Ga_(Zn)-V_(Zn) acceptor complex defect in Ga-doped Zn O

Gallium(Ga)-doped Zn O is regarded as a promising plasmonic material with a wide range of applications in plasmonics. In this study, zinc self-diffusion experiments are adopted to disclose the nature of the dominant compensating defect in Ga-doped Zn O isotopic heterostructures. The(Ga_(Zn)-V_(Zn))~- complex defect, instead of the isolated V_(Zn)~(2-), is identified as the predominant compensating acceptor center responsible for the low donor doping efficiency. The comparative diffusion experiments operated by the secondary ion mass spectrometry reveal a ~0.78 e V binding energy of this complex defect, which well matches the electrical activation energy derived from the temperature-dependent Hall effect measurements(~(0.82±0.02) e V). These findings contribute to an essential understanding of the(Ga_(Zn)-V_(Zn))~- complex defect and the potential engineering routes of heavily Ga-doped ZnO.     

Geometries and electronic structures of Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript>, Ga<Subscript>3</Subscript>Se<Subscript>2</Subscript> and their anions. Theoretical insights

We hereby report a theoretical study on the equilibrium geometries, electronic structures and harmonic vibrational frequencies of Ga₂Se₃, Ga₃Se₂ and their anions. The ground and low-lying excited states of Ga₂Se₃⁻, Ga₂Se₃, Ga₃Se₂⁻ and Ga₃Se₂ are studied at the B3LYP and/or MP2 and CCSD(T) levels in conjunction with 6-311+G(d) and 6-311+G(2df) one particle basis sets. Ga₂Se₂⁻ adopts the C_2v kite geometry while Ga₂Se₃ has a ‘V’ geometry. Ga₃Se₂⁻ has a three-dimensional ‘D_3h ’ geometry and Ga₃Se₂ prefers the three-dimensional ‘C_2v ’ structure. Electron detachment energies from the ground electronic states of the anions to several neutral states are reported and discussed. At CCSD(T)//MP2 level, the adiabatic electron affinity (AEA) of Ga₂Se₃ is calculated to be 3.23 eV when using the 6-311+G(2df) basis set and that of Ga₃Se₂ is 2.77 eV with the 6-311+G(d) basis set. The findings of this research are analyzed and compared with gallium oxide and sulfide analogues.     

Effect of interdiffusion of In and Al atoms on excitonic states in In<Subscript>x</Subscript>Ga<Subscript>1−x</Subscript>As/Al<Subscript>y</Subscript>Ga<Subscript>1−y</Subscript>As quantum dots

The effect of interdiffusion of aluminum and indium atoms on the exciton emission energy and binding energy in In_xGa_1?xAs/Al_yGa_1?yAs quantum dots is studied. It is shown that the emission energy increases monotonically with increasing diffusion length, while the binding energy has a maximum.     

Electronic and structural properties of zincblende Al<Subscript>x</Subscript>Ga<Subscript>1-x</Subscript>N

Numerical calculations based on first-principles are applied to study the electronic and structural properties of zincblende Al_xGa_1-xN. The results show that the lattice constant has a very small deviation from the linear Vegard’s law. The direct and indirect bowing parameters of 0.295±0.034 eV and -0.125±0.060 eV are obtained, respectively, and there is a direct-indirect crossover near x=0.692. Besides, the bulk moduli and their pressure derivatives are monotonically increased with an increase of the aluminum composition x. The deviation parameter of the bulk modulus of -5.32±1.60 GPa is obtained. PACS 71.15.-m; 71.15.Nc; 71.55.Eq; 71.20.Nr; 42.70.Qs     

Magnetic linear birefringence in Yb<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> gallate garnet

The magnetic linear birefringence and the magnetic susceptibility of Yb₃Ga₅O₁₂ gallate garnet was investigated experimentally in the temperature range 78–295 K. It was shown that, in this temperature range, the magnetic linear birefringence of the garnet studied depends linearly on inverse temperature 1/T. The magnitude of this effect is determined only by the part of the crystal magnetization that is due to the difference in the thermal population of the ground state of the Yb³⁺ ion rather than the total magnetization. The results obtained are interpreted within the microscopic theory. According to this theory, the magnetic linear birefringence is determined by the quadrupole moment of the magnetoactive ion, which is induced by an external magnetic field.     

Catalytic growth and characterization of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

β-Ga₂O₃ nanowires have been synthesized using Ga metal and H₂O vapor at 800 °C in the presence of Ni catalyst on the substrate. Remarkable reduction of the diameter and increase of the length of the Ga₂O₃ nanowires are achieved by separation of Ga metal and H₂O vapor before they reach the substrate. Transmission electron microscopy analyses indicate that the β-Ga₂O₃ nanowires possess a single-crystalline structure. Photoluminescence measurements show two broad emission bands centered at 290 nm and 390 nm at room temperature. Received: 27 June 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +886-6/234-4496, E-mail: wujj@mail.ncku.edu.tw     

Piezoelectric spectroscopic studies of Zn<Subscript>1-x-y</Subscript>Be<Subscript>x</Subscript>Mn<Subscript>y</Subscript>mixed crystals

This paper presents results of experimental and theoretical piezoelectric studies of a group of mixed crystals of the type Zn_{1 - x - y}Be_xMn_ySe. The fittings of theoretical to experimental amplitude and phase piezoelectric spectra were performed in a modified Jackson and Amer model. The influence of the surface treatment such as grinding, polishing and etching on the PZE spectra is analysed in the model of surface defects applied for the interpretation of the spectra for energies of photons below the energy gap of the crystal.     

Rashba effect in Ga<Subscript>x</Subscript>In<Subscript>1-x</Subscript>As/InP quantum wire structures

An overview is given on the Rashba effect in Ga_xIn_1-xAs/InP quantum wires. First, the effect of Rashba spin–orbit coupling on the energy level spectrum of quantum wires with different shapes of the confining potential is theoretically investigated. The wave functions as well as the spin densities in the quantum wire are analyzed for different magnetic fields. It is found that, owing to the additional geometrical confinement, a modification of the characteristic beating pattern in the magnetoresistance can be expected. The theoretical findings are compared to measurements on two different types of wires: First, single wires and, second, sets of parallel wires. A characteristic beating pattern in the Shubnikov–de Haas oscillations is observed for wires with an effective width down to approximately 400 nm. The beating pattern is significantly better resolved for the samples with sets of parallel wires, owing to the effective suppression of conductance fluctuations. A comparison with theoretical simulations confirms that the strength of the Rashba effect is basically not affected by the geometrical confinement of the wires. However, for wires with a very small effective width the strong carrier confinement leads to a suppression of the characteristic beating pattern in the Shubnikov–de Haas oscillations. PACS 71.70.Ej; 73.63.-b; 71.70.Di     

Polarization effects in quantum-well In<Subscript>28</Subscript>Ga<Subscript>72</Subscript>As/GaAs heterolasers

The effect of externally introduced variable strains on the polarization properties of quantum-well In₂₈Ga₇₂As/GaAs laser radiation at room temperature is studied experimentally and theoretically. An analysis of the polarization effects at various values of the excess of the working current over the threshold is performed. Data on the energy for the splitting of the levels of light and heavy holes in the quantum well of the structure under consideration are obtained. It is experimentally proven that the effectiveness of the action of a variable strain on the polarization twist substantially increases with increasing quantum well width.     

Temperature-controlled synthesis of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanobelts and nanosheets

We have investigated the effect of growth temperature on structural morphology and photoluminescence (PL) properties of as-synthesized gallium oxide (Ga₂O₃) nanostructures. The products consisted of Ga₂O₃ nanobelts and nanosheets (i.e. wider nanobelts), which had monoclinic crystalline structures. The average width of structures grown at 1000 °C was relatively greater than those at 800 °C, revealing that higher temperature favored the formation of nanosheets. PL measurements of 800 °C- and 1000 °C-grown samples indicated that both samples exhibited a broad emission band peaked around the blue-light region, while only the 800 °C-grown sample showed a red peak. PACS 81.07.-b; 81.05.Je; 61.10.Nz; 68.37.Hk; 68.37.Lp     

Magnetic behaviour of nano-particles of Fe<Subscript>2.8</Subscript>Zn<Subscript>0.2</Subscript>O<Subscript>4</Subscript>

Magnetization measurements are reported on a nano-particle sample of Znsubstituted spinel ferrite Fe_2.8Zn_0.2O₄ in the temperature range 20–300 K. Analysis of small-angle neutron scattering data shows the sample to have a log-normal particle size distribution of median diameter 64.4 Å and standard deviation 0.38. Magnetization evolves over a long period of timet going nearly linearly with logt. Magnetic anisotropy, estimated by fitting M-logt curve, shows many fold increase over that of bulk particle sample. Major enhancement owes to disordered moments in surface layer. In the nano-particle state as well increasing amount of Zn causes anisotropy to decrease.     

Magneto-elastic properties of Tb<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> (TGG)

The temperature dependence of the elastic constants in Tb₃Ga₅O₁₂ was measured and analysed with a simple crystal field model. The magneto-elastic coupling constants have been deduced from this experiment. The coupling constant g_Γ5, related to the c₄₄ mode, is anomalously large. These coupling constants are important for the interpretation of the phonon Hall effect.     

Magnetic behaviour of nano-particles of Fe<Subscript>2.9</Subscript>Zn<Subscript>0.1</Subscript>O<Subscript>4</Subscript>

DC magnetization measurements are reported in the temperature range 20–100 K on a poly-disperse nano-particle sample of the spinel ferrite Fe_2.9Zn_0.1O₄ with a log-normal size distribution of median diameter 43.6 Å and standard deviation 0.58. Outside a core of ordered spins, moments in surface layer are disordered. Results also show some similarities with conventional spin glasses. Blocking temperature exhibits a near linear variation with two-third power of the applied magnetic field and magnetizationM evolves nearly linearly with logarithm of timet. Magnetic anisotropy has been estimated by analysing theM-logt curve. Anisotropy values show a large increase over that of bulk particle samples. Major contribution to this enhancement comes from the disordered surface spins.     

Specific features of magneto-optical spectra of Tb<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript>

The spectra of magnetic circular dichroism in the range of the ⁷ F ₆→⁵ D ₄ absorption band and the spectra of magnetic circular polarization of luminescence in the range of the ⁵ D ₄→⁷ F ₅ band in the terbium-gallium garnet Tb₃Ga₅O₁₂ are studied at a temperature of 80 K. The optical transitions between the Stark sublevels of the ⁷ F ₆, ⁷ F ₅, and ⁵ D ₄ multiplets are identified based on the analysis of the magneto-optical and optical spectra. It is shown that the experimentally determined symmetry and energy of the Stark sublevels of these multiplets confirm the results of numerical calculations of the energy spectrum of the Tb³⁺ rare-earth ion in terbium-gallium garnet.     

Structural properties of zinc-blende Ga<Subscript>x</Subscript>In<Subscript>1-x</Subscript>N: ab initio calculations

We present a theoretical study of the structural properties, namely lattice constant, bulk modulus and its pressure derivative of zinc-blende Ga_xIn_1-xN. The calculations are performed using first-principles calculations in the framework of the density-functional-theory within the local density approximation under the virtual crystal approximation. The computed values are in good agreement with the available experimental data. The composition dependence of the studied quantities is examined. Besides, the deviation of the alloy lattice constant from Vegard's law is evaluated.     

Multilayer metallization of ferrite Mg<Subscript>0.54</Subscript>Zn<Subscript>0.46</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

The character of interatomic interaction in ferrite Mg_0.54Zn_0.46Fe₂O₄ was studied using the x-ray spectroscopy technique and theoretically. It was found that the electronic structure of samples is rearranged during annealing at high temperatures (1280°C, 0.5–0.8 h). The electronic structure rearrangement was shown to be associated with multilayered ferrite metallization in which alternating layers with metallic and ionic-covalent bonds form.     

Photoacoustic spectra of Zn<Subscript>1-x</Subscript>Be<Subscript>x</Subscript>Te near the energy gap

The results of experimental studies of optical and structural properties in bulk crystals of Zn_1-xBe_xTe (x = 0.02, 0.06 and 0.12) were presented. The amplitude and phase photoacoustic (PA) spectra were measured and analyzed in dependence on the wavelength of the excitation optical beam, at different frequencies of modulation, using the PA microphone (PAmic) and PA piezoelectric (PApze) spectroscopy methods. The differences in PA spectra of as grown and annealed in zinc vapor samples were observed.     

The magnetic mechanism of Zn<Subscript>0.93</Subscript>Co<Subscript>0.07</Subscript>O thin films

Zn_0.93Co_0.07O thin films infiltrated with nitrogen and aluminum were prepared by means of magneton sputtering. The structural and magnetic properties of the films were studied systematically. The materials were single phase (wurtzite structure) with surfaces showing signs of homogeneous growth. The films were ferromagnetic at room temperature, and magnetic domains could be clearly observed on the surfaces. In the case of Al infiltration, saturated magnetization increased with Al concentration increasing; whereas in the case of N infiltration, saturated magnetization decreased with the increase in N concentration. The results show that ferromagnetic interactions in Co-doped ZnO diluted magnetic semiconductor may be transferred by electrons. Supported by the National Natural Science Foundation of China (Grant No. 10674059) and the Major Project of National Basic Research Program of China (Grant No. 2005CB623605)     

Structure-Dependent Magnetoresistance in the Zn<Subscript>0.1</Subscript>Cd<Subscript>0.9</Subscript>GeAs<Subscript>2</Subscript> + MnAs Hybrid Nanocomposite

The effect of high pressure on electron transport and on the field dependence of the transverse magnetoresistance has been studied in a hybrid nanocomposite based on the Zn0.1Cd0.9GeAs2 matrix and MnAs clusters. A record high negative magnetoresistance of ~74% is formed near a pressure-induced structural transition (P≈ 3.5 GPa). The considered scattering mechanisms include both the contribution from MnAs clusters at relatively low pressures (up to 0.7 GPa) and spin-dependent scattering by localized magnetic moments in the Mn-substituted structure of the matrix in the region of the structural transition. The presence of the positive magnetoresistance region associated with the two-band transport model in the high-pressure phase, as well as the large negative magnetoresistance, is described in the framework of the semiempirical Khosla–Fischer expression.     

First-principles investigation of electronic and optical properties in wurtzite Zn<Subscript>1-x</Subscript>Mg<Subscript>x</Subscript>O

A first-principles study has been performed to evaluate the electronic and optical properties of wurtzite Zn_1-xMg_xO. Substitutional doping is considered with Mg concentrations of x = 0, 0.0625, 0.125, 0.1875 and 0.25, respectively. Mg incorporation can induce band gap widening due to the decrease of Zn 4s states. The imaginary part of the dielectric function shows that the optical transition from band edge emission decreases slightly with increasing Mg contents. The optical band gap also increases from 3.2 to 3.7 eV with increasing Mg contents from 0.0625 to 0.25. The calculated results suggest that relatively high Mg concentration is necessary for effective band gap engineering of wurtzite Zn_1-xMg_xO.