Photosensitivity of thin-film structures based on CuIn<Subscript>3</Subscript>Se<Subscript>5</Subscript> and CuIn<Subscript>5</Subscript>Se<Subscript>8</Subscript> ternary semiconductor compounds

Polycrystalline n-type CuIn₃Se₅ and CuIn₅Se₈ films with thicknesses from 0.4 to 1 μm have been grown by pulsed laser ablation of bulk p-CuIn₃Se₅ and n-CuIn₅Se₈ crystals in vacuum. The temperature dependences of the resistivities of these crystals are determined by deep donor levels with energies E _D ? 0.2–0.3 eV. Photosensitive thin-film structures based on these films have been created for the first time and their photosensitivity spectra have been measured. The possibility of using thin CuIn₃Se₅ and CuIn₅Se₈ films in broadband photoconverters is demonstrated.     

Photoluminescence and raman spectra of (Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.95</Subscript>(Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0.05</Subscript> crystals

We have measured the photoluminescence and Raman spectra of (Ga₂S₃)_0.95(Sm₂O₃)_0.05 crystals and identified the mechanism of the energy transfer from the host to the rare-earth ion and the vibrational modes of the constituent atoms.     

The Multiferroic Properties of (Bi<Subscript>0.9</Subscript>Ba<Subscript>0.1</Subscript>)(Fe<Subscript>0.95</Subscript>Mn<Subscript>0.05</Subscript>)O<Subscript>3</Subscript> Films

(Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ films were prepared on LaNiO₃-coated surface oxidized Si substrates. XRD and Raman measurements confirm that the (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ film has pure R3c structure. Clear ferromagnetism with saturated magnetization of about 25 emu/cm³ has been observed at room temperature. The ferroelectric properties of the (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ film was confirmed by the observation of the ferroelectric domains and the converse piezoelectric coefficient d ₃₃ versus applied voltage hysteresis loops by piezoelectric force microscopy (PFM). The observation of ferromagnetism and ferroelectricity in (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ films indicates the potential multiferroic applications.     

Magnetoelectric interactions in BiFeO<Subscript>3</Subscript>, Bi<Subscript>0.95</Subscript>Nd<Subscript>0.05</Subscript>FeO<Subscript>3</Subscript>, and Bi<Subscript>0.95</Subscript>La<Subscript>0.05</Subscript>FeO<Subscript>3</Subscript> multiferroics

The technology of ceramic BiFeO₃, Bi_0.95Nd_0.05FeO₃, and Bi_0.95La_0.05FeO₃ multiferroics is described. The room-temperature magnetization, magnetoelectric (ME), and magnetodielectric (MDE) effects in these compounds have been studied. It is established that even a small fraction (x = 0.05) of rare-earth additives (La, Nd) to bismuth ferrite not only enhance its magnetic properties, but also significantly influence the ME and MDE effects. The dependence of the ME effect on the frequency of modulation of the alternating magnetic field in Bi_0.95Nd_0.05FeO₃, and Bi_0.95La_0.05FeO₃ is more pronounced than in pure BiFeO₃.     

Structural,optical, and opto-dielectric properties of W-doped Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films

A layer-by-layer deposition technique of Ga₂O₃ and WO₃ by vacuum evaporation method on glass and silicon substrates and subsequent annealing in oxygen atmosphere to form W-doped Ga₂O₃ (or Ga₂O₃:W) films was attempted here. The W doping level was measured by the energy dispersive X-ray fluorescence radiographic analysis. The crystalline structure of Ga₂O₃:W films was determined by the X-ray diffraction method. Experimental data indicate that W⁶⁺ ions doped in host Ga₂O₃ forming solid solutions (SS), in which the molar ratio (r) of W to Ga is 9.6, 13.4, 18.2, 22.7 and 30.4%. All the prepared SS have the known β-Ga₂O₃ crystalline structure. This doping controls the optical and electrical properties of the host Ga₂O₃. The optical properties of the prepared Ga₂O₃:W films were studied by UV–VIS–NIR absorption spectroscopy method from which the bandgap was determined. In general, it was found that the prepared Ga₂O₃:W films are wide-bandgap semiconductors with bandgap 4.69–4.47 eV and have dielectric properties. The optical sensitivity of the capacitance, dissipation factor and ac-conductance of the Ga₂O₃:W films grown on Si was studied as a function of W-doping level. It was observed that the prepared Ga₂O₃:W film of r = 22.7% has the highest photosensitivity amongst the other samples.     

Effect of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> concentration in Bi-containing high-temperature solutions on the luminescence of epitaxial Gd<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> films

Single-crystal gadolinium gallium garnet films have been grown by liquid-phase epitaxy on (111) Gd₃Ga₅O₁₂ substrates from supercooled Bi₂O₃-B₂O₃ fluxed melts at different Gd₂O₃ concentrations. The luminescence spectra of the films have been measured at 10 and 300 K under unmonochromatized synchrotron X-ray excitation and selective UV synchrotron excitation. The Bi³⁺ luminescence is discussed.     

Spectral optoelectronic features of Cu-containing arsenic sulfide (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.95</Subscript>Cu<Subscript>0.05</Subscript>

Chalcogenide amorphous thin films of the modification (As₂S₃)_0.95Cu_0.05 were prepared using a thermal evaporation technique. The optical properties of the resultant films were investigated based on the transmittance spectra in the photon energy range 1.6–2.82 eV. Thicknesses of the films under study were determined using the envelope technique based on the transmittance spectra. The optical measurements were carried out over the conditional temperature extending from 77 to 300 K. The results of the mentioned measurements are conductive tools in investigating the electronic structures of the Chalcogenide Glasses, however the analysis of the experimental results provide information about the optical gap width and elucidate the broadness of the band tail that may disturb the band gap edges. Moreover, the single-effective oscillator was implemented in calculating both the oscillation and dispersion energies of the films under investigation. The static refractive index and the static dielectric constant were also determined for these films.     

The effect of annealing time on r.f. magnetron sputtered La<Subscript>3</Subscript>Ga<Subscript>5</Subscript>SiO<Subscript>14</Subscript> films

La₃Ga₅SiO₁₄ (LGS) thin films have been grown by r.f. sputtering at 600 °C on (200)-textured MgO buffer layers deposited also by r.f. sputtering on Si substrates. The evolution of crystalline phases in the thin films as a function of time was examined by X-ray diffraction and scanning electron microscopy before and after annealing in air for various times. The morphology of the crystals formed and their formation mechanism were discussed.     

Influence of Mg<Superscript>2+</Superscript>/Ga<Superscript>3+</Superscript> doping on luminescence of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphors

Mg²⁺/Ga³⁺ doped Y₃Al₅O₁₂:Ce³⁺ phosphors were synthesized through a solid state reaction. The phase and luminescent of the synthesized phosphors were investigated. For Ga³⁺ codoped Y_2.96Ce_0.04Al_(5?x)Ga_xO₁₂ phosphors, the emission intensity increases with the increase of Ga³⁺ concentration up to Y_2.96Ce_0.04Al_4.80Ga_0.20O₁₂ and then decreases with a further increase of Ga³⁺ concentration, but the emission peak shifts to shorter wavelength continuously in the Ga³⁺ doping concentration range of 0.05–0.25. For Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors, the emission intensity decreases and the emission peak shifts to longer wavelength continuously in the Mg²⁺ doping concentration range of 0.02–0.12. The emission spectra of Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors demonstrate that the codoped Mg²⁺/Ga³⁺ ions not only induce the enhancement of Y_2.96Ce_0.04Al₅O₁₂ emission intensity but also lead to the red shift of Y_2.96Ce_0.04Al₅O₁₂ emission peak. The decay lifetimes decrease in Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al₅O₁₂ phosphors due to defects formed by substitutions of Y³⁺ by Mg²⁺/Ga³⁺.     

Crystal structure of Gd<Subscript>14</Subscript>Cu<Subscript>48</Subscript>Ga<Subscript>3</Subscript> and Tb<Subscript>14</Subscript>Cu<Subscript>48</Subscript>Ga<Subscript>3</Subscript>

The compounds Gd₁₄Cu₄₈Ga₃ and Tb₁₄Cu₄₈Ga₃ have been synthesized, and their structures have been determined by powder x-ray diffraction (Gd₁₄Ag₅₁ type).     

Study on the Magnetic and Ferroelectric Properties of Bi<Subscript>0.95</Subscript>Dy<Subscript>0.05</Subscript>Fe<Subscript>0.95</Subscript>M<Subscript>0.05</Subscript>O<Subscript>3</Subscript> (M = Mn,Co) Ceramics

The co-doped Bi_0.95Dy_0.05Fe_0.95M_0.05 O ₃ (M = Mn, Co) samples were successfully prepared by a solid-state reaction method. At room temperature, the structural, ferromagnetic, and ferroelectric properties of the samples were measured and analyzed. An x-ray diffraction (XRD) experiment shows that co-doping leads to some structure changes. Magnetic hysteresis loops indicate that Dy-Mn and Dy-Co co-doping both can increase the ferromagnetic but the latter is superior to the former caused by the different magnetic arrangement. Furthermore, it is found that Dy-Mn co-doping is better than Dy-Co co-doping on enhancing its ferroelectricity.     

Microstructure and phase transformations in a Ni<Subscript>50</Subscript>Mn<Subscript>29</Subscript>Ga<Subscript>16</Subscript>Gd<Subscript>5</Subscript> alloy with a high transformation temperature

A Heusler Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy with a high transformation temperature has been obtained by substituting 5 at% Gd for Ga in a ternary Ni₅₀Mn₂₉Ga₂₁ ferromagnetic shape memory alloy. The microstructure and phase transformations in the Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy have been investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. It is shown that the microstructure of the Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy consists of matrix and hexagonal Gd (Ni,Mn)₄Ga phase, which indicates a eutectic structure composed of these two phases. One-step thermoelastic martensitic transformation occurs in this quaternary alloy. Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy exhibits a martensite transformation start temperature up to 524 K, approximately 200 K higher than that of Ni₅₀Mn₂₉Ga₂₁ alloy. At room temperature, non-modulated martensite with twin substructure is observed in Ni₅₀Mn₂₉Ga₁₆Gd₅ alloy.     

Effect of excess Bi content on electrical properties of BiFe<Subscript>0.95</Subscript>Cr<Subscript>0.05</Subscript>O<Subscript>3</Subscript> thin films

The Bi_1?+?xFe_0.95Cr_0.05O₃ (BFCO) (x?=?0, 5, 10, 15 and 20%) thin films are fabricated on FTO/glass substrate using a chemical solution deposition method and sequential-layer annealing process. The effects of the excess Bi content on crystalline structure, morphology, and electrical performance of BFCO thin films are investigated. All the BFCO thin films are crystallized into polycrystalline perovskite structure and belonging to the space group of R3c. The BFCO thin films with 5 and 10% excess Bi contents possess no impurity phase. Especially, a dense surface morphology and columnar crystal structure can be obtained for the film with 5% excess Bi content. Especially, the one possesses superior ferroelectricity with a relative high remnant polarization (P _r) of 69.8 µC/cm² and low coercive electric field (E _c) of 291 kV/cm at 1 kHz due to the relatively low leakage current density of 3.04?×?10^??5 A/cm² at 200 kV/cm.     

Photosensitive point structures based on CuIn<Subscript>2<Emphasis Type="Italic">m</Emphasis> + 1</Subscript>Se<Subscript>3<Emphasis Type="Italic">m</Emphasis> + 2</Subscript> crystals

Photosensitive point structures based on CuIn_{2m + 1}Se_{3m + 2} (m = 0, 1, 2) single crystals have been obtained for the first time by means of electric-discharge welding (EDW). The stationary current-voltage characteristics and the photovoltaic properties of the structures based on CuInSe₂, CuIn₃Se₅, and CuIn₅Se₈ ternary semiconductors have been studied, which show evidence for the rectification effect and photoconversion. The character of interband transitions is established and the bandgap width variation in this series of compounds is traced. It is concluded that EDW can be successfully used for the fabrication of photoconverters based on multicomponent semiconductors.     

Effects of gate sidewall recess on Al<Subscript>0.2</Subscript>Ga<Subscript>0.8</Subscript>As/ In<Subscript>0.15</Subscript>Ga<Subscript>0.85</Subscript>As PHEMTs by citric-based selective etchant

In this report, an effective and simple method of selective gate sidewall recess is proposed to expose the low barrier channel at mesa sidewalls during device isolation for Al_0.2Ga_0.8As/ In_0.15Ga_0.85As PHEMTs (pseudomorphic high electron mobility transistors) by using a newly developed citric-acid-based etchant with high selectivity (> 250) for GaAs/Al_0.2Ga_0.8As or In_0.15Ga_0.85As/Al_0.2G_0.8 As interfaces. After sidewall recess, a revealed cavity will exist between the In_0.15Ga_0.85As layers and gate metals. Devices with 1 × 100μm² exhibit a very low gate leakage current of 2.4μA/mm even at V_GD = −10 V and high gate breakdown voltage over 25 V. As compared to that of no sidewall recess, nearly two orders of reduction in magnitude of gate leakage current and 100% improvement in gate breakdown voltage can be achieved.     

Electron traps in Gd<Subscript>3</Subscript>Ga<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>12</Subscript>:Ce garnets doped with rare-earth ions

The curves of thermally stimulated luminescence of Gd₃Ga₃Al₂O₁₂:Ce³⁺ ceramics (a nominally pure sample and samples doped with rare-earth ions) are measured in the temperature range of 80–550 K. The depth and the frequency factor of electron traps established by Eu and Yb impurities are determined. An energy-level diagram of rare-earth ions in the bandgap of Gd₃Ga₃Al₂O₁₂ is presented.     

Martensitic phase transformation in single crystal Co<Subscript>5</Subscript>Ni<Subscript>2</Subscript>Ga<Subscript>3</Subscript>

The magnetic, thermal, and transport properties of martensitic phase transformation in single crystal Co₅Ni₂Ga₃ have been investigated. The single crystal Co₅Ni₂Ga₃ shows martensitic transformation at 251 K on cooling and 254 K on warming. Large jumps in the temperature-dependent resistance curve, temperature-dependent magnetization curve, and temperature-dependent thermal conductivity curve are observed at martensitic transformation temperature (T _M). Negative magnetoresistance due to spin disorder scattering was observed in Co₅Ni₂Ga₃ single crystal at all temperature range. The temperature-dependent negative magnetoresistance shows a peak at T _M, which indicates that the spin disorder increases in the process of phase transition. Co₅Ni₂Ga₃ sample exhibits a temperature dependence of thermal conductivity κ(T) (dκ/dT > 0) due to electrons being above temperature 100 K.     

Room-Temperature Photomagnetic Effect of Fe<Subscript>3</Subscript>Ga<Subscript>4</Subscript> Grown on GaAs Substrates

Ga–As–Fe composite films prepared by molecular beam epitaxy at 600°C on GaAs(100) substrates with the stacking sequence of [100-nm GaAs/50-nm Fe₃Ga_{2− x} As _x /100-nm GaAs] exhibit the distinct photo-enhanced magnetization at room temperature. Transmission electron microscopy reveals the formation of metamagnetic Fe₃Ga₄ grains on the sample surface. Illumination power dependence of the enhanced magnetization has been carefully compared with the antiferromagnetic-type magnetization–temperature (M–T) curve (Neel temperature of T _N = 340–390 K), from which we have discussed the existence of photon-mode photo-enhanced magnetization of some sort in addition with the enhancement due to the light-induced heating.     

Annealing behavior of TiO<Subscript>2</Subscript>-sheathed Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

TiO₂-sheathed Ga₂O₃ one-dimensional (1D) nanostructures were synthesized by thermal evaporation of GaN powders and then sputter-deposition of TiO₂. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis results indicate that the Ga₂O₃ cores are of a single crystal nature with a monoclinic structure while the TiO₂ shells are amorphous. Photoluminescence (PL) emission is slightly decreased in intensity by TiO₂ coating, but it is significantly increased by thermal annealing in an oxygen atmosphere. The emission peak is also shifted from ~500 to ~550 nm by oxygen annealing. The increase in the green emission is due to the increase in the concentration of the Ga vacancies in the cores by the inflow of oxygen during oxygen annealing. On the other hand, annealing in a nitrogen atmosphere leads to a red shift of the emission to ~700 nm originating from nitrogen doping.     

Preparation and characterisation of nanostructural TiO<Subscript>2</Subscript>–Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> binary oxides with high surface area derived form particulate sol–gel route

Nanostructured and nanoporous TiO₂–Ga₂O₃ films and powders with various Ti:Ga atomic ratios and high specific surface area (SSA) have been prepared by a new straightforward particulate sol–gel route. Titanium isopropoxide and gallium (III) nitrate hydrate were used as precursors and hydroxypropyl cellulose (HPC) was used as a polymeric fugitive agent (PFA) in order to increase the SSA. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that powders contained both rhombohedral α-Ga₂O₃ and monoclinic β-Ga₂O₃ phases, as well as anatase and rutile. It was observed that the Ga₂O₃ formed from the nitrate precursor retarded anatase-to-rutile transformation. Furthermore, transmission electron microscope (TEM) analysis also showed that Ga₂O₃ hindered the crystallisation and crystal growth of powders. SSA of powders, as measured by Brunauer–Emmett–Teller (BET) analysis, was enhanced by introducing Ga₂O₃. Ti:Ga = 50:50 (at%/at%) binary oxide annealed at 500 °C produced the smallest crystallite size (2 nm), the smallest grain size (18 nm), the highest SSA (327.8 m²/g) and the highest roughness. Ti:Ga = 25:75 (at%/at%) annealed at 800 °C showed the smallest crystallite size (2.4 nm) with 32 nm average grain size and 40.8 m²/g surface area. Ti:Ga = 75:25 (at%/at%) annealed at 800 °C had the highest SSA (57.4 m²/g) with 4.4 nm average crystallite size and 32 nm average grain size. One of the smallest crystallite size and one of the highest SSA reported in the literature is obtained, and they can be used in many applications in areas from optical electronics to gas sensors.