Low temperature UV/ozone oxidation formation of HfSiON gate dielectric

Physical and electrical properties of hafnium silicon oxynitride (HfSi_xO_yN_z) dielectric films prepared by UV ozone oxidation of hafnium silicon nitride (HfSiN) followed by annealing to 450 °C are reported. Interfacial layer growth was minimized through room temperature deposition and subsequent ultraviolet/ozone oxidation. The capacitance–voltage (C–V) and current–voltage (I–V) characteristics of the as-deposited and annealed HfSi_xO_yN_z are presented. These 4 nm thick films have a dielectric constant of 8–9 with 12 at.% Hf composition, with a leakage current density of 3×10⁻⁵ A/cm² at V_fb+1 V. The films have a breakdown field strength >10 MV/cm.     

Highly conducting indium tin oxide (ITO) thin films deposited by pulsed laser ablation

Highly conducting and transparent indium tin oxide (ITO) thin films were prepared on SiO₂ glass and silicon substrates by pulsed laser ablation (PLA) from a 90 wt.% In₂O₃-10 wt.% SnO₂ sintered ceramic target. The growths of ITO films under different oxygen pressures (P_O2) ranging from 1×10⁻⁴–5×10⁻² Torr at low substrate temperatures (T_s) between room temperature (RT) and 200°C were investigated. The opto-electrical properties of the films were found to be strongly dependent on the P_O2 during the film deposition. Under a P_O2 of 1×10⁻² Torr, ITO films with low resistivity of 5.35×10⁻⁴ and 1.75×10⁻⁴ Ω cm were obtained at RT (25°C) and 200°C, respectively. The films exhibited high carrier density and reasonably high Hall mobility at the optimal P_O2 region of 1×10⁻² to 1.5×10⁻² Torr. Optical transmittance in excess of 87% in the visible region of the solar spectrum was displayed by the films deposited at Po₂≥1×10⁻² Torr and it was significantly reduced as the P_O2 decreases.     

Excited-state absorption at 1.57 μm in U:CaF2 and Co:ZnSe saturable absorbers

Appreciable excited-state absorption (ESA) in U²⁺:CaF₂ and Co²⁺:ZnSe saturable absorbers was measured at λ=1.573 μm by optical transmission versus light fluence curves of 30–40 ns long pulses. The ground- and excited-state absorption cross-sections obtained were (9.15±0.3)×10⁻²⁰ and (3.6±0.2)×10⁻²⁰ cm², respectively, for U²⁺:CaF₂, and (57±4)×10⁻²⁰ and (12.5±1)×10⁻²⁰ cm² for Co²⁺:ZnSe. Thus, ESA is not negligible in U²⁺:CaF₂ and Co²⁺:ZnSe, as previously estimated.     

Up-conversion dynamics in GdAlO3:Er single crystal fibre

Green fluorescence has been obtained under continuous laser excitation in the 780–860 nm range in GdAlO₃:Er³⁺. With the help of the Judd-Ofelt treatment we built a model based on population rate equations to describe its time evolution. We found the intensity parameters to be Ω₂ = 2.045 × 10⁻²⁰ cm², Ω₄ = 1.356 × 10⁻²⁰ cm² Ω₆ = 1. 125 × 10⁻²⁰ cm². Even if a two-photon absorption and a looping mechanism are necessary to well describe the dynamics, the main process responsible for up-conversion is energy transfer between erbium ions.     

Field-lowering carrier excitation in cadmium arsenide thin films

Cadmium arsenide is a II–V semiconductor which exhibits n-type intrinsic conductivity with high mobility up to μ_n=1.0–1.5 m²/V s. Potential applications include magnetoresistors and both thermal and photodetectors, which require electrical characterization over a wide range of deposition and measurement conditions. The films were prepared by vacuum evaporation with deposition rates in the range 0.5–6.0 nm/s and substrate temperatures maintained at constant values of 20–120°C. Sandwich-type samples were deposited with film thicknesses of 0.1–1.1 μm using evaporated electrodes of Ag and occasionally Au or Al. Above a typical electric field F_b of up to 5×10⁷ V/m all samples showed instabilities characteristic of dielectric breakdown or electroforming. Below this field they showed a high-field conduction process with logJ∝V^1/2, where J is the current density and V the applied voltage. This type of dependence is indicative of carrier excitation over a potential barrier whose effective barrier height has been lowered by the high electric field. The field-lowering coefficient β had a value of (1.2–5.3)×10⁻⁵ eV m^1/2/V^1/2 which is reasonably consistent with the theoretical value of β_PF=2.19×10⁻⁵ eV m^1/2/V^1/2 expected when the field-lowering occurs at donor-like centres in the semiconductor (Poole–Frenkel effect). For thinner films Schottky emission was more probable. The effects of the film thickness, electrode materials, deposition rate, and substrate temperature on the conductivity behaviour are discussed.     

Preparation and characterization of Bi2Ti2O7 thin films by chemical solution deposition technique

Transparent and crack-free Bi₂Ti₂O₇ thin films with strong (111) orientation were successfully prepared on n-Si(100) by chemical solution deposition (CSD) using bismuth nitrate and titanium butoxide as starting materials. The structural properties were studied by X-ray diffraction. The dielectric constant at 100 kHz at room temperature was 118 and loss factor was 0.074, for a 0.4-μm-thick film annealed at 500°C for 30 min. The leakage current density was 4.06×10⁻⁷ A/cm² at an applied voltage of 15 V.     

New transparent conducting MgIn2O4---Zn2In2O5 thin films prepared by magnetron sputtering

New materials for a transparent conducting oxide film are demonstrated. Highly transparent Zn₂In₂O₅ films with a resistivity of 3.9 × 10⁻⁴ Ω cm were prepared on substrates at room temperature using a pseudobinary compound powder target composed of ZnO (50 mol.%) and In₂O₃ (50 mol.%) by r.f. magnetron sputtering. MgIn₂O₄---Zn₂In₂O₅ films were prepared using MgIn₂O₄ targets with a ZnO content of 0–100 wt.%. The resistivity of the deposited films gradually decreased from 2 × 10⁻³ to 3.9 × 10⁻⁴ Ω cm as the Zn/(Mg + Zn) atomic ratio introduced into the films was increased. The greatest transparency was obtained in a MgIn₂O₄ film. The optical absorption edge of the films decreased as the Zn/(Mg + Zn) atomic ratio was increased, corresponding to the bandgap energy of their materials. It was found that the resistance of the undoped Zn₂In₂O₅ films was more stable than either the undoped MgIn₂O₄, ZnO or In₂O₃ films in oxidizing environments at high temperatures.     

The optical and electrical properties of copper indium di-selenide thin films

Thin films of copper indium di-selenide (CIS) with a wide range of compositions near stoichiometry have been formed on glass substrates in vacuum by the stacked elemental layer (SEL) deposition technique. The compositional and optical properties of the films have been measured by proton-induced X-ray emission (PIXE) and spectrophotometry (photon wavelength range of 300–2500 nm), respectively. Electrical conductivity (σ), charge-carrier concentration (n), and Hall mobility (μ_H) were measured at temperatures ranging from 143 to 400 K. It was found that more indium-rich films have higher energy gaps than less indium-rich ones while more Cu-rich films have lower energy gaps than less Cu-rich films. The sub-bandgap absorption of photons is minimum in the samples having Cu/In ≈ 1 and it again decreases, as Cu/In ratio becomes less than 0.60. Indium-rich films show n-type conductivities while near-stoichiometric and copper-rich films have p-type conductivities. At 300 K σ, n and μ_H of the films vary from 2.15 × 10⁻³ to 1.60 × 10⁻¹ (Ω cm)⁻¹, 2.28 × 10¹⁵ to 5.74 × 10¹⁷ cm⁻³ and 1.74 to 5.88 cm² (V s)⁻¹, respectively, and are dependent on the composition of the films. All the films were found to be non-degenerate. The ionization energies for acceptors and donors vary between 12 and 24, and 3 and 8 meV, respectively, and they are correlated well with the Cu/In ratios. The crystallites of the films were found to be partially depleted in charge carriers.     

Thermal conductivity of BaWO4 single crystal

Barium tungstate (BaWO₄) single crystal has been grown using Czochralski technique. It belongs to the scheelite structure, forming the space group I4₁/a at room temperature and the primitive cell contains two formular units. The thermal expansion, specific heat and thermal diffusivity were measured, and then the thermal conductivity was calculated. These results show that BaWO₄ possesses large anisotropic thermal expansion and its thermal expansion coefficients are _a = 1.10 × 10⁻⁵/K, _b = 1.08 × 10⁻⁵/K, and _c = 3.51 × 10⁻⁵/K in the temperature range from 303 to 1423 K. However, its thermal conductivity shows small anisotropic in the temperature range from 297 to 563 K and even displays isotropic at about 428 K. The calculated thermal conductivities are 2.59 and 2.73 W m⁻¹ K⁻¹ at room temperature, along [1 0 0] and [0 0 1] directions, respectively.     

Charge trapping in polymer diodes

We report studies focusing on the nature of trap states present in single layer ITO/poly(phenylene vinylene)/Al light emitting diodes. At high applied bias the IV characteristics from 11 to 290 K can be successfully modelled by space charge limited current (SCLC) theory with an exponential trap distribution, giving a trap density H_t of 4(±2) × 10¹⁷ cm⁻³, μ_p, between 10⁻⁶ and 5 × 10⁻⁸ cm² V⁻¹ s⁻¹ and a characteristic energy E_t of 0.15 eV at high temperatures. The transient conductance follows a power-law relationship with time whose decay rate decreases with decreasing temperature. This can be directly related to the emptying of the trap distribution found in the SCLC analysis. Due to variations in structure, conformation and environment, the polymer LUMO and HOMO density of states form Gaussian distributions of chain sites. The deep sites in the tail of the distributions are the observed traps for both positive and negative carriers. The same sites dominate the photo- and electroluminescence emission. This implies that the emissive layer in organic LED's should be made as structurally disordered as possible.     

Structure and electrical properties of (100)-oriented Pb(Zn1/3Nb2/3)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films on La0.7Sr0.3MnO3 electrode by chemical solution deposition

(100)-oriented 0.462Pb(Zn_1/3Nb_2/3)O₃–0.308Pb(Mg_1/3Nb_2/3)O₃–0.23PbTiO₃ (PZN-PMN-PT) perovskite ferroelectric thin films were prepared on La_0.7Sr_0.3MnO₃/LaAlO₃ (LSMO/LAO) substrate via a chemical solution deposition route. The perovskite LSMO electrode was found to effectively suppress the pyrochlore phase while promote the growth of the perovskite phase in the PZN-PMN-PT film. The film annealed at 700 °C exhibited a high dielectric constant of 2130 at 1 kHz, a remnant polarization, 2P_r, of 29.8 μC/cm², and a low leakage current density of 7.2 × 10^− 7 A/cm² at an applied field of 200 kV/cm. The ferroelectric polarization was fatigue-free at least up to 10¹⁰ cycles. Piezoelectric coefficient, d₃₃, of 48 pm/V was also demonstrated. The results showed that much superior properties could be achieved with the PZN-PMN-PT thin films on the solution derived LSMO electrode than on Pt electrode by sputtering.     

Investigation of stress behaviors and mechanism of void formation in sputtered TiSix films

We have investigated the stress behaviors and a mechanism of void formation in TiSi_x films during annealing. TiSi_x thin films were prepared by DC magnetron sputtering using a TiSi_2.1 target in the substrate temperature range of 200–500 °C. The as-deposited TiSi_x films at low substrate temperature (<300 °C) have an amorphous structure with low stress of 1×10⁸ dynes/cm². When the substrate temperature increases to 500 °C, the as-deposited TiSi_x film has a mixture of C49 and C54 TiSi₂ phase with stress of 8×10⁹ dynes/cm². No void was observed in the as-deposited TiSi_x film. Amorphous TiSi_x film transforms to C54 TiSi₂ phase with a random orientation of (311) and (040) after annealing at 750 °C. The C49 and C54 TiSi₂ mixture phase transforms to (040) preferred C54 TiSi₂ phase after annealing over 650 °C. By increasing substrate temperature, the transformation temperature for C54 TiSi₂ can be reduced, resulting in relieved stress of TiSi₂ film. The easy nucleation of the C54 phase was attributed to an avoidance of amorphous TiSi_x phase. We found that amorphous TiSi_x→C54 TiSi₂ transformation caused higher tensile stress of 2×10¹⁰ dynes/cm², resulting in more voids in the films, than C49→C54 transformation. It was observed that void formation was increased with thermal treatment. The high tensile stress caused by volume decreases in the silicide must be relieved to retard voids and cracks during C54 TiSi₂ formation.     

A kinetic model for the degradation of benzothiazole by Fe3+-photo-assisted Fenton process in a completely mixed batch reactor

The degradation of benzothiazole in aqueous solution by a photo-assisted Fenton reaction has been studied in a batch reactor in the pH range 2.0–3.2 and for H₂O₂ and Fe(III) concentrations respectively between 1.0×10⁻³–1.5×10⁻¹ and 1.0×10⁻⁶–4.0×10⁻⁶ M.

A kinetic model has been developed to predict the decay of benzothiazole at varying reaction conditions. The use of kinetic constants from the literature in the model allows to simulate the system behavior by taking into account the influence of pH, hydrogen peroxide, Fe(III) and sulfate concentrations and the ionic strength.     

Transparent conductive In2O3:Mo thin films prepared by reactive direct current magnetron sputtering at room temperature

An amorphous transparent conductive oxide thin film of molybdenum-doped indium oxide (IMO) was prepared by reactive direct current magnetron sputtering at room temperature. The films formed on glass microscope slides show good electrical and optical properties: the low resistivity of 5.9 × 10^− 4 Ω cm, the carrier concentration of 5.2 × 10²⁰ cm^− 3, the carrier mobility of 20.2 cm² V^− 1 s^− 1, and an average visible transmittance of about 90.1%. The investigation reveals that oxygen content influences greatly the carrier concentration and then the photoelectrical properties of the films. Atomic force microscope evaluation shows that the IMO film with uniform particle size and smooth surface in terms of root mean square of 0.8 nm was obtained.     

Highly conducting doped poly-Si deposited by hot wire CVD and its applicability as gate material for CMOS devices

Highly conducting p- and n-type poly-Si:H films were deposited by hot wire chemical vapor deposition (HWCVD) using SiH₄+H₂+B₂H₆ and SiH₄+H₂+PH₃ gas mixtures, respectively. Conductivity of 1.2×10² (Ω cm)⁻¹ for the p-type films and 2.25×10² (Ω cm)⁻¹ for the n-type films was obtained. These are the highest values obtained so far by this technique. The increase in conductivity with substrate temperature (T_s) is attributed to the increase in grain size as reflected in the atomic force microscopy results. Interestingly conductivity of n-type films is higher than the p-type films deposited at the same T_s. To test the applicability of these films as gate contact Al/poly-Si/SiO₂/Si capacitor structures with oxide thickness of 4 nm were fabricated on n-type c-Si wafers. Sputter etching of the poly-Si was optimized in order to fabricate the devices. The performance of the HWCVD poly-Si as gate material was monitored using C–V measurements on a MOS test device at different frequencies. The results reveal that as deposited poly-Si without annealing shows low series resistance.     

Structure-composition-property dependence in reactive magnetron sputtered ZnO thin films

Thin films of zinc oxide (ZnO) were prepared by dc reactive magnetron sputtering on glass substrates at various oxygen partial pressures in the range 1×10⁻⁴–6×10⁻³ mbar and substrate temperatures in the range 548–723 K. The variation of cathode potential of zinc target on the oxygen partial pressure was explained in terms of target poisoning effects. The stoichiometry of the films has improved with the increase in the oxygen partial pressure. The films were polycrystalline with wurtzite structure. The films formed at higher substrate temperatures were (0 0 2) oriented. The temperature dependence of Hall mobility of the films formed at various substrate temperatures indicated that the grain boundary scattering of charge carriers was predominant electrical conduction mechanism in these films. The optical band gap of the films increased with the increase of substrate temperature. The ZnO films formed under optimized oxygen partial pressure of 1×10⁻³ mbar and substrate temperature of 663 K exhibited low electrical resistivity of 6.9×10⁻² Ω cm, high visible optical transmittance of 83%, optical band gap of 3.28 eV and a figure of merit of 78 Ω⁻¹ cm⁻¹.     

(Fe,Ti) 16N2 films with high saturation magnetization prepared by facing target sputtering

(Fe,Ti)-N films with a Ti concentration of 10 at.% were prepared on Si(100) and NaCl substrates by facing targets sputtering. The effects of the nitrogen pressure (P_N) and the substrate temperature (T_s) on the formation of various (Fe,Ti)-N phases and their microstructures were investigated in detail. X-ray diffractometer and transmission electron microscope provided complete identification of the phases present in the films and the characterization of their microstructures. Films deposited at a lower P_N = 1 3 × 10⁻² Pa or a lower T_s = RT consist of mainly -phase. Films deposited at a higher P_N = 1.3 2 × 10⁻¹ Pa or a higher T_s = 200 °C contain a great many γ' and Fe₂N phases with a higher nitrogen content. When P_N = 4 7 × 10⁻² Pa and T_s = 100 150 °C, it is advantageous to the formation of ′' phase. These films exhibit a high saturation magnetization (M_s) up to the range of 2.3 2.5 T, which is larger than that of pure iron.     

Atomic layer deposition growth of zirconium doped In2O3 films

Zirconium doped indium oxide thin films were deposited by the atomic layer deposition technique at 500 °C using InCl₃, ZrCl₄ and water as precursors. The films were characterised by X-ray diffraction, energy dispersive X-ray analysis and by optical and electrical measurements. The films had polycrystalline In₂O₃ structure. High transparency and resistivity of 3.7×10⁻⁴ Ω cm were obtained.     

Normal metal, ohmic contacts to high-temperature superconducting YBa2Cu3O7-δ thin films suitable for multichip modules

Normal metal, ohmic contacts to high-temperature superconductor (HTSC) materials will be used to form via structures between HTSC interconnect levels, and also, substrate bonding pads in a superconducting multichip module (SMCM). Specific contact resistivities below 10⁻⁸ Ω cm² will be required for such contacts to control signal attenuation and local contact heating of the LN₂cooled SMCM. Previous work on normal metal/superconducting contacts has not focused on metallization schemes which will be stable during subsequent high-temperature processing. Metal contacts of gold, silver, and palladium were formed on superconducting thin films of YBa₂Cu₃O_7-δ via evaporation and sputtering through a shadow mask followed by annealing in various ambients and at several temperatures. Palladium contacts oxidized readily during anneal, and sputtered gold contacts required additional processing and exhibited higher specific contact resistivities. The best contacts were obtained by a controlled-cooling oxygen anneal of evaporated gold or silver, as indicated by normal-state specific contact resistivities of 3 × 10⁻⁵ Ω cm² and 4 × 10⁻⁵ Ω cm², respectively. This work differs from previously published results by describing contacts which required no extensive preparation of the HTSC surface and were stable to 700 °C, indicating these contacts would be compatible with subsequent high-temperature processing of the additional HTSC layers required in a multi-level SMCM.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.