Ferromagnetism in transition-metal-doped semiconducting oxide thin films

A rather complete work on transition-metal (TM)-doped TiO₂ thin films has been done and room ferromagnetism (FM) is found in the whole series of Sc/V/Cr/Mn/Fe/Co/Ni-doped TiO₂ films. Not only is it remarkable that for the first time, FM at high temperature was achieved in TM-doped TiO₂, but also a very big magnetic moment of 4.2μ_B/atom could be obtained, and direct evidences of real ferromagnets with big domains were shown as well. A similar chemical trend was achieved in TM-doped In₂O₃ films, however, the observed magnetic moment is rather modest, with the maximal value is of only 0.7μ_B/atom for Ni-doped In₂O₃ films. As regards TM-doped SnO₂ films, observed magnetic moments could be very large, with the maximum saturation of 6μ_B per impurity atom for Cr-doped SnO₂ thin films, but it could be influenced very much depending on substrate types. On the other hand, results on TM-doped ZnO films interestingly have revealed that in these systems, the magnetism more likely resulted from defects and/or oxygen vacancies.     

Dynamical properties of thin ferromagnetic semiconducting films

A Green's function technique is used to investigate the temperature dependence of the spin-wave energies of ferromagnetic semiconducting thin films including the damping effects. It is shown that the frequencies of thin ferromagnetic films are smaller, whereas the damping effects are larger compared to the bulk.     

Insulated-ceystal method for measuring electrical properties of thin semiconducting films

Procedure and apparatus are described for measuring the resistivity, free-charge density, and free-charge mobility in thin semiconducting films. The method is based on the dependence of the power transmitted to a microwave transmission line on the density and mobility of free charge in a semiconductor in the line insulated from electrodes on both sides by dielectric layers. Experimental results are reported.Translated from Izvestiya VUZ. Fizika, No. 5, pp. 105–109, May, 1971.     

Studies on electrosynthesized semiconducting zinc selenide thin films

The electrosynthesis of ZnSe thin films from aqueous acidic bath onto transparent conducting oxide coated glass substrates is described. The deposition potential range suitable for the deposition has been optimized using cyclic voltammetry. The influence of various deposition parameters on the structural and optical properties of the films is described. The optical constants ‘n’ and ‘k’ and the complex dielectric constants of the electrosynthesized ZnSe thin films are estimated for various wave length region. The surface morphological studies and the composition analysis are carried out and the results are discussed. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Optical properties of semiconducting iron disilicide thin films

The iron silicides samples were prepared by annealing of iron films evaporated onto silicon wafers and capped with amorphous silicon thin overlayers. Semiconducting FeSi₂ phase is formed by annealing at the temperatures from 550°C to 850°C. The optical properties of the FeSi₂ layers have been deduced from reflectance and transmittance measurements carried out in the temperature range of (77–380) K. The spectral dependence of the absorption coefficient favours direct allowed transitions with forbidden energy gap of 0.87eV at the room temperature. The application of a simple three-parameter semiempirical formula to the temperature dependence of the direct energy gaps leads to the following best fit parameters: the band gap at zero temperature E _g (0) = (0.895 ± 0.004)eV, the dimensionless coupling parameter S = 2.0 ± 0.3, and the average phonon energy <hw> = (46 ± 8)meV. By examining all the reported triplets of parameters for -FeSi₂ fabricated by different techniques and thermal processes, an obvious discrepancy can be found for the lattice coupling parameter and average phonon energy, although the bandgaps at 0 K are very similar. Unlike the theoretical prediction and the earlier reported result, our results do not show any evidence of a particularly strong electron-phonon interaction, which would give the lower carrier mobilities. -FeSi₂ seems to be an intriguing material where states with energies near the band edges permit ambiguous interpretation of the character of transitions. From optical model for the thin film-substrate system we found the index of refraction to be (5–5.9) in the photon energy interval from 0.65 to 1.15eV. There is also indication of an additional higher-energy absorption edge at l.05eV.     

Properties of thin manganite films grown on semiconducting substrates for spintronics applications

La_0.7Sr_0.3MnO₃ (LSMO) manganite thin films were grown by pulsed plasma deposition on silicon (Si) and gallium arsenide (GaAs) substrates covered by an amorphous oxide. Manganite films are characterized by polycrystalline structure. Ferromagnetic transition is above room temperature and for 50 nm thick film the Curie temperature was as high as 325 K and 305 K for LSMO/SiO_x/Si and LSMO/AlO_x/GaAs, respectively.     

Depletion layers and domain walls in semiconducting ferroelectric thin films

Commonly used ferroelectric perovskites are also wide-band-gap semiconductors. In such materials, the polarization and the space-charge distribution are intimately coupled, and this Letter studies them simultaneously with no a priori ansatz on either. In particular, we study the structure of domain walls and the depletion layers that form at the metal-ferroelectric interfaces. We find the coupling between polarization and space charges leads to the formation of charge double layers at the 90 degrees domain walls, which, like the depletion layers, are also decorated by defects like oxygen vacancies. In contrast, the 180 degrees domain walls do not interact with the defects or space charges. Implications of these results to domain switching and fatigue in ferroelectric devices are discussed.     

Magnetic field dependence of the dynamical properties of ferromagnetic semiconducting thin films

The effect of external magnetic field, temperature and film thickness on the spin wave energy and the spin-wave damping in thin ferromagnetic semiconducting films is studied using the s-d interaction model and a Green's function formalism beyond the random phase approximation.     

Influence of surface roughness on the electrical conductivity of semiconducting thin films

The Green function solution of the Boltzmann transport equation has been applied in case of no magnetic field by ignoring any volume impurities. Gaussian, exponential and power law models for the surface roughness correlation function have been studied and the results have been compared with the ones obtained by other methods. It has been found that the electrical conductivity σ$\sigma$ increases with increasing correlation length l$l$ for the first two models, while for the third model σ$\sigma$ value is of the same order as the first two models. Therefore we show that the shape of the surface roughness can strongly influence the electrical properties.     

Chemical analysis of semiconducting and metallic SmS thin films by X-ray photoelectron spectroscopy

We studied the chemical state of semiconducting and metallic SmS thin films by X-ray photoelectron spectroscopy (XPS), which were fabricated using dual-target magnetron sputtering by controlling the power applied to both metal and chalcogenide targets. On the basis of the valence band spectra obtained, it was suggested that semiconducting SmS has the final state corresponding to the Sm²⁺(4f⁶) configuration below the Fermi level, and metallic SmS has mainly the Sm³⁺(4f⁵) final state and a virtual band state in the Sm 5d band, contributing to the delocalization of 4f electrons and the emergence of metallic conductivity (4f⁶d⁰-4f⁵d¹). Thus, the spectra of our fabricated SmS thin films correspond to the band structure obtained from the dielectric property. This is the first work performed on the intrinsically prepared metallic SmS while the former works done for the sample transformed from semiconductor to metal phase by hard polishing.     

Preparation of ferromagnetic semiconducting HgCr2Se4 thin films by molecular-beam deposition

Summary Polycrystalline thin films of the ferromagnetic semiconductor HgCr₂Se₄ have been prepared for the first time on insulating MgAl₂O₄ single-crystal substrates by molecular-beam deposition and subsequent annealing with HgSe. The optimum conditions for preparing single-phase thin films of HgCr₂Se₄ were obtained. The magnetoresistance and Hall effects of these films were measured from 77 to 295 K in magnetic fields up to 1.19·10⁶ A/m. It becomes evident that these electrical properties of the films are affected by the interdiffusion layers in the films near the substrates or the magnetically disordered layers such as amorphous or grain boundaries in the films. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Conductivity of thin semiconducting cadmium sulfide films deposited chemically from an aqueous solution

Russian Physics Journal -     

Pulsed laser deposition of semiconducting crystalline double-doped barium titanate thin films on nickel substrates

We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO₃ and (Ba,Pb,Y)TiO₃ thin films on mechanically polished nickel substrates.The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements.We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature.     

Epitaxial ferromagnetic thin films and heterostructures of Mn-based metallic and semiconducting compounds on GaAs

We present two approaches to integrate magnetic materials with III–V semiconductors. One is epitaxial ferromagnetic metallic films and heterostructures on GaAs (0 0 1) substrates. Although crystal structure, lattice constant, chemical bonding and other properties are dissimilar, ferromagnetic hexagonal MnAs thin films and MnAs/NiAs ferromagnet/nonmagnet heterostructures (HSs) are grown on GaAs by molecular beam epitaxy (MBE). Multi-stepped magnetic hysteresis are controllably realized in MnAs/NiAs HSs, making this material promising for the application to multi-level nonvolatile recording on semiconductors. The other approach is to prepare a new class of GaAs based magnetic semiconductor, GaMnAs, by low-temperature molecular beam epitaxy (LT-MBE) on GaAs (0 0 1). New III–V based superlattices consisting of ferromagnetic semiconductor GaMnAs and nonmagnetic semiconductor AlAs are also successfully grown. Structural and magnetic properties of these new heterostructures are presented.     

Thermodynamic conditions for formation of single phase in Bi-superconductor thin films

High quality BSCCO thin films have been fabricated by means of an ion beam sputtering at various substrate temperatures, T_sub, and ozone gas pressures, pO₃. The correlation diagrams of the BSCCO phases appearing against T_sub and pO₃ have been established in the 2212 and 2223 compositional films. In spite of 2212 compositional sputtering, Bi2201 and Bi2223 phases as well as Bi2212 have emerged as stable phases depending on T_sub and pO₃. From these results, the thermodynamic evaluations of ΔH and ΔS, which are related with Gibbs’ free energy change for single Bi2212 or Bi2223 phase have been performed.     

Influence of deposition conditions on nanostructured InSe thin films

In this study, nanostructured indium selenide (InSe) thin films were deposited on Indium tin oxide (ITO)-coated glass substrate using electrochemical deposition (ECD) from aqueous solution containing In(SO₄)₃.H₂O and SeO₂. The effects of deposition potential (−0.70 to −1.35 V), time (30-3600 s), temperature (25-80 °C) and pH (2.58 for A samples; 2 for B samples and 1.45 for C samples) on growth of the InSe thin films were examined in terms of their structural, morphological and optical properties. X-ray diffraction (XRD) analysis confirmed that the InSe thin films are in polycrystalline structure. It was found that the values of grain size decreased and the full width half maximum (FWHM) values increased with the increasing deposition potential. According to the absorption measurements, optical properties of the thin films varied with changes in deposition conditions. Based on the atomic force microscopy (AFM) and the scanning electron microscopy (SEM) images, surface morphology of the thin films was influenced by deposition potential and pH of the electrolyte, and non-homogeneous depositions distributed across the entire surface were observed. In addition, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FT-IR) analyses were used to further examine crystal quality, vibration, chemical binding conditions, In/Se orientation and structure of the prepared InSe thin films. When Raman results are examined, the B12 sample shows a more intensity and narrow peak at 248 cm⁻¹. XPS measurements sowed that A6 sample exhibited more growth in low potential for a long time and better film stoichiometry compared to the other three samples. Also, FT-IR studies prove the presence of InSe. According to the results, the film did not form at low temperatures and short times. However, the film formation began with the increasing deposition temperature and time at the low potential value of −0.730 V. But, it is clear that a high quality film can be obtained in cathodic potential with −1.3 V and shorter deposition time with 300 s at room temperature respectively. Overall results showed that the high quality thin films can be obtained by the ECD technique. However, deposition conditions must be sensitively adjusted to control morphology of the electrodeposited nanoparticles.     

Laser-induced synthesis of compound semiconducting films

Compound semiconducting films are synthesized by laser irradiation of sandwich films of the constituants, under various conditions (time of irradiation, laser power, temperature, etc.). Experimental data give evidence of the roles of various parameters. After a presentation of the experimental results, the fundamental physico-chemical mechanisms of laser material interactions are analyzed. Particular emphasis is given to effects that need to be treated by using very-far-from-equilibrium concepts.     

Pulsed laser deposition conditions and superconductivity of FeSe thin films

We report the effects of growth conditions on the superconducting properties of FeSe films epitaxially grown on LaAlO₃ substrates by pulsed laser deposition (PLD). Customary materials characterization techniques [X-ray diffraction (XRD), in-situ X-ray photoelectron spectroscopy (XPS), in-situ ultra-violet photoelectron spectroscopy (UPS), and scanning electron microscopy (SEM)] revealed the films had a c-axis oriented tetragonal structure with lattice constants dependent on the growth temperature (varied from 100 to 600°C). The standard four-point probe method was used to measure the resistivity and superconducting transitions. Films grown at 400–550°C showed a clear superconducting onset but no zero resistance down to 2 K. The highest superconducting onset temperature (T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}}) of 8 K was observed in films grown at 500°C and the onset temperature was clearly correlated to the ratio of the lattice constants (c/a). As the thickness of the FeSe films increased from 27 nm to 480 nm, T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}} also increased as the strain in the system was relaxed.