Structural and electronic properties of zinc blende BxGa1−xN nitrides

First principles total energy calculations were carried out to investigate structural and electronic properties of zinc blende GaN, BN and B_xGa_1?xN solid solutions. We have calculated lattice parameters, bulk modulus, pressure derivative and B_xGa_1?xN band gap energy for zinc blende-type crystals of the compositions x = 0, 0.25, 0.5, 0.75, 1. Discussions will be given in comparison with results obtained with other available theoretical and experimental results.     

First principles study on the structural,electronic, and optical properties of Sc-doped AlN

Based on the density functional pseudo-potential method, the structural properties, the band structure, the density of states and the optical properties of the pure and Sc-doped AlN are calculated. The calculation results indicate that the defect of Sc(Al) exists steadily with a certain solubility in the doped system. Sc substitution of the Al site induces effective reduction of the band gap of AlN and the band gap being continuously reduced when increasing Sc concentrations. The existence of the strong hybridization between Sc 3d and N 2p indicates the transport of electrons from Sc atoms to N atoms. Besides, it is shown that the insertion of Sc atom leads to redshift of the optical absorption edge. The intensity of both the imaginary part of the dielectric function and the optical absorption of Al_{1 ? x} Sc _x N are found to decrease with increasing Sc concentrations in the low energy range.     

First principles calculations of electronic structure and magnetic properties of Cr-based magnetic semiconductors Al1−xCrxX (X=N, P, As, Sb)

First principles calculations based on the density functional theory (DFT) within the local spin density approximation are performed to investigate the electronic structure and magnetic properties of Cr-based zinc blende diluted magnetic semiconductors Al_1−xCr_xX (X=N, P, As, Sb) for 0≤x≤0.50.The behaviour of magnetic moment of Al_1−xCr_xX at each Cr site as well as the change in the band gap value due to spin down electrons has been studied by increasing the concentration of Cr atom and through changing X from N to Sb. Furthermore, the role of p-d hybridization is analyzed in the electronic band structure and exchange splitting of d-dominated bands. The interaction strength is stronger in Al_1−xCr_xN and becomes weaker in Al_1−xCr_xSb. The band gap due to the spin down electrons decreases with the increased concentration of Cr in Al_1−xCr_xX, and as one moves down along the isoelectronic series in the group V from N to Sb. Our calculations also verify the half-metallic ferromagnetic character in Cr doped AlX.     

Mechanochemical-thermal preparation and structural studies of mullite-type Bi2(GaxAl1−x)4O9 solid solutions

A series of Bi₂(Ga_xAl_1−x)₄O₉ solid solutions (0≤x≤1), prepared by mechanochemical processing of Bi₂O₃/Ga₂O₃/Al₂O₃ mixtures and subsequent annealing, was investigated by XRD, EDX, and ²⁷Al MAS NMR. The structure of the Bi₂(Ga_xAl_1−x)₄O₉ solid solutions is found to be orthorhombic, space group Pbam (No. 55). The lattice parameters of the Bi₂(Ga_xAl_1−x)₄O₉ series increase linearly with increasing gallium content. Rietveld refinement of the XRD data as well as the analysis of the ²⁷Al MAS NMR spectra show a preference of gallium cations for the tetrahedral sites in Bi₂(Ga_xAl_1−x)₄O₉. As a consequence, this leads to a far from random distribution of Al and Ga cations across the whole series of solid solutions.     

Electron energy structure of GaN when titanium or zinc atoms substitute for gallium

A calculation scheme based on density functional theory with full geometry optimization, modified for structures with translational symmetry is applied to study the electron energy spectrum and magnetic characteristics of hexagonal gallium nitride and structures such as Y _x Ga_1?x N (Y: donor (Ti) or acceptor (Zn) impurity). The dependence of relaxation shifts of interstitial atoms, the position of the chemical potential level, energy band boundaries, valence band widths, and energies corresponding to the intraband maxima of the density of states on the dopant concentration is discussed.     

Lu掺杂AlN的电子结构和光学性质的第一性原理研究

为了探索AlN在光电器件中的潜在应用,采用第一性原理计算了不同Lu掺杂浓度(以原子分数x表示)的AlN(Al_1-xLu_xN)的电子结构和光学性质。研究结果表明,Al_1-xLu_xN的超胞体积随着Lu掺杂浓度的增加而增加,而带隙则相反。Al_1-xLu_xN的静态介电常数在低能区随掺杂浓度的提高而提高,随后逐渐趋向一致。随着Lu掺杂浓度的增加,反射率和吸收系数的峰值强度降低,峰值向较低能量方向移动。Al_1-xLu_xN的能量损失光谱表现出明显的等离子体振荡特性,且峰值低于本征AlN。Al_1-xLu_xN的光电导率在低能区随能量的增加而急剧增加。     

Lu掺杂AlN的电子结构和光学性质的第一性原理研究

为了探索 AlN在光电器件中的潜在应用,采用第一性原理计算了不同 Lu掺杂浓度(以原子分数 x表示)的 AlN(Al_1-xLu_xN)的电子结构和光学性质。研究结果表明,Al_1-xLu_xN的超胞体积随着Lu掺杂浓度的增加而增加,而带隙则相反。Al_1-xLu_xN的静态介电常数在低能区随掺杂浓度的提高而提高,随后逐渐趋向一致。随着Lu掺杂浓度的增加,反射率和吸收系数的峰值强度降低,峰值向较低能量方向移动。Al_1-xLu_xN的能量损失光谱表现出明显的等离子体振荡特性,且峰值低于本征AlN。Al_1-xLu_xN的光电导率在低能区随能量的增加而急剧增加。     

Gallium-containing catalysts for oxidative dehydrogenation of organic compounds

A method was developed for introducing gallium into Mg-Al hydrotalcites—precursors of oxide catalysts for oxidative dehydrogenation of alkanes. Samples of oxide catalysts were synthesized that contained gallium oxide and also oxides of magnesium, aluminum, chromium, vanadium, molybdenum, and niobium in various combinations. The catalytic properties of the produced catalysts were studied in the oxidative dehydrogenation of ethane, propane, isobutane, and hexane. It was established that the addition of gallium to catalysts increases the ethylene and propylene yields in the oxidative dehydrogenation of ethane and propane. New hydroxo salts with a layered structure of the hydrotalcite type were synthesized: ternary magnesium gallium aluminum hydroxonitrate of variable composition [Al_{1 ? n} Ga _n Mg _m (OH)_{3 + 2m ? 1}][NO₃ · nH₂O] and quaternary magnesium gallium chromium aluminum hydroxonitrate of the composition [AlGaCrMg_1.8(OH)_11.6][NO₃ · nH₂O]; these salts were found to be isostructural.     

Synthesis and characterization of new aluminium and gallium heteropoly complexes with chromium,iron, cobalt or coppercentred undecatungstate ligand

Summary Eight aluminium and gallium heteropoly undecatungstometalate complexes of general formula K_n[M(H₂O)-XW₁₁O₃₉]·nH₂O, where M=Al^III, Ga^III, and X=Cr^III, Fe^III, Co^II or Cu^II, have been prepared and characterized by elemental analysis, cation exchange i.r., u.v., x-ray powder diffraction and by thermal analyis. The compounds are stable in acidic solution. I.r., u.v. spectra and x-ray diffraction studies show that the structure of the compounds derives from the Keggin structure. Their thermostability is higher than that of the homologous dodecatungstometalates.     

Electronic structure and related properties for quasi-binary (GaP)1−x (ZnSe) x crystals

The results of pseudopotential calculations of the band structure and related electronic and optical properties of quasi-binary (GaP)_1?x (ZnSe) _x crystals in the zinc blende structure are presented. Trends in bonding and ionicity are discussed in terms of electronic charge densities. Moreover, the composition dependence of the refractive index and dielectric constants are reported. The computed values are in reasonable agreement with experimental data. The results suggest that for a proper choice of the composition x, (GaP)_1?x (ZnSe) _x could provide more diverse opportunities to achieve the desired electronic and optical properties of the crystals which would improve the performances of devices fabricated on them.     

An IR Spectroscopic Investigation of Nanostructured AlN and GaN Powder Surfaces

By combining the results of IR spectroscopy experiments, both in the transmission and diffuse reflectance modes, with data obtained by HRTEM, XRD and XPS an overall picture of AlN and GaN nanoparticle surface structures and functionality were deduced. The surface species from the IR data analysis indicated that the nanostructured AlN powder surfaces had acidic and weak basic sites in the form of Al³⁺ and Al₃N^–, respectively. Also present were -OH, -NH₂, and -NH. For GaN, the bulk core of the particle had a zincblendel (FCC) structure with nitrogen vacancies, and the only functionality detected was Ga–H. The surface of the particles had a wurtzite(HCP) structure, with abundant NH and NH₂ groups as well as OH and Ga³⁺ functionalities.     

Absorption Spectra of CrIII in some lattices of spinel and pseudo-brookite Type

Spinel mixed crystals ZnCr_xAl_2?xO₄, Cd_yZn_1?yCrAlO₄, Cd_0.5Zn_0.5Cr_0.4Ga_1.6O₄ and pseudo-brookite compounds Al_2?xGe_yCr_xTi_1?yO₅ were synthesized and x-rayed. The reflectance spectra were measured. The Δ-dependent absorption band was shifted towards IR-region in case of the spinels, whereas it remains nearly unshifted in pseudo-brookite. Generally, the results are discussed with the help of the ligand field parameters Δ and B.     

On the Role of Amides and Imides for Understanding GaN Syntheses from Ammonia Solution: Molecular Mechanics Models of Ammonia,Amide and Imide Interactions with Gallium Nitride

A key requisite to characterizing GaN precipitation from ammonia solution from molecular simulations is the availability of reliable molecular mechanics models for the interactions of gallium ions with NH₃, NH₂⁻, and NH²⁻ species, respectively. Here, we present a tailor-made force field which is fully compatible to an earlier developed GaN model, thus bridging the analyses of Ga³⁺ ions in ammonia solution with the aggregation of [Ga_x(NH)_y(NH₂)_z]^+3x−2y−z precursors and the modelling of GaN crystals. For this, quantum mechanical characterization of a series of Ga-coordination clusters is used for parameterization and benchmarking the generalized amber force field (GAFF2) and tailor-made refinements needed to achieve good agreement of both structural features and formation energy, respectively. The perspectives of our models for larger scale molecular dynamics simulations are demonstrated by the analyses of amide and imide defects arrangement during the growth of GaN crystal faces.     

Room Temperature Ferromagnetism in Ga1-xHoxN (x=0.0 and 0.05) Diluted Magnetic Semiconductor Thin Films

Holmium doped GaN diluted magnetic semiconductor thin films have been prepared by thermal evaporation technique and subsequent ammonia annealing. X-ray diffraction mea-surements reveal all peaks belong to the purely hexagonal wurtzite structure. Surface mor-phology and composition analysis were carried out by scanning electron microscopy and energy dispersive spectroscopy respectively. The room temperature ferromagnetic proper-ties of Ga_1-xHo_xN(x=0.0, 0.05) films were analyzed using vibrating sample magnetometer at room temperature. Magnetic measurements showed that the undoped films (i.e. GaN) exhibited diamagnetic behavior, while the Ho-doped (Ga_0.95Ho_0.05N) film exhibited a ferro-magnetic behavior.     

Spectrophotometric and solvent extraction study of o-hydroxybenzaldehyde isonicotinoyl hydrazone complexes with gallium and indium

Complex formation of o-hydroxybenzaldehyde isonicotinoyl hydrazone with Ga^III, In^III and Tl^III has been studied. The thallium complex is unstable. The composition and the instability constants of gallium and indium complexes were determined. Molar absorptivity of gallium complex at 390 nm is 3.40 × 10⁴ and that of indium at 380 nm is 3.20 × 10⁴ l mole^?1 cm^?1. Both complexes were found to be rapidly and quantitatively transfered into 1-pentanol. The corresponding aluminum complex is not extracted. Possible analytical application for separation and spectrophotometric determination of these elements is also examined.     

Dependence of the magnetic properties of MnGaN epitaxial layers on external electrical field

Investigation of the magnetic properties of MnGaN epitaxial layers as a function of external electrical field was performed on the basis of field effect structure. The structure included substrate of n-type GaN, epitaxial layer of n-type Mn_xGa_1-xN, dielectric layer and metal layer acting as field effect device gate. Each Mn atom in Mn_xGa_1-xN contributes 4 net spins due to the electrons occupying energy levels ⁴F, ⁴D, ⁴P and ⁴G belonging to 3d orbital, and these levels are in the energy band gap and in the top of the valence band of Mn_xGa_1-xN. The position of the Fermi level is determined to be in the energy band gap of the layer of GaN and to be above the level 4F in the layer of Mn_xGa_1-xN. In this way application of external negative voltage on the gate causes change in the number of electrons contributing net spins and the saturation magnetization M_sat of Mn_xGa_1-xN changes as well. It was found that M_sat changes in the range 1.15 × 10⁻³–0.7 × 10⁻³ A μm⁻¹ if the external voltage changes in the interval 0–−5V. The application of this structure for the design of spintronic devices is discussed in this paper.      

Evaluation of GaN and In0.2Ga0.8N Semiconductors as Potentiometric Anion Selective Electrodes

The response of potentiometric anion selective electrodes consisting of undoped GaN or In_0.2Ga_0.8N films grown on Al₂O₃ (sapphire) was measured in electrolyte solutions of F^?, NO₃^?, Cl^?, SCN^?, ClO₄^? or Br^? anions at concentrations ranging from 10^?6 to 10^?1 M. The slope of the linear regions varied between ?32.8 and ?51.9 mV/decade for the GaN electrode and between ?31.0 and ?72.0 mV/decade for the In_0.2Ga_0.8N electrode. The drift of the GaN electrode reached 1.57 mV/day in KNO₃ solutions, whereas the drift of the In_0.2Ga_0.8N electrode could not be evaluated due to large drops in the slope of its linear range over time. Both electrodes were sensitive to pH variations over the pH range from 12.8 to 1.3. The GaN electrode surface could be electrochemically etched under anodic polarization; however, both GaN and In_0.2Ga_0.8N electrodes remained chemically stable and mechanically intact under open circuit conditions even after prolonged use.     

Analysis of layered AlxGa1 − xAs on gallium arsenide by electron microprobe and secondary-ion mass spectrometry

Two samples containing Al_xGa_{1 ? x}As layers (several micrometers thick) of different composition deposited on a gallium arsenide substrate were analyzed by two techniques. Electron microprobe analysis was used on a cross-section of the samples to measure layer thickness, to obtain qualitative information by means ov x-ray line scans, and to determine the composition of the layers accurately by energy-dispersive x-ray spectrometry. Depty profiles obtained by secondary-ion mass spectrometry were used to study depth resolution at large depth ranges. Results obtained by the two techniques are in excellent agreement and compare favourably with other published results concerning the same type of sample.     

The distinction of gallium(I) tetrachloroaluminate,Ga[AlCl4], from gallium dichloride

Ga[AlCl₄] is obtained as single crystals via the reduction of gallium trichloride with aluminum and slow cooling of the melt. It crystallizes in the monoclinic system, space group p2₁/n, with a = 716.4(1), b = 1017.9(2), c = 926.7(1) pm, β = 93.21(1)°. Unlike in gallium dichloride, Ga[GaCl₄]], where Ga⁺ has a dodecahedral, eight-coordinate surrounding, a 6 + 2 + 1 coordination is adopted in Ga[AlCl₄] that is similarly observed not only in Ga₂[Ga₂Br₆] and in tin (II) and lead (II) chalcogenides but also in (the almost isotypic) K[AlCl₄].     

Spectroscopic and magnetic studies on electrogenerated mixed-valence ruthenium complexes

Electrochemical synthesis has enabled several sequences of triple chloride bridged diruthenium complexes of general type [L_3?xCl_xRuCl₃RuCl_yL_3?y]^z/z+1/z+2 (L = soft neutral ligand) to be generated. The intervalence charge transfer bands in the optical spectra of the mixed-valence Ru^II,III₂ compounds and variable temperature magnetic measurements for the corresponding Ru^III.III₂ complexes reveal that the degree of metal—metal interaction in these confacial bioctahedral systems decreases as the molecular asymmetry (y?x) increases.