passivation layers (as grown) and annealed at (15, 30, and 45 min) showed a crystalline structure, respectively. As observed, the sample annealed for 30 min attained the highest crystallinity, around 39.51 nm. Surface morphology analysis revealed different surface structures in response to different annealing durations when observed using the field emission scanning electron microscopy (FESEM) technique. Atomic force microscopy (AFM) was utilized to investigate the top surface of the examined samples, and a higher surface roughness of around 2.37 nm was obtained for the sample annealed for 30 min. The band gap energies (Eg) were estimated by applying the Kubelka-Munk (KM) approach for all the investigated samples, and the obtained values were within a range between (1.94–3.07 eV) earlier reported in the literature. Previous studies have shown that the Tb4O7 passivation layer deposited onto Si substrates using RF sputtering and then annealed for 5 min at 900 °C in an Ar atmosphere, resulted in the formation of a highly crystalline passivation layer. However, there is a lack of a clear explanation for the observation, and the authors mainly concentrated on the electrical properties of the Tb4O7 material. This inspired us to carry out this study to investigate the impact of various annealing durations on the formation of Tb4O7 passivation layers, focusing on their structure, composition, morphology, and optical properties.

Bandgap variation in semiconductor thin films of the solid solution (CdTe)1-x(In2Te3)x deposited by RF sputtering

(CdTe)1-x(In2Te3)x films, with 0.1 ≤ x ≤ 1, were deposited by radio frequency sputtering on glass substrates employing different targets, prepared for each composition. The x-ray diffractograms were consistent with substitutional In incorporation into the CdTe lattice up to a value of x = 0.2. For higher In contents, the films presented structural disorder without reaching full amorphous characteristics. For x = 1, corresponding to In2Te3, preferential growth was observed. The bandgap of the solid solution varied between 1.46 and 1.2 eV, reaching a maximum of 1.58 eV for x = 0.3. For both end binary compounds the random incorporation of a third chemical element produced a significant broadening of the Raman modes consistent with a reduction of the lifetime of the optical phonons. The electrical resistivity was dependent on the Cd concentration reaching a minimum for x = 0.8.

Characterization of NiOAg thin film applicated as photocatalyst for degradation of methylene blue dye waste in Yogyakarta textile factory

Thin films of NiOAg were grown onto glass substrates by radio frequency (RF) sputtering technique at 13.56 MHz RF with variation in oxygen pressure. The research was conducted on preparation and characterization of NiOAg thin films, applicated as a photocatalyst for the degradation of methylene blue. X-ray diffraction analysis showed stronger intensity (111) and (200) planes at peak 2θ of 37.66° and 43.23°. Energy dispersive x-ray analysis showed the following composition: Ni = 40.45%, Ag = 13.01%, and O = 46.53%. Based on UV–vis, it was found that the bandgap energy was 2.8, 3.1, and 3.2 eV for oxygen pressures of 0.05, 0.1, and 0.15 × 10−2 mbar, respectively. From the experiment on the degradation of methylene blue, which was taken from textile factory dye waste in Yogyakarta/Indonesia, the best value of degradation was obtained as 91.96%.

Investigation on thermoelectric properties of SnSe thin films as prepared by RF magnetron sputtering

In this work, we investigated the thermoelectric properties of SnSe (Tin Selenide) thin films onto SiO2/Si-wafer substrates as prepared by RF (radio frequency) magnetron sputtering technique. The sputtering conditions used base pressure below 5.5 10-4 Pa and working pressure at 0.93 Pa within the Ar atmosphere as a flow rate fixed 40 sccm. The RF sputtering power was applied at 80 W and sputtering time for 30 min. After thin film deposition, as-deposited thin films were annealed by the vacuum annealing method at 300-450 oC. The crystal structure, morphology and film thickness, and atomic composition of SnSe thin film were carried out by X-ray diffraction (XRD), the field emission scanning electron microscope (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques, respectively. The thermoelectric properties (electrical resistivity; ρ) and Seebeck coefficient; S) were measured by the ZEM-3 method to calculate the power factor (PF) value. The results showed that the as-deposited thin films had improved the crystallography of SnSe from amorphous to crystalline phases after thin films were annealed at a temperature range of 300-400 oC. At room temperature, the maximum power factor of 0.35 mW m˗1 K˗2 (ρ = 202 mΩ m and S = 165 μV K˗1) could be found to estimate the dimensionless Figure of Merit (ZT) values around 0.44 for annealing thin film sample at 400 oC.

Stability Enhancement in Copper-Doped Iron Oxide Resistive Random Access Memory via RF Co-Sputtering

In the study, the ITO/Cu-doped Fe2O3/ITO thin film RRAM is prepared using an RF sputtering system. The XRD pattern shows that the Cu:Fe2O3 thin film has a rhombohedral structure and does not display secondary or impurity phases for copper. Results revealed that the standard deviation and average voltage of Cu:Fe2O3 thin film are −1.98 and 0.92 V for Vset, respectively, while those for Vreset are 1.31 and 0.39 V, respectively. The resistive switching cycles and data retention test times of the Cu:Fe2O3 thin film device show that the on/off ratio is 39.4 and over 104 s. These results indicated that the Cu-doped Fe2O3 thin film can improve the performance of RRAM.

Effect of annealing temperature on the structure and dielectric characterization of ITO thin films on a boro-float substrate prepared by radio frequency sputtering

Effect of annealing temperature on the structure and dielectric characterization of ITO thin films on a boro-float substrate prepared by radio frequency sputtering

One-step sputtering of MoSSe metastable phase as thin film and predicted thermodynamic stability by computational methods

We present the fabrication of a MoS2−xSex thin film from a co-sputtering process using MoS2 and MoSe2 commercial targets with 99.9% purity. The sputtering of the MoS2 and MoSe2 was carried out using a straight and low-cost magnetron radio frequency sputtering recipe to achieve a MoS2−xSex phase with x = 1 and sharp interface formation as confirmed by Raman spectroscopy, time-of-flight secondary ion mass spectroscopy, and cross-sectional scanning electron microscopy. The sulfur and selenium atoms prefer to distribute randomly at the octahedral geometry of molybdenum inside the MoS2−xSex thin film, indicated by a blue shift in the A1g and E1g vibrational modes at 355 cm−1 and 255 cm−1, respectively. This work is complemented by computing the thermodynamic stability of a MoS2−xSex phase whereby density functional theory up to a maximum selenium concentration of 33.33 at.% in both a Janus-like and random distribution. Although the Janus-like and the random structures are in the same metastable state, the Janus-like structure is hindered by an energy barrier below selenium concentrations of 8 at.%. This research highlights the potential of transition metal dichalcogenides in mixed phases and the need for further exploration employing low-energy, large-scale methods to improve the materials’ fabrication and target latent applications of such structures.

Barium titanate write-once read-many times resistive memory with an ultra-high on/off current ratio of 108

Write-once read-many times (WORM) resistive memories fabricated using perovskite barium titanate (BaTiO3, BTO) resistive switching (RS) layer are demonstrated in this study. The BTO RS layers with thicknesses of 3.2–8.5 nm are fabricated by radio frequency sputtering at room temperature. Annealing processes at 400–600 °C are used to modify the oxygen vacancy content in the BTO layer and thereby control the OFF-state current of an Al/BTO/n+-Si WORM device. The ION/IOFF ratio increases with increasing annealing temperature until 500 °C. A negative effect is observed when the temperature further rises to 600 °C. The optimal Al/BTO/n+-Si device shows an ultra-high ION/IOFF ratio of 108 and a low coefficient of variation of 6% for set voltages. The writing speed is 80 ns and the power consumption is 400 pJ. In addition, retention and stress tests are performed to confirm high data storage reliability of the device. Mechanisms for voltage-polarity independent writing process and the related energy band diagrams are explored.

Dispersion properties of (La0.06Ga0.94)2O3:Eu thin films

The dispersion of the refractive index of (La0.06Ga0.94)2O3:Eu thin films obtained by radio-frequency ion-plasma sputtering has been studied. It was found that the films have a polycrystalline structure corresponding to the monoclinic structure of β- Ga2O3. It is shown that the freshly deposited films are characterised by an abnormal dispersion, and after annealing in argon, a normal dispersion of the refractive index is observed. It was found that at normal dispersion, the spectral dependence of the refractive index in the visible region of the spectrum is mainly determined by electronic transitions from the 2p-state oxygen band, which form the upper filled level of the valence band to the bottom of the conduction band formed by hybridised 2p-states of oxygen and 4s-states of gallium. Two single-oscillator approximation models were analysed and compared for the films annealed in argon, and the approximation parameters, dispersion energy, degree of chemical bond ionicity, coordination number, and static refractive index were determined.

Highly oriented crystalline si on epitaxial Gd2O3/Si(111) substrate using low-cost Radio Frequency sputtering for Silicon on Insulator application

Silicon-on-Insulator (SOI) technology has been the center of attraction with the advancement in Radio Frequency (RF) technology and the advent of Internet-of-Things due to its low-power operation with reduced parasitic and short-channel effects. However, the state-of-the-art smart-cut method used for the SOI wafer is costly. Alternatively, the notion of using the Si channel layer on epitaxial rare-earth oxide has been proposed. In literature, the existing techniques used to achieve the same, such as Molecular beam Epitaxy or reduced-pressure chemical vapor deposition technique, are either costly or non-high-volume manufacturable. In this context, we propose a method to fabricate the highly oriented crystalline Si(111) channel layer (Top-Si) on an epitaxial Gd2O3/Si(111) virtual substrate (SOXI) utilizing the solid phase epitaxy using the high-volume manufacturing friendly (HVM), low-cost RF magnetron sputtering technique. First, we have shown the multicrystalline Si and epitaxial Gd2O3 layer grown on Si(111) substrate, as confirmed using high-resolution X-ray diffraction (HRXRD) and Transmission Electron Microscopy (TEM). Second, we investigated the impact of rapid thermal annealing at 850 °C on the heterostructure using HRXRD and TEM. It is observed that the high-temperature annealing transforms the Top-Si layer into the highly oriented crystalline Si(111) layer by fusing smaller grains towards larger grains. Hence, we demonstrate a low-cost, HVM-friendly technique for the fabrication of SOXI wafers.

Nanostructured TiO2 thin films sputtered at room temperature as electron transport layer for flexible perovskite solar cell applications: Impact of varying RF power

This work examines the adoption of radio frequency (RF) sputtering at power ranging from 100 to 300 W to deposit nanostructured titanium dioxide (TiO2) thin films on indium tin oxide (ITO)-coated polyethylene terephthalate (PET) flexible substrate (ITO/PET) at room temperature. At higher RF power, X-ray diffraction (XRD) results exhibited evolution from amorphous into crystalline anatase with preferred (101) orientation and the films revealed spherical-like nanostructures with increasing grain size from 15.71 to 21.57 nm. Films transparency decreased from 79% to 70%. Estimated energy gap decreased from 3.57 to 3.36 eV, while refractive index increased from 2.19 to 2.25, denoting a red shift in the films. The thin film deposited at 300 W exhibited high conductivity and mobility of 19.65 × 10−5 Ω−1 cm−1 and 0.30 cm2/Vs, respectively. The film demonstrated its capability as an electron transport layer for flexible perovskite solar cells.

Nanocomposite thin films containing Pt nanoparticles dispersed in an α-Fe2O3 matrix by RF sputtering

The preparation of nanocomposite thin films that phase-separate Pt and α-Fe2O3 was investigated. These films were prepared on water-cooled glass substrates by radio frequency sputtering in an Ar atmosphere. X-ray diffraction patterns reveal that iron oxide forms Fe3O4 in the as-deposited state and undergoes a phase transition to α-Fe2O3 after heat treatment in the air. Pt is phase-separated from iron oxides in the as-deposited state and during heat treatment in the air, with a crystallite size of less than 2 nm in the as-deposited state, which varies between 2 and 15 nm after heat treatment in the air, estimated from the x-ray diffraction peaks. High-resolution transmission electron microscopy of the sample after heat treatment in the air reveals that spherical particles with a relatively uniform size are dispersed, which are assigned to Pt from fast Fourier transform analysis, while the surrounding area is assigned to α-Fe2O3. Thus, the thin film forms a nanocomposite thin film in which Pt nanoparticles are dispersed in α-Fe2O3.

Enhancement of the thermoelectric performance of (BiSb)2Te3 films by single target sputtering

In this study, (BiSb)2Te3 thin films were deposited onto glass substrates at a temperature of 300 °C, utilizing radio frequency (RF) sputtering across a range of growth conditions. The primary focus of this investigation was to analyzse the effects of varying RF power, chamber gas pressure, and annealing temperature on the thermoelectric properties of the films, deposited by an exclusively-made single target.Notably, it was observed that increasing the annealing temperature significantly boosted both the deposition rate and grain size. Through carefully optimizsing growth conditions and subsequent annealing procedures, it was discerned that thin films cultivated at higher RF power levels exhibited markedly improved electrical conductivity, attributed to a discernible rise in carrier concentration. Furthermore, films generated under the RF power of 37.5 W showed a noteworthy augmentation in the Seebeck coefficient, recording approximately 147 μV/K. This enhancement in Seebeck coefficient correlated with the attainment of the highest power factor, reaching an impressive 220.57 μW/mK2.

Investigation of Resistive Switching of Insulating Hafnium Nitride for Nonvolatile Memory Applications

In this study, nitrogen-rich Hafnium Nitride (HfN) featuring insulating properties was investigated for achieving resistive switching, crucial for the functionality of resistive random-access memory (ReRAM) devices. Devices were fabricated with a 15-nm HfN resistive switching layer using a Radio Frequency (RF) sputtering system. The fabricated devices successfully exhibited a bipolar switching characteristic with a high On/Off ratio (up to 104). An interesting 2-step behavior was also observed during the formation of the conduction filament which was suspected to be tied to the migration of the nitrogen ions. This is the first attempt at using HfN as the resistive switching material for nonvolatile memory applications.

Ga, Mg, F ternary-doped ZnO-based transparent conductive film prepared by radio-frequency sputtering with high transmittance

Ga/Mg/F ternary-doped ZnO transparent conductive films were prepared by radio-frequency (RF) magnetron sputtering. The influences of RF power, work pressure, and substrate temperature on the films are studied. The electrical and optical properties, structure and surface morphology of the films are discussed. Compared to other doped systems, the deposited films in this work exhibit excellent electrical and optical properties (ρ: 4.79 × 10−4 Ω·cm, T: 91.4%), which is comparable to commercial ITO. Besides, the films with the best performance show good stability. Our work has verified the advantages of triple-doped ZnO transparent conductive films, which is meaningful for future research and applications.

Sputter grown CuO thin films: Impact of growth pressure and annealing temperature on their microstructural architectures

High-quality copper oxide (CuO) thin films were deposited on the silicon (Si) substrate at the room temperature using the physical vapour deposition (PVD) technique named radio frequency (RF) sputtering. The copper-oxide thin-films were single crystalline and of uniform thickness. Subsequently, the influence of growth pressure (low gas pressure - 3 mTorr and high gas pressure - 100 mTorr) and post growth annealing at different temperatures (300 °C to 700 °C) were investigated to understand the microstructural and morphological changes of the thin film. With the influence of growth pressure and post thermal annealing temperature, significant changes in crystallinity, surface roughness, and surface oxidation rate of the CuO thin film were detected, which were adequately analyzed via several characterization techniques. X-ray diffraction (XRD) patterns revealed the phase formation with good crystallinity of the film, which is substantiated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) characterization. Atomic force microscopy (AFM) images disclosed that the surface roughness of the film and grain size. By gaining insights into the structural and surface properties of CuO/Si thin films, this research presents new prospects for tuning of CuO phases, structures, and compositions for multifunctional applications.

Multifunctional capabilities of radio frequency sputtered GO-TiO2 nanocomposite ultra-thin films

The work presents the successful synthesis of ultra-thin Graphene Oxide-Titanium (GOT) nanocomposite films using radio frequency sputtering. It was employed a thorough characterization encompassing structural, optical, and morphological aspects, with a focus on practical applications such as photocatalysis, anti-corrosion, anti-reflective properties, and superhydrophobicity (PAAS). Notably, the GOT film exhibited outstanding photocatalytic efficiency, achieving a significant 96% photodegradation rate, and offering promise for environmental remediation. Additionally, it demonstrated excellent visible-light-induced photocatalytic disinfection against E. coli K12 contamination. Furthermore, the film displayed notable corrosion resistance, a fivefold improvement over pristine surfaces, and excellent anti-reflective properties with 98% transmittance in the visible light range, making it suitable for advanced optical devices with multifunctional benefits.

Indium-gallium-zinc oxide thin-film preparation via single-step radio frequency sputter deposition using mixed-oxide powder targets

Indium-gallium-zinc oxide thin-film preparation via single-step radio frequency sputter deposition using mixed-oxide powder targets