Atomic layer deposition of BN thin films

Boron nitride has for the first time been deposited from gaseous BBr₃ and NH₃ by means of atomic layer deposition. The deposition temperatures were 400 and 750 °C, and the total pressure was 10 torr. The BN films, deposited on silica substrates, showed a turbostratic structure with a c-axis of 0.70 nm at a deposition temperature of 750 °C as determined by X-ray diffraction. The films deposited at 400 °C were significantly less ordered. The film density was obtained by means of X-ray reflectivity, and it was found to be 1.65–1.70 and 1.90–1.95 g cm⁻³ for the films deposited at 400 and 750 °C, respectively. Furthermore, the films were, regardless of deposition temperature, fully transparent and very smooth. The surface roughness was 0.3–0.5 nm as measured by optical interferometry.     

Optical and structural characteristics of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films synthesized from yttrium acetylacetonate

Yttrium oxide thin films are deposited on silicon substrates using the ultrasonic spray pyrolysis technique from the thermal decomposition of a β-diketonate, yttrium acetylacetonate (Y(acac)₃). The decomposition of Y(acac)₃ was studied by thermogravimetry, differential scanning calorimetry, mass spectrometry, and infrared spectroscopy. It was found that a β-diketone ligand is lost during the initial steps of decomposition of the Y(acac)₃. The rest of the complex is then dissociated or degraded partially until Y₂O₃ is obtained in the final step with the presence of carbon related residues. Then the Y(acac)₃ was used to synthesize Y₂O₃ thin films using the spray pyrolysis technique. The films were deposited on silicon substrates at temperatures in the range of 400–550 °C. The films were characterized by ellipsometry, infrared spectroscopy, atomic force microscopy, and X-ray diffraction. The films presented a low surface roughness with an index of refraction close to 1.8. The crystalline structure of the films depended on the substrate temperature; films deposited at 400 °C were mainly amorphous, but higher deposition temperatures (450–550 °C), resulted in polycrystalline with a cubic crystalline phase.     

Effect of Firing Temperature on the Structure and Properties of YBa2Cu3O7−x Films by TFA-MOD Method

YBa₂Cu₃O_7−x (YBCO) films were fabricated on LaAlO₃ (LAO) substrate under various firing temperatures (760–870 °C) in the crystallization process by metalorganic deposition (MOD) method using trifluoroacetates. The effect of firing temperature on the structure and properties of YBCO films was systematically investigated. According to the XRD and SEM images, the films fired at low temperature (760–800 °C) showed poor electrical performance due to rough surfaces and impurity phases. However, the films fired at 850 °C showed the highest critical temperature of 90 K and the highest J _c of 3.1 MA/cm² which attribute to the formation of a purer YBCO phase, fewer pores, and stronger biaxial texture.     

Investigation of forming-gas annealed CeO<Subscript>2</Subscript> thin film on GaN

The effects of post-deposition annealing temperatures (400, 600, 800, and 1,000°C) in forming gas (95% N₂ + 5% H₂) ambient on metal–organic decomposed cerium oxide (CeO₂) thin films deposited on n-type GaN substrate had been investigated. The occurrence of CeO₂ phase transformation was reported and presence of CeO₂, α-Ce₂O₃, and β-Ga₂O₃ had been detected, depending on the annealing temperature. As the annealing temperature increased, grain size and microstrains of CeO₂ films were, respectively, increased and reduced. Metal–oxide–semiconductor characteristics of the annealed samples were systematically investigated. The highest dielectric breakdown field was perceived by sample annealed at 400°C due to the reduction of semiconductor–oxide interface trap density and effective oxide charge.     

Effect of deposition temperature on the structure and electrical properties of thin barium strontium titanate films

We have studied the properties of thin ferroelectric films of barium strontium titanate (Ba,Sr)TiO₃ (BSTO) obtained by RF ion-plasma deposition at various substrate temperatures in the 700–900°C range. It is established that BSTO films deposited at 700–800°C exhibit a polycrystalline structure. Beginning with 800°C, the film structure changes so that an (111)-oriented phase appears and becomes predominating. The effect of the deposition temperature on the grain size and the relationship between the structural features and electrical properties of the films are considered.     

Influences of Ni–5 at.%W Alloy Substrates on the Epitaxial Growth and Surface Morphologies of CeO<Subscript>2</Subscript> Films Deposited by PLD

We fabricated CeO₂ films using pulsed laser deposition (PLD) for YBa₂Cu₃O_7−δ coated conductors on Ni–5 at.%W alloy substrates and investigated the effect of Ni–5 at.%W tapes on the epitaxial growth and surface morphologies of CeO₂ deposited on various substrates at various temperatures ranging from 650 to 770 °C. The texture and microstructure of substrates and CeO₂ films were measured by X-ray diffraction (XRD), optical microscope (OM), field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). It was found that the texture and microstructure of Ni–5 at.%W substrates, such as Ni(111), grain size, the depth of grain boundary grooves and surface roughness, affected the growth of CeO₂ films. Especially, the depth of grain boundary grooves of substrates resulted in high intensity of CeO₂(111) peak and high surface roughness of CeO₂ films. We also found that high growth temperature effectively reduced the influence of substrate surface roughness on the epitaxial growth of CeO₂ films. CeO₂ films with high in-plane and out-of-plane alignments (Δφ=5.54°, Δω=3.40°) were obtained under optimum condition.     

Effects of substrate temperatures on the thermal stability of Al-doped ZnO thin films grown by DC magnetron sputtering

In this work, Al-doped (4 at%) ZnO(AZO) thin films were prepared by DC magnetron sputtering using a home-made ceramic target at different substrate temperatures. The microstructure, optical, electrical and thermal stability properties of these thin films were characterized systematically using scanning electron microscopy, UV–Vis-NIR spectrometry, X-ray diffraction, and Hall measurements. It was observed that the AZO thin films deposited at 350 °C exhibited the lowest resistivity of 5.76 × 10⁻⁴ Ω cm, high average visible transmittance (400–800 nm) of 92%, and the best thermal stability. Comparing with the AZO thin films deposited at low substrate temperatures, the AZO thin films deposited at 350 °C had the highest compact surface morphology which could hinder the chemisorbed and diffused oxygen. This was considered to be the main mechanism which was responsible for the thermal degradation of AZO thin films.     

Synthesis and characterization of CeO<Subscript>2</Subscript> thin films deposited by spray pyrolysis

Cerium dioxide (CeO₂) thin films were deposited on glass substrates by spray pyrolysis using a solution of alcohol–water and CeCl₃ · 7H₂O as precursor. The structural, morphological, optical and electrical properties of these films were investigated. SEM images reveal the presence of cracks in the films that depend on substrate temperature and deposition time. Films deposited in temperatures between 400 and 500 °C during up to 10 min are crack free and also present high optical transmittance, reaching up to 90% in the visible range and close to infrared. X-ray diffraction shows that all films are polycrystalline and the growth preferential direction is altered from (111) to (200) with the increase of the deposition temperature. The activation energy of the electrical conduction process is 0.67 ± 0.03 eV.     

Preparation and thermoelectric properties of BP films on SOI and sapphire substrates

The chemical vapor deposited (CVD) BP films on Si(100) (190 nm)/SiO _x (370 nm)/Si(100) (625 μm) (SOI) and sapphire (R-plane) (600 μm) substrates were prepared by the thermal decomposition of the B₂H₆–PH₃–H₂ system in the temperature range of 800–1050 °C for the deposition time of 1.5 h. The BP films were epitaxially grown on the SOI substrate, but a two-step growth method, i.e., a buffer layer at lower temperature and sequent CVD process at 1000 °C for 1.5 h was effective for obtaining a smooth film on the sapphire substrate. The electrical conduction types and electrical properties of these films depended on the growth temperature, gases flow rates and substrates. The thermal conductivity of the film could be replaced by the substrate, so that the calculated thermoelectric figure-of-merit (Z) for the BP films on the SOI substrate was 10⁻⁴–10⁻³/K at 700–1000 K. Those on the sapphire substrate were 10⁻⁶–10⁻⁵/K for the direct growth and 10⁻⁵–10⁻⁴/K for the two-step growth at 700–900 K, indicating that the film on a sapphire by two-step growth would reduce the defect concentrations and promote the electrical conductivity.     

Sol–gel derived Co<Subscript>3</Subscript>O<Subscript>4</Subscript> thin films: effect of annealing on structural,morphological and optoelectronic properties

Nanocrystalline Co₃O₄ thin films were prepared on glass substrates by using sol–gel spin coating technique. The effect of annealing temperature (400–700 °C) on structural, morphological, electrical and optical properties of Co₃O₄ thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy, Electrical conductivity and UV–visible Spectroscopy. XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. The crystallite size increases with increasing annealing temperature (53–69 nm). These modifications influence the optical properties. The morphology of the sol–gel derived Co₃O₄ shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 to 2.07 eV with increasing annealing temperature between 400 and 700 °C. These mean that the optical quality of Co₃O₄ films is improved by annealing. The dc electrical conductivity of Co₃O₄ thin films were increased from 10⁻⁴ to 10⁻² (Ω cm)⁻¹ with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co₃O₄ films annealed at 400–700 °C were estimated to be of the order of 2.4–4.5 × 10¹⁹ cm⁻³ and 5.2–7.0 × 10⁻⁵ cm² V⁻¹ s⁻¹ respectively. It is observed that Co₃O₄ thin film annealing at 700 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Fabrication and ferroelectric properties of sol–gel derived 1–1 intergrowth-superlattice-structured Bi<Subscript>3</Subscript>TiNbO<Subscript>9</Subscript>-Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

1–1 intergrowth-superlattice-structured Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT) ferroelectric thin films have been prepared on p-Si substrates by sol-gel processing. The precursor films are crystallized in the desired intergrown BTN–BIT superlattice structures by optimizing the processing conditions. Synthesized BTN–BIT thin films annealed below 750 °C are polycrystalline, uniform and crack-free, no pyrochlore phase or other second phase, and exhibited good ferroelectric properties. As the annealing temperature increases from 600 to 700 °C, both remanent polarization P _r and coercive electric field E _c of BTN–BIT thin films increase, but the pyrochlore phase in BTN–BIT films annealed above 750 °C will impair the ferroelectric properties. The BTN–BIT thin films annealed at 700 °C have a P _r value ~19.1μC/cm² and an E _c value ~135 kV/cm.     

Effect of Firing Temperature on the Structure and Superconducting Properties of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript> Films

YBa₂Cu₃O_7−x (YBCO) films were prepared on LaAlO₃ single crystal substrate under various firing temperatures (750–800 °C) in the crystallization process by metalorganic deposition (MOD) method. The coating solution was made by mixing the fluorine-free precursor solution containing Y and Cu with Ba–fluorine precursor solution (Ba-TFA). The effect of firing temperature on the structure and superconducting properties of YBCO films was systematically investigated. The results indicated that YBCO-films were smooth, crack-free, exhibited good textures and retain high oxygen content according to the XRD and SEM images. Sample of YBCO-film fired at 780 °C showed highest superconducting properties including high critical transition temperature T _c=89 K, sharp transition temperature ΔT _c<1 K, and critical current density J _c=2.8 MA cm⁻², which are attributable to excellent in-plane textures and dense microstructures with good connectivity between the grains.     

Effects of post-deposition annealing temperature and ambient on RF magnetron sputtered Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> gate on n-type silicon substrate

Samarium oxide (Sm₂O₃) thin films with thicknesses in the range of 15–30 nm are deposited on n-type silicon (100) substrate via radio frequency magnetron sputtering. Effects of post-deposition annealing ambient [argon and forming gas (FG) (90% N₂ + 10% H₂)] and temperatures (500, 600, 700, and 800 °C) on the structural and electrical properties of deposited films are investigated and reported. X-ray diffraction revealed that all of the annealed samples possessed polycrystalline structure with C-type cubic phase. Atomic force microscope results indicated root-mean-square surface roughness of the oxide film being annealed in argon ambient are lower than that of FG annealed samples, but they are comparable at the annealing temperature of 700 °C (Argon—0.378 nm, FG—0.395 nm). High frequency capacitance–voltage measurements are carried out to determine effective oxide charge, dielectric constant and semiconductor-oxide interface trap density of the annealed oxide films. Sm₂O₃ thin films annealed in FG have smaller amount of effective oxide charge and semiconductor-oxide interface trap density than those oxide films annealed in argon. Current–voltage measurements are conducted to obtain barrier heights of the annealed oxide films during Fowler–Nordheim tunneling.     

Dielectric property and electrical conduction mechanism of ZrO2–TiO2 composite thin films

ZrO₂–TiO₂ composite films were fabricated by radio frequency magnetron sputtering and post annealing in O₂. It was found the films remained amorphous below the annealing temperature of 500 °C. The as-deposited ZrO₂–TiO₂ film has a high dielectric constant of 22, and which increases to 34 after annealing at 400 °C. At low electric field, the dominant conduction mechanisms are Schottky emission for both the as-deposited and the annealed thin films. At high electric field, the conduction mechanism changes to space-charge-limited current and then changes to Poole–Frenkel (PF) emission after annealing at 400 °C.     

Atmospheric pressure chemical vapor deposition of transparent conducting films of fluorine doped zinc oxide and their application to amorphous silicon solar cells

Transparent conducting ZnO:F was deposited as thin films on soda lime glass substrates by atmospheric pressure chemical vapor deposition (CVD) deposition at substrate temperatures of 480–500 °C. The precursors diethylzinc, tetramethylethylenediamine and benzoyl fluoride were dissolved in xylene. The solution was nebulized ultrasonically and then flash vaporized by a carrier gas of nitrogen preheated to 150 °C. Ethanol was vaporized separately, and these vapors were then mixed to form a homogeneous vapor mixture. Good reproducibility was achieved using this new CVD method. Uniform thicknesses were obtained by moving the heated glass substrates through the deposition zone. The best electrical and optical properties were obtained when the precursor solution was aged for more than a week before use. The films were polycrystalline and highly oriented with the c-axis perpendicular to the substrate. The electrical resistivity of the films was as low as 5 × 10⁻⁴ Ωcm. The mobility was about 45 cm²/Vs. The electron concentration was up to 3 × 10²⁰/cm³. The optical absorption of the films was about 3–4% at a sheet resistance of 7 Ω/square. The diffuse transmittance was about 10% at a thickness of 650 nm. Amorphous silicon solar cells were deposited using the textured ZnO:F films as the front electrode. The short circuit current was increased over similar cells made with fluorine doped tin oxide, but the voltages and fill factors were reduced. The voltage was restored by overcoating the ZnO:F with a thin layer of SnO₂:F.     

Synthesis and Optical Studies of Superconducting MgB2 Thin Films

Synthesis and optical transmission of MgB₂ thin films on optically transparent glass are reported. In the 400–1000 nm regime as deposited films show high metallic reflectivity and very little transmission. After deposition, the films were annealed ex situ and rendered superconducting with T _c of 38 K, approaching that of the bulk material. The reaction conditions where quite soft ∼10 min at 550°C. The optical absorption coefficient, α and photon energy, E followed a Tauc-type behavior, = _T (E - E_g )(\alpha E)^{1/2} = \beta _T (E - E_{\rm g} ). The band gap (E _g) was observed to peak at 2.5 eV; but, the slope parameter β _T behaved monotonically with reaction temperature. Our results indicate that an intermediate semiconducting phase is produced before the formation of the superconducting phase; also optical measurements provide valuable information in monitoring the synthesis of MgB₂ from its metallic constituents. In addition these films have interesting optical properties that may be integrated into optoelectronics.     

Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10⁻² ω-cm to 3.57 × 10⁻³ ω-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1.2 × 10⁻¹ to 1.69 × 10⁻² ω-cm in the temperature range 250–370° C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7.74 × 10⁻⁴ ω-cm, which was deposited at 350°C with 0.26 g of SbCl₃ and 4 g of SnCl₄ (SbCl₃/SnCl₄ = 0.065). Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300– 370°C were poly crystalline. The morphology of tin oxide films was studied using SEM.     

Properties of CdSe films produced via spray pyrolysis of [Cd((NH<Subscript>2</Subscript>)<Subscript>2</Subscript>CSe)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>]

Data are presented on microwave photoconductivity kinetics in CdSe films prepared via spray pyrolysis of aqueous solutions of thiourea complexes on quartz and glass-ceramic substrates at temperatures from 300 to 600°C. The films were characterized by x-ray diffraction and optical absorption and reflection spectroscopies. Microwave photoconductivity (excitation with 8-ns laser pulses at 337 nm) was measured at 295 K by a resonator method in the 9-and 36-GHz ranges. The results indicate that the photoresponse decay kinetics depend on deposition temperature and incident intensity. In the films deposited below 400°C, the photoresponse decay follows a first-order rate law. At deposition temperatures above 450°C, the photoresponse decay cannot be represented by a first-or second-order rate law at low excitation intensities and approaches second-order kinetics at high intensities (> 10¹⁵ photons/cm² per pulse). Analysis of the photoresponse decay kinetics in terms of the interaction between free and trapped electrons, holes, and ions allowed us to formulate a model for the processes involved and to evaluate the rate constant of electron-hole recombination in CdSe: (4–6) × 10^?11 cm³/s.     

Characterization of Tin disulphide thin films prepared at different substrate temperature using spray pyrolysis technique

Thin films of tin disulphide on glass substrates were prepared by spray pyrolysis technique using precursor solutions of SnCl₂·2H₂O and n–n dimethyl thiourea at different substrate temperatures varied in the range 348–423 K. Using the hot probe technique the type of conductivity is found to be n type. X ray diffraction analysis revealed the polycrystalline nature with increasing crystallinity with respect to substrate temperature. The preferential orientation growth of SnS₂ compound having hexagonal structure along (002) plane increased with the substrate temperature. The size of the tin disulphide crystallites with nano dimension were determined using the Full Width Half Maximum values of the Bragg peaks and found to increase with the substrate temperature. The surface morphology had been observed on the surface of these films using scanning electron microscope. The optical absorption and transmittance spectra have been recorded for these films in the wavelength range 400–800 nm. Thickness of these films was found using surface roughness profilometer. The absorption coefficient (α) was determined for all the films. Direct band gap values were found to exist in all the films deposited at different substrate temperatures. The value of room temperature resistivity in dark decreased from 5.95 × 10³ Ω cm for the amorphous film deposited at low temperature (348 K) to 2.22 × 10³ Ω cm for the polycrystalline film deposited at high temperature (423 K) whereas the resistivity values in light decreased from 1.48 × 10³ to 0.55 × 10³ Ω cm respectively, which is determined using the four probe method. Activation energy of these thin films was determined by Arrhenius plot.     

Properties of indium tin oxide films prepared by ion-assisted deposition

Conducting transparent films of indium tin oxide were deposited by 100 eV oxygen-ion-assisted deposition. A refractive index of 2.13 at 550 nm was obtained for films deposited onto ambient temperature substrates. The refractive index decreased with increasing substrate temperature to a value of 2.0 at 400°C. The sheet resistance of films 135 nm thick decreased from 800 Ω/□ for layers deposited onto room temperature substrates to around 25 Ω/□ at 400°C. Structural studies revealed that ion-assisted deposition onto ambient temperature substrates produced amorphous films, and that at temperatures above 100°C the films exhibit In₂O₃ crystallinity. In addition, it was found that the number of voids in the ion-bombarded films was reduced relative to that in films produced by conventional reactive evaporation.