Investigation of germanium films and GeSi interface structure by transmission electron microscopy

The structure of germanium films (d≌0.3 μm) evaporated onto a silicon substrate and the GeSi interface have been investigated by transmission electron microscopy (TEM). Ge was evaporated in a vacuum of approximately 10^?6 Torr onto (111) Si. Epitaxial growth was observed at substrate temperatures T_s>500°C. The films grown at T_s = 520°–600°C (low temperature epitaxy) were characterized by a high density of stacking faults (SF), microtwin lamellae and dislocations which lay normal to the film surface. In this case the interface dislocations were regular and the dislocation density was equal to (3–4)×10¹⁰ cm^?2. At T_s = 700°–850°C (high temperature epitaxy) few stacking faults were discovered. Dislocations in the interior of the film formed three-dimensional networks as a result of interactions of different slip systems and dislocation climb. The formation of misfit dislocations was apparent at the interface. The region T_s = 630°–700°C is an intermediate region.     

Effect of substrate temperature on the properties of pyrolytically deposited nitrogen-doped zinc oxide thin films

The effect of substrate temperature (T_s) on the properties of pyrolytically deposited nitrogen (N) doped zinc oxide (ZnO) thin films was investigated. The T_s was varied from 300 °C to 500 °C, with a step of 50 °C. The positive sign of Hall coefficient confirmed the p-type conductivity in the films deposited at 450 °C and 500 °C. X-ray diffraction studies confirmed the ZnO structure with a dominant peak from (1 0 0) crystal plane, irrespective of the variation in T_s. The presence of N in the ZnO structure was evidenced through X-ray photoelectron spectroscopy (XPS) analysis. The obtained high N concentration reveals that the 450 °C is the optimal T_s. Atomic force microscope (AFM) analysis showed that the surface roughness was increased with the increasing T_s until 400 °C but then decreased. It is found that the transmittance of the deposited films is increased with the increasing T_s. The optical band gap calculated from the absorption edge showed that the films deposited with T_s of 300 °C and 350 °C possess higher values than those deposited at higher T_s.     

Properties of electron-beam-evaporated tin oxide films

Transparent conducting thin films of tin oxide were prepared by electron beam evaporation of sintered pellets of SnO₂ under controlled conditions. Variations in such parameters as the substrate temperature T_s and the post-deposition annealing temperature T_A and time t_A were studied. Structural, electrical and optical properties were measured to characterize the films. The film structure changed gradually from amorphous to crystalline (SnO phase) as T_S was varied from 150 to 350 °C. A sharp decrease in the room temperature resistivity together with the growth of a crystalline phase occured in the as-deposited films at T_S ≈ 250°C. On annealing in air (T_A = 550°C, t_A = 2 h) a radical structural transformation from amorphous to crystalline occurred with a sharp fall in resistivity for T_S ⩽ 225°C. For T_S = 350°C the lowest resistivity achieved for the undoped annealed films was 6.6×10^-3 Ω cm, the average visible transmittance was about 90% and the structure was characteristic of pure SnO₂.     

The compositional and structural properties of sprayed SnO2:F thin films

Thin films of SnO₂ doped with fluorine were produced by the conventional spraying method using Corning 7059 glass substrates. The electrical and optical properties of these films were determined as a function of the substrate temperature T_s and dopant concentration in the basic spraying solution. The visible and near-IR transmittance as well as the electrical resistivity of the films decreased with an increase in the fluorine concentration. The best electro-optical properties (an average transmittance of 75% and an electrical resistivity of 10⁻³ Ω cm) were achieved for 250°C⩽T_s⩽350°C and fluorine concentrations (relative to tin) in the spraying solution of around 2 at.%. The surface texture of the films was investigated by scanning electron microscopy and optical microscopy. The fluorine content of the samples was analysed by secondary ion mass spectroscopy, Auger electron spectroscopy and electron spectroscopy for chemical analysis. Structural changes were studied using X-ray diffractometry. A systematic change in the intensity of the X-ray diffraction lines as a function of the fluorine content was observed. Theoretical calculations of the structure factors associated with the SnO₂ lattice if fluorine atoms are introduced into substitutional and interstitial positions were performed.     

The orientation and morphology of chromium deposits on hot Cu{111} substrates

Chromium (1.5–20 nm thick) was vapour deposited in ultrahigh vacuum (2×10^-9 Torr) onto single-crystal Cu{111} films. The copper substrate temperatures T_s were in the range 75–256 °C. Transmission electron microscopy and electron diffraction were used to study the orientation and morphology of the deposits. For T_s ≲ °C the electron diffraction patterns showed arced chromium reflections consistent with a distribution of orientations between Nishiyama- Wassermann (NW) and Kurdjumov-Sachs (KS) at ±5° 16′ from NW. A greater tendency towards KS was observed as T_s increased to about 130 °C. For T_s = 190 and 256 °C relatively well-defined KS orientations occured. These results are interpreted in terms of various geometric models of f.c.c.-b.c.c. interfaces. At T_s ≲ 85 °C the morphology was qualitatively similar to that observed for room temperature substrates: flat irregularly shaped crystals within which a substructure of parallel-oriented crystallites with elongated shape existed. For T_s ≲ 130 °C the morphology changed from the flat irregularly shaped crystals to isolated three- dimensional crystals with an elongated shape. The long direction of the crystals was approximately parallel to the direction of least misfit, i.e. Cr〈111〉  Cu〈110〉.     

Influence of deposition temperature on the superconductivity of Y1−x HoxBa2Cu3O7 −δfilms produced by dc-magnetron sputtering

Experimental results of research on the influence of deposition temperature (T _s) on crystal structure and superconductivity of Y_1?x HoxBa₂Cu₃O_{7 ?δ} (YHBCO) films deposited by dcmagnetron sputtering are reported. X-ray diffraction analysis showed that the films grew with preferential orientation of thec-axis normal to the substrate surface in the range of temperature 750–820°C. The single-crystal structure of the YHBCO films grown epitaxially at the optimal substrate temperatures of 820, 800, 760, and 750°C, respectively, have been established by rocking curves, Φ-scan, and electron channeling pattern (ECP). Typical values of the critical current density (A · cm^?2) at 77 K and 0.1 T field are 2.1×10⁵, 4×10⁵, 6.2×10⁵, and 3.1×10⁵ for thex=0, 0.2, 0.4, 0.7 films respectively, measured by a Quantum Design magnetrometer (H∥c).     

On the zinc nitride properties and the unintentional incorporation of oxygen

Zinc nitride films were prepared by radio-frequency magnetron sputtering in N₂/Ar ambient using different substrates (glass and thermally-oxidized-Si) and buffer layers (low-temperature Zn₃N₂ and ZnO). Resonant Rutherford backscattering (RBS) allowed determining Zn_xN_y stoichiometry and thickness. Despite the sputtering system was operated in high vacuum conditions, unintentional oxygen incorporation during growth was detected. Calculations of the relative oxygen concentration showed that the oxygen content was very dependent on the growth rate. Ex-situ oxidation was also analyzed by resonant RBS and compared with the results of as-grown layers. Scanning electron microscopy and X-ray diffraction revealed that surface morphology and crystal orientation were strongly dependent on the substrate temperature (T_s). In addition, optical transmission measurements show a reduction of the optical energy band gap from 1.46 to 1.25 eV as T_s increased. The electrical properties were examined as a function of growth rate, total working gas flux and T_s aiming to maximize electron mobility. From those studies, it was found that Hall mobility increased significantly as the growth rate decreased. A maximum mobility of 100 cm²/Vs and a minimum carrier concentration of 3.2 × 10¹⁸ cm⁻³ were achieved at a T_s of 423 K and a growth rate of 4.44 nm/min.     

Indium selenide film formation by the double-source evaporation of indium and selenium

Films of γ-In₂Se₃ are easily obtained by the evaporation of indium and selenium with the supply ratio R = [Se]/[In] above 1.7 and the substrate temperature T_s above 170°C. InSe films are obtained when R ≈ 1.2 and T_s > 100°C. The electrical conductivities of γ-In₂Se₃ and InSe films are about 10⁻¹⁰−10⁻⁷ and 10⁻⁶ S cm⁻¹ respectively. The band gap of γ-In₂Se₃ is estimated to be about 2 eV in this study.The mechanism of film formation is also discussed.     

The epitaxial growth of germanium and silicon on an Ag(111) film on a mica substrate

With the aim of finding a method of obtaining self-supporting single-crystal films of silicon for solar cells we studied the epitaxial growth of silicon and germanium prepared by evaporation in ultrahigh vacuum onto an Ag(111) film evaporated in situ onto a mica substrate cleaved in air. The films were examined mainly by reflection high energy electron diffraction. Silicon and germanium films 50–200 Å thick were composed of crystallites with two main orientations relative to the substrate and unoriented crystallites in varying proportions depending on the substrate temperature T_s and the previous heat treatment temperature T_H of the mica. Nearly single-crystal films of silicon could be obtained for T_s = 350 °C and T_H = 250 °C. The sticking coefficient for silicon on silver was found to decrease almost to zero for T_s = 420 °C with T_H = 250 °C. No single-crystal films of germanium were obtained.     

Preparation and dielectric properties of Si3N4 thin films

Thin Si₃N₄ films of thickness 50–1500 nm were prepared by a low pressure, room temperature chemical vapour deposition process. The dielectric properties of the layers were studied in the frequency range from 10 Hz to 1 MHz and at temperatures between 77 and 400 K. We observed a σ'(ω, T) = A(T)ω^s(T) dependence with s?1 (where σ' is the real part of the a.c. conductivity). For samples prepared in various ways, A varied between a constant value and a superlinear dependence on temperature. At 77 K, however, σ' for all the samples was found to be approximately the same (about 8 × 10^?12 Ω^?1 cm^?1 at 1 kHz) irrespective of the preparation parameters.     

Structural, electrical, and optical properties of copper indium diselenide thin film prepared by thermal evaporation method

Stoichiometric compound of copper indium diselenide (CuInSe₂) was synthesized by direct reaction of high-purity elemental copper, indium and selenium in an evacuated quartz ampoule. The phase structure and composition of the synthesized pulverized material analyzed by X-ray diffraction (XRD) and energy dispersive analysis of X-rays (EDAX) revealed the chalcopyrite structure and stoichiometry of elements. Thin films of CuInSe₂ were deposited onto organically cleaned soda lime glass substrates held at different temperatures (i.e. 300 K to 573 K) using thermal evaporation technique. CuInSe₂ thin films were then thermally annealed in a vacuum chamber at 573 K at a base pressure of 10^− 2 mbar for 1 h. The effect of substrate temperature (T_s) and thermal annealing (T_a) on structural, compositional, morphological, optical and electrical properties of films were investigated using XRD, transmission electron microscopy, EDAX, atomic force microscopy (AFM), optical transmission measurements and Hall effect techniques. XRD and EDAX studies of CuInSe₂ thin films revealed that the films deposited in the substrate temperature range of 423-573 K have preferred orientation of grains along the (112) plane and near stoichiometric composition. AFM analysis indicates that the grain size increases with increase of T_s and T_a. Optical and electrical characterizations of films suggest that CuInSe₂ thin films have high absorption coefficient (10⁴ cm^− 1) and resistivity value in the interval 10^− 2-10¹ Ω cm influenced by T_s and T_a.     

Electrical and optical properties of MoSe2 films prepared by r.f. magnetron sputtering

The electrical resistivity of MoSe₂ films prepared by r.f. magnetron sputtering was measured between 300 and 10 K. The main sputtering parameter governing the physical properties of the films was found to be the substrate temperature T_sub. The room temperature resistivity of the as-sputtered films increased from $\text{1.7 × 10}{}^{-1}\text{Ω}\text{cm}$(T_sub = -70 °C) to $\text{1.4 × 10}{}^1\text{Ω}\text{cm}\text{(T}{}_{\mathrm{<mtext>sub</mtext>}}\text{= 150 °}\text{C}\text{)}$. A check of the thermo-electrical response showed that the majority charge carriers are holes except for films deposited at T_sub = 150 °C which are n type. Hall effect measurements indicated very low Hall mobilities (3–5 cm² V^-1 s^-1). Thermal annealing increased the room temperature resistivities by more than one order of magnitude for the specimens sputtered at a low substrate temperature. The optical properties were weakly influenced by the process conditions. The optical gap was determined to be 1.06 eV.     

Thickness Dependence of Critical Current Density in MgB2 Films Prepared by Thermal Evaporation Method

MgB₂ films with the thickness of 350 to 1150 nm have been prepared on the Al₂O₃ (001) single crystal substrates from high purity B and Mg powder by the thermal evaporation method. Films were then heat treated ex-situ under Mg vapor at 950?°C to achieve actual MgB₂ stoichiometry. Thickness of the films, so the deposition time, was varied to investigate its influence on critical current density of the films. The films fabricated were analyzed by means of microstructural, transport, and magnetic properties. The best T _c and T _zero values were obtained to be 39.5 K and 38 K, respectively, and decreased with increasing the thickness. We found that the critical current density of the films prepared is highly thickness dependent. The maximum $J_{c}^{\mathrm{mag}}$ value was calculated to be 3.18×10⁶ A?cm^?2 at 10 K and zero field for 1150 nm thick films but dropped drastically by thickness.     

Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O₂) at high substrate temperature (T_s = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high T_s by inputting Ar + O₂. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high T_s by PLD is rarely reported. The influence of the Ar + O₂ gas pressure on thickness, structural performance, surface morphology, optical property and band gap (E_g) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O₂ gas pressure from 5 to 12 Torr, the deposition rate and the E_g of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm² were prepared successfully.     

Lattice and grain boundary diffusion of copper in thin aluminum films

The lattice D₁ and grain boundary δD_b diffusivities of Cu in Al thin films at 130–185°C are calculated from measurements employing Auger electron spectroscopy and Ar ion beam etching. The calculated values are D₁ = 0.065 cm² s^-1 × exp(-122 kJ/RT) and δD_b = 4.5 × 10^-9 cm³s^-1 exp(-97.4 kJ/RT). The D₁ value is 3–5 times larger at 130–185°C than that predicted by an extrapolation of radioactive tracer measurements of large grain bulk specimens at 433–652°C. The higher value measured here is attributed to the higher density of subgrain defect structures in the thin film.     

Molecular beam epitaxial growth of high-quality InP layers from solid phosphorus using a valved phosphorus cracker cell

We report the molecular beam epitaxial (MBE) growth of epitaxial InP using a valved phosphorus cracker cell at a range of cracking-zone temperatures (T_cr = 875–950°C), V/III flux ratios (V/III = 1.2–9.3) and substrate temperatures (T_s = 360–500°C). The as-grown epitaxial InP on an InP (100) substrate is found to be n-type from Hall measurements. The background electron concentration and mobility exhibit a pronounced dependence on the cracking-zone temperature, V/III flux ratio and substrate temperature. Using a T_cr of 850°C, the highest 77 K electron mobility of 40 900 cm² (V s)⁻¹ is achieved at a V/III ratio of 2.3 and a T_s of 440°C. The correponding background electron concentration is 1.74 × 10¹⁵ cm⁻³. The photoluminescence (PL) spectra show two prominent peaks at 1.384 and 1.415 eV, with the intensity of the low-energy peak becoming stronger at higher cracking-zone temperatures. The lowest PL FWHM achieved at 5 K is 5.2 meV. Within the range of substrate temperatures investigated, the effect on the crystalline quality determined from X-ray diffraction (XRD) measurements is not significant.     

Structure and AC conductivity of nanocrystalline Yttrium oxide thin films

Yttrium oxide (Y₂O₃) thin films were grown at substrate temperatures (T_s) ranging from room temperature (RT) to 500 °C and their structural and electrical properties were evaluated. The results indicate that Y₂O₃ films grown at RT-100 °C were amorphous (a-Y₂O₃). Y₂O₃ films began to show cubic phase (c-Y₂O₃) at T_s = 200 °C. The average grain size varies from 5 to 40 nm as a function of T_s. Room temperature ac electrical conductivity increases from 0.4 (Ω-m)^− 1 to 1.2 (Ω-m)^− 1 with increasing T_s from RT to 500 °C. The frequency dispersion of the electrical resistivity reveals the hopping conduction mechanism. Frequency dispersion of the electrical resistivity fits to the modified Debye's function, which considers more than one ion contributing to the relaxation process. The mean relaxation time decreases from 2.8 to 1.4 μs with increasing T_s indicating that the effect of microstructure of the Y₂O₃ films is significant on the electrical properties.     

Characterization of gallium-nitrogen co-doped zinc oxide thin films prepared by RF diode sputtering

We investigated the possibility of achieving p-type zinc oxide (ZnO) by RF diode sputtering and gallium-nitrogen co-doping. ZnO:Ga:N thin films were prepared with a different N₂ content in Ar/N₂ working gas, ranging from 0 to 100%, and at a varying substrate temperature, from room temperature (RT) to 300 °C. A hole conduction with maximum carrier concentration of 2.6 × 10¹⁸ cm⁻³, mobility of 2 cm²/Vs and resistivity of 1.5 Ω cm resulted from deposition at RT with 100% N₂. It arose from N incorporation and formation of N_O acceptors. In the secondary ion mass spectrometry (SIMS) depth profiles of the co-doped films were observed NO/NO₂ negative ions. Average transmittance (including Corning glass substrate) across the visible spectrum varied (60 ÷ 66%) with increasing nitrogen content (50 ÷ 100% N₂). As the substrate temperature increased (RT - 300 °C), highly transparent (T ∼72-83%) and conductive (electron concentrations of 10¹⁷-10¹⁹ cm⁻³) n-type ZnO:Ga:N films were attained. Reduction of optical band gap (E_g) (∼3.13-3.08 eV) was observed for co-doped ZnO films. Atomic force microscopy (AFM) images revealed that the films grown at RT have roughness of approximately 5.3 nm while roughness of those grown at 300 °C is approximately 3.9 nm.     

Role of annealing time and temperature on structural and superconducting properties of (Bi,Pb)-2223 thin films produced by sputtering

This study reports the effect of annealing time (15 min, 1.5 and 3 h) and temperature (850, 860 and 870 °C) on the structural and superconducting properties of thin films by means of scanning electron microscopy (SEM), X-Ray analysis (XRD), electron dispersive X-Ray (EDX), resistivity and transport critical current density (J_c) measurements. Zero resistivity transition temperatures (T_c) of the films produced are estimated from the dc resistivity measurements. In addition, the phase and lattice parameters are determined from XRD patterns when the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. The results indicate that T_c values of the films obtained are observed to be in a range of 23–102 K. The T_c of the film annealed at 870 °C for 3 h is found to be the smallest (23 K) while the film annealed at 860 °C for 3 h is noted to obtain the maximum T_c value (102 K). On the other hand, the maximum (minimum) J_c is found to be about 2068 A/cm² (20 A/cm²) for the film annealed at 860 °C for 3 h (870 for 3 h). Moreover, according to the refinement of cell parameters done by considering the structural modulation, the greatest Bi-2223 phase fraction is noticed to belong to the film annealed at 860 °C for 3 h. Furthermore, SEM measurements show that the best surface morphology, largest grain size and grain connectivity are observed for that film. Based on these results, T_c and J_c values of the samples studied are found to depend strongly on the microstructure. As for EDX results, the elements used for the preparation of samples are observed to distribute homogeneously. The aim of this study is not only to investigate the changes of structural and superconducting properties of the films produced in the varied time and temperature but also to determine the best ambient for the film fabrication and show the feasibility of obtaining Bi-2223 film with tailored structure.     

The ferroelectric and optical properties of (Pb0.92La0.08)(Zr0.65Ti0.35)O3 thin films deposited by radio-frequency magnetron sputtering

Ferroelectric (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ (PLZT) films have been prepared on Pt/Ti/SiO₂/Si and fused quartz substrates using radio-frequency (rf) magnetron sputtering at a deposition temperature of 650°C. X-ray diffraction analysis shows that the PLZT thin films on platinized silicon are polycrystalline with (100)-preferential orientation. A Al/PLZT/Pt capacitor has been fabricated and it shows that the films have excellent ferroelectric character, with saturation polarization (P _s), remanent polarization (P _r) and coercive field (E _c) of 32.8μC/cm², 24.3μC/cm² and 142 kV/cm, respectively. The PLZT thin films exhibit good insulating property and the leakage current density of the films on platinized silicon is only about 0.86 × 10⁻⁷ A/cm² at 200 kV/cm. By the optical transmission spectra measurements, the energy gap (E _g) of the PLZT films on fused quartz is found to be about 3.54 eV. The optical constants (n and k) of the films in the wavelength range of 250–900 nm are obtained by a Filmetrics F20 reflectance spectrometer.