Dual Ion Beam Sputtering System Research Articles

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.

Thin film deposition from dual ion beam sputtering system

In this report, we study different device applications which utilizes oxide layers grown by dual ion beam sputtering (DIBS) system. DIBS system is noteworthy since it produces high-quality thin films with reasonably better compositional stoichiometry, small surface roughness and good adhesion to the substrate even for films grown at room temperature. DIBS system parameters affect the oxide and non-oxide layer in a very significant manner and control of these parameters allows for fine-tuning the as-grown thin films specialize for specific applications.

Investigation of valence electron excitation and plasmonic enhancement in sputter grown NMZO thin films: For energy harvesting applications

We report a novel approach of sputter-stimulated plasmonic generation in Na-doped MgZnO (NMZO) thin films. Sputtering of material during film growth by utilizing secondary direct-coupled ion-source present in dual-ion beam sputtering system leads to the generation of nanoclusters of its constituent elements due to different sputtering-out rates of various elements present in the films. The authentication of plasmonic generation in NMZO is conducted as follows a) identification of plasmonic signature in electron energy loss spectra obtained by ultraviolet photoelectron spectroscopy measurement, b) valence bulk, valence surface, and particle plasmon resonance energy calculations are performed, and each plasmon peak is indexed with corresponding plasmon energy peak of different nanoclusters, and c) spectroscopic ellipsometric measurement is deployed to verify plasmonic behavior by investigating different optical properties. Additionally, incorporation of the plasmonic feature along with alkali metals plays a crucial role in the improvement of the performance of solar cells. Therefore, plasmon enhanced NMZO as a backscattering layer in between CIGSe/back contact is probed to ascertain the additional benefits of 1) Na incorporation into the absorber layer as a result of the Na diffusion from the NMZO layer, and 2) improvement in the morphology of the CIGSe thin film with the incorporation of NMZO layer in between the back-contact and CIGSe. The diffusion of Na into the absorber layer is probed by deploying secondary ion mass spectroscopy measurements, and improvement in the morphology of CIGSe with the incorporation of NMZO layer between the back-contact/absorber is investigated using field-emission scanning electron microscope analysis.

Two-dimensional electron gases in MgZnO/ZnO and ZnO/MgZnO/ZnO heterostructures grown by dual ion beam sputtering

This work reports on the formation of high-density (~1013–1014 cm−2) two-dimensional electron gas (2DEG) in ZnO-based heterostructures, grown by a dual ion beam sputtering system. We probe 2DEG in bilayer MgZnO/ZnO and capped ZnO/MgZnO/ZnO heterostructures utilizing MgZnO barrier layers with varying thickness and Mg content. The effect of the ZnO cap layer thickness on the ZnO/MgZnO/ZnO heterostructure is also studied. Hall measurements demonstrate that the addition of a 5 nm ZnO cap layer results in an enhancement of the 2DEG density by about 1.5 times compared to 1.11 1014 cm−2 for the uncapped bilayer heterostructure with the same 30 nm barrier thickness and 30 at.% Mg composition in the barrier layer. From the low-temperature Hall measurement, the sheet carrier concentration and mobility are both found to be independent of the temperature. The capacitance–voltage measurement suggests a carrier density of ~1020 cm−3, confined in 2DEG at the MgZnO/ZnO heterointerface. The results presented are significant for the optimization of 2DEG for the eventual realization of cost-effective and large-area MgZnO/ZnO-based high-electron-mobility transistors.

Realization of synaptic learning and memory functions in Y2O3 based memristive device fabricated by dual ion beam sputtering

Single synaptic device with inherent learning and memory functions is demonstrated based on a forming-free amorphous Y2O3 (yttria) memristor fabricated by dual ion beam sputtering system. Synaptic functions such as nonlinear transmission characteristics, long-term plasticity, short-term plasticity and ‘learning behavior (LB)’ are achieved using a single synaptic device based on cost-effective metal-insulator-semiconductor (MIS) structure. An ‘LB’ function is demonstrated, for the first time in the literature, for a yttria based memristor, which bears a resemblance to certain memory functions of biological systems. The realization of key synaptic functions in a cost-effective MIS structure would promote much cheaper synapse for artificial neural network.

Investigation of barrier inhomogeneities and interface state density in Au/MgZnO: Ga Schottky contact

The electrical characteristics of Au/MgZnO:Ga (GMZO) Schottky contact, which is fabricated using a dual ion beam sputtering system, have been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements over a wide temperature range of 80 to 300 K. The apparent Schottky barrier height (SBH) and ideality factor obtained from the I–V measurements are observed to increase and reduce, respectively, with increasing measurement temperature. This anomalous observation in the behaviour of the SBH is in good agreement with the predictions of a double Gaussian distribution (DGD) of the inhomogeneous SBH at a metal–semiconductor (MS) interface. The values of the SBH as determined from C–V measurements are expectedly higher than those extracted from I–V measurements. The DGD model is observed to fit with experimentally obtained data for the temperature-dependent SBH with mean values of the SBH of 0.95 and 0.54 eV and standard deviations of 0.131 and 0.072 eV in the temperature range of 160–300 K and 80–160 K, respectively. The larger value of the SBH standard deviation confirms more SBH inhomogeneity at the MS interface, and these inhomogeneities are attributed to the presence of deep level or surface level interface states. The calculated interface states density is seen to vary from 6.46 × 1014 eV−1 cm−2 at EC-0.27 eV to 1.58 × 1014 eV−1 cm−2 at EC-0.74 eV, where EC is the bottom of a conduction band at 300 K.

Growth and characterization of dual ion beam sputtered Cu2ZnSn(S, Se)4 thin films for cost-effective photovoltaic application

A systematic growth optimization of Cu2ZnSn(S,Se)4 (CZTSSe) thin films by dual ion beam sputtering system from a single CZTSSe target is presented. It is observed that the ratio of Cu/(Zn+Sn) varies from 0.86 to 1.5 and that of (S+Se)/metal varies between 0.62 and 0.97 when substrate temperature (Tsub) is increased from 100 to 500°C. The crystal structure of all CZTSSe films are identified to be preferentially (112)-oriented, polycrystalline in nature, and without the existence of secondary phases such as Cu2(S,Se) or Zn(S,Se). The full-width at half-maximum of (112) diffraction peak is the minimum with a value of 0.12° and the maximum crystallite size 75.11nm for CZTSSe grown at 300°C. Morphological investigation reveals the achievement of the largest grain size at Tsub=300°C. The band gap of CZTSSe thin films at room temperature, as determined by spectroscopic ellipsometry, varies from 1.23 to 1.70eV, depending on Tsub. The optical absorption coefficient of all CZTSSe thin films is >104cm−1.

Plasmon generation in sputtered Ga-doped MgZnO thin films for solar cell applications

The crystalline, electrical, morphological, optical properties and plasmonic behaviour of Ga doped MgZnO (GMZO) thin films grown at different substrate temperatures (200–600 °C) by a dual ion beam sputtering (DIBS) system are investigated. Transmittance value of more than ∼94% in 400–1000 nm region is observed for all GMZO films. The particle plasmon features can be detected in the absorption coefficient spectra of GMZO grown at 500 and 600 °C in the form of a peak at ∼4.37 eV, which corresponds to a plasmon resonance peak of nanoclusters formed in GMZO. The presence of such plasmonic features is confirmed by ultraviolet photoelectron spectroscopy measurements. The values of particle plasmon resonance energy of various nanoclusters are in the range of solar spectrum, and these can easily be tuned and excited at the desirable wavelengths while optimizing the efficiency of solar cells (SCs) by simple alteration of DIBS growth temperature. These nanoclusters are extremely promising to enhance the optical scattering and trapping of the incident light, which increases the optical path length in the absorber layer of cost-effective SCs and eventually increases its efficiency.

Growth and characterizations of dual ion beam sputtered CIGS thin films for photovoltaic applications

The growth of CIGS thin films on soda-lime glass substrates at different substrate temperatures by dual ion beam sputtering system in a single-step route from a single quaternary sputtering target with the composition of Cu (In0.70 Ga0.30) Se2 was reported. The effects of the substrate temperature on structural, optical, morphological and electrical properties of CIGS films were investigated. Stoichiometry of one such film was investigated by X-ray photoelectron spectroscopy. All CIGS films had demonstrated a strong (112) orientation located at 2θ ~26.70o, which indicated the chalcopyrite structure of films. The value of full-width at half-maximum of (112) peak was reduced from 0.58° to 0.19° and crystallite size was enlarged from 14.98 to 43.05 nm as growth temperature was increased from 100 to 400 °C. However, atomic force microscope results showed a smooth and uniform surface at lower growth temperature and the surface roughness was observed to increase with increasing growth temperature. Hall measurements exhibited the minimum film resistivity of 0.09 Ω cm with a hole concentration of 2.42 × 1018 cm−3 and mobility of 28.60 cm2 V−1 s−1 for CIGS film grown at 100 °C. Film absorption coefficient was found to enhance nominally from 1 × 105 to 2.3 × 105 cm−1 with increasing growth temperature from 100 to 400 °C.

Influence of assistant ion beam on the opto-electrical properties of molybdenum doped zinc oxide films deposited on polyethersulfone via dual ion beam sputtering

An alternative transparent conductive oxide, molybdenum doped zinc oxide (MZO) was deposited onto a flexible polyethersulfone (PES) substrate by using a dual ion beam sputtering system. One argon ion beam was used to sputter a MZO target and another assistant argon ion beam was for bombarding deposits simultaneously. The assistant ion source discharge voltage and current were changed respectively for investigating their influences on the conductivity of deposited MZO films. Changing the discharge voltage shows that, the film crystallinity, carrier concentration and mobility in films all increase with the discharge voltage and subsequently decrease when the applied voltage is over 100 V. Changing the discharge current also shows a similar trend. The film crystallinity and carrier concentration initially increase with the discharge current, and thereafter a minimum for 1.4 A, and a subsequent increase in resistivity is observed. According to the results, properly raising the discharge voltage and current of assistant ion source can improve both electrical conductivity and optical transparency of deposited MZO films, but the excess discharge voltage and current will cause the grain refinement which may retard the carrier mobility and result in the lower conductivity of MZO films.

Growth, structural, and magnetic characterizations of nanocrystalline γ′-FeNiN(220) thin films

The authors have developed a fabrication process of nanocrystalline γ′-FeNiN[220] thin ferromagnetic films by using a dual ion beam sputtering system. The films show well defined in-plane magnetic uniaxial anisotropy, with high anisotropy field and high macroscopic saturation magnetization, requisites of crucial importance for high-frequency applications. The estimated ferromagnetic resonance frequency goes within the gigahertz regime, and the magnetic response can be tailored by the deposition conditions. Element-selective measurements reveal a reduction of the total Fe and Ni magnetic moments in γ′-FeNiN with respect to pure Fe and Ni due to hybridization between Fe and Ni 3d and N 2p states.

Deposition Characteristics of AlN Thin Film Prepared by the Dual Ion Beam Sputtering System

In this experiment, a radio frequency dual ion beam sputtering (DIBS) system was used to prepare aluminum nitride (AlN) films with a bottom Al electrode on a Si (100) substrate. After systematic testing of the processing variables, a high-quality film with preferred c-axis orientation was grown successfully on the Si (100) substrate with an Al target under 700 eV energy flux, N 2 /(N 2 + Ar) ratio of 55%, and 4 × 10 -4 torr in vacuum. The characteristics of the deposited AlN thin films were studied by x-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), secondary ion mass spectrometry (SIMS), and electronic spectroscopy for chemical analysis (ESCA). The surface roughness was also measured. It was found that AlN films prepared by DIBS at room temperature are better than those prepared at 300°C, and those prepared with an Al target are better than those prepared with an AlN target. The inferiority of AlN films prepared with AlN targets is due to the AlN bond being broken down by the ion beam source.

Magnetic properties of nanocrystalline FeNiN thin films

AbstractFeNiN thin films with a Ni content varying between 5 and 36 at% (as determined by X‐ray photoelectron spectroscopy) have been deposited in a Dual Ion Beam Sputtering System at room temperature. The structure and crystalline size were studied by X‐ray diffraction while the magnetic properties were investigated by vectorial kerr magnetometry. In general, the deposited films present a nanocrystaline cubic structure and well defined in‐plane magnetic anisotropy. The variation of the magnetic properties was attributed to changes in composition and nanocrystalline structure. FeNiN thin films with a Ni content of about 15 at% show the better soft magnetic properties with a minimum in the coercivity of 9 Oe. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural, chemical and magnetic characterization of iron nitride thin films

AbstractIron nitride thin films were deposited on Si (100) substrates at 150 °C using a dual ion beam sputtering system. The structure, chemical composition and magnetic properties of the films were studied as a function of the deposition conditions. The bombardment with N2+ ions during the deposition of Fe by sputtering enabled control of the nitrogen content in the films and the formation of different iron nitride phases with different magnetic properties.The chemical, electronic and structural characterization of the films were performed by Rutherford backscattering spectrometry (RBS), AES‐depth profiling, and X‐ray diffraction (XRD), whereas the magnetic behavior was studied using a vibrating sample magnetometer (VSM).The results show that the magnetic moment of the Fe atoms decreases and the coercivity of the films increases almost linearly as the nitrogen content in the films increases up to the formation of ζ‐Fe2N, which is not magnetic. Copyright © 2006 John Wiley & Sons, Ltd.

Quantitative analysis of CN∕TiCN∕TiN multilayers and their thermal stability by Auger electron spectroscopy and Rutherford backscattering spectrometry depth profiles

CN∕TiCN∕TiN multilayers and the respective single layers have been deposited on Si(100) substrates using a dual ion-beam sputtering system. Both the multilayers and the respective single layers have been chemically characterized by Auger electron spectroscopy (AES) depth profiling combined with factor analysis and by Rutherford backscattering spectrometry (RBS). The combination of AES and RBS allows a quantitative chemical characterization of the multilayer and the respective single layers. Whereas RBS has some difficulties to determine the in-depth distribution of the light elements along the multilayer, AES depth profiling enables their quantitative analysis and even their chemical state along the multilayer. On the contrary, RBS shows its advantages to determine the heavy elements, including the contaminants incorporated during the deposition process (e.g., W). Under special experimental conditions it is shown that RBS is able to determine the composition of the single layers (i.e., CN∕Si, TiCN∕Si, and TiN∕Si) in good agreement with AES depth profiling. As a result of this complementary use we obtain a complete quantitative chemical characterization of the single layers and multilayers. In addition, the thermal stability of the multilayers upon heating for 1h in vacuum and ambient atmospheres at 500°C has been studied by AES depth profiling. The results show that whereas the multilayer is stable in vacuum it undergoes significant changes when it is heated in air. In fact, it is shown that annealing in air for 1h causes the disappearance of the CN top layer and the oxidation of the TiCN layer that leads to the formation of TiO2 on its surface.

Argon ion beam voltages influence the microstructure of aluminum nitride films in a dual ion beam sputtering system

Aluminum nitride (AlN) films, using a dual ion beam sputtering, were prepared over the argon ion beam voltage ranging from 800 to 1200V at room temperature. The AlN films were (002) and (100) planes. Excepting for operating at 1000V, the AlN films exhibited the (002) preferred orientation. The growth exponents ranged from 0.27 to 0.23 and decreased with increasing argon ion beam voltage. The concentration of aluminum was richer than that of nitrogen in the films at all argon ion beam voltages. The concentration of aluminum decreased markedly with increasing the texture coefficient of AlN(002) plane.

Dual Ion Beam Sputtering for Chromium Nitride as an Alternative to Electroplated Hexavalent Chromium

The hexavalent chromium used in chromium plating is so toxic that it is very hazardous to human body and even carcinogenic. Therefore, it is indispensable to develop an alternative deposition technique. To explore the feasibility of sputtering as an alternative technique for chromium plating, we investigated the dependences of the deposition rate, the phases, the hardness, the surface roughness and the corrosion-resistance of CrNx deposited on the high speed steel substrate by using a dual ion beam sputtering system on the rf-powers. The deposition rate of CrNx depends more strongly upon the rf-power for argon ion beam than that of the nitrogen ion beam. The hardness of the CrNx film can be maximized by optimizing the rf-power, so that the volume percent of the Cr2N phase in the film is highest. Amorphous films are obtained when the rf-power for nitrogen ion beam is much higher than that for argon ion beam. The CrNx film deposited by using the sputtering technique under the optimal condition provides corrosion-resistance comparable to that of the electroplated chromium.

Argon ion beam voltage in a dual ion beam sputtering system influence on the aluminum nitride films microstructure

The aluminum nitride (AlN) film has been successfully prepared at argon ion beam voltages ranging from 600 to 1200 V in the dual ion beam sputtering system. The AlN film had the (0 0 2) preferred orientation at 800 V and then changed to AlN (1 0 0) above 1000 V. Moreover, the nano-grain size presented in AlN film was observed using TEM. The Al-2p 3/2 and N-1s spectra were, respectively, centered at 74.2±0.2 eV and 397.4±0.2 eV at all voltages, which indicated the formation of Al–N bond. Furthermore, the Al concentration decreased monotonically with argon ion beam voltages. The stoichiometric AlN films can be synthesized around 960 V in the present study. The microstructure changes associated with argon ion beam voltages are also discussed.

The influence of secondary ion beam irradiation on the formation of Si nanocrystals during dual ion beam sputtering

We investigate the deposition of SiOx films by dual ion beam sputtering system with emphasis on secondary ion beam irradiation effect. We observe the intense photoluminescence (PL) from SiOx samples with apparent oxygen contents, xapp, in the narrow range of 1.1≤xapp≤1.4, after post-deposition annealing at 1100 °C. This indicates the formation of Si nanocrystals as evidenced by cross-sectional transmission electron microscope (TEM) image. Ar ion beam irradiation changes PL peak positions in ion-beam exposed region. This effect is utilized for achieving the area-selective formation of Si nanocrytals by inserting a shadow mask in secondary ion beam during deposition.

Effect of argon ion beam voltages on the microstructure of aluminum nitride films prepared at room temperature by a dual ion beam sputtering system

Aluminum nitride (AlN) films were successfully deposited at room temperature onto p-type (1 0 0) silicon wafers by manipulating argon ion beam voltages in a dual ion beam sputtering (DIBS). X-ray diffraction spectra showed that aluminum nitride films could be synthesized above 800 V. The (0 0 2) orientation was dominant at 800 V, above which the orientation was random. The atomic force microscope (AFM) images displayed a relatively smooth surface with the root-mean-square roughness of 2–3 nm, where this roughness decreased with argon ion beam voltage. The Al 2p 3/2 and N 1s spectra indicated that both the aluminum-aluminum bond and aluminumnitrogen bond appeared at 600 V, above which only the aluminumnitrogen bond was detected. Moreover, the atomic concentration in aluminum nitride films was concentrated in aluminum-rich phases in all cases. Nevertheless, the aluminum concentration markedly increased with argon ion beam voltages below 1000 V, above which the concentration decreased slightly. The correlation between the microstructure of aluminum nitride films and argon ion beam voltages is also discussed.