Effect of substrate temperature on structural, optical and electrical properties of ZnO thin films deposited by pulsed laser deposition

ZnO thin films were grown by the pulse laser deposition (PLD) method using Si (100) substrates at various substrate temperatures. The influence of the substrate temperature on the structural, optical, and electrical properties of the ZnO thin films was investigated. All of the thin films showed c-axis growth perpendicular to the substrate surface. At a substrate temperature of 500 °C, the ZnO thin film showed the highest (002) peak with a full width at half maximum (FWHM) of 0.39°. The X-ray Photoelectron Spectroscopy (XPS) study showed that Zn was in excess irrespective of the substrate temperature and that the thin film had a nearly stoichiometrical composition at a substrate temperature of 500 °C. The photoluminescence (PL) investigation showed that the narrowest UV FWHM of 15.8 nm and the largest ratio of the UV peak to the deep-level peak of 32.9 were observed at 500 °C. Hall effect measurement systems provided information about the carrier concentration, mobility and resistivity. At a substrate temperature of 500 °C, the Hall mobility was the value of 37.4 cm²/Vs with carrier concentration of 1.36 × 10¹⁸ cm⁻³ and resistivity of 2.08 × 10⁻¹ Ω cm.     

Effect of deposition conditions on the InP thin films prepared by spray pyrolysis method

InP thin films were prepared by spray pyrolysis technique using aqueous solutions of InCl₃ and Na₂HPO₄, which were atomized with compressed air as carrier gas. The InP thin films were obtained on glass substrates. Thin layers of InP have been grown at various substrate temperatures in the range of 450–525°C. The structural properties have been determined by using X-ray diffraction (XRD). The changes observed in the structural phases during the film formation in dependence of growth temperatures are reported and discussed. Optical properties, such as transmission and the band gap have been analyzed. An analysis of the deduced spectral absorption of the deposited films revealed an optical direct band gap energy of 1.34–1.52 eV for InP thin films. The InP films produced at a substrate temperature 500°C showed a low electrical resistivity of 8.12 × 10³ Ω cm, a carrier concentration of 11.2 × 10²¹ cm⁻³, and a carrier mobility of 51.55 cm²/Vs at room temperature.     

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.     

Synthesis of isotopically-labeled graphite films by cold-wall chemical vapor deposition and electronic properties of graphene obtained from such films

We report the synthesis of isotopically-labeled graphite films on nickel substrates by using cold-wall chemical vapor deposition (CVD). During the synthesis, carbon from ¹²C- and ¹³C-methane was deposited on, and dissolved in, a nickel foil at high temperature, and a uniform graphite film was segregated from the nickel surface by cooling the sample to room temperature. Scanning and transmission electron microscopy, micro-Raman spectroscopy, and X-ray diffraction prove the presence of a graphite film. Monolayer graphene films obtained from such isotopically-labeled graphite films by mechanical methods have electron mobility values greater than 5000 cm²·V⁻¹·s⁻¹ at low temperatures. Furthermore, such films exhibit the half-integer quantum Hall effect over a wide temperature range from 2 K to 200 K, implying that the graphite grown by this cold-wall CVD approach has a quality as high as highly oriented pyrolytic graphite (HOPG). The results from transport measurements indicate that ¹³C-labeling does not significantly affect the electrical transport properties of graphene.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junctions in ZnO implanted with group V ions

n-Type ZnO〈Ga〉 films were implanted with 150-keV N⁺ (As⁺) ions to a dose of 7 × 10¹⁵ cm⁻² and then annealed in atomic oxygen at different temperatures. p-Type conductivity was obtained at annealing temperatures in the range 770–870 K. The parameters of the p-type layers were determined by photoluminescence spectroscopy, secondary ion mass spectrometry, and Hall effect measurements. According to the Hall data, the p-type layers had a resistivity of ∼30 Ω cm, carrier mobility of ∼2 cm²/(V s), and carrier concentration of ∼10¹⁸ cm⁻³. The electroluminescence spectra of the p-n junctions produced by ion implantation showed a band at 440 nm, due to recombination via donor-acceptor pairs.     

Surface morphology and properties of GaAs epilayers controlled by temperature difference method of liquid phase epitaxy

Epilayers of gallium arsenide were grown by using the steady-state temperature difference method of liquid phase epitaxy. The surface of grown layers was smooth and shiny. Carrier concentrations of films varying from 10¹⁶ to 10¹⁷ cm⁻³ could be obtained with good reproducibility. The surface morphology growth rate, carrier concentration and Hall mobility of the epilayers were studied. Several distinct types of surface features were also investigated and explained. A segregation coefficient for the net carrier concentration versus tin concentration in the growth melt was calculated as 1·84 × 10⁻⁴ at 700°C for (100) GaAs substrate. Thickness control for epilayers down to submicron can be obtained reproducibly.     

Hydrothermal synthesis of improved ZnO crystals for epitaxial growth of GaN thin films

ZnO single crystals with thickness up to 12 mm, 2 inches in “diameter” and weight of about 150 g have been grown from KOH, NaOH, and K₂CO₃ based hydrothermal solutions on the seeds of (0001) orientation. The addition of LiOH up to 3.0–4.5 mol/L allowed to decrease the growth rate of ZnO crystals along the 〈0001〉 crystallographic direction. For positive and negative monohedra, it was achieved 0.12 and 0.01 mm/day, respectively, at temperature 340 °С and ΔТ = 10 °С. The best ZnO etching agent was found to be the solutions 25 mol% HCl + 3 mol% NH₄F at room temperature, and etching time 5 min. The dislocation density of ZnO crystals varied from 240 cm⁻² to 3,200 cm⁻² in the case of growth rates 0.04 mm/day to 0.11 mm/day, respectively. It was also found that ZnO crystals grown are stable in air, oxygen, nitrogen, and argon atmosphere as well as in vacuum at the temperatures up to 1,000 °C under thermal treatment during 4 h.     

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.     

Structural and optical characterization of thick and thin polycrystalline diamond films deposited by microwave plasma activated CVD

Preliminary results of growth of thin diamond film in a recently installed 3 kW capacity microwave plasma activated CVD (MW-PACVD) system are being reported. The films were deposited on Si (100) substrate at 850°C using methane and hydrogen mixture at 1·5 kW MW power. The grown polycrystalline films were characterized by micro-Raman, transmission electron microscope (TEM), spectrophotometer and atomic force microscope (AFM). The results were compared with that of a thicker diamond film grown elsewhere in a same make MW-PACVD system at relatively higher power densities. The presence of a sharp Raman peak at 1332 cm^− 1 confirmed the growth of diamond, and transmission spectra showed typical diamond film characteristics in both the samples. Typical twin bands and also a quintuplet twinned crystal were observed in TEM, further it was found that the twinned region in thin sample composed of very fine platelet like structure.     

Polycrystalline silicon films doped with aluminum during deposition

Aluminum-doped polycrystalline silicon films have been grown by molecular-beam deposition at substrate temperatures between 540 and 600 °C. The grain size increases to 1–8 μm with increasing substrate temperature. High Hall mobilities of the carriers were measured, in the range 30–90 cm²/V·s. Pis’ma Zh. Tekh. Fiz. 23, 83–87 (June 12, 1997)     

The Effect of Sintering Temperature Variation on the Superconducting Properties of ErBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Superconductor Prepared via Coprecipitation Method

The effect of heat treatment on the superconducting properties of ErBa₂Cu₃O_7−δ (ErBCO) ceramic materials has been studied. The nano-metal oxalate precursor was prepared using coprecipitation (COP) method. The prepared materials were subjected to calcination process at 900 °C for 12 h and then sintered under oxygen environment for 15 h at 920 °C, 930 °C, 940 °C, and 950 °C, respectively. All samples showed a metallic behavior and single-step transition in the R–T curves. The best zero critical current, T _C(R=0)=91.4 K, was for the sample sintered at 920 °C. XRD data showed single phase of an orthorhombic structure. As the sintering temperature increases, the formation of nonsuperconducting phases (impurities) was observed when the samples sintered above 920 °C. The formation of nano-oxalate powders via COP method is a very efficient procedure to produce high-quality superconductors with less processing temperature required.     

Fabrication and characterization of ferroelectric PLZT film capacitors on metallic substrates

We have grown ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on Hastelloy C276 (HC) substrates by chemical solution deposition. Samples of 1.15-μm-thick PLZT films were prepared on HC with and without lanthanum nickel oxide (LNO) films as an intermediate buffer layer. On samples with and without LNO buffers at room temperature, we measured dielectric constants of ≈1,300 and ≈450 and loss tangents of ≈0.06 and ≈0.07, respectively. For PLZT films grown on HC with LNO buffer, the dielectric constant increases, while the dielectric loss decreases, with increasing temperature. A dielectric constant of ≈2,000 and loss of ≈0.05 were observed at 150 °C. Samples with LNO buffer also exhibited slimmer hysteresis loops and lower leakage current density when compared to samples without LNO buffer. The following results were measured on samples with and without LNO buffers: remanent polarization (P _r) values of 21.3 and 36.4 μC/cm², coercive electric field (E _c) values of 41 and 173 kV/cm, and leakage current densities of ≈1.1 × 10⁻⁸ and ≈1.6 × 10⁻⁷ A/cm², respectively. The energy storage capability was measured at ≈65 J/cm³ for the PLZT film-on-foil capacitor deposited on HC with LNO buffer.     

Properties of Heavily Mn-doped GaMnAs with Curie Temperature of 172.5 K

The authors have investigated the magnetic properties of heavily Mn-doped ferromagnetic semiconductor Ga_1−x Mn _x As thin film with the Mn concentration x of 15.2% grown by molecular-beam epitaxy at relatively high growth temperature of 250 °C. Magnetic circular dichroism and the anomalous Hall effect measurements indicate that this thin film holds the intrinsic ferromagnetic semiconductor features. By low-temperature annealing, the resistivity was significantly decreased and the Curie temperature was largely enhanced from 95 K to 172.5 K.     

Influence of Heat Treatment on Structure and Superconducting Properties of YBCO Film by Chemical Solution Deposition Method

YBCO films have been fabricated on a (00l) LaAlO₃ single-crystal substrate via self-developed fluorine-free polymer-assisted metal organic deposition (PA-MOD) method. The influence of heat treatment on texture, microstructure and superconducting properties of YBCO films has been investigated. After a pyrolysis process ranging from 145 °C to 500 °C with different heating rates, the samples were fired at 760–780 °C in Ar and O₂ mixture gas followed by annealing at 450 °C in pure O₂. The results indicate the film fired at 770 °C after decomposition at the rate of 0.5 °C/min showed the highest T _c of 90.4 K and J _c (77 K, 0 T) over 2 MA/cm². According to the XRD patterns, phi-scan and omega-scan curves as well as SEM images, the good properties may be attributed to better biaxial texture and purer YBCO phase as well as better grain connectivity.     

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.     

Preparation of ferroelectric PZT films by thermal decomposition of organometallic compounds

Transparent PZT thin films with perovskite structure were successfully obtained by thermal decomposition of organometallic compounds at the temperatures of 500 to 700° C. The films deposited on platinum substrates were smooth and uniform, but microcrackings were observed in the films deposited on fused silica substrates. The ratio of metal composition in the PZT film agreed with that in the mixture of starting materials. Films obtained at 700° C on platinum substrate showed a hysteresis loop. A spontaneous polarization was 35.65μC cm⁻², a saturation remanent polarization was 30.56μC cm⁻² and a coercive field was 45 kV cm⁻¹. Dielectric constant and dielectric loss angle were about 300 and 0.05, respectively.     

Multiple implantation of29Si+ in semi-insulating GaAs and its characterisation

Formation of a uniformn-layer by multiple²⁹Si⁺ implantation on LEC grown semi-insulating GaAs 〈100〉 substrate and its characterisation by differential Hall measurement at room temperature is reported. The implantation energies are 60, 160 and 260 keV with corresponding doses of 1 × 10¹², 2·55 × 10¹² and 3 × 10¹² cm⁻². Asimplanted, uncapped substrates were furnace-annealed with face-to-face configuration in an N₂ ambient at 850°C with arsenic overpressure. After annealing, the samples were subjected to Hall measurements using Van der Pauw configuration. Experimental and theoretical (LSS) profiles are compared. Electrical activation of the dopant atoms was found to range from 65–90% with average mobility values lying between 2000–2300 cm² V⁻¹ s⁻¹. Uniform concentration of then-layer ∼ 10¹⁷ cm⁻³ up to a depth of 0·3 μm has been achieved. These layers are used for the fabrication of power MESFETs.     

Electrical and optical properties of P-doped ZnO thin films by annealing temperatures in Nitrogen ambient

The effects of post-annealing temperature on the optical and electrical properties of P-doped ZnO thin films, grown on sapphire substrate, have been investigated when the annealing is performed under nitrogen ambient. Analysis of the XRD shows that regardless of the post-annealing temperature, the P-doped ZnO thin films have grown the (002) peak. The full width of half maximum decreases from 0.194 to 0.181° as the annealing temperature increases from 700 to 900 °C. This phenomenon means that the increase of annealing temperature causes enhancement of the thin film’s crystalline properties. The results of Hall effect measurements indicate that the P-doped ZnO thin films, annealed at 750 and 800 °C exhibit p-type behavior, with hole concentrations of 5.71 × 10¹⁷ cm⁻³ and 1.20 × 10¹⁸ cm⁻³, and hole mobilities of 0.12 cm²/Vs and 0.08 cm²/Vs, respectively. The low-temperature (10 K) photoluminescence results reveal that the peaks related to the neutral-acceptor exciton (A⁰X) at 3.355 eV, free electrons to neutral acceptor (FA) at 3.305 eV and donor acceptor pair (DAP) at 3.260 and 3.170 eV are observed in the films showing p-type behavior with the acceptors. Because P atoms replace O atoms to produce acceptors from P-doped ZnO thin films by the thermal activation process at the appropriate annealing temperature with nitrogen ambient, the p-type ZnO thin films can be fabricated in this way.     

Doping of high-quality epitaxial silicon grown by hot-wire chemical vapor deposition near 700 °C

We demonstrate that epitaxial layers with a wide range of controllable dopant densities (7 × 10¹⁵-3 × 10¹⁸/cm³ and 10¹⁷-10¹⁸/cm³ for n-type and p-type, respectively) can be grown on wafer substrates at 700 ± 25 °C by hot-wire chemical vapor deposition. Phosphorus from PH₃ is incorporated into the film more efficiently than silicon from SiH₄, leading to efficient doping. Comparison of Hall carrier concentrations to secondary ion mass spectrometry atomic dopant concentration shows that all incorporated dopants are electrically active. The Hall measurements also reveal that the electron mobility in the P-doped films is close to the impurity-scattering limit for crystal Si wafers at room temperature, indicating that our deposited epitaxial materials are high quality.     

Formation of nanoscale tungsten oxide structures and colouration characteristics

In this work, pH dependent evolution of tungsten oxide (WO₃) nanostructures is being reported along with physical characteristics. The synthesis was carried out via an inexpensive solvothermal cum chemical reduction route, with sodium tungstate (Na₂WO₄) and cetyl trimethyl ammonium bromide (C₁₉H₄₂NBr) as main reactants. The X-ray diffraction, together with transmission electron microscopic studies have revealed formation of regular polyhedral nanocrystalline structures and fractals as one goes from higher pH (= 5·5) to lower pH (= 2) values. The average crystallite size, as calculated through Williamson–Hall plots, was varied within 2·8–6·8 nm for different pH samples. Fourier transform infrared spectroscopy reveals in-plane bending vibration δ (W–OH), observable at ∼1630 cm^− 1 and strong stretching ν (W–O–W) located at ∼814 cm^− 1. Raman spectroscopy has divulged WO₃ Raman active optical phonon modes positioned at ∼717 and 805 cm^− 1. The thermochromic and photochromic properties of the nanoscale WO₃ sample prepared at pH = 5·5, are also highlighted.