Structural,optical and electrical properties of Fe-doped SnO2 fabricated by sol–gel dip coating technique

Nanosized Fe³⁺-doped SnO₂ thin film was prepared by the sol–gel dip coating (SGDC) technique on quartz class substrate and sintered at 800 °C. The microstructures, surface morphology and optical properties of these films were then characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption measurements, respectively. Electrical properties were analyzed, and resistivity, type and number of carrier concentration, Hall mobility measured as a function of Fe³⁺ doping and temperature. The XRD spectrum shows the decrease in peak heights as a result of Fe³⁺-doping while SEM images reveal reduction in crystallite size with increase in Fe³⁺ content. The optical studies showed a direct band gap reducing with increase in Fe³⁺-doping from 3.87 to 3.38 eV. From the electrical measurements, it was found that the resistivity initially increased with Fe³⁺-doping before reducing at higher doping level. Hall mobility measurements showed n-type conductivity at lower Fe³⁺-doping levels and p-type at higher levels. The increase in conductivity with temperature ascertained the semiconducting behavior of these films.     

The structure and magnetic properties of β-(Ga0.96Mn0.04)2O3 thin film

High quality epitaxial single phase (Ga0.96Mn0.04)2O3 and Ga2O3 thin films have been prepared on sapphire substrates by using laser molecular beam epitaxy (L-MBE).X-ray diffraction results indicate that the thin films have the monoclinic structure with a (-201) preferable orientation.Room temperature (RT) ferromagnetism appears and the magnetic properties of β-(Ga0.96Mn0.04)2O3 thin film are enhanced compared with our previous works.Experiments as well as the first principle method are used to explain the role of Mn dopant on the structure and magnetic properties of the thin films.The ferromagnetic properties are explained based on the concentration of transition element and the defects in the thin films.     

Interrelation of the construction of the metamorphic InAlAs/InGaAs nanoheterostructures with the InAs content in the active layer of 76–100% with their surface morphology and electrical properties

The influence of the construction of a metamorphic buffer on the surface morphology and electrical properties of InAlAs/InGaAs/InAlAs nanoheterostructures with InAs content in the active layer from 76 to 100% with the use of the GaAs and InP substrates is studied. It is shown that such parameters as the electron mobility and the concentration, as well as the root-mean-square surface roughness, substantially depend on the construction of the metamorphic buffer. It is established experimentally that these parameters largely depend on the maximal local gradient of the lattice constant of the metamorphic buffer in the growth direction of the layers rather than on its average value. It is shown that, with selection of the construction of the metamorphic buffer, it is possible to form nanostructured surfaces with a large-periodic profile.     

Electronic structure and optical properties of F-doped β-Ga2O3 from first principles calculations

The effects of F-doping concentration on geometric structure, electronic structure and optical property of β-Ga₂O₃ were investigated. All F-doped β-Ga₂O₃ with different concentrations are easy to be formed under Ga-rich conditions, the stability and lattice parameters increase with the F-doping concentration. F-doped β-Ga₂O₃ materials display characteristics of the n-type semiconductor, occupied states contributed from Ga 4s, Ga 4p and O 2p states in the conduction band increase with an increase in F-doping concentration. The increase of F concentration leads to the narrowing of the band gap and the broadening of the occupied states. F-doped β-Ga₂O₃ exhibits the sharp band edge absorption and a broad absorption band. Absorption edges are blue-shifted, and the intensity of broad band absorption has been enhanced with respect to the fluorine content. The broad band absorption is ascribed to the intra-band transitions from occupied states to empty states in the conduction band.     

Fabrication of polymer blend composites based on [PVA-PVP](1−x):(Ag2S)x (0.01 ≤ x ≤ 0.03) with small optical band gaps: Structural and optical properties

In this paper composite materials, based on polymer blends of polyvinyl alcohol (PVA): polyvinyl pyrrolidone (PVP) with small optical band gap, has been studied. Silver sulfide (Ag₂S) semiconductor particles have been synthesized in PVA:PVP blend host polymer, using in situ method. X-ray diffraction (XRD) analyses and Fourier transform infrared (FTIR) spectroscopy for the composite samples were carried out. From the XRD pattern, distinguishable crystalline peaks caused by the Ag₂S semiconductor particles were observed. From the result of FTIR spectroscopy, the intensity of the FTIR bands were shifted and increased, revealing the occurrence of interactions between the PVA:PVP blend system and Ag₂S particles. The composite samples were found to exhibit absorption spectra that cover UV–visible to near infrared regions. The absorption edge was found to be 5 eV for pure PVA:PVP system and shifted to 1.15 eV for incorporated PVA:PVP with 3 M of Ag₂S. The refractive index was also evaluated for the samples and observed to be increased from 1.15 to 1.52 as doping increased to the highest. A linear relationship between the refractive index and the filler fraction has been reported. Theoretical discussion of optical dielectric loss, which is a crucial parameter for the band gap estimation, was given. The achieved results reveal that spectra of the optical dielectric loss (ɛ_i) can be used to study the band gap structure and Tauc's model can be important in determining the types of electronic transition. The optical band gap was found to decrease from 5.2 eV for the pure PVA:PVP to 1.1 eV for doped PVA:PVP with 3 M of Ag₂S. Such reduction can be associated with the increase of optical dielectric constant. Finally, the correlation between optical dielectric constant and density of states was discussed.     

Synthesis and characterization of EuBa2Ca2Cu3O9−x: The influence of temperature on dielectric properties and charge transport mechanism

High dielectric constant materials have a crucial importance for various microelectronic applications such as memory devices, supercapacitors etc. Among other insulators, perovskite structured oxide materials attract great interest not only for their high dielectric constants but also their unique electrical and magnetic properties such as superconductivity etc. From this point of view, a new Europium based copper oxide layered material with perovskite structure (EuBa₂Ca₂Cu₃O_9−x coded as Eu-1223) has been synthesized by solid state reaction method in this work. The physical and chemical properties of Eu-1223 have been determined by FTIR, SEM, XRF, XRD, TGA and DTA techniques. The influence of temperature on impedance and dielectric properties of Eu-1223 has been investigated by impedance spectroscopy measurements performed within the frequency interval of 5 Hz–13 MHz between 298 K and 408 K temperatures. It has been found that the Eu-1223 material has high dielectric constants at each temperature operated. In addition, Eu-1223 sample behaves as a colossal dielectric material up to 300 kHz for 408 K due to observation of dielectric constant values which are greater than 10³. Furthermore, it has been revealed that Eu-1223 material can be used as thermally sensitive resistors in electronic circuits due to its decreasing resistance with increasing temperature. Moreover, it has been observed that the relaxation frequency of the system shifts from 46.5 kHz (low frequency radio wave band) to 1.57 MHz (mid frequency radio wave band) as the temperature increasing from 298 K to 408 K. According to dc conductivity investigations, the variation of dc conductivity with the inverse of temperature satisfies linear relationship that indicates a thermally activated nearest neighbor hopping conduction. On the other hand, it has been determined that ac conductivity has frequency dependent relation which obeys ω^s for the high frequency region. Furthermore, the frequency exponent, s, which takes values between 0.7 and 0.4, shows a decreasing behavior with increasing temperature. In conclusion, ac charge transport mechanism has been predicted as correlated barrier hoping for Eu-1223.     

Study of the composition, structure, and optical properties of a-Si1 − x C x :H〈Er〉 films erbium doped from the Er(pd)3 complex compound

Rutherford backscattering, IR spectroscopy, ellipsometry, and atomic-force microscopy are used to perform an integrated study of the composition, structure and optical properties of a-Si_{1 ? x} C _x :H〈Er〉 amorphous films. The technique employed to obtain the a-Si_{1 ? x} C _x :H〈Er〉 amorphous films includes the high-frequency decomposition of a mixture of gases, (SiH₄) _a + (CH₄) _b , and the simultaneous thermal evaporation of a complex compound, Er(pd)₃. It is demonstrated that raising the amount of CH₄ in the gas mixture results in an increase in the carbon content of the films under study and an increase in the optical gap E _g ^opt from 1.75 to 2.2 eV. Changes in the composition of a-Si_{1 ? x} C _x :H〈Er〉 amorphous films, accompanied, in turn, by changes in the optical constants, are observed in the IR spectra. The ellipsometric spectra obtained are analyzed in terms of multiple-parameter models. The conclusion is made on the basis of this analysis that the experimental and calculated spectra coincide well when variation in the composition of the amorphous films with that of the gas mixture is taken into account. The existence of a thin (6–8 nm) silicon-oxide layer on the surface of the films under study and the validity of using the double-layer model in ellipsometric calculations is confirmed by the results of structural analyses by atomic-force microscopy.     

Highly improved light extraction with a reduced spectrum distortion of organic light-emitting diodes composed by the sub-visible wavelength nano-scale periodic (∼250 nm) structure and micro-lens array

Out-coupling enhanced organic light-emitting diodes (OLEDs) with micro-lens arrays and a nano-scale periodic light-extraction structure—a photonic crystal (PC)—utilizing laser interference lithography (LIL) are demonstrated. Generally, PC-based OLEDs suffer from a distorted and shifted spectrum, despite a highly improved intensity. However, in this study, we demonstrate PC-based OLEDs with a distortion-free spectrum and a highly improved out-coupling performance. It was found that spectrum distortion decreased with the pitch size of the PC. The PC-based OLED with a 250 nm pitch size showed a dramatically reduced spectral shift: International Commission on Illumination 1931 color coordinate of (Δ0.00, Δ0.00) and Δpeak wavelength of 0 nm as compared with the reference. Simultaneously, the external quantum efficiency and the power efficiency were enhanced by up to 178% and 264%, respectively, as compared with the reference. Moreover, through the LIL, simple and maskless processes were achieved for a light-extraction structure over a large area.     

First principles study of the electronic structure and photovoltaic properties of β-CuGaO2 with MBJ + U approach

Based on the density functional theory, the energy band and electronic structure of β-CuGaO₂ are calculated by the modified Becke-Johnson plus an on-site Coulomb U (MBJ + U) approach in this paper. The calculated results show that the band gap value of β-CuGaO₂ obtained by the MBJ + U approach is close to the experimental value. The calculated results of electronic structure indicate that the main properties of the material are determined by the bond between Cu-3d and O-2p energy levels near the valence band of β-CuGaO₂, while a weak anti-bond combination is formed mainly by the O-2p energy level and Ga-4s energy level near the bottom of the conduction band of β-CuGaO₂. The β-CuGaO₂ thin film is predicted to hold excellent photovoltaic performance by analysis of the spectroscopic limited maximum efficiency (SLME) method. At the same time, the calculated maximum photoelectric conversion efficiency of the ideal CuGaO₂ solar cell is 32.4%. Relevant conclusions can expand β-CuGaO₂ photovoltaic applications.     

The electronic spectrum and electrical properties of germanium with a doubly charged gold impurity on both sides of the L 1 ⇄ Δ1 intervalley transition for uniform pressures of up to 7 GPa

The dependences of resistivity ρ and the Hall coefficient R<0 on hydrostatic pressure P(P≤7 GPa) were studied at room temperature in Ge:(Au, Sb) with a partially populated (at 0 K) doubly charged Au level E _Au ^2? on both sides of the intervalley transition that occurred for P?2.8 GPa. In terms of the two-band model, the baric dependences ρ(P) and R(P) and also the similar dependence of the Hall mobility with allowance made for interband scattering were calculated; the results agree satisfactorily with the experimental data. Characteristic parameters of the charge carriers and the baric coefficients for energy gaps between the edges of the L ₁ and Δ₁ subbands in the conduction band and the E _Au ^2? level were determined. It was ascertained that the position of the energy level for a doubly charged gold impurity in germanium is fixed with respect to the valence-band top. The density-of-state effective mass of electrons in the (100) minimum of the conduction band of germanium was determined experimentally (and using the known values of the band parameters) and was found to be m _dΔ=6^2/3(m _∥ m _⊥ ² )^1/3=1.05m ₀. It is shown that Ge:Au^2? can be used to check the uniformity of pressure of up to 10 GPa.     

Growth,structure, and properties of GaAs-based (GaAs)1–x–y (Ge2) x (ZnSe) y epitaxial films

The possibility of growing the (GaAs)_1–x–y (Ge₂) _x (ZnSe) _y alloy on GaAs substrates by the method of liquid-phase epitaxy from a tin solution–melt is shown. X-ray diffraction shows that the grown film is single-crystal with the (100) orientation and has the sphalerite structure. The crystal-lattice parameter of the film is a _f = 0.56697 nm. The features of the spectral dependence of the photosensitivity are caused by the formation of various complexes of charged components. It is established that the I–V characteristic of such structures is described by the exponential dependence I = I ₀exp(qV/ckT) at low voltages (no higher than 0.4 V) and by the power dependence J ~ V ^α, where the exponent α varies with increasing voltage at high voltages (V > 0.5 V). The results are treated within the framework of the theory of the drift mechanism of current transfer taking into account the possibility of the exchange of free carriers within the recombination complex.     

Structural and optical properties of ZrB2 and HfxZr1−xB2 films grown by vicinal surface epitaxy on Si(1 1 1) substrates

ZrB₂ and Hf_xZr_1?xB₂ films were grown on 4° miscut Si(1 1 1) substrates by chemical vapor deposition of gaseous Hf(BH₄)₄ and Zr(BH₄)₄. The films display superior structural and optical properties when compared with ZrB₂ films grown on on-axis Si(1 1 1). The observed improvements include an optically featureless surface with rms roughness of ～2.5–3.5 nm, a ～50% reduction in the amount of residual strain, and a ～50% lower resistivity. These properties should promote the use of diboride films as buffer layers for nitride semiconductor epitaxy on large-area Si substrates.     

The frequency and voltage dependent electrical characteristics of Al-TiW-Pd2Si/n-Si structure using I-V, C-V and G/ω-V measurements

The forward and reverse bias capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of Al-TiW-Pd₂Si/n-Si structures have been investigated over a wide frequency range of 5 kHz-5 MHz. These measurements allow to us the determination of the interface states density (N_ss) and series resistance (R_s) distribution profile. The effect of R_s on C and G is found noticeable at high frequencies. The C-V-f and G/w-V-f characteristics of studied structures show fairly large frequency dispersion especially at low frequencies due to N_ss in equilibrium with the semiconductor. The N_ss profile was obtained both forward bias current-voltage (I-V) characteristics by using into account the bias dependent of the ideality factor and effective barrier height (Φ_e) and low frequency (C_LF)-high frequency (C_HF) method. The plot of series resistance vs. voltage for the low frequencies gives a peak, decreasing with increasing frequencies. The frequency dependent C-V and G/w-V characteristics confirm that the R_s and N_ss of the Al-TiW-Pd₂Si/n-Si structures are important parameters that strongly influence the electric parameters in device.     

Detailed analysis and contact properties of low-voltage organic thin-film transistors based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) and its didecyl and diphenyl derivatives

Low-voltage organic thin-film transistors (TFTs) based on four different small-molecule semiconductors (pentacene, DNTT (dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene), C₁₀-DNTT and DPh-DNTT) were fabricated, and a detailed comparison of the semiconductor thin-film morphology, of the current-voltage characteristics of transistors with channel lengths ranging from 100 to 1 μm, and of the contact resistances is provided. The three thienoacene derivatives DNTT, C₁₀-DNTT and DPh-DNTT all have significantly larger charge-carrier mobilities and smaller contact resistances than pentacene. In terms of the intrinsic channel mobility (determined using the transmission line method), C₁₀-DNTT and DPh-DNTT perform quite similarly and notably better than DNTT, suggesting that the decyl substituents in C₁₀-DNTT and the phenyl substituents in DPh-DNTT provide a similar level of enhancement of the charge-transport characteristics over DNTT. However, the DPh-DNTT TFTs have a substantially smaller contact resistance than both the DNTT and the C₁₀-DNTT TFTs, resulting in notably larger effective mobilities, especially in transistors with very small channel lengths. For DPh-DNTT TFTs with a channel length of 1 μm, an effective mobility of 0.68 cm²/V was determined, together with an on/off ratio of 10⁸ and a subthreshold swing of 100 mV/decade.     

Surface morphology and electrical properties of Au/Ni/?C?/n-Ga2O3/p-GaSe?KNO3? hybrid structures fabricated on the basis of a layered semiconductor with nanoscale ferroelectric inclusions

Features of the formation of Au/Ni/〈C〉/n-Ga₂O₃ hybrid nanostructures on a Van der Waals surface (0001) of “layered semiconductor-ferroelectric” composite nanostructures (p-GaSe〈KNO₃〉) are studied using atomic-force microscopy. The room-temperature current-voltage characteristics and the dependence of the impedance spectrum of hybrid structures on a bias voltage are studied. The current-voltage characteristic includes a resonance peak and a portion with negative differential resistance. The current attains a maximum at a certain bias voltage, when electric polarization switching in nanoscale three-dimensional inclusions in the layered GaSe matrix occurs. In the high-frequency region (f > 10⁶ Hz), inductive-type impedance (a large negative capacitance of structures, ∼10⁶ F/mm²) is detected. This effect is due to spinpolarized electron transport in a series of interconnected semiconductor composite nanostructures with multiple p-GaSe〈KNO₃〉 quantum wells and a forward-biased “ferromagnetic metal-semiconductor” polarizer (Au/Ni/〈C〉/n ⁺-Ga₂O₃/n-Ga₂O₃). A shift of the maximum (current hysteresis) is detected in the current-voltage characteristics for various directions of the variations in bias voltage.     

The adsorption of basic dye (Alizarin red S) from aqueous solution onto activated carbon/γ-Fe2O3 nano-composite: Kinetic and equilibrium studies

The adsorption behavior of Alizarin red S (ARS) from aqueous solution onto magnetic activated carbon (MAC) nano-composite was investigated under various experimental conditions. Characterization of the obtained MAC nano-composite was achieved by FT-IR, BET, FE-SEM, EDX, XRD and VSM techniques. The influence of variables including pH, concentration of the dye, amount of adsorbents and contact time was investigated by the batch method. High maximum adsorption capacity was obtained at 108.69 mg g⁻¹ for ARS. The equilibrium data was evaluated using Langmuir and Freundlich isotherm. The Langmuir model best describes the uptake of ARS dye, which implies that the adsorption of ARS dye onto MAC nano-composite is homogeneous. The kinetic data were analyzed using Lagergren pseudo-first order and pseudo-second equation. The pseudo-second order exhibited the best fit for the kinetic studies (R²=0.9999), which indicates that adsorption of ARS is limited by chemisorption process. This study shows that the as-prepared MAC composite could be utilized as an efficient, magnetically separable adsorbent for the environmental cleanup.     

Current-voltage characteristic and the spectrum width of electrons tunneling through W-WO2-(Au 147? )-Al2O3-Al and Nd-Nd2O3-(Au 55? )-Nd2O3-Nd nanosandwiches. Part II: Construction and analysis of 1D models for 3D nanosandwiches

This is the second part of the series of two articles devoted to the analysis of electron tunneling through magic nanoclusters of Au₅₅ and Au₁₄₇. Models of 1D projections of W-WO₂-(Au₁₄₇⁻)-Al₂O₃-Al and Nd-Nd₂O₃-(Au₅₅⁻)-Nd₂O₃-Nd 3D tunnel nanostructures are constructed with the use of the highest occupied molecular orbital (HOMO) levels E_HOMO^- E_{HOMO^ - } of the anions of the nanoclusters of Au₅₅ and Au₁₄₇, and the potentials of Au, W, Al, and Nd atoms calculated in the first part of this study. The levels of the bottom of the potential wells of 1D structures are chosen so that they include resonance energy levels coinciding with the anion level E_HOMO^- E_{HOMO^ - } for an appropriate 3D structure (Au₁₄₇⁻ or Au₅₅⁻). With regard to the potentials in the structures of a nanocapacitor and the image forces, the current-voltage characteristic (CVC) and the width of the resonance peak in the spectrum of tunneling electrons are calculated as a function of the potential difference across the external electrodes of metal-metal nanodiodes. A scheme of a hypothetical high-frequency nanoscale metal transistor is proposed that is based on a cluster of Au₁₄₇ that does not produce hot electrons.     

Influence of technological defects on the optical and photoelectric properties of AgCd<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GaSe<Subscript>4</Subscript> alloys

The study is concerned with the photoelectric and optical properties of a AgCd_{2 − x} Mn _x GaSe₄ alloy with a Mn → Cd isovalent substitution. The positions of the photoconductivity and photoluminescence peaks are determined, and the band gap of the alloy is estimated, based on compositional analysis. The influence of technological defects on specific features of the alloy’s photoelectric and optical properties is analyzed. It is established that the centers controlling the alloy crystals’ photosensitivity are cation vacancies. The photoluminescence centers responsible for emission at awavelengths from 0.77 to 0.88 μm (dependent on the relation between components in the alloy) are defect complexes consisting of cation and anion vacancies. A physically consistent model is proposed to interpret the effects observed in the alloy.