(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.     

Surface and electrical studies of CuO:V2O5 thin films

Results from the studies of multicomponent CuO:V₂O₅ bulk material and thermally evaporated thin films of highly conducting bulk composition prepared at different substrate temperatures are thus compared and discussed. The electronic conductivity is enhanced on increase in the substrate temperature T_s and reaches a maximum value of 12.3 × 10⁻⁶Ω⁻¹ cm⁻¹ for T_s = 423 K. X-ray photoelectron spectroscopy studies indicate an increase in the reduced states of vanadium and copper ions in going from the bulk glass to the thin film. Dynamic secondary-ion mass spectroscopy studies on thin films over a depth of 3000 Å show a strong dependence of T_s on the Cu-to-V intensity ratio. Even though stoichiometric values for thin films are achievable by varying the T_s, the oxidation states of Cu in these films are predominantly monovalent. The electrical behaviors of these materials and their thin film counterparts are finally being discussed in relation to the surface analysis data.     

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.     

Synthesis of AlN by reactive sputtering

We present a systematic study of the sub-band gap optical absorption coefficients (hν) in the range 1.2–6 eV vs. deposition-temperature (T_s from 27 to 450°C) films deposited on silica by 13.6 MHz magnetron sputtering of an Al target with 53 and 72% N₂ in the reactive mixture. X-ray diffraction, infrared absorption and Raman diffusion are also presented, mainly on films deposited on Si in the same run to help in the characterisation of the films. All signals are specific of AlN polycrystalline films, which are of better quality when deposited with 72% N₂. The lowest sub-band gap optical absorption around 5×10² cm⁻¹ is obtained for deposition on silica at T_s=300°C with 72% N₂ and is close to that of heteroepitaxial films deposited on sapphire.     

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.     

Characterization of indium zinc oxide thin films prepared by pulsed laser deposition using a Zn3In2O6 target

Using a Zn₃In₂O₆ target, indium-zinc oxide films were prepared by pulsed laser deposition. The influence of the substrate deposition temperature and the oxygen pressure on the structure, optical and electrical properties were studied. Crystalline films are obtained for substrate temperatures above 200°C. At the optimum substrate deposition temperature of 500°C and the optimum oxygen pressure of 10⁻³ mbar, both conditions that indeed lead to the highest conductivity, Zn₃In₂O₆ films exhibit a transparency of 85% in the visible region and a conductivity of 1000 S/cm. Depositions carried out in oxygen and reducing gas, 93% Ar/7% H₂, result in large discrepancies between the target stoichiometry and the film composition. The Zn/In (at.%) ratio of 1.5 is only preserved for oxygen pressures of 10⁻²–10⁻³ mbar and a 93% Ar/7% H₂ pressure of 10⁻² mbar. The optical properties are basically not affected by the type of atmosphere used during the film deposition, unlike the conductivity which significantly increases from 80 to 1400 S/cm for a film deposited in 10⁻² mbar of O₂ and in 93% Ar/7% H₂, respectively.     

High deposition rate of amorphous silicon thick layers using a gas mixture of 10% silane in hydrogen

The deposition rate of amorphous silicon of the order of 0.9 μm/h, has been obtained using a gas mixture of 10% silane (SiH₄) in hydrogen (H₂), with a RF source of 13.56 MHz. Best films were deposited at a total flow rate of 100–200 sccm, 300°C substrate temperature, 66.7 Pa, and RF power density of 150 mW/cm². The geometrical configuration of the reaction chamber included a gas injector that was specially designed for this purpose. Films were characterized by Fourier transform infrared (FTIR), secondary ion mass spectrometry (SIMS), and profilometer. In addition, thick p-i-n diodes were prepared and characterized, obtaining reverse current densities lower than 5×10⁻⁶ A/cm² at full depletion.     

Quantitative analysis of tungsten, oxygen and carbon concentrations in the microcrystalline silicon films deposited by hot-wire CVD

In order for hot-wire chemical vapor deposition to compete with the conventional plasma-enhanced chemical vapor deposition technique for the deposition of microcrystalline silicon, a number of key scientific problems should be cleared up. Among these points, the concentration of tungsten (nature of the filament), as well as the concentration of oxygen and carbon (elements issued when vacuum is broken between two runs), should not exceed threshold values, beyond which electronic properties of the films could be degraded, as in the case of monocrystalline silicon. Quantitative chemical analysis of these elements has been carried out using the secondary ion mass spectrometry technique through depth profiles. It has been shown that for a high effective filament surface area (S_f=27 cm²), the W content increases steadily from 5×10¹⁴ to 2×10¹⁸ atoms cm⁻³ when the filament temperature T_f increases from 1500 to 1800 °C. For a fixed T_f, the W content increases with the effective surface area S_f. Thus, considering our reactor geometry, the W content does not exceed the detection limit (5×10¹⁴ atoms cm⁻³) when T_f and S_f are limited to 1600 °C and 4 cm², respectively. For O and C elements, under deposition conditions of high dilution of silane in hydrogen (96%), O and C concentrations approaching 10²⁰ atoms cm⁻³ have been obtained. The introduction of an inner vessel inside the reactor, the addition of a load-lock chamber and a decrease in substrate temperature to 300 °C have led to a drastic decrease in these contents down to 3×10¹⁸ atoms cm⁻³, compatible with the realization of 6% efficiency HWCVD μc-Si:H solar cells.     

Highly conductive microcrystalline silicon carbide films deposited by the hot wire cell method and its application to amorphous silicon solar cells

Microcrystalline silicon carbide (μc-Si_1−xC_x) films were successfully deposited by the hot wire cell method using a gas mixture of SiH₄, H₂ and C₂H₂. It was confirmed by Fourier transform infrared and X-ray diffraction analyses that the films consisted of μc-Si grains embedded in a-Si_1−xC_x tissue. The p-type μc-Si_1−xC_x films were deposited using B₂H₆ as a doping gas. A dark conductivity of 0.2 S/cm and an activation energy of 0.067 eV were obtained. The p-type μc-Si_1−xC_x was used as a window layer of a-Si solar cells, in which the intrinsic layer was deposited by photo-chemical vapor deposition, and an initial conversion efficiency of 10.2% was obtained.     

Effect of hydrogen radical on growth of μc-Si in hetero-structured SiCx alloy films

The changes of the crystallinity of μc-Si phase are studied in samples deposited with hydrogen dilution ratio, H₂/SiH₄, from 9.0 to 19.0 by hot-wire CVD (Cat-CVD). In the samples deposited at filament temperature, T_f, of 1850 °C, the crystalline fraction and the crystallite size of μc-Si phase increased with increasing the H₂/SiH₄. The carbon content, C/(Si+C), was almost constant. In the XRD patterns, the intensity of Si(1 1 1) peak decreased and that of Si(2 2 0) peak increased with increasing the H₂/SiH₄. In the samples deposited at T_f of 2100 °C with H₂/SiH₄ over 11.4, the μc-Si phase was not formed and the C/(Si+C) increased. The growth mechanism of μc-Si in hetero-structured SiC_x alloy films is discussed.     

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.     

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.     

D.c. properties of ZnO thin films prepared by r.f. magnetron sputtering

In the development of ZnO-based varistors the electrical properties of ZnO/Bi₂O₃ junctions and of the two individual oxides are being investigated. Following our recent work on a.c. conductivity in Al---ZnO---Al sandwich structures we currently report d.c. measurements. The structures were prepared by r.f. magnetron sputtering in an argon/oxygen mixture in the ratio 4:1. Capacitance-voltage data confirm that the Al/ZnO interface does not form a Schottky barrier and measurements of the dependence of capacitance on film thickness indicate that the relative permittivity of the films is approximately 9.7. With increasing voltage the current density changed from an ohmic to a power-law dependence with exponent n≈3. Furthermore measurements of current density as a function of reciprocal temperature showed a linear dependence above about 240 K, with a very low activation energy below this temperature consistent with a hopping process. The higher temperature results may be explained assuming a room-temperature electron concentration n₀ and space-charge-limited conductivity, dominated by traps exponentially distributed with energy E below the conduction band edge according to N = N₀exp(−E/kT_t), where k is Boltzmann's constant. Typical derived values of these parameters are: n₀ = 7.2 × 10¹⁶ m⁻³, N₀ = 1.31 × 10⁴⁵ J⁻¹ m⁻³ and T_t = 623 K. The total trap concentration and the electron mobility were estimated to be 1.13 × 10²⁵ m⁻³ and (5.7−13.1) ×10⁻³m²V⁻¹s⁻¹ respectively.     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

Phase formation at rapid thermal annealing of Al/Ti/Ni ohmic contacts on 4H-SiC

Ohmic contacts to the top p-type layers of 4H-SiC p⁺–n–n⁺ epitaxial structures having an acceptor concentration lower than 1×10¹⁹ cm⁻³ were fabricated by the rapid thermal anneal of multilayer Al/Ti/Pt/Ni metal composition. The rapid thermal anneal of multilayer A1/Ti/Pt/Ni metal composition led to the formation of duplex cermet composition containing Ni₂Si and TiC phases. The decomposition of the SiC under the contact was found to be down to a depth of about 100 nm. The contacts exhibited a contact resistivity R_c of 9×10⁻⁵ Ω cm⁻² at 21°C, decreasing to 3.1×10⁻⁵ Ω cm⁻² at 186°C. It was found that thermionic emission through the barrier having a height of 0.097 eV is the predominant current transport mechanism in the fabricated contacts.     

Growth and spectroscopy of Dy doped in ZnWO4 crystal

Single-crystal ZnWO₄:Dy³⁺ was grown by Czochralski technique. The XRD, absorption spectra as well as fluorescence spectrum are investigated and the Judd–Ofelt intensity parameters Ω₂, Ω₄, Ω₆ are obtained to be 7.76 × 10⁻²⁰ cm², 0.57 × 10⁻²⁰ cm², 0.31 × 10⁻²⁰ cm², respectively. Calculated radiative transition rate, branching ratios and radiative lifetime for different transition levels of ZnWO₄:Dy³⁺ crystals are presented. Fluorescence lifetime of ⁴F_9/2 level is 158 μs and quantum efficiency is 66%.The most intense fluorescence line at 575 nm correlative with transition ⁴F_9/2 → ⁶H_13/2 is potentially for application of yellow lasers.     

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.     

Infrared optical properties of Bi2Ti2O7 thin films by spectroscopic ellipsometry

Bi₂Ti₂O₇ thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. X-ray diffraction analysis shows that the Bi₂Ti₂O₇ thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0–12.5 μm). By fitting the measured ellipsometric parameter (Ψ and Δ) data with a three-phase model (air/Bi₂Ti₂O₇/GaAs), and Lorentz–Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency ω_p is 1.64×10¹⁴ Hz, and the electron collision frequency γ is 1.05×10¹⁴ Hz, and it states that the electron average scattering time is 0.95×10⁻¹⁴ s. The absorption coefficient variation with respect to increasing wavelength has been obtained.     

The Rectification Studies on the P -Ion Implanted C60/Si Films

N-type doping of the C₆₀ films deposited on Si substrates has been achieved by 80 keV P⁺-ion implantation with doses of 2×10¹⁴ cm^-2 at room temperature. The heterostructures composed of the n-type doped C₆₀ films and n- or p-type Si(111), Si(100) substrates are studied in view of semiconductor heterojunctions. The rectification and other electrical characteristics of the P⁺-ion implanted n-C₆₀/n-(p-)Si heterostructures are disclosed by the current-voltage (I-V) measurements at room temperature. The n-C₆₀/p-Si heterostructures show stronger rectification than n-C₆₀/n-Si heterostructures and Si(111) substrates are found to be more suitable for forming n-C₆₀/Si heterostructures than Si(100) substrates.     

Transparent conducting F-doped SnO2 thin films grown by pulsed laser deposition

Transparent conducting fluorine-doped tin oxide (SnO₂:F) films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of the SnO₂:F films have been investigated as a function of F-doping level and substrate deposition temperature. The optimum target composition for high conductivity was found to be 10 wt.% SnF₂ + 90 wt.% SnO₂. Under optimized deposition conditions (T_s = 300 °C, and 7.33 Pa of O₂), electrical resistivity of 5 × 10^− 4 Ω-cm, sheet resistance of 12.5 Ω/□, average optical transmittance of 87% in the visible range, and optical band-gap of 4.25 eV were obtained for 400 nm thick SnO₂:F films. Atomic force microscopy measurements for these SnO₂:F films indicated that their root-mean-square surface roughness ( 6 Å) was superior to that of commercially available chemical vapor deposited SnO₂:F films ( 85 Å).