Millimeter and submillimeter detection using Ga1?xAlxAs/GaAs heterostructures

We have shown that a Ga_1–xAl_xAs/GaAs heterostructure can be used as a sensitive tunable detector of mm-wave/sub-mm-wave radiation. The mechanism for detection requires the application of a magnetic field varying from approximately 0.2T at 94GHz (3.2mm wavelength) to 6.2T at 2500GHz (119m wavelength). The responsivity and N.E.P. at 3.2mm have been roughly estimated at 200V/W and 5×10^–11W/Hz respectively. The speed of such a detector could be several orders of magnitude greater than comparable InSb detectors.     

Electronic and optical properties of Full-Heusler alloy Fe3?xMnxSi

The electronic and optical properties of the nonstoicheiometric Heusler alloys Fe_3−x Mn _x Si with (x = 0,0.75,1,1.25,2) have been studied by the first principles study in the framework of the density functional theory (DFT). Optical properties including the dielectric function, refractive index, energy-loss spectra, absorption spectra, optical conductivity and reflectivity were also calculated. Results show that the electronic structure of Fe_3−x Mn _x Si alloys have half-metallic property for (x = 0.75,1,1.25). The real part of dielectric function has two main peaks in high energies. From absorption spectra it can be seen that absorption curves in low energy are broadened with respect to higher energies. The refractive index has a nonlinear dispersion in the energy range of 45–55 eV. The energy of plasmon peaks obtained from electron energy loss function (ELF) are about 25 eV.     

First principles calculations of the structural,electronic and optical properties of the mixed fluorides SrxCd1−xF2

In the present work, we have investigated the structural, electronic and optical properties of SrF₂ and CdF₂ and their ternary mixed Sr_xCd_1?xF₂ alloys at some selected concentrations x (x?=?0.25, 0.50, 0.75 and 1). The parent compounds SrF₂ and CdF₂ crystallize in Fm-3?m space group, whereas the alloys adopt the cubic structure with Pm-3?m space group for the composition x?=?0.25 and 0.75 and the tetragonal structure with space group P4/mmm for x?=?0.50. The calculations were performed using the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential was handled with Wu and Cohen GGA approximation (WC-GGA). Moreover, the Engel–Vosko's (EV-GGA) formalism and the modified Becke Johnson (mBJ) approximation were also applied to improve the electronic band structure calculations. The computed structural parameters for SrF₂ and CdF₂ such as the equilibrium lattice constants and the bulk moduli are in good agreement with the available experimental and theoretical data. It is found that the lattice parameters increase with increasing composition (x) while the bulk modulus decreases for Sr_xCd_1?xF₂ alloys. The calculated band structures reveal an indirect band gap (W-Γ), (X-Γ) and (M-Γ) for CdF₂, SrF_{2 and} Sr_xCd_1?xF₂ for x?=?0.25, 0.75 and x?=?0.5, respectively. The optical constants, including the dielectric function, refractive index, reflectivity, absorption, extinction coefficient and the energy loss function were calculated using both WC-GGA and mBJ schemes for a radiation up to 40?eV. This is the first quantitative theoretical prediction of the optical properties for these alloys that requires experimental confirmation.     

GaNxAs1－x(x<0.01)中合金态的光学特性

应用多种光谱手段研究了分子束外延生长在半绝缘的(001)GaAs衬底上的低氮含量的GaNAs中 三元合金态的光学特性.变温PL谱揭示了合金态的本征特性以及其与氮的杂质态的根本区别 ，而脉冲激发的光荧光谱则进一步显示了合金态的本征光学特性.最后还研究了GaNAs的吸收 光谱特征.     

Response of Granular La1??xCaxMnO3 Film to 10?GHz and 35?GHz Frequency Electromagnetic Radiation

The nonbolometric response of La_1 − xCa_xMnO₃ film to 10 GHz and 35 GHz frequency electromagnetic radiation is investigated in the case when, in addition to the strong electric field of the wave, the film is subjected to a stationary electric bias field. Dependences of responses on the radiation power P at temperature T = 80 K are presented. In the low power region, a linear dependence of the response on P is observed at both frequencies whereas for high powers the dependence behaves as ~P ^1/2. The obtained results are explained taking into account that the nonbolometric response originates from the intergranular junctions that operate in the reverse current regime. There two effects take place: (i) at low powers the detection resistance decreases with increasing power P, and (ii) at higher powers in addition to that the film resistance decreases as P ^1/2 due to the avalanche of charge carriers in the electric field of the electromagnetic wave.     

Elektronen-Spin-Resonanz an (La1??xGdyCex)Al2

In the EPR of (La_1––x Gd _y Ce _x )Al₂ a bottleneck in the relaxation of the conduction electrons to the lattice is present at sufficiently high Gd-concentrations. The bottleneck can be broken by decreasing the Gd-concentration or by adding Cerium as a spin-flip-scatterer.g-factor and line broadening are measured for (La_1–y Gd _y )Al₂ and (La_1––x Gd _y Ce _x )Al₂ as a function of temperature and Gd- and Ce-concentrations. The Cerium induced relaxationsrate _eL (Ce) increases linearly with Ce-concentration up tox0.025. This corresponds to the fact, well known by measurements of the Kondo anomalies, that Cerium impurities show no significant interaction up to rather high concentrations.     

Influence of the illumination on the subband structure and?occupation in AlxGa1?xN/GaN heterostructures

The subband structure and occupation in the triangular quantum well at Al _x Ga_1−x N/GaN heterointerfaces have been investigated by means of temperature dependent Shubnikov–de Haas (SdH) measurements at low temperatures and high magnetic fields under illumination. After the illumination of the heterostructures, the total two-dimensional electron gas concentration increases, and the SdH oscillation amplitudes are enhanced when there is no additional subband occupation. It is also found that the energy separation between the subbands decreases after the illumination. We suggest that the illumination decreases the electric field and thus weakens the quantum confinement of the triangular quantum well at Al _x Ga_1−x N/GaN heterointerfaces. The GaN layer is thought to be the primary contributor of the excited electrons by the illumination.     

Dependences of the dielectric and pyroelectric properties of (1 ? x)PbFe1/2Nb1/2O3?xPbTiO3 ferroelectric ceramics solid solutions on the PbTiO3 content in a compositional range of 0 ≤ x ≤ 0.08

(1 − x)PbFe_1/2Nb_1/2O_3−x PbTiO₃ (PFN-xPT) ferroelectric ceramics with low dielectric loss and pronounced anomalies of dielectric and pyroelectric properties near the ferroelectric-ferroelectric phase transition was obtained by doping with lithium. The temperature dependence of the position of the morphotropic boundary between the rhombohedral (monoclinic) and tetragonal phases in the x-T phase diagram of the PFN-xPT system was determined for the first time.     

Research of the behaviour of O chemisorption on the (110) surface of Rhx--Pt1－x alloy

An atomic group model of the disordered binary alloy Rhx-Pt1-x has been constructed to investigate surface segregation. According to the model, we have calculated the electronic structure of the Rhx-Pt1-x alloy surface by using the recursion method when O atoms are adsorbed on the Rhx-Pt1-x （110） surface under the condition of coverage 0.5. The calculation results indicate that the chemical adsorption of O changes greatly the density of states near the Fermi level, and the surface segregation exhibits a reversal behaviour. In addition, when x 〈 0.3, the surface on which O is adsorbed displays the property of Pt; whereas when x 〉 0.3 it displays the property of Rh.     

Effect of the spin and valence states of cobalt ions on the kinetic properties of Ho1 ? xSrxCoO3 ? δ and Er1 ? xSrxCoO3 ? δ compounds

The electrical conductivity and Seebeck effect in ceramics based on cobaltites Ho_{1 − x} Sr _x CoO_{3 − δ} (x = 0.65, 0.75, 0.85, 0.95) and Er_{1 − x} Sr _x CoO_{3 − δ} (x = 0.75, 0.85, 0.95) with a perovskite-like structure have been investigated in the temperature range T > 77 K. All the compounds under study are characterized by the variable-range-hopping conductivity with the temperature dependence of the electrical resistivity corresponding to the Mott law. It has been found that, in the Ho_0.35Sr_0.65CoO_{3 − δ} compound, thermally excited Co³⁺ ions contribute to the electrical conductivity with an increase in temperature to 250 K. The Seebeck coefficient of the systems studied decreases as the strontium concentration and temperature increase. It has been shown that, for an adequate explanation of this behavior, proper allowance must be made for the splitting of the 3d levels, as well as for the charge disproportionation of the cobalt ions.     

Effect of polarization on the intensity of anomalous electron emission in the (1 ? x)PbMg1/3Nb2/3O3 + xPbTiO3 system

Spectra of anomalous electron emission from the surface of solid solutions in the (1 − x)PbMg_1/3Nb_2/3O₃ + xPbTiO₃ system with x = 0.06, 0.10, 0.13, 0.20, and 0.25 have been studied. While the energy characteristics of the anomalous electron emission spectra vary monotonically with x, the behavior of integrated intensity was found to be nonmonotonic with a maximum occurring at x = 0.1. According to the proposed interpretation, the results obtained are explained by the effect of the potential barrier on the electron emission; the potential barrier depends, in turn, on the permittivity ε of the samples. Original Russian Text ? A.T. Kozakov, A.V. Nikol’skiĭ, V.P. Sakhnenko, A.N. Pavlov, V.G. Smotrakov, V.V. Eremkin, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 7, pp. 1310–1314.     

Hydrostatic pressure effect on the electron mobility in a ZnSe/Zn1－xdx Se strained heterojunction

With a memory function approach, this paper investigates the electronic mobility parallel to the interface in a ZnSe/Zn1-xCdxSe strained heterojunction under hydrostatic pressure by considering the intersubband and intrasubband scattering from the optical phonon modes. A triangular potential approximation is adopted to simplify the potential of the conduction band bending in the channel side and the electronic penetrating into the barrier is considered by a finite interface potential in the adopted model. The numerical results with and without strain effect are compared and analysed. Meanwhile, the properties of electronic mobility under pressure versus temperature, Cd concentration and electronic density are also given and discussed, respectively. It shows that the strain effect lowers the mobility of electrons while the hydrostatic pressure effect is more obvious to decrease the mobility. The contribution induced by the longitudinal optical phonons in the channel side is dominant to decide the mobility. Compared with the intrasubband scattering it finds that the effect of intersubband scattering is also important for the studied material.     

Determination of the far infrared optical constants of η-doped bulk CdxHg1?xTe (CMT) by dispersive fourier transform spectroscopy

Far infrared phase and amplitude reflectivity measurements have been made on two bulk Cd_xHg_1–xTe mixed crystals with composition x=0.29 and x=0.22 by dispersive Fourier transform spectroscopy (DFTS). The results have been used to calculate the real and imaginary parts of the dielectric function (, ) from the Fresnel relations. A plasma contribution is observed in the spectra in addition to the phonon response. For both samples a broad but weak reflection band around 95–105 cm^–1 is observed as well as the expected two-oscillator response from the HgTe-like and CdTe-like optical phonons. This feature is attributed to absorption due to phonon combination bands, but it is too broad to enable assignments to be made. There is no evidence of additional features in the CdTe region due to clustering.     

MOCVD制备InxGa1－xN/GaN MQWs的温度依赖性

利用方势阱模型对In_xGa_1－xN/GaN MQWs结构的光特性进行了量子力学定性理论分析.并在MO源流量恒定条件下，在570℃～640℃范围内进行了不同生长温度的多量子阱制备实验，对In_xGa_1－xN制备过程中的In组份掺入效率的温度依赖关系进行研究.通过对制备样品的PL谱测量分析，得到了587℃～600℃的In组份最佳掺入温度区间.     

Ti1－xCoxO2铁磁性半导体薄膜研究

利用射频磁控反应溅射制备了Ti1-xCoxO2薄膜样品.超导量子干涉仪(SQUID)测量了样品在常温，低温下的磁特性.结果显示样品在常温下已经具有明显的铁磁性.常温时其矫顽力32×103A/m,饱和磁化强度55emu／cm3磁性元素的磁矩达0679μB／Co.饱和场12×104A/m.x射线衍射(XRD)和x射线光电子能谱(XPS)实验分析初步表明样品中没有钴颗粒. 关键词： 铁磁半导体 TiO2 薄膜     

Sm1－xGdxA12低温下的磁性

分别测量了Sm1-xGdxAl2在低温下不同外加磁场时的电阻和磁化率.实验 结果表明，铁磁性物质Sm1-xGdxAl2在居里温度以下时，自旋磁矩和轨 道磁矩反平行有序排列，且对温度的依赖关系不同，导致在磁性抵消点出现自旋铁磁有序而 总磁矩为零的磁现象.并发现外加强磁场时自旋 轨道发生翻转. 关键词： Sm1-xGdxAl2 铁磁有序 自旋磁矩 轨道磁矩     

质子入射AlxGa1–xN材料的位移损伤模拟

氮化镓材料由于优良的电学特性以及耐辐照性能,其与不同含量Al_xGa_1–xN材料组成的电子器件,有望应用于未来空间电子系统中.然而目前关于氮化镓位移损伤机理研究多关注于氮化镓材料,对于Al_xGa_1–xN材料位移损伤研究较少.本文通过两体碰撞近似理论模拟了10 keV—300 MeV质子在不同Al元素含量的Al_xGa_1–xN材料中的位移损伤机理.结果表明质子在Al_xGa_1–xN材料中产生的非电离能损随质子能量增大而下降,当质子能量低于40 MeV时,非电离能损随着Al含量的增大而变大,当质子能量升高时该趋势相反;分析由质子导致的初级撞出原子以及非电离能量沉积,发现不同Al_xGa_1–xN材料初级撞出原子能谱虽然相似,然而Al元素含量越高,由弹性碰撞产生的自身初级撞出原子比例越高;对于质子在不同深度造成的非电离能量沉积,弹性碰撞导致的能量沉积在径迹末端最大,而非弹性碰撞导致的能...     

1D-ACAR Spectra of YBa2－xSrxCu3Oy

The measurements of one-dimensional angular correlation of positron annihilation radiation (1D-ACAR) spectra,superconducting critical temperature,lattice parameters and oxygen contents have been made on YBa_2－xSr_xCu₃O_y high temperature supercnductor system.It was found that the substitution of Sr for Ba weakens the orthorhombic symmery,suppresses T_C,hardly changes oxygen content and does not disturb the electronic structure of Cu-O chains.Based on the above results.the authors propose that the localized electronic structure of Cu-O plane is a dominating factor for high temperature superconductivity in 1:2:3 phase superconductors.     

Renner-Teller and Spin-Orbit Interactions between the ÃA1 and the X?B1 States of NH2: The Stretch-Bender Approach

The stretch-bender model, developed originally to describe the effects of stretch-bend interactions and Renner-Teller coupling in symmetrical triatomic molecules, has been extended to incorporate the effects of spin-orbit interaction and of overall rotation. A comparison is made between the treatment of spin-orbit interaction and of overall rotation in our model and in the MORBID approach of P. Jensen, M. Brumm, W. P. Kraemer, and P. R. Bunker (J. Mol. Spectrosc.171, 31-57 (1995)).     

一种具有“1111”型结构的新型稀磁半导体(La1–xSrx)(Zn1–xMnx)SbO

利用高温固相反应法,成功合成了一种新型块状稀磁半导体(La_1–xSr_x)(Zn_1–xMn_x)Sb O(x=0.025, 0.05,0.075, 0.1).通过(La³⁺, Sr²⁺)、(Zn²⁺, Mn²⁺)替换,在半导体材料La Zn Sb O中分别引入了载流子与局域磁矩.在各掺杂浓度的样品中均可观察到铁磁有序相转变,当掺杂浓度x=0.1时,其居里温度Tc达到了27.1 K,2 K下测量获得的等温磁化曲线表明其矫顽力为5000 Oe.(La_1–xSr_x)(Zn_1–xMn_x)Sb O与"1111"型铁基超导体母体LaFeAsO、"1111"型反铁磁体LaMnAsO具有相同的晶体结构,且晶格参数差异很小,为制备多功能异质结器件提供了可能的材料选择.