This paper concerns the study of growth and characterizations of Co2YZ with Y an element of transition metal group and Z, a III-V group element deposited onto Si, GaAs and InAs substrates. Two PLD configurations have been explored, the conventional 1-Beam-PLD and the 2-Crossed-Beams-PLD one. We demonstrated that depending on the configuration we got Co2YZ polycrystalline structure with unwanted droplets or droplet-free, single crystalline oriented thin films at substrate temperature as low as 353 K. Optical conductivity and magnetic properties are presented.
This present work concerns the growth and the characterization of Co2MnSi thin films deposited onto GaAs substrates. Two PLD configurations have been explored, the conventional 1-Beam-PLD and the 2-Crossed-Beams-PLD one. We demonstrated that, with 1B-PLD conditions, we got Co2MnSi polycrystalline structure with unwanted droplets. The 2CB-PLD allowed us to get droplet-free, single crystalline thin films at substrate temperature as low as 353 K.
The half-metallic ferromagnetic chromium dioxide (Tc = 390 K) is a prospective material for spintronics applications. We employed pulsed laser deposition (PLD) to grow thin films of various chromium oxides. The experiments have been carried out in oxygen at different dynamical pressures, using a KrF* laser source (λ = 248 nm, τFWHM ≥ 30 ns), various chromium oxide targets, such as CrO3, Cr8O21 (the latter ones both pure and doped with Y and Sb respectively, for stabilization purposes) and sapphire substrates (c-cut). We optimized the laser fluence. To avoid CrO2 reduction to Cr2O3 in very thin films when kept in atmospheric air, we applied a protection with gold. X-ray diffraction, electron microscopy and Raman spectroscopy evidence uniform films containing CrO2.
This work presents our attempts to grow thin films of the ferromagnetic half-Heusler alloy NiMnSb and also a bi-layered structure MnSb/NiMnSb onto (100) semiconductor substrates using Single Beam and respectively Double Beam Pulsed Laser Deposition. We investigated the samples by XRD, scanning electron microscopy (SEM), Energy Dispersive X ray (EDX) analysis and SQUID magnetometry. The thin films obtained in both configurations are crystalline, single phase with stoichiometry corresponding to the bulk material. The out of plane magnetisation of the bi-layered structure reaches the saturation value more rapidly than the NiMnSb/Si film.
We report on the reproducible growth of stoichiometric thin films of ferromagnetic intermetallic compound NiMnSb by pulsed laser deposition (PLD) on various substrates. The films are grown at moderate temperature (around 200 degree(s)C) using polycrystalline targets. Two different substrates were employed - single crystalline silicon and InAs polycrystalline - to investigate the influence of the thin layer/substrate lattice mismatch on the quality of the grown film. XRD and EDX analyses indicate that the layers are of high crystalline quality and their stoichiometry is very close to that of the corresponding targets, respectively. SEM images show that there are droplets on the surface of the films and their composition is similar to that of the targets. Magnetic measurements performed at both room temperature and 5K find that the investigated samples have small Hc values.
To investigate the optical homogeneity of crystals some methods based on the analysis of the laser beams interacting with a sample have been recently proposed. The emergent beam is acquired by a data acquisition/image processing system which offers the possibility for both local and global analysis of the sample. Combined with microscopy techniques these methods enable the study of submicron defects such as scattering centers, clusters of punctual defects, microcracks. A map of the absorption coefficient (alpha) equals(alpha) (x,y) can be obtained by recording the transmitted light when scanning the sample with the laser beam. This result is particularly useful for determining some growth parameters because spatial variation of the absorption coefficient is a consequence of thermal oscillations in the crystallization system. Our paper is a short study on the optical homogeneity of sapphire crystals grown by different techniques as related to the particular defects induced by the growth process. Laser beam analysis has been mainly employed to characterize the samples. The results provide important information on the dynamics of the crystallization interface during the growth processes, on the number and types of growth defects, foreign phase precipitations, inclusions, thermal stress, etc., which may help with optimization of the growth parameters.
This paper reports on the optical properties of polycrystalline p-type InxGa1-xSb (x equals 0.20) over the wavelength range 15 - 30 micrometers , at room temperature. The material was obtained by direct synthesis from the elements and rapidly crystallized following a particular temperature regime. Transmittance and reflectance measurements were performed at room temperature by using a SPECORD M80 spectrophotometer. From the resulted values we calculated the absorption coefficient (alpha) as a function of the photon energy. Considerations are made concerning the peculiarities involved by the polycrystalline structure and the surface imperfections on the absorption phenomena over the mentioned wavelength range.
This paper reports on controlled electric and optical properties of single crystalline sapphire for substrates use. The crystals were grown by the Czochralski method from a graphite crucible by using an original non-conventional crystal growth assembly. We paid a special attention to the homogeneity of the crystal. A new model for the electric conduction mechanisms is considered, the validity of which was confirmed by experimental measurements.
This paper reports on the new performance obtained for n-type InSb photoconductive element detectors, made of bulk crystals. It is taken into account the important drop of the electric conductivity, by one magnitude order over the temperature range 77 K - 90 K, that forced us to optimize the heat transfer among the elements of the device. The maximum value obtained for the spectral detectivity is 4 by 1012 cmHz1/2W-1, at lambda equals 4.9 micrometer, for a field of view of 60 degrees. The calculations show that the device is limited by the generation-recombination noise.
A new structure is proposed for the PbS based photoresistors. This structure consists from a thin film of PbS (about 1 micrometer) chemically deposited on a dielectric layer (SiO2 or Si3N4 of about 2000 angstroms) grown, using different methods, on a single crystal Si wafer. The drain and the source contacts are the two gold electrodes evaporated on the surface of the PbS film. The resulting active area is of 6 by 6 mm2 and is subjected to an incident light with the wavelength in the domain 0.8 - 3 micrometer (at room temperature). The gate contact is the aluminum electrode evaporated on the back side of the Si substrate. Spectral distribution measurements were performed for different voltages applied on the gate electrode. It was found that the shape of the spectral distribution remains the same but the amplitude of the signal depends on the value and on the polarity of the applied voltage. An improvement of about 40% was obtained for the PbS photoconductive signal compared with the situation when the gate electrode is in air. The new structure offer the possibility to improve the photoconductive signal generated by the PbS film. This improvement is due to a field effect.
This paper refers to the influence of the electrical and transport properties of n-type InSb single crystal on the parameters of the IR (3 - 5 micrometers ) photoconductive (PC)-detector. We consider a simple n-type PC element made of InSb single crystal. Some general physical features of the device, the device performance related to the material properties and the characterization techniques involved are described.
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