Electrical properties of metal-oxide-semiconductor capacitors using liquid-phase deposited silicon-dioxide gate dielectric on sulfur-passivated germanium

After depositing silicon-dioxide (SiO₂) on a geranium (Ge) substrate at room temperature using a liquid-phase deposition (LPD) method, fabricated metal-oxide-semiconductor (MOS) capacitors were used to extract the passivating properties of LPD-SiO₂ on the surface. The procedure employed X-ray photoelectron spectroscopy, current-voltage and capacitance-voltage measurements. Our observation shows that (NH₄)₂S treatment completely removes the native oxide (GeO₂) from the Ge surface and passivate surface dangling bond. Hence, the (NH₄)₂S treated MOS capacitor reveals a lower leakage current than an untreated capacitor by one order. Different temperatures (200-400 °C) for annealing were proposed to improve the passivating properties of LPD-SiO₂. With increasing annealing temperature, flat-band voltage shift, fixed oxide-charge density, and interface trap density significantly decrease. Such a result indicates that the LPD-SiO₂ and (NH₄)₂S treatment qualifies as a potential candidate in passivating the Ge substrate.     

Trapping properties of sputtered hafnium oxide films: Bulk traps vs. interface traps

The purpose of this work is to investigate the influence of the spatial distribution of traps on the electrical characteristics of hafnium oxide films deposited by physical vapor deposition. Samples were Al gated metal-oxide-semiconductor capacitors with hafnium oxide films deposited on SiO₂ layer thermally grown on Si. During capacitance-voltage measurements large hysteresis, up to 10 V, are observed in all samples. It is shown that depending on the hafnium oxide deposition conditions, the spatial distribution of the traps responsible for the hysteresis can be either two dimensional (interface/border traps) or three dimensional (bulk traps).     

Electrical properties and structure of laser-spike-annealed hafnium oxide

We studied the effects of laser-spike annealing (LSA) on hafnium oxide high-k dielectrics using high power diode laser. The equivalent oxide thickness of HfO₂ gate stacks annealed using a moderate laser power decreased noticeably as compared to as-grown films due to densification and crystallization of HfO₂. Transmission electron microscope and X-ray photoelectron spectroscopy show that regrowth of interfacial oxide and silication of HfO₂ layer are suppressed in case of LSA compared with rapid thermal annealing. Capacitance voltage hysteresis revealed stronger charge trapping/de-trapping behavior for LSA gate stacks as compared to rapid thermal annealed gate stack. However, bias-stress-induced flat band voltage shifts of LSA gate stacks were within acceptable levels, ? 30 mV, showing controllable threshold voltage.     

Further work function and interface quality improvement on Al2O3 capped high-k/metal gate p-type metal-oxide-semiconductor field-effect-transistors by incorporation of fluorine

The impact of fluorine (F) incorporation into TiN/HfO₂/SiO₂ on work function has been investigated. By process scheme optimization, F implanted through sacrificial oxide layer reveals sufficient the flat-band voltage (V_FB) shift ~ 170 mV without an equivalent oxide thickness (EOT) penalty. On the contrary, apparent EOT increasing was observed if F implanted directly through Si. Moreover, F incorporation into TiN/Al₂O₃/HfO₂/SiO₂, the V_FB shift can be up to about 250 mV or 410 mV at 10 keV with a dose of 2 × 10¹⁵ cm^− 2 or 5 × 10¹⁵ cm^− 2, respectively. Effective work function has been boosted to 4.95 eV closer to the valence band edge. Besides, interface defect density also can be improved ~ 20% by F incorporation from charge pumping result.     

Effects of UV-ozone treatment on radio-frequency magnetron sputtered ZnO thin films

The effects of UV-ozone treatment on ZnO thin films prepared by using radio-frequency magnetron sputtering are investigated. Decrease in the density of oxygen vacancy as well as increase in the density of oxygen interstitial were inferred from the UV-ozone treated samples. It was also found that a considerable difference in the work function (0.25 eV) is induced by UV-ozone treatment implying a shift in Fermi level. This shift was confirmed by capacitance-voltage measurements, which demonstrated that the boundary between the inversion region and the depletion region of a ZnO-based metal-oxide-semiconductor (MOS) capacitor positively shifts when UV ozone treated. Our results clearly indicate that the threshold voltage of a thin film transistor can be adjusted by modifying the ZnO surface via UV ozone treatment. MOS capacitors fabricated with UV-ozone treated HfO₂ and/or ZnO also yielded a smaller leakage current (~ 73%-90% smaller) and a larger breakdown voltage (~ 8%-11% larger). The physical mechanism behind the effect of the UV ozone treatment is addressed in this study with the help of X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy.     

Preparation and characterization of indium oxide (In2O3) films by activated reactive evaporation

The electrical and optical properties of In₂O₃ films prepared at room temperature by activated reactive evaporation have been studied. Hall effect measurements at room temperature show that the films have a relatively high mobility 15 cm²v⁻¹s⁻¹, high carrier concentration 2·97 × 10²⁰/cm³, with a low resistivityρ = 1·35 × 10⁻³ ohm cm. As-prepared film is polycrystalline. It shows both direct and indirect allowed transitions with band gaps of 3·52eV and 2·94eV respectively.     

Developments in hot-filament metal oxide deposition (HFMOD)

Hot-filament metal oxide deposition (HFMOD) is a variant of conventional hot-filament chemical vapor deposition (HFCVD) recently developed in our laboratory and successfully used to obtain high-quality, uniform films of MO_x, WO_x and VO_x. The method employs the controlled oxidation of a filament of a transition metal heated to 1000 °C or more in a rarefied oxygen atmosphere (typically, of about 1 Pa). Metal oxide vapor formed on the surface of the filament is transported a few centimetres to deposit on a suitable substrate. Key system parameters include the choice of filament material and diameter, the applied current and the partial pressures of oxygen in the chamber. Relatively high film deposition rates, such as 31 nm min^− 1 for MoO_x, are obtained. The film stoichiometry depends on the exact deposition conditions. MoO_x films, for example, present a mixture of MoO₂ and MoO₃ phases, as revealed by XPS. As determined by Li⁺ intercalation using an electrochemical cell, these films also show a colouration efficiency of 19.5 cm² C^− 1 at a wavelength of 700 nm. MO_x and WO_x films are promising in applications involving electrochromism and characteristics of their colouring/bleaching cycles are presented. The chemical composition and structure of VO_x films examined using IRRAS (infrared reflection-absorption spectroscopy), RBS (Rutherford backscattering spectrometry) and XPS (X-ray photoelectron spectrometry) are also presented.     

Electron microscopy and physical studies of a new tungsten doped indium oxide transparent conductor

Advanced electron microscopy techniques - HREM and EFTEM - were used to study a new transparent conductive material: Indium Tungsten Oxide (IWO, in this work), which was synthesized from an aerosol. Indium oxide thin films doped with tungsten were deposited by spray pyrolysis for several %W concentration using (NH₄)10W₁₂O₄₁ and InCl₃ dissolved in ethanol as starting compounds. The W⁶⁺ ions fulfill the electronic and structural requirements to work like a donor impurity in In₂O₃ materials. The solution was sprayed onto silicon and glass substrates kept at 525 °C. Structural analysis was carried out from X-ray diffraction and selected area electron diffraction results reveal the structure of In₂O₃ with very small variations in crystallographic parameters. From electron microscopy observations, the nanostructured nature of the IWO compound was derived and from EFTEM micrographs the distribution of W reveals an increasing concentration in grain boundaries. Also scanning electron and atomic force microscopy techniques were used in order to determine the morphological and topological characteristics of the films. Also the number of carrier increases when W grows up to 5% weight and remains constant close to η_e = 28 × 10¹⁹ cm^− 3. The mobility grows up 2% W weight and the decreases monotonically. The optical transmittance of the IWO was close to 78% for all the cases. From XPS studies, low intensity signals form W orbitals were detected. The identified signals correspond to W-4d_5/2 and to W-4f_7/2 which were found very close to 250 and 37 eV respectively. These signals correspond to W atoms surrounded by O atoms in a similar configuration to the one reported for WO₃.     

Surface acoustic wave properties of aluminum oxide films on lithium niobate

Aluminum oxide (Al₂O₃) films have been deposited on lithium niobate (LiNbO₃) substrates by electron beam evaporation without any interlayer between them to ensure a good adhesion of the Al₂O₃ films to LiNbO₃ substrates. As Al₂O₃ thin films can sufficiently increase the surface acoustic wave (SAW) velocity, they can be used to improve the performance of the SAW device. The SAW phase velocity in the Al₂O₃/LiNbO₃ structure was found to increase with the insertion of an Al₂O₃ film, which can be attributed to the stiffening effect of the Al₂O₃ layer. The velocity change ratio of SAW was about 4.39% (at 304 MHz) for the Al₂O₃ (9.7 μm)/LiNbO₃ sample. A comparison with other findings in literature reveals that this result is better than what is available from diamond-like carbon/SiC buffer layer/LiNbO₃ structure, whose the velocity change ratio is 2%.     

Photodecomposition effects of graphene oxide coated on TiO2 thin film prepared by electron-beam evaporation method

Morphological, structural and photocatalytic properties of graphene oxide (GO)/TiO₂ thin-film deposited on quartz substrate were investigated. The TiO₂ film was prepared by electron-beam evaporation and the GO film by spin coating method. The photocatalytic activities of the GO/TiO₂ film were evaluated by photodecomposition of methylene blue. There was synergistic effect between TiO₂ and GO which causes a rapid photo-induced charge separation and the reduction of the recombination of electron-hole pairs under the UV-visible light irradiation. GO on TiO₂ film also promotes the properties of adsorption of the dye, photon scattering probability, and interacting surface area. As a result, it leads to the enhancement of the efficiency of the photodegradation in GO/TiO₂ film.     

Thin films of iron oxide by low pressure MOCVD using a novel precursor: tris(t-butyl-3-oxo-butanoato)iron(III)

Deposition of thin films of iron oxide on glass has been carried out using a novel precursor, tris(t-butyl-3-oxo-butanoato)iron(III), in a low-pressure metalorganic chemical vapor deposition (MOCVD) system. The new precursor was characterized for its thermal properties by thermogravimetry and differential thermal analysis. The films were characterized by X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy, and by optical measurements. XRD studies reveal that films grown at substrate temperatures below ∼550 °C and at low oxygen flow rates comprise only the phase Fe₃O₄ (magnetite). At higher temperatures and at higher oxygen flow rates, an increasing proportion of α-Fe₂O₃ is formed along with Fe₃O₄. Films of magnetite grown under different reactive ambients—oxygen and nitrous oxide—have very different morphologies, as revealed by scanning electron microscopic studies.     

Characterization of n-type and p-type semiconductor gas sensors based on NiOx doped TiO2 thin films

This work presents the development of n-type and p-type gas-sensitive materials from NiO_x doped TiO₂ thin films prepared by ion-assisted electron-beam evaporation. TiO₂ gas-sensing layers have been deposited over a wide range of NiO_x content (0-10 wt.%). The material analysis by atomic force microscopy, X-ray photoemission spectroscopy, and X-ray diffraction suggests that NiO_x doping does not significantly affect surface morphology and Ni element may be a substitutional dopant of the TiO₂ host material. Electrical characterization shows that NiO_x content as high as 10% wt. is needed to invert the n-type conductivity of TiO₂ into p-type conductivity. There are notable gas-sensing response differences between n-type and p-type NiO_x doped TiO₂ thin film. The responses toward all tested reducing gases tend to increase with operating temperature for the n-type TiO₂ films while the response decreases with temperature for p-type TiO₂ film. In addition, the p-type NiO_x doping results in the significant response enhancement toward tested reducing gases such as acetone and ethanol at low operating temperature of 300 °C.     

Structure and microstructure of EB-PVD yttria thin films grown on Si (111) substrate

Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500° and 700 °C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the Y oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 °C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 °C whereas no texture was found for 700 °C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns.     

Structural properties of epitaxial SrCuO2 thin films on SrTiO3 (001) substrates

Thin films of SrCuO₂ with tetragonal structure have been epitaxially grown on SrTiO₃ (001) substrates by high-oxygen pressure sputtering technique. The interface structure between SrCuO₂ and SrTiO₃ and configuration of defects in SrCuO₂ thin films have been characterized by means of high-resolution transmission electron microscopy. Two types of film-substrate interface structure coexist and are determined as bulk-SrO-TiO₂-Sr(O) -CuO₂-Sr-bulk and bulk-SrO-TiO₂-SrO-Sr(O) -CuO₂-Sr-bulk. The planar faults with double SrO atomic layers in {100} planes in SrCuO₂ thin films are observed, which mainly arise from the coalescence of these two types of film-substrate interface structure. Meanwhile, planar faults in {110} planes are observed in thin films and structural models are proposed.     

Preparation of fluorine-doped tin oxide (SnO2:F) film on polyethylene terephthalate (PET) substrate

Fluorine-doped tin oxide (FTO), one of the most popular transparent conductive oxide (TCO) materials, coated on glass has been used in various applications including many new-generation solar cells. However, there is a lack of reporting when it comes to FTO coated on flexible transparent substrate. For this paper, spray pyrolysis technique was used to have FTO firstly coated on to a brass substrate, which was then dissolved away after cementing an upper flexible transparent polyethylene terephthalate (PET) substrate, finally leaving high quality FTO film on PET substrate. Their structural, electrical, optical and flexible properties were investigated. The lowest resistivity was 7.6 × 10^− 4 Ω cm, which is as good as conventional FTO deposited on glass. Their fold ability could be significantly improved to transcend commercial ITO/PET only by increasing the pretreating time of the brass substrate.     

Growth of silicon nanowires by electron beam evaporation using indium catalyst

For the first time silicon nanowires have been grown on indium (In) coated Si (100) substrates using e-beam evaporation at a low substrate temperature of 300 °C. Standard spectroscopic and microscopic techniques have been employed for the structural, morphological and compositional properties of as grown Si nanowires. The as grown Si nanowires have randomly oriented with an average length of 600 nm for a deposition time of 15 min. As grown Si nanowires have shown indium nanoparticle (capped) on top of it confirming the Vapor Liquid Solid (VLS) growth mechanism. Transmission Electron Microscope (TEM) measurements have revealed pure and single crystalline nature of Si nanowires. The obtained results have indicated good progress towards finding alternative catalyst to gold for the synthesis of Si nanowires.     

Growth and characterization of germanium nanowires by electron beam evaporation

Germanium nanowires were grown on Au coated Si substrates at 380 °C in a high vacuum (5 × 10^− 5 Torr) by e-beam evaporation of Germanium (Ge). The morphology observation by a field emission scanning electron microscope (FESEM) shows that the grown nanowires are randomly oriented with an average length and diameter of 600 nm and 120 nm respectively for a deposition time of 60 min. The nanowire growth rate was measured to be ∼ 10 nm/min. Transmission electron microscope (TEM) studies revealed that the Ge nanowires were single crystalline in nature and further energy dispersive X-ray analysis (EDAX) has shown that the tip of the grown nanowires was capped with Au nanoparticles, this shows that the growth of the Ge nanowires occurs by the vapour liquid solid (VLS) mechanism. HRTEM studies on the grown Ge nanowire show that they are single crystalline in nature and the growth direction was identified to be along [110].     

Mechanical properties and scratch resistance of filtered-arc-deposited titanium oxide thin films on glass

The mechanical properties and the scratch resistance of titanium oxide (TiO₂) thin films on a glass substrate have been investigated. Three films, with crystalline (rutile and anatase) and amorphous structures, were deposited by the filtered cathodic vacuum arc deposition technique on glass, and characterized by means of nanoindentation and scratch tests. The different damage modes (arc-like, longitudinal and channel cracks in the crystalline films; Hertzian cracks in the amorphous film) were assessed by means of optical and focused ion beam microscopy. In all cases, the deposition of the TiO₂ film improved the contact-mechanical properties of uncoated glass. Crystalline films were found to possess a better combination of mechanical properties (i.e. elastic modulus up to 221 GPa, hardness up to 21 GPa, and fracture strength up to 3.6 GPa) than the amorphous film. However, under cyclic sliding contact above the critical fracture load, the amorphous film was found to withstand a higher number of cycles. The results are expected to provide useful insight for the design of optical coatings with improved contact-damage resistance.     

Microstructure evolution and age hardening in (Ti,Si)(C,N) thin films deposited by cathodic arc evaporation

Ti_1 − xSi_xC_yN_1 − y films have been deposited by reactive cathodic arc evaporation onto cemented carbide substrates. The films were characterized by X-ray diffraction, elastic recoil detection analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron-energy loss spectroscopy and nanoindentation. Reactive arc evaporation in a mixed CH₄ and N₂ gas gave films with 0 ≤ x ≤ 0.13 and 0 ≤ y ≤ 0.27. All films had the NaCl-structure with a dense columnar microstructure, containing a featherlike pattern of nanocrystalline grains for high Si and C contents. The film hardness was 32-40 GPa. Films with x > 0 and y > 0 exhibited age-hardening up to 35-44 GPa when isothermally annealed up to 900 °C. The temperature threshold for over-ageing was decreased to 700 °C with increasing C and Si content, due to migration of Co, W and Cr from the substrate to the film, and loss of Si. The diffusion pathway was tied to grain boundaries provided by the featherlike substructure.     

Galvanostatic electrodeposition and microstructure of copper (I) oxide film

 Polycrystalline copper (I) oxide films were deposited on stainless steel substrate by galvanostatic electrodeposition method and were characterized by X-ray diffraction and scanning electron microscopy. The effect of bath temperature, bath pH and current density on the compositon, grain size, surface texture and surface morphology of the electrodeposited films were investigated. The films deposited at low bath pH (≤7) consisted of copper (I) oxide and metallic copper; while the films deposited at bath pH between 8 and 12 and bath temperature of 60°C were pure copper (I) oxide. The preferred orientation of the copper (I) oxide films depended on the relative growth rate of {111} and {200} faces and could be controlled by adjusting the bath pH and/or the cathodic current density. (100)-oriented copper (I) oxide films could be deposited at pH=9 and current densities in the range of 0.25–1 mA/cm², while (111)-oriented films could be prepared at pH=12 or at pH=9 using the current densities between 1.5–2.5 mA/cm². Computer simulated crystallite shapes showed that the crystal shape changed from octahedral for (100)-oriented film to trucated pyramids and cubs for (111)-oriented film. And they were approved by scanning electron microscopy. Received: 1 December 1997 / Accepted: 13 December 1997