Structural, Electrical, And Optical Properties Of Inasxsb1-X Epitaxial Films Grown By Liquid-Phase Epitaxy

The InAsxSb1-x films were grown on (100) GaSb substrates by liquid-phase epitaxy, and their structural, electrical, and optical properties were investigated. The high-resolution x-ray diffraction results reveal that the single crystalline InAsxSb1-x films with a midrange composition are epitaxially grown on the GaSb substrates. Temperature dependence of the Hall mobility was theoretically modeled by considering several predominant scattering mechanisms. The results indicate that ionized impurity and dislocation scatterings dominate at low temperatures, while polar optical phonon scattering is important at room temperature (RT). Furthermore, the InAsxSb1-x films with the higher As composition exhibit the better crystalline quality and the higher mobility. The InAs0.35Sb0.65 film exhibits a Hall mobility of 4.62x10(4) cm(2) V-1 s(-1). The cutoff wavelength of photoresponse is extended to about 12 mu m with a maximum responsivity of 0.21 V/W at RT, showing great potential for RT long-wavelength infrared detection. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2989116]

The magnetic and structure properties of room-temperature ferromagnetic semiconductor (Ga,Mn)N

Diluted magnetic semiconductor (Ga,Mn)N were prepared by the implantation of Mn ions into GaN/Al2O3 substrate. Clear X-ray diffraction peak from (Ga,Mn)N is observed. It indicates that the solid solution (Ga,Mn)N phase was formed with the same lattice structure as GaN and different lattice constant. Magnetic hysteresis-loops of the (Ga,Mn)N were obtained at room temperature (293 K) with the coercivity of about 2496.97 A m(-1). (C) 2003 Elsevier B.V. All rights reserved.

Effect of chloride ions' introduction on structural, thermal stability, and spectroscopic properties in Yb3+Er3+-codoped germanate-bismuth-lead glasses

Yb3+Er3+-codoped chloride-modified germanate-bismuth-lead glasses have been synthesized by the conventional melting and quenching method. Structural and thermal stability properties have been obtained on the basis of the Raman spectra and differential thermal analysis, which indicate that the PbCl2 addition has an important influence on the phonon density of states, maximum phonon energy, and thermal stability of host glasses. The Judd-Ofelt intensity parameters and quantum efficiencies were calculated on the basis of the Judd-Ofelt theory and lifetime measurements. For the 1.53 mu m emission band, the full widths at the half-maximum increase and peak wavelengths are blueshifted with increasing PbCl2 content. Moreover, the effect of the PbCl2 addition on the phonon density of states, OH- content, and upconversion luminescence has been discussed and evaluated. Our results reveal that, with increasing PbCl2 content, the decrease of phonon density and OH- content contributes more to the enhanced upconversion emissions than that of maximum phonon energy. (c) 2005 Optical Society of America

Structural and upconversion fluorescence properties of Er3+/Yb3+-codoped lead-free germanium-bismuth glass

We study the structural and infrared-to-visible upconversion fluorescence properties of Er3(+)/Yb3+-codoped lead-free germanium-bismuth glass. The structure of lead-free germanium-bismuth-lanthanum glass is investigated by peak-deconvolution of Raman spectroscopy. Intense green and red emissions centred at 525, 546, and 657nm, corresponding to the transitions H-2(11/2) -> (IT15/2)-I-4 -> S-4(3/2) -> 4I(15/2), and F-4(9/2) -> I-4(15/2), respectively, are observed at room temperature. The quadratic dependence of the 525, 546, and 657nm emissions on excitation power indicates that a two-photon absorption process occurs under 975nm excitation.

Structural and upconversion fluorescence properties of Er3+/Yb3+-codoped oxychloride lead-germanium-bismuth glass

Structural and infrared-to-visible upconversion fluorescence properties of Er3+/Yb3+-codoped oxychloride lead-germanium-bismuth glass have been studied. The Raman spectrum investigation indicates that PbCl2 plays an important role in the formation of glass network, and has an important influence on the upconversion luminescence owing to lower phonon energy. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions H-2(11/2)-->I-4(15/2,) I-4(3/2)-->I-4(15/2), and F-4(9/2)-->I-4(15/2), respectively, were observed at room temperature. The quadratic dependence of the 525, 546, and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation. (C) 2004 Elsevier Ltd. All rights reserved.

Structural and up-conversion luminescence properties in Tm (3+)/Yb3+-codoped heavy metal oxide-halide glasses

Tm3+/Yb3+-codoped heavy metal oxide-halide glasses have been synthesized by conventional melting and quenching method. Structural properties were obtained based on the Raman spectra, indicating that halide ion has an important influence on the phonon density and maximum phonon energy of host glasses. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions (1)G(4) -> H-3(6) and (1)G(4) -> H-3(4), respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. With increasing halide content, the up-conversion luminescence intensity and blue luminescence lifetimes of Tm3+ ion increase notably. Our results show that with the substitution of halide ion for oxygen ion, the decrease of phonon density and maximum phonon energy of host glasses both contribute to the enhanced up-conversion emissions. (c) 2005 Elsevier B.V. All rights reserved.

Structural, optical and electrical properties of ZnO films grown on c-plane sapphire and (100)gamma-LiAlO2 by pulse laser deposition

ZnO thin films were grown on single-crystal gamma-LiAlO2 (LAO) and sapphire (0001) substrate by pulsed laser deposition (PLD). The structural, optical and electrical properties of ZnO films were investigated. The results show that LAO is more suitable for fabricating ZnO films than sapphire substrate and the highest-quality ZnO film was attained on LAO at the substrate temperature of 550 degrees C. However, when the substrate temperature rises to 700 degrees C, lithium would diffuse from the substrate (LAO) into ZnO film which makes ZnO film on LAO becomes polycrystalline without preferred orientation, the stress in ZnO film increases dominantly and the resistivity of the film decreases exponentially. (c) 2005 Elsevier B.V. All rights reserved.

Structural, morphological and optical properties of ZnO thin films grown on gamma-LiAlO2 substrate by pulsed laser deposition

ZnO thin films were deposited on the substrates of (100) gamma-LiAlO2 at 400, 550 and 700 degrees C using pulsed laser deposition (PLD) with the fixed oxygen pressure of 20 Pa, respectively. When the substrate temperature is 400 degrees C, the grain size of the film is less than 1 mu m observed by Leitz microscope and measured by X-ray diffraction (XRD). As the substrate temperature increases to 550 degrees C, highly-preferred c-orientation and high-quality ZnO film can be attained. While the substrate temperature rises to 700 degrees C, more defects appears on the surface of film and the ZnO films become polycrystalline again possibly because more Li of the substrate diffused into the ZnO film at high substrate temperature. The photoluminescence (PL) spectra of ZnO films at room temperature show the blue emission peaks centered at 430 nm. We suggest that the blue emission corresponds to the electron transition from the level of interstitial Zn to the valence band. Meanwhile, the films grown on gamma-LiAlO2 (LAO) exhibit green emission centered at 540 nm, which seemed to be ascribed to excess zinc and/or oxygen vacancy in the ZnO films caused by diffusion of Li. from the substrates into the films during the deposition.

Optical, structural and laser-induced damage threshold properties of HfO2 thin films prepared by electron beam evaporation

We prepare HfO2 thin films by electron beam evaporation technology. The samples are annealed in air after deposition. With increasing annealing temperature, it is found that the absorption of the samples decreases firstly and then increases. Also, the laser-induced damage threshold (LIDT) increases firstly and then decreases. When annealing temperature is 473K, the sample has the highest LIDT of 2.17J/cm(2), and the lowest absorption of 18 ppm. By investigating the optical and structural characteristics and their relations to LIDT, it is shown that the principal factor dominating the LIDT is absorption.

Structural, mechanical, thermodynamic, and electronic properties of thorium hydrides from first-principles

We perform first-principles calculations of the structural, electronic, mechanical, and thermodynamic properties of thorium hydrides (ThH2 and Th4H15) based on the density functional theory with generalized gradient approximation. The equilibrium geometries, the total and partial densities of states, charge density, elastic constants, elastic moduli, Poisson's ratio, and phonon dispersion curves for these materials are systematically investigated and analyzed in comparison with experiments and previous calculations. These results show that our calculated equilibrium structural parameters are well consistent with experiments. The Th-H bonds in all thorium hydrides exhibit weak covalent character, but the ionic properties for ThH2 and Th4H15 are different due to their different hydrogen concentration. It is found that while in ThH2 about 1.5 electrons transfer from each Th atom to H, in Th4H15 the charge transfer from each Th atom is around 2.1 electrons. Our calculated phonon spectrum for the stable body-centered tetragonal phase of ThH2 accords well with experiments. In addition we show that ThH2 in the fluorite phase is mechanically and dynamically unstable.

Structural, electrical, and optical properties of InAsxSb1-x epitaxial films grown by liquid-phase epitaxy

The InAsxSb1-x films were grown on (100) GaSb substrates by liquid-phase epitaxy, and their structural, electrical, and optical properties were investigated. The high-resolution x-ray diffraction results reveal that the single crystalline InAsxSb1-x films with a midrange composition are epitaxially grown on the GaSb substrates. Temperature dependence of the Hall mobility was theoretically modeled by considering several predominant scattering mechanisms. The results indicate that ionized impurity and dislocation scatterings dominate at low temperatures, while polar optical phonon scattering is important at room temperature (RT). Furthermore, the InAsxSb1-x films with the higher As composition exhibit the better crystalline quality and the higher mobility. The InAs0.35Sb0.65 film exhibits a Hall mobility of 4.62x10(4) cm(2) V-1 s(-1). The cutoff wavelength of photoresponse is extended to about 12 mu m with a maximum responsivity of 0.21 V/W at RT, showing great potential for RT long-wavelength infrared detection. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2989116]

Using different carrier gases to control AlN film stress and the effect on morphology, structural properties and optical properties

On the metalorganic chemical vapour deposition growth of AlN, by adjusting H-2+N-2 mixture gas components, we can gradually control island dimension. During the Volmer - Weber growth, the 2-dimensional coalescence of the islands induces an intrinsic tensile stress. Then, this process can control the in-plane stress: with the N-2 content increasing from 0 to 3 slm, the in-plane stress gradually changes from 1.5 GPa tensile stress to - 1.2GPa compressive stress. Especially, with the 0.5 slm N-2 + 2.5 slm H-2 mixture gas, the in-plane stress is only 0.1 GPa, which is close to the complete relaxation state. Under this condition, this sample has good crystal and optical qualities.

Structural, elastic, and electronic properties of cubic perovskite BaHfO3 obtained from first principles

We investigated the structural, elastic, and electronic properties of the cubic perovskite-type BaHfO3 using a first-principles method based on the plane-wave basis set. Analysis of the band structure shows that perovskite-type BaHfO3 is a wide gap indirect semiconductor. The band-gap is predicted to be 3.94 eV within the screened exchange local density approximation (sX-LDA). The calculated equilibrium lattice constant of this compound is in good agreement with the available experimental and theoretical data reported in the literatures. The independent elastic constants (C-11, C-12, and C-44), bulk modules B and its pressure derivatives B', compressibility beta, shear modulus G, Young's modulus Y, Poisson's ratio nu, and Lame constants (mu, lambda) are obtained and analyzed in comparison with the available theoretical and experimental data for both the singlecrystalline and polycrystalline BaHfO3. The bonding-charge density calculation make it clear that the covalent bonds exist between the Hf and 0 atoms and the ionic bonds exist between the Ba atoms and HfO3 ionic groups in BaHfO3. (C) 2009 Elsevier B.V. All rights reserved.

Nitrogen defects and ferromagnetism in Cr-doped dilute magnetic semiconductor AlN from first principles

High Curie temperature of 900 K has been reported in Cr-doped AlN diluted magnetic semiconductors prepared by various methods, which is exciting for spintronic applications. It is believed that N defects play important roles in achieving the high-temperature ferromagnetism in good samples. Motivated by these experimental advances, we use a full-potential density-functional-theory method and supercell approach to investigate N defects and their effects on ferromagnetism of (Al,Cr)N with N vacancies (V-N). We investigate the structural and electronic properties of V-N, single Cr atom, Cr-Cr atom pairs, Cr-V-N pairs, and so on. In each case, the most stable structure is obtained by comparing different atomic configurations optimized in terms of the total energy and the force on every atom, and then it is used to calculate the defect formation energy and study the electronic structures. Our total-energy calculations show that the nearest substitutional Cr-Cr pair with the two spins in parallel is the most favorable and the nearest Cr-V-N pair makes a stable complex. Our formation energies indicate that V-N regions can be formed spontaneously under N-poor condition because the minimal V-N formation energy equals -0.23 eV or Cr-doped regions with high enough concentrations can be formed under N-rich condition because the Cr formation energy equals 0.04 eV, and hence real Cr-doped AlN samples are formed by forming some Cr-doped regions and separated V-N regions and through subsequent atomic relaxation during annealing. Both of the single Cr atom and the N vacancy create filled electronic states in the semiconductor gap of AlN. N vacancies enhance the ferromagnetism by adding mu(B) to the Cr moment each but reduce the ferromagnetic exchange constants between the spins in the nearest Cr-Cr pairs. These calculated results are in agreement with experimental observations and facts of real Cr-doped AlN samples and their synthesis. Our first-principles results are useful to elucidate the mechanism for the ferromagnetism and to explore high-performance Cr-doped AlN diluted magnetic semiconductors.

Growth Parameter Dependence of Structural Characterizations of Diluted Magnetic Semiconductor (Ga, Cr)As

We report the influence of growth parameters and post-growth annealing on the structural characterizations and magnetic properties of (Ga, Cr)As films. The crystalline quality and magnetic properties are sensitive to the growth conditions. The single-phase (Ga, Cr)As film with the Curie temperature of 10 K is synthesized at growth temperature T-s = 250 degrees C and with nominal Cr content x = 0.016. However, for the films with x > 0.02, the aggregation of Cr atoms is strongly enhanced as both T. and x increase, which not only brings strong compressive strain in the epilayer, but also roughens the surface. The origin of room-temperature ferromagnetism in (Ga, Cr)As films with nanoclusters is also discussed.