RF Magnetron Sputtering Deposition Technique Research Articles

Investigation of crystalline and band alignment properties of NiO/GaN and Ni0.5Co0.5O/GaN heterojunctions using synchrotron radiation based techniques

Epitaxial layers of NiO and Ni0.5Co0.5O have been deposited on GaN templates using RF magnetron sputtering deposition technique. The epitaxial relationship in out-of-plane and in-plane directions for NiO and Ni0.5Co0.5O layers with respect to GaN is [111]NiO(Ni0.5Co0.5O)∥[0001]GaN and [1̅10]NiO(Ni0.5Co0.5O)∥[1̅21̅0]GaN, respectively. The epi-layers are found to have two triangular domain structures oriented along [111] direction with an in-plane rotation of 60° with respect to each other. Photoelectron spectroscopy (PES) has been used to determine the valence band offset (∆EV) and the band alignment at the heterojunctions (HJs). The ∆EV at NiO/GaN and Ni0.5Co0.5O/GaN HJs are 1.2 ± 0.2 eV and 1.8 ± 0.2 eV, respectively. The conduction band offsets (∆EC) have also been estimated using the determined values of optical band gap (NiO: Eg = ∼ 3.5 eV; Ni0.5Co0.5O: Eg = ∼ 3.3 eV) from optical transmission measurements. The values of ∆EC are found to be 1.5 ± 0.2 eV and 1.9 ± 0.2 eV at NiO/GaN and Ni0.5Co0.5O/GaN HJs, respectively. A type-II band alignment is observed at both the HJs. Higher values of valence band and conduction band offsets are observed at Ni0.5Co0.5O/GaN HJ in comparison to NiO/GaN. These experimentally determined values of band offsets can be used to design wide band gap HJ based devices like photodetectors, where higher values of band off-set at the Ni0.5Co0.5O/GaN HJ can be utilized to confine the carriers.

Transition regime from step-flow to step-bunching in the growth of epitaxial SrRuO3 on (001) SrTiO3

We present a study of the surface morphology of SrRuO3 thin films grown on TiO2 terminated (001) SrTiO3 substrates using an off-axis RF magnetron sputtering deposition technique. We investigated the step bunching formation and the evolution of the films by varying deposition parameters. The thin films were characterized using atomic force microscopy methods, allowing us to study the various growth regimes of SrRuO3 as a function of the growth parameters. We observe a strong influence of both the miscut angle and growth temperature on the evolution of the SrRuO3 surface morphology. In addition, a thickness dependence is present. Remarkably, the formation of a smooth, regular, and uniform “fish-skin” structure at the step-bunch transition is observed. The fish-skin morphology results from the merging of 2D flat islands predicted by previous models. The direct observation of surface evolution allows us to better understand the different growth regimes of SrRuO3 thin films.

Infrared metamaterial by RF magnetron sputtered ZnO/Al:ZnO multilayers

Hyperbolic metamaterials create artificial anisotropy using metallic wires suspended in dielectric media or alternating layers of a metal and dielectric (Type I or Type II). In this study we fabricated ZnO/Al:ZnO (AZO) multilayers by the RF magnetron sputtering deposition technique. Our fabricated multilayers satisfy the requirements for a type II hyperbolic metamaterial. The optical response of individual AZO and ZnO films, as well as the multilayered film were investigated via UV-vis-IR transmittance and spectroscopic ellipsometry. The optical response of the multilayered system is calculated using the nonlocal-corrected Effective Medium Approximation (EMA). The spectroscopic ellipsometry data of the multilayered system was modeled using a uniaxial material model and EMA model. Both theoretical and experimental studies validate the fabricated multilayers undergo a hyperbolic transition at a wavelength of 2.2 μm. To our knowledge this is the first AZO/ZnO type II hyperbolic metamaterial system fabricated by magnetron sputtering deposition method.

Residual stress effect on coupling electromechanical factor of epitaxial Barium Strontium Titanate (BST) thin films

Acoustoelastic (AE) effect of a mechanically pre-stressed layered piezoelectric structure of BST is investigated. Two samples of BST (Ba0.8Sr0.2TiO3) thin films were grown by rf-magnetron sputtering deposition techniques on a Pt(100)/MgO(100) and Pt(110)/MgO(110) substrates. The crystallographic orientation of BST thin films is analyzed by X-ray diffraction (XRD). A laser acoustic waves (LA-waves) technique is used to generate surface acoustic waves (SAW) propagating in both samples for epitaxial relationship examination. We perform an extended model to determine the residual stress and strain in BST films using the (XRD) X-ray diffraction measurement and the piezoelectric constitutive equations. Theoretical analysis of (SAW) propagation in a pre-stressed layered piezoelectric structure is achieved to discuss the effect of the measured residual stresses of BST films on the propagation behavior of Rayleigh waves and on the coupled electromechanical factor.

The effect of the thickness of tunneling layer on the memory properties of (Cu2O)0.5(Al2O3)0.5 high-k composite charge-trapping memory devices

The charge-trapping memory devices namely Pt/Al2O3/(Al2O[Formula: see text](Cu2O)[Formula: see text]/SiO2/[Formula: see text]-Si with 2, 3 and 4 nm SiO2 tunneling layers were fabricated by using RF magnetron sputtering and atomic layer deposition techniques. At an applied voltage of ±11 V, the memory windows in the C–V curves of the memory devices with 2, 3 and 4 nm SiO2 tunneling layers were about 4.18, 9.91 and 11.33 V, respectively. The anomaly in memory properties among the three memory devices was ascribed to the different back tunneling probabilities of trapped electrons in the charge-trapping dielectric (Al2O[Formula: see text](Cu2O)[Formula: see text] due to the different thicknesses of SiO2 tunneling layer.

Acoustoelastic effect of textured (Ba,Sr)TiO3 thin films under an initial mechanical stress

Acoustoelastic (AE) analysis of initial stresses plays an important role as a nondestructive tool in current engineering. Two textured BST (Ba0.65Sr0.35TiO3) thin films, with different substrate to target distance, were grown on Pt(111)/TiO2/SiO2/Si(001) substrate by rf-magnetron sputtering deposition techniques. A conventional “sin2 ψ” method to determine residual stress and strain in BST films by X-ray diffraction is applied. A laser acoustic waves (LA-waves) technique is used to generate surface acoustic waves (SAW) propagating in both samples. Young's modulus E and Poisson ratio ν of BST films in different propagation directions are derived from the measured dispersion curves. Estimation of effective second-order elastic constants of BST thin films in stressed states is served in SAW study. This paper presents an original investigation of AE effect in prestressed Ba0.65Sr0.35TiO3 films, where the effective elastic constants and the effect of texture on second and third order elastic tensor are considered and used. The propagation behavior of Rayleigh and Love waves in BST thin films under residual stress is explored and discussed. The guiding velocities affected by residual stresses, reveal some shifts which do not exceed four percent mainly in the low frequency range.

Effect of 750 keV Argon ion irradiation on nc ZnO[sbnd]SiOx thin films

Nanocomposite (nc) ZnOSiOx thin films were grown using rf magnetron sputter deposition technique and post-deposition annealing at 750°C. These films were irradiated with 750keV Argon ions at fluences in the range from 1×1015 to 1×1017ions/cm2, using Low Energy Ion Beam Facility (LEIBF) at IUAC. X-ray diffraction (XRD) patterns of the as-deposited irradiated films show decrease in intensity of ZnO peaks relative to pristine film. Fourier transform infrared (FT-IR) spectroscopy measurements of the as-deposited irradiated films indicate the breakage of ZnO, ZnOSi and SiOSi bonds in them, which is substantiated by FT-IR measurements of 750°C annealed films that were irradiated at a fluence of 1016ions/cm2. Photoluminescence (PL) measurements show drastic decrease of visible PL emission from as-deposited irradiated films. Current−Voltage (I–V) measurements show decrease in surface resistance of irradiated films by three orders of magnitude. The results suggest that 750keV argon ion irradiation of nc ZnO−SiOx films has resulted in the formation of non-radiative defects in ZnO phase and damage in SiOx, and amorphization in Zinc silicate phase. These results are explained on the basis of the dominant energy loss mechanism of low energy ions in materials.

Integration of CdTe–ZnO nanocomposite thin films into photovoltaic devices

Quantum-scale semiconductor nanoparticles offer unique, size-dependent optical and electronic properties of import to enhanced photovoltaic conversion efficiency. The present study addresses the integration of CdTe nanocrystal assemblies, used as spectral sensitizers, into thin film photovoltaic heterojunction devices. CdTe nanocrystals, embedded in an electrically active ZnO matrix, form a nanocomposite offering control of both spectral absorption and photocarrier transport behavior through the manipulation of nanophase assembly (ensemble effects). A sequential RF-magnetron sputter deposition technique affords the control of semiconductor nanophase spatial distribution relative to the heterojunction plane in a hybrid, ZnO–P3HT test structure. Energy conversion performance, (J–V and quantum efficiency (QE) response) was examined as a function of the location of the CdTe nanophase absorber region using both 1-D device modeling (SCAPS) and the experimental examination of analogous P3HT–ZnO based hybrid thin film devices. Enhancement in simulated QE over a spectral range consistent with the absorption region of the CdTe nanophase (i.e. 400–475nm) is confirmed in the experimentally determined external quantum efficiency (EQE). Moreover, a trend of decreasing efficiency in this spectral range with increasing separation between the CdTe nanophase region and the heterojunction plane is observed. The results are interpreted in terms of carrier scattering/recombination length mitigating the successful transport of photocarriers across the junction.

The roles of the dielectric constant and the relative level of conduction band of high-k composite with Si in improving the memory performance of charge-trapping memory devices

The memory structures Pt/Al2O3/(TiO2)x(Al2O3)1−x/Al2O3/p-Si(nominal composition x = 0.05, 0.50 and 0.70) were fabricated by using rf-magnetron sputtering and atomic layer deposition techniques, in which the dielectric constant and the bottom of the conduction band of the high-k composite (TiO2)x(Al2O3)1−x were adjusted by controlling the partial composition of Al2O3. With the largest dielectric constant and the lowest deviation from the bottom of the conduction band of Si, (TiO2)0.7(Al2O3)0.3 memory devices show the largest memory window of 7.54 V, the fast programming/erasing speed and excellent endurance and retention characteristics, which were ascribed to the special structural design, proper combination of dielectric constant and band alignment in the high-k composite (TiO2)0.7(Al2O3)0.3.

In-situ x-ray diffraction study of the growth of highly strained epitaxial BaTiO3 thin films

In-situ synchrotron x-ray diffraction was performed during the growth of BaTiO3 thin films on SrTiO3 substrates using both off-axis RF magnetron sputtering and pulsed laser deposition techniques. It was found that the films were ferroelectric during the growth process, and the presence or absence of a bottom SrRuO3 electrode played an important role in the growth of the films. Pulsed laser deposited films on SrRuO3 displayed an anomalously high tetragonality and unit volume, which may be connected to the previously predicted negative pressure phase of BaTiO3.

Irradiation effects of 6 MeV electron on electrical properties of Al/Al2O3/n-Si MOS capacitors

The influence of 6MeV electron irradiation on the electrical properties of Al/Al2O3/n-Si metal–oxide–semiconductor (MOS) capacitors has been investigated. Using rf magnetron sputtering deposition technique, Al/Al2O3/n-Si MOS capacitors were fabricated and such twelve capacitors were divided into four groups. The first group of MOS capacitors was not irradiated with 6MeV electrons and treated as virgin. The second group, third group and fourth group of MOS capacitors were irradiated with 6MeV electrons at 10kGy, 20kGy, and 30kGy doses, respectively, keeping the dose rate ∼1kGy/min. The variations in crystallinity of the virgin and irradiated MOS capacitors have been compared from GIXRD (Grazing Incidence X-ray Diffraction) spectra. Thickness and in-depth elemental distributions of individual layers were performed using Secondary Ion Mass Spectrometry (SIMS). The device parameters like flat band voltage (VFB) and interface trap density (Dit) of virgin and irradiated MOS capacitors have been calculated from C vs V and G/ω vs V curve, respectively. The electrical properties of the capacitors were investigated from the tan δ vs V graph. The device parameters were estimated using C–V and G/ω–V measurements. Poole–Frenkel coefficient (βPF) of the MOS capacitors was determined from leakage current (I)–voltage (V) measurement. The leakage current mechanism was proposed from the βPF value.

X-ray diffraction and surface acoustic wave analysis of BST/Pt/TiO2/SiO2/Si thin films

High dielectric constant and electrostriction property of (Ba, Sr)Ti03 (BST) thin films result in an increasing interest for dielectric devices and microwave acoustic resonator. Barium strontium titanate (Ba0.645Sr0.355TiO3) films of about 300 nm thickness are grown on Pt(111)/TiO2/SiO2/Si(001) substrates by rf magnetron sputtering deposition techniques. X-ray diffraction is applied for the microstructural characterization. The BST films exhibit a cubic perovskite structure with a dense and smooth surface. A laser acoustic waves (LA-waves) technique is used to generate surface acoustic waves (SAW) propagating in the BST films. Young’s modulus E and the Poisson ratio ν of TiO2, Pt and BST films in different propagation directions are derived from the measured dispersion curves. Estimation of BST elastics constants are served in SAW studies. Impact of stratification process on SAW, propagating along [100] and [110] directions of silicon substrate, has been interpreted on the basis of ordinary differential equation (ODE) and stiffness matrix method (SMM). A good agreement is observed between experimental and calculated dispersion curves. The performed calculations are strongly related to the implemented crystallographic data of each layer. Dispersion curves are found to be sensitive to the SAW propagation direction and the stratification process for the explored frequency ranges 50−250 MHz, even though it corresponds to a wave length clearly higher than the whole films thickness.

Nitrogen [N]-incorporated ZnO piezoelectric thin films and their application for ultra-small film bulk acoustic wave resonator device fabrication

Nitrogen [N]-incorporated ZnO films with columnar grains of a preferred c-axis orientation were deposited on p-Si (100) wafers, using an RF magnetron sputter deposition technique. For the N incorporation into the ZnO films, an N2O gas was used as a doping source and also various process conditions such as N2O gas fraction and RF power were applied. Besides, some of the ZnO films were treated with the post annealing process. And then, the micro-structural characteristics of the N-incorporated ZnO films were investigated by a scanning electron microscope, an X-ray diffractometer, and an atomic force microscope techniques. Finally, employing the N-incorporated ZnO films, the solidly mounted resonator-type film bulk acoustic wave resonator devices were fabricated and their resonance characteristics were extracted. As a result, an excellent return loss (S11) of− 63 dB was observed at∼ 0.6 GHz, better than ever reported.

Fabrication of Si nanocrystals in an amorphous SiC matrix by magnetron sputtering

Si nanocrystals embedded in a wide bandgap material have been of interest for various electronic devices, including third-generation solar cells with efficiency values exceeding theoretical limits. In this work, Si-rich amorphous SiC layers with different Si contents were fabricated by the RF magnetron sputtering deposition technique. Si nanocrystal formation was induced by a high-temperature annealing process in a series of samples with different Si contents controlled by the DC power applied to the Si target during the sputtering. Nanocrystal formation was monitored to understand the basic kinetics as a function of process parameters, such as DC power and annealing temperature. In the SiC films containing excess Si, nanocrystal formation was clearly identified by Raman spectroscopy and high-resolution Transmission Electron Microscopy (TEM). Si nanocrystals with a mean size of 2 nm were imaged by TEM in the samples annealed at 1100 °C. The presence of Si–Si bonds was also detected by XPS through a series of experiments, including depth profiling of the chemical bonds of O, Si and C as a function of depth from the surface. Infrared spectroscopy was employed to study the stoichiometry of the SiC matrix with or without nanocrystals.

Effect of rf-power density on the resistivity of Ga-doped ZnO film deposited by rf-magnetron sputter deposition technique

Gallium-doped zinc oxide (GZO) films were studied using rf-magnetron sputter deposition technique for the use of transparent conducting oxide film. The effects of deposition parameters such as pressure, rf-power, and film thickness on electrical and optical characteristics of GZO films were evaluated to obtain transparent conducting film with high transmittance and low resistivity for a-Si:H thin film solar cells. The resistivity and the structural properties of GZO film strongly depended on rf-power density and film thickness. The 1200 nm-thick GZO film deposited at 15 mTorr and 150 °C with rf-power density of 4.46 W/cm 2 showed the resistivity as low as 6.2 × 10 −4 Ω cm and the average transmittance of 86.5% in visible light wavelength region of 400–800 nm.

RF-sputtered Ge–ITO nanocomposite thin films for photovoltaic applications

Nanocomposite thin films, composed of a germanium nanocrystalline phase embedded within a tin-doped indium oxide (ITO) matrix, were produced using a multisource, sequential, RF-magnetron sputter deposition technique. The influence of nanocomposite structure on the resulting optical absorption and carrier transport properties was investigated in the context of the use of such materials as functional elements in thin film photovoltaic architectures. Deposition controls and post-deposition thermal anneals were successful in modifying the phase assembly of the nanocomposites, enabling the manipulation of Ge volume fraction, nanocrystallite size and morphology, and spatial distribution within the ITO embedding phase. Modifications in semiconductor nanostructure were correlated with changes in nanocomposite spectral absorption that were consistent with quantum-size-induced variation in Ge absorption onset energy, despite the close agreement in electron affinity between the Ge and ITO components. This suggests the formation of a high band-gap (low electron affinity) interfacial phase between the Ge and ITO components of the nanocomposite. Increased free-carrier (n-type) densities and spectrally resolved photoconductivity were also associated with the presence of the Ge phase. These results emphasize the impact of local and extended length scale structure on properties of importance to photovoltaic performance in semiconductor-based nanocomposites and the utility of the sequential sputter deposition method as a means to manipulate nanocomposite structure.

Bonelike Apatite Formation Utilizing Carbon Nanotubes as Template

Template-induced hydroxyapatite (HA) has broad prospects in the applied fields of regenerative medicine and bone repair. HA thin coatings have been deposited on vertically aligned multiwalled carbon nanotubes (CNTs) via the high-temperature radio-frequency (rf) magnetron sputtering deposition technique. Simulated body fluid (SBF) solution has been used to soak and incubate the HA/CNTs nanocomposites at 37 degrees C. SEM, EDS, XRD, and FTIR characterizations revealed bonelike apatite formation on top of HA/CNTs composites. Coating HA material on well-aligned CNT-template provides a way of combining the superior mechanical properties and chemical stability of the CNTs with the excellent biochemical properties of HA.

Growth and characterizations of ZnO nanorod/film structures on copper coated Si substrates

ZnO deposits were obtained on electroless copper coated Si substrates using a conventional RF magnetron sputter deposition technique at room temperature. The deposition pressure was varied from 6.67Pa to 0.667Pa. The RF powers were from 100 to 200W and the electrode distance was fixed at 5cm. The ZnO deposition time was varied from 1 to 30min. The deposits consist of ZnO nanorods and a ZnO film, with the roots of the nanorods embedded in the film. The growth of the nanorods far exceeds the growth of the film in the beginning of the deposition process. The nanorod lengthening rate then slows down and becomes lower than the film growth rate. Effects of sputter deposition parameters on the growth of ZnO nanorods/film structures were also investigated.

Inorganic Photo-sensitized Transparent Conductive Oxide (TCO) Nanocomposite Thin Films for Photovoltaic (PV) Energy Conversion

AbstractNanophase semiconductor composites are widely researched for the development of third-generation photovoltaic (PV) devices. Through quantum-size effects and phase assembly manipulation the optical absorption and carrier transport properties of nanocomposite films can be influenced. We investigate the potential for improved PV-relevant material performance by examining the photo-sensitization of indium-tin-oxide (ITO) with nanophase germanium (Ge). Nanocomposite films are produced by a sequential, RF-magnetron sputter deposition technique. Deposition control and post-deposition annealing are used to demonstrate the manipulation of the extended-assembly of the nanocrystalline Ge phase. Optical absorption characteristics were correlated to variations in the composite film structure as confirmed by transmission electron microscopy. In addition to structure-dependent variation in spectral absorption, spectrally resolved photoconductivity measurements demonstrate enhanced photoconductivity of composite films associated with the incorporation of the Ge phase into the ITO host. These results support the further evaluation of such nanocomposite TCO materials in optoelectronic devices, including PV systems.

Characteristics of vanadium dioxide films deposited by RF-magnetron sputter deposition technique using V-metal target

Vanadium dioxide films were deposited using reactive RF-magnetron sputter deposition technique and characterized without or with post-annealing process for the application of thermal sensors. The film thickness variation on a 4-in wafer was less than ±2%. As-deposited film showing an abrupt metal–insulator transition (MIT) could be obtained with O 2 fraction of 6%. The films deposited at 400 and 450 °C showed abrupt changes of resistance in the order of 10 3 near typical MIT temperature of VO 2 without post-annealing. The 110-nm-thick VO 2 film deposited at 450 °C on c-sapphire revealed the resistance change of 1.2×10 4 near 68 °C after annealing at 510 °C.