Effect of temperature on microstructure and electrical properties of TaSi2 thin films grown on Si substrates

Tantalum silicide (TaSi₂) thin films were deposited on n-type silicon single crystal substrates using a dual electron-gun system and with Ta and Si targets. The thicknesses of TaSi₂ thin films considered in this study are in the range 200-500 nm, respectively. The TaSi₂/Si samples were annealed at temperature 1173 K for 2 h in a vacuum of 10⁻⁸ mbar. The structure of the tantalum silicide thin films was investigated by X-ray diffraction (XRD). X-ray diffraction results show changes in the structure of TaSi₂ thin films from amorphous to crystalline after annealing. According to XRD analysis, a complete conversion to single-phase disilicide TaSi₂ was achieved from a sample composition of Ta:Si = 1:2. DC conductivity was measured for the TaSi₂ thin films in the temperature range 300-900 K before and after annealing. It has been observed that the DC conductivity and activation energy was affected by changing the TaSi₂ film thickness and by annealing. The experimental results indicate that, the conduction phenomena of the investigated sample proceeded via two distinct mechanisms. The first one in the low-temperature range T < 500 K can be described by thermally-assisted tunneling of the carriers in the localized states near the band edge. The value of the pre-exponential factor before and after annealing is less than 10⁴ Ω⁻¹ cm⁻¹. The other process appears in the high temperature region T > 500 K, where thermally activated conduction occurs through the extended states. Here the value of the pre-exponential factor before and after annealing is larger than 10⁴ Ω⁻¹ cm⁻¹. The conductivity is greater in the crystalline phase than in the amorphous phase. The activation energy ΔE for our films before and after annealing is increased with increasing film thickness.     

Facing target sputtered iron-silicide thin film

The FeSi_x thin films with the flatness to an atomic scale for mechanical and optical applications can be grown by a facing target sputtering method. Optical properties indicate the films contain nano-crystalline FeSi₂. The nano-indentation hardness of 10 GPa was obtained. An interesting point is that Young's modulus is larger than that of the carbon-based materials with the same hardness. This means that the FeSi_x is more elastic, which could be characteristic of the chemical bonding of the FeSi₂ with the large contribution of d-electrons. Furthermore, results of the Hall measurement at room temperature shows that the films have p-type conductivity, a carrier concentration of p = 2.49 × 10²⁰ cm^− 3 and a Hall mobility of μ = 6.42 cm² V^− 1 s^− 1.     

Computational design of high efficiency FeSi2 thin-film solar cells

A novel PV cell structure in the form of a p-i-n construction is proposed by inserting a layer of FeSi₂ between two layers of crystalline silicon. The energy band diagram and PV properties are simulated. The structure parameters, such as the thickness, doping concentration and defect density of states of each layer, are taken into account. The optimized structure with a thickness less than 1 μm shows a large open circuit voltage (Voc) of 0.68 V and a high photoelectric conversion efficiency (Eff) of 24.7%, which is significantly larger than that of the FeSi₂/Si double-layer pn-heterojunction structure, and is comparable with the performance of crystalline Si solar cells with a thickness of 250 μm. The Voc and Eff increase further when replacing the crystalline Si at both sides of the FeSi₂ layer with amorphous Si layers. The present work is expected to open a new avenue in developing low-cost thin film solar cells on the basis of the well established Si technology.     

Single crystalline β-FeSi2 grown using high-purity FeSi2 source

We have investigated the effect of FeSi₂ source purity on the electrical property of β-FeSi₂ grown from solution. A high-purity FeSi₂ source avoided a contamination of Cu and W metals was synthesized by melting a high-purity Fe (5N) and Si (5N-up) in a quartz ampoule. Glow discharge mass spectrometry revealed that the purity of the FeSi₂ source synthesized using 5N-Fe and a quartz-ampoule-melting process is one order of magnitude higher than that of the conventional arc-melted FeSi₂ source using 4N-Fe. The β-FeSi₂ crystals grown using the high-purity FeSi₂ and Zn solvent showed n-type conduction, whereas those grown using the arc-melted FeSi₂ showed p-type. The carrier concentration of the n-type crystals was (4.9-6.3) × 10¹⁸ cm^− 3, which was more than 10 times higher than that of the p-type crystals (5.2 × 10¹⁷ cm^− 3). From the ICP-MS and SIMS analysis of the grown crystals, we found that dominant impurity concentrations (Cr, Mn, Co, Ni, Cu, Zn and W) in the p-type crystals were higher than those in the n-type ones. Therefore, the p-type conductivity of undoped crystals grown using Zn solvent results from unintentional doping by the high impurity level of the used FeSi₂ source.     

Synthesis of β-FeSi2/Si heterojunctions for photovoltaic applications by unbalanced magnetron sputtering

We report here the possibility of the growth of semiconducting FeSi₂ layers on Si(100) substrates by depositing iron with unbalanced magnetron sputtering. The originality of the study is the achievement of heterojunction without any further treatment of the deposited films. Pure iron is deposited on Si(100) substrates with unbalanced magnetron sputtering for the production of β-FeSi₂/Si heterojunctions. Prior to coating process the substrates are cleaned with neutral molecular source. Microstructure of β-FeSi₂ films were investigated by X-Ray Diffraction analysis and Raman Spectroscopy. Dark current-voltage characteristic of the deposited coatings showed a rectifying behavior for the β-FeSi₂/Si heterojuctions. Open-circuit voltage (V_oc) and short-circuit current density (J_sc) were measured under 100 mWcm^− 2 illumination and a V_oc of 360 mV and J_sc of 180 μAcm^− 2 were measured. The illumination of the silicon side gave higher photosensitivity than the illumination of the iron silicide side.     

Effect of TiOx seed layer on the texture and electric properties in La and Ca modified PbTiO3 thin films

Lanthanum-and calcium-modified PbTiO₃ (PLCT) ferroelectric thin films were successfully prepared on Pt(111)/Ti/SiO₂/Si substrates by pulsed laser deposition. Influence of TiO_x seed layer on texture and electric properties of PLCT films was investigated. It is found the PLCT films without seed layer exhibited highly (100)-textured, while using about 9 nm TiO_x as seed layer lead to highly (301)-textured. The PLCT film with TiO_x seed layer possess higher remnant polarization (Pr = 26 µC/cm²), better pyroelectric coefficient and figure of merit at room temperature (p = 370 µC/m²k, F_d = 190 × 10^− 5 Pa^− 1/2) than that of film without seed layer. The mechanism of the enhanced electric properties was also discussed.     

Pyroelectric Ta-modified LiNbO3 thin films and devices for thermal infrared detection

High-performance pyroelectric infrared (IR) detectors have been fabricated using tantalate-doped lithium niobate LiNb_1 − xTa_xO₃ (abbreviated as LNT, with x = 0-1.0) thin films deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by diol-based sol-gel processing, in which, tantalate (Ta) is adopted as dopant in lithium niobate. The randomly oriented LNT thin film exhibits a relatively small dielectric constant and a large pyroelectric coefficient. The pyroelectric characteristics of detectors with various tantalate contents, as a function of modulation frequency, were investigated. It was found that LiNb_0.8Ta_0.2O₃ had the largest voltage responsivity of 7020 (V/W) at 70 Hz, and a specific detectivity (D^?) of 7.76 × 10⁷ cm Hz^1/2/W at 200 Hz. These results indicate that the LNT thin film with x = 0.20 is most suitable for application as high-performance pyroelectric thin-film detectors.     

Pb(Zr0.52Ti0.48)O3/TiNi multilayered heterostructures on Si substrates for smart systems

Ferroelectric/shape memory alloy thin film multilayered heterostructures possess both sensing and actuating functions and are considered to be smart. In this article, Pb(Zr_0.52Ti_0.48)O₃ (PZT) ferroelectric thin films and Ti-riched TiNi shape memory alloy thin films have been deposited on Si and SiO₂/Si substrates in the 400-600 °C temperature range by pulsed laser deposition technique. Deposition processing, microstructure and surface morphology of these films are described. The TiNi films deposited at 500 °C had an austenitic B2 structure with preferred (110) orientation. The surfaces of the films were very smooth with the root-mean-square roughness on a unit cell level. The structure of the TiNi films had a significant influence on that of the subsequently deposited PZT films. The single B2 austenite phase of the TiNi favored the growth of perovskite PZT films. The PZT/TiNi heterostructures with the PZT and TiNi films respectively deposited at 600 and 500 °C exhibited a polarization-electric field hysteresis behavior with a leakage current of about 2 × 10^− 6 A/cm².     

Growth of β-FeSi2 thin films on β-FeSi2 (110) substrates by molecular beam epitaxy

We have investigated the preparation of β-FeSi₂ substrate and growth condition of β-FeSi₂ thin film on β-FeSi₂ (110) substrate by molecular beam epitaxy. The surface of the substrate was prepared by a wet-etching using HF(50%):HNO₃(60%):H₂O = 1:1:5 solution at 25 °C. It is clear that the optimal etching period to obtain a flat surface was 3 min. The β-FeSi₂ thin film with streak RHEED pattern was obtained at Si/Fe flux ratio of 2.9. Average surface roughness (Ra) of the β-FeSi₂ film was about 0.5 nm in 5 × 5 μm² area.     

Epitaxial multi-component rare earth oxide for high-K application

We studied the growth and electrical properties of single crystalline mixed (Nd_1 − xGd_x)₂O₃ (NGO) thin films and compared the results with those of the binary Gd₂O₃ and Nd₂O₃ thin films, respectively. Epitaxial ternary NGO thin films were grown on Si(100) substrates using modified solid state molecular beam epitaxy. The films were characterized physically using various techniques. The capacitance equivalent oxide thickness of a 4.5 nm NGO thin film extracted from capacitance-voltage (C-V) characteristics was 0.9 nm, which is lower than all values reported earlier for other crystalline oxides. The leakage current density and the density of interface traps were 0.3 mA/cm² at |Vg − V_FB| =  1 V and 1.4 × 10¹²/cm², respectively. These excellent electrical properties of NGO thin films demonstrate that such ternary oxides could be one of the promising candidates for gate dielectrics in the upcoming generations of complementary metal oxide semiconductor (CMOS) devices.     

Influence of annealing treatments for ZnO-doped Zr0.8Sn0.2TiO4 thin films by RF magnetron sputtering

Zirconium tin titanium oxide doped 1 wt.% ZnO thin films on n-type Si substrate were deposited by rf magnetron sputtering at a fixed rf power of 300 W, a substrate temperature of 450 °C, a deposition pressure of 5 mTorr and an Ar/O₂ ratio of 100/0 with various annealing temperatures and annealing times. Electrical properties and microstructures of 1 wt.% ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films prepared by rf magnetron sputtering on n-type Si(100) substrates at different annealing temperatures (500 °C-700 °C) and annealing times (2 h-6 h) have been investigated. The structural and morphological characteristics analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM) were sensitive to the treatment conditions such as annealing temperature and annealing time. At an annealing temperature of 600 °C and an annealing time of 6 h, the ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films possess a dielectric constant of 46 (at f = 10 MHz), a dissipation factor of 0.059 (at f = 10 MHz), and a low leakage current density of 3.8 × 10^− 9 A/cm² at an electrical field of 1 kV/cm.     

Preparation, dielectric and ferroelectric properties of Pb5Ge3O11 and Pb5Ge2.85Si0.15O11 thin films fabricated by sol-gel process

Lead germanate-silicate (Pb₅Ge_2.85Si_0.15O₁₁) ferroelectric thin films were successfully fabricated on Pt/Ti/SiO₂/(100)Si substrates by the sol-gel process. The thin films were fabricated by multi-coating at preheating temperatures of 350 and 450 °C. After annealing the thin films at 600 °C, the films exhibited c-axis preferred orientation. The degree of c-axis preferred orientation of the thin films preheated at 350 °C was higher than that of films preheated at 450 °C. Grain growth was influenced by the annealing time. The thin films exhibited a well-saturated ferroelectric P-E hysteresis loop when preheated at 350 °C and annealed at 600 °C for 1.5 h. The values of the remanent polarization (Pr) and the coercive field (Ec) were approximately 2.1 μC/cm² and 100 kV/cm, respectively.     

Development of CZTS-based thin film solar cells

The low cost, environmental harmless Cu₂ZnSnS₄ (CZTS)-based thin film solar cells are fabricated by using abundant materials. The CZTS film possesses promising characteristic optical properties; band-gap energy of about 1.5 eV and large absorption coefficient in the order of 10⁴ cm^− 1. All constituents of this CZTS film, which are abundant in the crust of the earth, are non-toxic. Therefore, if we can use CZTS film practically as the absorber of solar cells, we will be free from both of the resource saving problem and the environmental pollution.In our CZTS project, CZTS absorber films were prepared by two independent techniques. One is three rf sources co-sputtering followed by annealing in sulfurized atmosphere. The latest conversion efficiency of over 6.7% was achieved by this technique. The other is co-evaporation technique. CZTS films were grown on Si (100) by vacuum co-evaporation using elemental Cu, Sn, S and binary ZnS as sources. XRD patterns indicated that the polycrystalline growth was suppressed and the orientational growth was relatively induced in a film grown at higher temperatures.In this presentation, the development of CZTS-based thin film solar cells will be surveyed.     

Overview about the optical properties and mechanical stress of different dielectric thin films produced by reactive-low-voltage-ion-plating

Thin films of Ta₂O₅, Nb₂O₅, and HfO₂ were deposited by reactive-low-voltage-ion-plating (RLVIP) on unheated glass and silicon substrates. The film thickness was about 200 nm. Optical properties as well as mechanical film stress of these layers were investigated in dependence of various deposition parameters, i.e. arc current and oxygen partial pressure. For an arc current in the range between 40 and 50 A and an oxygen partial pressure of at least 11 · 10^− 4 mbar good results were obtained. The refractive index and film thickness were calculated from spectrophotometric transmission data using the Swanepoel theory. For example at 550 nm wavelength the refractive index for thin RLVIP-Nb₂O₅-films was found to be n₅₅₀ = 2.40. The optical absorption was obtained by photo-thermal deflection spectrometry. For the investigated materials absorption coefficients in the range of k = 5 · 10^− 4 at 515 nm wavelength were measured. The mechanical film stress was determined by measuring the difference in bending of silicon substrates before and after the deposition process. For dense films, i.e. no water vapour sorption on atmosphere, the mechanical film stress was always compressive with values of some hundred MPa. In case of films deposited with higher arc currents (I_arc > 60A) and lower oxygen pressure (< 15 · 10^− 4 mbar) the influence of a post deposition heat treatment at 350 °C for 4 h on air was also investigated. For these films the properties could clearly be improved by such treatment. However, by using lower arc currents and higher oxygen partial pressure during the ion plating process, immediately dense and environmental stable films with good optical as well as mechanical properties could be achieved without post deposition heat treatment. All the results obtained will be presented in graphs and diagrams.     

Nickel diffusion in polycrystalline CuInSe2 thin films with a <112> fiber texture

Nickel diffusion in CuInSe₂ thin films was studied in the temperature range 430-520 °C. Thin films of copper indium diselenide (CuInSe₂) were prepared by selenization of CuInSe₂-Cu-In multilayered structure on glass substrate. A thin film of Nickel was deposited and annealed at different temperatures. Surface morphologies of the Ni diffused and undiffused CuInSe2 films were investigated using scanning electron microscope. The alteration of Nickel concentration in the CuInSe₂ thin film was measured by Energy Dispersive X-Ray Fluorescence (EDXRF) technique. These measurements were fitted to a complementary error function solution and the diffusion coefficients at four different temperatures were evaluated. The diffusion coefficients of Ni in CuInSe₂ films were estimated from concentration profiles at temperatures 430-520 °C as D = 1.86 × 10^− 7(cm²s^− 1)exp[− 0.68(eV)/kT].     

The influence of annealing temperatures on the properties of Bi2VO5.5/LaNiO3/Si thin films

Bi₂VO_5.5 ferroelectric thin films were fabricated on LaNiO₃/Si(100) substrate via chemical solution deposition. Ferroelectric and dielectric properties of the thin films annealed at 500-700 °C were studied. The thin film annealed at 700 °C exhibited more favorable ferroelectric and dielectric properties than those annealed at lower temperatures. The values of remnant polarization 2P_r and coercive field E_c for the film annealed at 700 °C are 10.62 µC/cm² and 106.3 kV/cm, respectively. The leakage current of the film is about 1.92 × 10^− 8 A/cm² at 6 V. The possible mechanism of the dependence of electrical properties of the films on the annealing temperature was discussed.     

V-doping effects on ferroelectric properties of K0.5Bi4.5Ti4O15 thin films

V-doped K_0.5Bi_4.5Ti₄O₁₅ (K_0.5Bi_{4.5 − x/3}Ti_4 − xV_xO₁₅, KBTiV-x, x = 0.00, 0.01, 0.03, and 0.05) thin films were prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The thin films were annealed by using a rapid thermal annealing process at 750 °C for 3 min in an oxygen atmosphere. Among them, KBTiV-0.03 thin film exhibited the most outstanding electrical properties. The value of remnant polarization (2P_r) was 75 μC/cm² at an applied electric field of 366 kV/cm. The leakage current density of the thin film capacitor was 5.01 × 10⁻⁸ at 100 kV/cm, which is approximately one order of magnitude lower than that of pure K_0.5Bi_4.5Ti₄O₁₅ thin film capacitor. We found that V doping is an effective method for improving the ferroelectric properties of K_0.5Bi_4.5Ti₄O₁₅ thin film.     

Characteristics of NixFe100−x films deposited on SiO2/Si(1 0 0) by DC magnetron co-sputtering

Ni_xFe_100−x films with a thickness of about 200 nm were deposited on SiO₂/Si(1 0 0) substrates at room temperature by DC magnetron co-sputtering using both Fe and Ni₈₀Fe₂₀ targets. Compositional, structural, electrical and magnetic properties of the films were investigated. Ni₇₆Fe₂₄, Ni₆₅Fe₃₅, Ni₆₀Fe₄₀, Ni₅₅Fe₄₅, Ni₄₉Fe₅₁ films are obtained by increasing the sputtering power of the Fe target. All the films have a fcc structure. Ni₇₆Fe₂₄, Ni₆₅Fe₃₅, Ni₆₀Fe₄₀ and Ni₅₅Fe₄₅ films grow with crystalline orientations of [1 1 1] and [2 2 0] in the direction of the film growth while the Ni₄₉Fe₅₁ film has the [1 1 1] texture structure in the direction of the film growth. The lattice constant of the film increases linearly with increasing Fe content. All of the films grow with thin columnar grains and have void networks in the grain boundaries. The grain size does not change markedly with the composition of the film. The resistivity of the film increases with increasing Fe content and is one order of magnitude larger than that of the bulk. For all the films the magnetic hysteresis loop shows a hard magnetization. The Ni₇₆Fe₂₄ film has the lowest saturation magnetization of 6.75×10⁻² T and the lowest saturation field of 8.36×10⁴ A/m while the Ni₄₉Fe₅₁ film has a largest saturation magnetization of 9.25×10⁻² T and the largest saturation field of 1.43×10⁵ A/m.     

Thermal treatment effects on interfacial layer formation between ZrO2 thin films and Si substrates

This paper describes the growth condition of stoichiometric ZrO₂ thin films on Si substrates and the interfacial structure of ZrO₂ and Si substrates. The ZrO₂ thin films were prepared by rf-magnetron sputtering from Zr target with mixed gas of O₂ and Ar at room temperature followed by post-annealing in O₂ ambient. The stoichiometric ZrO₂ thin films with smooth surface were grown at high oxygen partial pressure. The thick Zr-free SiO₂ layer was formed with both Zr silicide and Zr silicate at the interface between ZrO₂ and Si substrate during the post-annealing process due to rapid diffusion of oxygen atoms through the ZrO₂ thin films. After post annealing at 650-750 °C, the multi-interfacial layer shows small leakage current of less than 10⁻⁸ A/cm² that is corresponding to the high-temperature processed thermal oxidized SiO₂.     

Microstructure and electrochemical properties of magnetron-sputtered LiCoO2/LiNiO2 multi-layer thin film electrode

LiCoO₂ single-layer and LiCoO₂/LiNiO₂ multi-layer thin film electrodes were successfully fabricated by magnetron sputtering. Their microstructure and electrochemical properties were investigated. Once annealed, both films had the (0 0 3) preferred orientation to minimize the surface energy. The initial discharge capacity of the multi-layer thin film was approximately 53.1 μAh/cm² μm, which was higher than that of the LiCoO₂ single-layer thin film having similar thickness. The capacity retention of the multi-layer thin film was superior to that of the single-layer thin film. These findings indicate that the multi-layer thin film is a promising cathode material for the fabrication of high-performance thin film batteries.