The influence of previous substrate heat treatment on the epitaxial growth of silver on mica

The growth of silver films prepared by evaporation in ultrahigh vacuum onto mica cleaved in air and previously heat treated at various temperatures T_H for 24 h was studied by reflection high energy electron diffraction. It was found that for T_H < 250 °C the silver films are well oriented from the initial stages of growth. At higher T_H the initial stages are characterized by crystallites with random orientation and with two main orientations (each with double positioning). With increasing thickness, first the randomly oriented crystallites disappear and then those with one of the main orientations; finally a single-crystal film is obtained (T_H < 320 °C. For films with a certain thickness it is found that, the higher T_H is, the higher is the fraction of randomly oriented crystallites. The results are explained by the decrease in water vapour concentration on the mica surface as T_H is increased, which in turn causes the reduction in the orientation of the initial nuclei as well as in their density.     

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.     

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〉.     

Effect of the substrate temperature on the structural, optical and electrical properties of spray-deposited CdS:B films

Boron doped CdS films have been deposited by spray pyrolysis method onto glass substrate temperature in the range of 350–450 °C. And the effect of substrate temperature (T _s) on the structural, electrical and optical properties of the films were studied. The structural properties of boron doped CdS films have been investigated by (XRD) X-ray diffraction techniques. The X-ray diffraction spectra showed that boron doped CdS films are polycrystalline and have a hexagonal (wurtzite) structure. By using SEM analysis, the surface morphology of the films was observed as an effect of the variation of substrate temperature. The substrate temperature is directly related with the shift detected in the band gap values derived from optical of parameters and the direct band gap values were found to be in the region of 2.08–2.44 eV. The electrical studies showed that the film deposited at the substrate temperature 400 °C had high carrier concentration and Hall mobility and minimum resistivity. This resistivity value decreased with increase in temperature up to 400 °C indicating the semiconducting nature of B- doped CdS films. The lattice parameter, grain size, microstrain and dislocation densities were calculated and correlated with the substrate temperature (T _s ).     

Effects of water on the growth of aluminium films deposited by vacuum evaporation

Aluminium films 500 nm thick were deposited onto oxidized silicon wafers by electron gun evaporation at 250°C. The evaporation rates were 0.5 and 1.5 nm s^-1. The water partial pressure p_H2O during evaporation was varied between 1.8 × 10^-6 and 1.5 × 10^-3 Pa. It was shown that the water partial pressure has a marked effect on the growth and the morphology of the deposited aluminium films as studied by scanning electron microscopy. At low water partial pressures a faceted surface structure is obtained. With increasing p_H2O the layer becomes rougher until a maximum is reached, after which the layer becomes smooth again and a granular structure is obtained. The changes in the morphology are accompanied by changes in the structural, optical and electrical properties. The observed phenomena can be explained by the dissociative adsorption of water and the formation of oxide-hydroxide phases on the surface of the crystallites. Finally, it was shown that, under the influence of the electron gun, large changes take place in the composition of the residual gas.     

Optical properties and solar selectivity of flash-evaporated copper sulphide films

The optical properties of copper sulphide films deposited onto glass and aluminium substrates using the flash evaporation technique were investigated. The films are stable and show good adhesive properties. A study of the optical properties of the films revealed that the films possess solar-selective properties. A film 7000 Å thick deposited onto aluminium showed a solar absorptance α_s of 0.92 with a thermal emittance ε_T (at temperature T = 100°C) of 0.20. The thermal emittance of the films increased linearly from 0.20 to 0.23 as the temperature was increased from 100 to 250°C. The films do not suffer from any UV degradation and can withstand temperatures as high as 150 °C for more than 250 h. Films coated on glass also show low values (about 0.20) of thermal emittance, thereby indicating the presence of intrinsic selective properties. The films on glass also possess excellent conducting properties and a film 2500 Å thick on glass has p-type conductivity with a sheet resistance of 25 Ω/□. X-ray and transmission electron microscopy studies revealed that the films were amorphous in nature. Auger electron spectroscopy studies carried out on the copper sulphide films indicated a slight excess of copper.     

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.     

Effect of substrate temperature on HWCVD deposited a-SiC:H film

Hydrogenated amorphous silicon carbon (a-SiC:H) films were deposited using pure SiH₄ and C₂H₂ without hydrogen dilution by hot wire chemical vapor deposition (HWCVD) technique. The photoluminescence, optical, and structural properties of these films were systematically studied as a function of substrate temperature (T_s). a-SiC:H films deposited at lower substrate temperature (T_s) show degradation in their structural, optical and network properties. The hydrogen content (C_H) in the films was found to be increased with decrease of T_s studied. Photoluminescence spectra shift to higher energy and less FWHM at high T_s. Raman spectroscopic analysis showed that structural disorder increases with decrease in the T_s.     

On the existence of a nanometric multilayered structure in Al2O3/Al thin films

Al₂O₃/Al films (period thickness Λ=20, 40 nm) were deposited onto (1 0 0) silicon substrate by reactive r.f. sputtering for substrate temperatures (T_s) ranging from −90 to 600 °C. Secondary ion mass spectrometry demonstrated the deposition of Al₂O₃/Al stratified thin films with the generation of periodic signals. X-ray reflectometry confirmed the periodicity with the presence of Bragg peaks in the experimental patterns. Nevertheless, the multilayered character of Al₂O₃/Al films is less and less pronounced as T_s increases. At low T_s, the relevant parameter to account for the absence of abrupt interfaces is the roughness of layers due to the aluminium layers, while at high T_s, the chemical interdiffusion clearly dominates.     

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.     

Low temperature NH3 adsorption on clean amorphous silicon and on crystalline silicon surfaces and nitrogen bonding in hydrogenated amorphous silicon nitride films: A comparative X-ray photoelectron spectroscopy study

Careful X-ray photoelectron spectroscopy studies of the nitrogen core levels were used to compare, in the same substrate temperature T_s range (between room temperature and 450 °C), the first interaction stages of amorphous and crystalline silicon surfaces (a-Si and c-Si(111)-(7 × 7)) with ammonia and the uptake of nitrogen on reactive evaporation of silicon in an ammonia ambient, i.e. during the growth of hydrogenated amorphous silicon nitride (a-SiN_x:H) films. In all cases we observed strongly correlated behaviours: the N 1s binding energy E_B decreased with increasing T_s, reflecting the presence of more dissociated species, probably NH₂ or NH and finally nitrogen, either on the silicon surfaces or in the bulk of the a-SiN_x:H films. The total N 1s core level intensities corresponding to hydronitride complexes NH_X decreased with increasing T_S up to 300 °C. Above this temperature the contribution of completely dissociated molecules relevant to nitride environments became prominent. The nitrogen coverage of the silicon surfaces at room temperature as a function of exposure was also compared with the nitrogen content x of a-SiN_x:H films as a function of NH₃ pressure during evaporation. Converted into dynamical exposures for a given evaporation rate, this pressure dependence is very well explained in terms of variations in the sticking coefficient deduced from the adsorption studies.     

Aerosol assisted chemical vapour deposition of germanium thin films using organogermanium carboxylates as precursors and formation of germania films

Diethyl germanium bis-picolinate, [Et₂Ge(O₂CC₅H₄N)₂], and trimethyl germanium quinaldate, [Me₃Ge(O₂CC₉H₆N)], have been used as precursors for deposition of thin films of germanium by aerosol assisted chemical vapour deposition (AACVD). The thermogravimetric analysis revealed complete volatilization of complexes under nitrogen atmosphere. Germanium thin films were deposited on silicon wafers at 700°C employing AACVD method. These films on oxidation under an oxygen atmosphere at 600°C yield GeO₂. Both Ge and GeO₂ films were characterized by XRD, SEM and EDS measurements. Their electrical properties were assessed by current?Cvoltage (I?CV) characterization.     

Influence of substrate temperature on the electrical and optical properties of amorphous germanium films

The influence of substrate temperature on electrical and optical properties of the amorphous germanium films deposited under well-defined conditions has been investigated. DC electrical conductivity in the temperature range of 80–573°K has been measured. In the low temperature region Mott’sT ^−1/4 law of conductivity is obeyed. The estimated values ofT ₀ andN show significant decrease with change inT _s in steps of 50°K. Similar results are seen in annealed films. The values of activation energy and optical energy increase withT _s.     

The electrical properties of CuInSe2 thin films deposited onto CaF2 substrates

CuInSe₂ thin films were deposited onto (111)-oriented CaF₂ substrates by flash evaporation in the substrate temperature range T_s = 650–890 K. Epitaxial growth was found at T_s = 770–800 K; at lower and higher substrate temperatures the films were partly polycrystalline. Films produced at T_s ? 675 K showed n-type conductivity due to a donor with an ionization energy of 78 ± 5 meV ascribed to indium interstitials. At T_s ? 725 K the films exhibited p-type conductivity due to a shallow acceptor with an ionization energy characteristic of indium vacancies. The important role of the substrate material in establishing the electrical parameters of CuInSe₂ thin films is proved by a comparative study of thin films deposited onto GaAs and CaF₂ substrates.     

Quantum size effect in thin Cd3As2 films

An investigation has been carried out of the resistivity ?, Hall coefficient R_H and Hall mobility μ_H as functions of film thickness for vacuum-evaporated thin Cd₃As₂ films. The films were evaporated in a vacuum of 10^?5 torr onto mica substrates heated to a temperature t_s of about 160 °C at a rate of deposition v of about 40 Å s^?1. The thicknesses of the films were in the range 0.02–0.2 μm. An oscillating character of the resistivity and the carrier mobility was observed for thicknesses of 0.03–0.1 μm. No distinct oscillations of the Hall coefficient were found. The analysis of the results obtained was performed on the basis of theories of the quantum size effect (QSE). The period of the oscillations measured from the experimental data was about 100 Å, which is in good agreement with the calculated value of about 80 Å.     

Control of orientation from random to (220) or (400) in polycrystalline silicon films

The control of grain orientation in polycrystalline silicon thin films on glass substrates by low-temperature techniques was investigated. Either (220) or (400) preferential grain orientation could be attained by control of source gas ratio over substrate temperatures between 250°C and 360°C. A remote type plasma chemical vapor deposition system was used with source gas mixtures of SiF₄, H₂ and Ar. The (220) preferential films were obtained with Ar/H₂/SiF₄ gas flow rates of 60/15/30 sccm (respectively), while the (400) preferential oriented films were obtained at higher SiF₄/H₂ ratios (SiF₄/H₂=90/10 sccm). At the higher SiF₄/H₂ ratio during the crystal nucleation stage, either randomly oriented or (400) grains formed followed by the highly preferred deposition of (400) oriented crystallites. Raman scattering and ellipsometry spectra indicated that the (400) oriented films had a very smooth surface.     

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).     

Doping Effect on the Structure of Polycrystalline Silicon Films Grown via Silane Pyrolysis

X-ray diffraction, transmission and scanning electron microscopy, and secondary-ion mass spectrometry data demonstrate that the grain size, structure, and composition of polycrystalline silicon (poly-Si) films grown using hydride pyrolysis depend on the GeH₄ : SiH₄ volume ratio in the gas mixture, dopant (boron or phosphorus) concentration, substrate temperature, and heat-treatment temperature. The films grown at substrate temperatures below 600°C are amorphous, and those deposited at 600°C are amorphous-crystalline. Textured poly-Si films are only obtained at 620°C or higher substrate temperatures. Doping with germanium, an isovalent impurity, improves the structural perfection of poly-Si films.     

Characterization of silicon oxynitride thin films deposited by electron beam physical vapor deposition technique

Thin films of silicon oxynitride (SiO_xN_y) were deposited successfully on silicon wafer substrates using electron beam physical vapor deposition (EB-PVD) technique by varying the substrate temperature (T=100–450 °C) and deposition time (t=0.5–2.5 min). The films were characterized by UV–Visible and X-ray photoelectron spectroscopy (XPS), Tally step measurement and Ellipsometry. The minimum reflectivity R=1.72% is obtained for the films deposited under the conditions of T=350 °C, t=1.5 min at λ=548 nm. Further, the characterization results revealed that the refractive index (RI) of the films increases with increase in the substrate temperature due to increase in silicon nitride content. The refractive index and the thickness of the films were found to be in the range of n=1.72–1.90 and d=40–138 nm, respectively. The values n=1.88 and d=79 nm observed corresponding to the minimum reflectivity R=1.72% satisfy the condition of near quarter wavelength single layer antireflection coating. Thus, the above films might have the tremendous potential for antireflective coating applications.     

Investigation of electrochromic properties of nanocrystalline tungsten oxide thin film

Thin films of tungsten oxide were grown by organometallic chemical vapor deposition (OMCVD) using tetra(allyl)tungsten, W(η³-C₃H₅)₄. X-Ray diffraction (XRD) analyses showed amorphous films at substrate temperatures (T_s) <350°C and polycrystalline films at T_s>350°C. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed grain sizes in the range 20–40 nm. In situ electrochemical reduction of WO_3.2/ITO (2.0 M HCl) produced a faint blue color in less than 1 s. The maximum coloration efficiency (CE) was found to be 22 cm²/mC at 630 nm. The density of the films decreases from 4.53 to 4.29 g/cm³ after annealing. An optical bandgap (E_g) of ∼3.2 eV was estimated for both as-deposited and annealed films.