Dual Ion Beam Sputtering Research Articles

Effect of annealing on ion-beam-sputtered hafnium oxide thin films properties

HfO2 films are high laser damage-threshold and low-absorption thin-films that can be utilized for a broad range of optoelectronic and optical applications. In this study, HfO2 thin films were prepared via dual ion beam sputtering followed by annealing in the atmosphere at temperatures ranging from 200 to 700 °C. The optical properties, microstructure, film stress, and absorption loss of the HfO2 films at various annealing temperatures were then systematically characterized. The results revealed that the properties of the films were improved after annealing at temperatures below 500 °C. Specifically, at an optimal annealing temperature of 400 °C, the residual stress of the films was minimized close to zero and the absorption loss was as low as 1 ppm. However, at annealing temperatures reaching 600 °C, the films began to crystallize, leading to the deterioration of their optical properties. Optimizing the process parameters for HfO2 thin film deposition is crucial for developing the next generation of high-performance laser optics.

Tailoring the Lithium Concentration in Thin Lithium Ferrite Films Obtained by Dual Ion Beam Sputtering.

Thin films of lithium spinel ferrite, LiFe5O8, have attracted much scientific attention because of their potential for efficient excitation, the manipulation and propagation of spin currents due to their insulating character, high-saturation magnetization, and Curie temperature, as well as their ultra-low damping value. In addition, LiFe5O8 is currently one of the most interesting materials in terms of developing spintronic devices based on the ionic control of magnetism, for which it is crucial to control the lithium's atomic content. In this work, we demonstrate that dual ion beam sputtering is a suitable technique to tailor the lithium content of thin films of lithium ferrite (LFO) by using the different energies of the assisting ion beam formed by Ar+ and O2+ ions during the growth process. Without assistance, a disordered rock-salt LFO phase (i.e., LiFeO2) can be identified as the principal phase. Under beam assistance, highly out-of-plane-oriented (111) thin LFO films have been obtained on (0001) Al2O3 substrates with a disordered spinel structure as the main phase and with lithium concentrations higher and lower than the stoichiometric spinel phase, i.e., LiFe5O8. After post-annealing of the films at 1025 K, a highly ordered ferromagnetic spinel LFO phase was found when the lithium concentration was higher than the stoichiometric value. With lower lithium contents, the antiferromagnetic hematite (α-Fe2O3) phase emerged and coexisted in films with the ferromagnetic LixFe6-xO8. These results open up the possibility of controlling the properties of thin lithium ferrite-based films to enable their use in advanced spintronic devices.

Effect of rapid thermal annealing on DC performance of Mg0.30Zn0.70O/Cd0.15Zn0.85O MOSHFET

This study focuses on a cost-effective method for fabrication of a metal oxide semiconductor-heterostructure field effect transistor (MOSHFET) based on MgZnO/CdZnO (MCO) using dual ion beam sputtering (DIBS), in contrast to the more expensive epitaxial growth system. The MOSHFETs developed in this research exhibit notable characteristics, such as a substantial two-dimensional electron gas (2DEG) transconductance (∼2.6 mS), a high ION/IOFF response ratio in the order of 108, and minimal gate leakage current. Furthermore, we explore the impact of rapid thermal annealing (RTA) on the drain current at various temperatures (600 °C and 800 °C). The results indicate a fourfold improvement in drain current compared to unannealed conditions, primarily attributed to reduced contact resistance and no degradation in term of MgZnO/CdZnO structure. Additionally, an analysis of post-RTA treatment under a nitrogen (N2) atmosphere on gate leakage current is presented. The investigation spans temperatures ranging from 400 °C to 800 °C, revealing that above 600 °C (gate leakage at 400 °C–600 °C is around ∼10−9 A), gate leakage in HFET is augmented by one order of magnitude (∼10−8 A) due to a phase change in the dielectric. These findings underscore the feasibility of DIBS-grown MCO MOSHFETs as an economical solution for the mass production of switching devices and sensors.

Hydrogen and deuterium permeation on niobium coated by ultrathin Pd25%Ag for tritium recovery in EU DEMO

The hydrogen and deuterium permeation in pure niobium and niobium Pd25%Ag coated are measured using a permeation gas phase technique. The coating with different thicknesses, are deposited on Nb by a Dual Ion Beam Sputtering Technique. Measurements are performed in the temperature range of 573–723 K with hydrogen or deuterium driving pressures in the range 1.0⋅102−1.2⋅104 Pa (1 to 120 mbar). This work highlights how PdAg-coated Nb membranes can be fruitfully rated in the design of tritium recovery plants where niobium pipes for lead lithium are under consideration. Ultra-thin PdAg coatings mitigate the effects of the oxide in reducing of hydrogen permeation through the niobium walls.

Effect of oxygen flow on the optical properties of hafnium oxide thin films by dual-ion beam sputtering deposition

Effect of oxygen flow on the optical properties of hafnium oxide thin films by dual-ion beam sputtering deposition

Analytical study of MgZnO/ZnO heterostructure field effect transistor for power switching

AbstractWe investigate the power switching mechanism to evaluate the power loss (PD) and efficiency (ɳ) in MgZnO/ZnO (MZO)‐based power heterostructure field effect transistor (HFET), and physical parameters responsible for PD in molecular beam epitaxy (MBE) and dual ion beam sputtering (DIBS) grown MZO HEFT and compare the performance with the group III‐nitride HFETs. This work extensively probes all physical parameters such as two‐dimensional electron gas (2DEG) density, mobility, switching frequency, and device dimension to study their impact on power switching in MZO HFET. Results suggest that the MBE and DIBS grown MZO HFET with the gate width (WG) of ~205 and ~280 mm at drain current coefficient (k) of 11 and 15, respectively, will achieve 99.96% and 99.95% of ɳ and 9.03 and 12.53 W of PD, respectively. Moreover, WG value for DIBS‐grown MZO HFET is observed to further reduce in the range of 112–168 mm by using a Y2O3 spacer layer leading to the maximum ɳ in the range of 99.98%–99.97% and the minimum PD in the range of 5–7 W. This work is significant for the development of cost‐effective HFETs for power switching applications.

Influence of Deposition Conditions on Properties of Ta2O5 Films Deposited by Ion Beam Sputtering Coating Technique

Investigation of deposition conditions on structural, optical, and surface properties of Tantalum pentaoxide (Ta2O5) thin films deposited without assisted ion beam (Single Ion Beam Sputtering technique, SIBS) and with assisted ion beam (Dual Ion Beam Sputtering technique, DIBS) is carried out. For both SIBS and DIBS identical coating process conditions are applied for deposition of Ta2O5 films onto highly polished and clean, fused silica substrates. Estimation of deposition rates of Ta2O5 with identical beam energies and coating chamber conditions is done. Benefits of O2 assist beam on the behavior of structural, optical, and surface properties of thin films deposited are studied. The films are characterized with an ellipsometer, optical profilometer, XRD, FE-SEM, and XPS techniques to bring the merits films coated of Ion Beam Sputtering deposition with and without assist Ion Beam. Configuration of ion sources and targets in the coating chamber for DIBS of oxide targets is carried out in the present work are useful for multi-layer coatings for high reflectivity mirrors for electro-optical instruments like ring laser-based rotation sensors.

High-dispersive mirror for pulse stretcher in femtosecond fiber laser amplification system

We present a high-dispersive multilayer mirror for pulse stretching in a femtosecond fiber laser amplification system. The designed mirror contains 54 layers with a total physical thickness of 7.3 μm, which can provide a positive group delay dispersion (GDD) of 600 fs2 and a high reflectance over 99.9% from 1010 to 1070 nm. The samples were prepared by dual ion beam sputtering. The measured transmittance matches well with the theoretical result. The GDD characteristics of samples were tested by home-made white light interferometer. The measured GDD is higher than the design results, an average GDD of +722 fs2 from 1010 nm to 1070 nm. The mirrors were employed in a Yb-doped large-mode-area photonic crystal fiber amplification system. An input pulse compressed by the gratings with autocorrelation function of 83 fs is obtained with a stretched FWHM of 1.29 ps after 28 bounces between the dispersive mirrors. The results show that the multilayer dispersive mirror could be an effective and promising technique for pulse stretching in femtosecond amplification systems.

Hydrogen and Deuterium Permeation Measure6 Ments on Niobium Coated by Pd25%Ag Dual Ion Beam Sputtering Ultra Thin Films

Hydrogen and Deuterium Permeation Measure6 Ments on Niobium Coated by Pd25%Ag Dual Ion Beam Sputtering Ultra Thin Films

Precision of Silicon Oxynitride Refractive-Index Profile Retrieval Using Optical Characterization

Layers with gradient refractive-index profile are an attractive alternative to conventional homogeneous stack coatings. However, the optical characterization and monitoring of the graded refractive-index profile is a complex issue, which has been typically solved by using a simplified model of mixed materials. Although this approach provides a solution to the problem, the precision, which can be expected from optical characterization of the refractive index gradient, remains unclear. In this work, we study optical characterization of SiO_xN_y layers deposited via reactive dual ion beam sputtering. To characterize the deposited layers, we use several methods including reflectance, and transmittance spectra at a broad range of incident angles, together with spectral ellipsometry. All the data were simultaneously fitted with a general profile of refractive index. The expected profile used in our fit was based on characterization of SiO_xN_y layers with a varying stoichiometry. By altering of the profile, we discussed sensitivity of such alternation on fit quality and we studied ambiguity of merit-function minimization. We demonstrate that while the scanning of particular parameters of the profile can be seemingly very precise, we obtain a very good agreement between the experimental data and model for a broad range of gradient shapes, where the refractive-index value on major part of the profile can differ as much as 0.02 from the mean value.

Plasmonic characteristics of niobium nitride thin films modulated by assisting ions

NbNx films were prepared by dual ion beam sputter deposition. Different assisting ion current density Ja and assisting ion energy Ea were used to modulate the structural and dielectric properties of the films. All the films are of fcc structure, and assisting ions can improve their crystallinity. Higher Ja and Ea can reduce the screened plasma frequency and the optical energy loss of the films. Importantly, with appropriate experimental parameters, the NbNx films exhibit tunable dual epsilon-near-zero behavior. The assisting ions cause the variation of the carrier concentration in the films, and then modulate the dielectric properties of the films. Our results show that NbNx films can be applied in different fields by tailoring their plasmonic properties by assisting ions.

Laser-induced layers peeling of sputtering coatings at 1064\xa0nm wavelength

Large-scale layers peeling after the laser irradiation of dual ion beam sputtering coatings is discovered and a model is established to explain it. The laser damage morphologies relate to the laser fluence, showing thermomechanical coupling failure at low energy and coating layers separation at high energy. High-pressure gradients appear in the interaction between laser and coatings, resulting in large-scale layer separation. A two-step laser damage model including defect-induced damage process and ionized air wave damage process is proposed to explain the two phenomena at different energy. At relatively high energies (higher than 20 J/cm2), ionization of the air can be initiated, leading to a peeling off effect. The peeling effect is related to the thermomechanical properties of the coating materials.

Optimization of dielectric films with dual ion beam sputtering deposition for high reflectivity mirrors

Abstract Dielectric thin films deposited by Ion beam sputtering deposition technique have superior properties of good adhesion and customized optical properties suits to many optical filters for electro-optical sensors. In the present work Tantalum Pentoxide (Tantala) and Silicon Dioxide (Silica) thin films are fabricated with dual ion beam sputtering deposition process. The process parameters are optimized to achieve better surface quality and optical constants. The effect of the assist ion beam on the film properties is evaluated. Multi-layer dielectric mirrors realized with 1000 ppm loss on optimization of single-layer Silica and Tantala films, which will be suitable for linear and Ring Laser Resonators. The films are characterized by ellipsometer, non-contact optical profiler, spectrophotometer, and cavity ring-down loss meter. The multi-layer mirrors were subjected to vacuum annealing and the effect of annealing on film reflectivity is evaluated. The work emphasizes the process requirements of Ion Beam Sputtering to realize high reflectivity and low loss mirrors of Tantala and Silica films from Ta2O5 and SiO2 target materials. It gives an insight into the process deficiencies in matching the theoretical design of multi-layer mirrors from the practical aspects of coatings.

Analytical Study of Sputter-Grown ZnO-Based p-i-n Homojunction UV Photodetector

Here, an analytical model for dark current and photoresponsivity of ZnO-based thin film homojunction p-i-n ultraviolet (UV) photodetector (PD) is presented. This work provides a succinct insight about the effect of reverse bias voltage, thickness variation on the responsivity and dark current of homojunction p-i-n UV PDs based on ZnO-based layers grown by dual ion beam sputtering. The results affirm that with the increase in the thickness of top ${p}$ -type layer from 50 to 200 nm, the peak responsivity reduces by 41.9%, while with the increase in the ${i}$ -ZnO layer thickness from 20 to 80 nm responsivity increases by 108.6%. The obtained outcome, vindicates that by incorporating Sb:ZnO in lieu of Li-N:ZnO as p- type layer, a rise of ~7.6-fold and reduction of ~2.1-fold in the peak responsivity at 0 V and dark current at -15 V, respectively, at room temperature are attained. Hence, the developed model is indispensable for assessing the design optimization of high-performance ZnO-based p-i-n homojunction UV PDs.

Investigation of DIBS-Deposited CdZnO/ZnO-Based Multiple Quantum Well for Large-Area Photovoltaic Application

Multiple quantum wells (MQWs) of CdZnO/ZnO are realized, for the first time, by dual ion beam sputtering (DIBS) system at different deposition conditions in terms of ion beam power, substrate temperature, and time cessation between deposition of successive layers. The effects of DIBS deposition conditions are analyzed by secondary ion mass spectroscopy (SIMS) and high-resolution transmission electron microscopy (HRTEM) and discussed systematically. The SIMS analysis has been used for depth profiling of CdZnO/ZnO-based MQWs structure. The deposition of CdZnO/ZnO-based MQW structure performed at 100 °C with time cessation of 30 min between successive layer growth and ion beam power of 14 W has displayed the best results in terms of distinct well and barrier layers formation. This work also includes an analytical study of CdZnO/ZnO-based MQW solar cell (MQWSC), in which a study is performed for solar irradiance dependence of performance parameters to explore the potential use of CdZnO/ZnO-based MQWSC for concentrator solar cell (SC). The short-circuit current density increases from 0.12 to 57.98 mA/cm2, the open-circuit voltage rises from 2.60 to 2.77 V, and the photon conversion efficiency is from 2.85% to 3.04%, as solar irradiance increases from 0.1 to 50 suns. The results show that the performance of SCs can be improved by using concentrators and also explore the possibility of efficiently absorbing short-wavelength photons.

Drain Current Optimization in DIBS-Grown MgZnO/CdZnO HFET

This article reports the fabrication of a dual-ion beam sputtering (DIBS)-grown MgZnO/CdZnO (MCO)-based gateless heterostructure field-effect transistor (HFET). In addition, this article presents that by introducing a 30-nm yttria spacer layer, the crystallinity of the CdZnO buffer layer can be enhanced and the interface roughness at the heterojunction of the MCO heterostructure can be reduced. Furthermore, the source and drain metal contacts were optimized for the least specific contact resistivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\rho }_{c}$ </tex-math></inline-formula> ) yielding metal combination and annealing conditions. The results suggest that the introduction of the yttria spacer layer improves the overall conductance [product of sheet carrier density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${n}_{s}$ </tex-math></inline-formula> ) and electron mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\mu }$ </tex-math></inline-formula> )] of MCO up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.5\times 10^{15}\,\,\text{V}^{-1}\text{s}^{-1}$ </tex-math></inline-formula> compared to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9\times 10^{14}\,\,\text{V}^{-1}\text{s}^{-1}$ </tex-math></inline-formula> in the non-yttria spacer-based MCO. In addition, the drain current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{d}$ </tex-math></inline-formula> )–drain voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{d}$ </tex-math></inline-formula> ) characteristic of the as-developed yttria spacer-based MCO HFET shows a high drain current value (~400 mA/mm). These results establish the DIBS-grown MCO heterostructure as a viable option for low-cost HFETs necessary for the fabrication of large-scale HFET-based power and sensor devices.

Confinement induced variation of composition ratio in amorphous silicon carbide thin films and effect in optical properties

Thickness dependency in the composition ratio of amorphous silicon carbide (SiC) thin films and its effect in optical properties are reported. SiC thin films (~ 20 nm to 450 nm range) with very low surface roughness (<1 nm) were grown using dual ion beam sputtered (DIBS) deposition technique. Thinnest SiC film (~ 20 nm) exhibited higher atomic concentration of silicon (Si) relative to that of carbon (C), with C:Si = 0.7, whereas carbon to silicon atomic concentration ratio (C:Si) was found to increase with increasing SiC film thickness, and reached 1:1 ratio for thickest SiC film (about 450 nm), using X-ray photoelectron spectroscopy (XPS) analysis. XPS was employed to investigate the chemical composition and bonding configuration of SiC. A thickness dependent distinct change in band gap as a consequence of variation in the composition ratio in SiC films, is reported, which indicates potential control on electrical and optical properties of the system.

Performance Analysis of p-LPZO/n-GZO and p-SZO/n-GZO Homojunction UV Photodetectors

Abstract A comprehensive analytical model for the dark current and photoresponsivity of ZnO thin film based homojunction ultraviolet (UV) photodetector (PD) is proposed in this study. The detailed insight about the effects of different acceptor doping materials in the illuminated surface layer is presented in this work. The recombination velocity of the carriers and the effect of applied reverse bias, specifically on the responsivity of p-n homojunction based UV PD are elucidated. The impact of two different types of dual ion beam sputtering (DIBS)-grown acceptor-doped ZnO (Sb:ZnO and Li–P:ZnO) materials on the responsivity is also discussed. The investigation results reveal that an increase in applied reverse bias results in higher responsivity due to depletion region increase leading to higher charge carrier photogeneration. Further, on comparing the results with the experimentally reported ZnO-based homojunction UV PDs, it is found that, by incorporating Sb:ZnO as p-type layer, dark current and responsivity values are improved by ~38 and ~63.7%, respectively. Hence, the developed model is significant for the design optimization of high-performance ZnO thin film-based UV homojunction PDs.

Analytical Performance Analysis of CdZnO/ZnO-Based Multiple Quantum Well Solar Cell

This article presents analytical and simulation evaluation of multiple quantum well solar cells (MQWSC) with CdZnO/ZnO as the intrinsic layer, Sb-doped ZnO (SZO) as a p-type layer, and Ga-doped ZnO (GZO) as an n-type layer of the p-i-n solar cell (SC). The material parameters used in this article are obtained from the experimental reports on the properties of ZnO and CdZnO thin films grown by dual-ion-beam sputtering (DIBS). The American Society for Testing and Materials (ASTM) standards data sheets have been utilized for attaining photon flux density instead of the blackbody radiation formula. The analytically obtained results show good agreement with the simulated results obtained by the ATLAS simulation tool. The variation of device performance parameters is examined for thermal stability. The results show that, for the proposed ZnO-based MQWSC, the open-circuit voltage ( ${V}_{{\text {oc}}}$ ) has a negative temperature coefficient (−2.63 mV/°C), and short-circuit current density ( ${J}_{{\text {sc}}}$ ) and conversion efficiency ( ${\eta }$ ) have positive temperature coefficients of $2.43\times 10^{{-{3}}} \,\,{\text {mA}/\text {cm}^{{{2}}}\cdot ^{\circ }}\text{C}$ and $2.91\times 10^{{-{3}}}$ %/°C, respectively. Further, the device performance has been explored for variation in the number of quantum wells. The results present that an increase in the number of quantum wells has a negative impact on the performance parameters of ZnO-based MQWSC.

The impact of nano-bubbles on the laser performance of hafnia films deposited by oxygen assisted ion beam sputtering method

Hafnia is a high refractive index material used in the manufacturing of dielectric coatings for next generation lasers. The formation of defects during deposition is the major barrier to realizing high laser-damage resistant coatings for future high energy density laser applications. Understanding the precursors responsible for laser-induced damage in hafnia is therefore critical. In this work, we investigate the mechanism of laser-induced damage in 90-nm thick hafnia films produced by an oxygen assisted dual ion beam sputtering (IBS) process. Under pulsed, nanosecond ultraviolet laser exposure (355 nm, 8 ns), the laser-induced damage onset is found to be strongly dependent on the amount of argon and excessive oxygen entrapped in the nanobubbles within the hafnia films. The presence of nanobubbles is revealed and confirmed by small angle X-ray scattering and scanning/transmission electron microscopy coupled with high-angle annular dark-field. The damage onset is stable initially but decreases as the energy of oxygen goes beyond 100 eV. The damage initiation is ascribed to a laser-induced plasma generation within the nanobubbles through multiphoton ionization. The results reveal that nanobubbles formed in the IBS produced coatings are a potent precursor. Although nanobubbles are commonly present in IBS films, their negative impact on laser damage resistance of hafnia films has not been previously recognized. Our findings provide a fundamental basis for the development of potential mitigation strategies required for the realization of laser damage resistant hafnia films.