Acta Physica Sinica
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Acta Physica Sinica  
  Acta Physica Sinica--1985, 34 (4)   Published: 15 April 1985
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BRIEF REPORT

ON THE LOW MOBILITY OF GaAs

ZHOU BING-LIN, CHEN ZHENG-XIU
Acta Physica Sinica. 1985, 34 (4): 0537 doi: 10.7498/aps.34.537
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The temperature dependence of electron mobility on 5 undoped LPE-GaAs samples has been measured. It was found that the experimental curves cross each other and this is difficult to explain by only one extrinsic scattering mechanism (ionized impurity scattering). Therefore, it's necessary to assume another extrinsic scattering mechanism, so called mobility killer. Because the samples we used are rather pure, the central-cell scattering suggested by Stringfellow et al. can certainly be neglected. The effect of illumination on the electron concentration and mobility at 77 K has been studied and it is considered that the nature of mobility killer is probably the spacecharge regior caused by the microscopic inhomogeneities in samples.

QUANTUM CHEMISTRY STUDY ON BONDING OF DEFECT STATES IN AMORPHOUS CHALCOGENIDE

PENG ZHOU-REN, DU QI-SHI, LI BING-RUI
Acta Physica Sinica. 1985, 34 (4): 0542 doi: 10.7498/aps.34.542
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The defect states in chalcogenide glasses, including positively charged, negatively charged and neutral three-fold coordinated sulphur clusters, were studied by SCF MO CNDO/2 method. By comparing energies of the clusters, net charges of atoms, bond order functions and other parameters, conclusion has been drawn which is in good agreement with that of Kastners, and thus supports his valence-alternation pairs theory. The effect of lone-pair electrons on bonding in defect states is also discussed and it is shown that they play a significant role in chalcogenide glasses.

DISTRIBUTION CHARACTERISTICS OF DEEP LEVEL WAVEFUNCTIONS IN BLOCH SPACE

LI MING-FU, REN SHANG-YUAN, MAO DE-QIANG
Acta Physica Sinica. 1985, 34 (4): 0547 doi: 10.7498/aps.34.547
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A simple method in the framework of Koster-Slater Green's function calculation and central cell defect potential (CGDP) approximation is used to calculate the distribution of deep level wavefunctions in Bloch space for Si, GaAs and GaP for the first time. Convergence properties are discussed. It is shown that for definite number of energy bands in the host crystal model, the convergence of deep level wavefunction calculations is faster than that of deep energy calculations.

SW -Xa-SCF METHOD CALCULATION FOR HYDROGEN CHEMISORPTION ON Al(111) SURFACE

TIAN ZENG-JU, HUANG YI, ZHANG KAI-MING
Acta Physica Sinica. 1985, 34 (4): 0552 doi: 10.7498/aps.34.552
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The chemisorptions for H/A1(111) with bridge site and top site models are studied by SCF-Xa scattered wave method. It is shown that the binding energy for the top site model is more favorable to that for the bridge model. In the case of top site chemi-sorption, the bonding properties between the adatom H and the substrate are discussed in some detail.

HARTREE-FOCK-ROOTHAAN WAVEFUNCTIONS FOR DIATOMIC MOLECULES IN A SAME BASIS SET (Ⅱ)——H2 AND FIRST-ROW HOMONUCLEAR SYSTEMS A2, A2~±AND A2

WU JI-AN
Acta Physica Sinica. 1985, 34 (4): 0558 doi: 10.7498/aps.34.558
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Ab initio calculations of electronic wavefunctions, orbital energies and total energies for H2 and first-row homonuclear diatomic systems have been performed with the same double zeta CGTF basis set which has been used in the previous paper. The repertory of states includes the ground states A2, a few lowlying excited states A2~*, and positive and negative ions A2~± where A denotes the elements Li through F. The calculations are restricted to states involving either closed-shell electron configurations or open-shell configurations with one incompletely filled open shell. Tables of electronic wavefunctions of H, and some ground states A2, as examples, are presented.

STUDIES ON PHASE EQUILIBRIUM RELATION IN PSEUDO-BINARY SYSTEMS BaB2O4-K2O AND BaB2O4-K2B2O4

WANG GUO-FU, HUANG QING-ZHEN
Acta Physica Sinica. 1985, 34 (4): 0562 doi: 10.7498/aps.34.562
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The pseudo-binary systems BaB2O4-K2O and BaB2O4-K2B2O4 have been studies by means of X-ray diffraction and thermal analysis. The system BaB2O4-K3B2O4 is a eutectic one with eutectic temperature at 850±3℃ and the eutectic composition of 45 mol% K2B2O4. In BaB2-K2O system there exist two new compounds. A new compound 5BaB2O4·3K2O melts congruently at 903±3℃. The BaB2O4-5BaB2O4 ·3K2O forms a eutetic system. Its eutetic reaction occurs at 813±3℃ and 25 mol% K2O. Another new compound Ba4K6B8O19 melts incongruently at 860±3℃. The Ba4K6B8O19-K2O also forms a eutectic system. Its eutectic reaction occurs at about 788±3℃ and 67.5 mol% K2O.

DISCRIMINATION OF THE STABILITY OF SIMULTANEOUS EQUATIONS FOR OBTAINING LATTICE CONSTANTS OF LOW-SYMMETRY CRYSTAL SYSTEMS

GUO CHANG-LIN, HUANG YUE-HONG, YAO GONG-DA, LIU YUN-JI
Acta Physica Sinica. 1985, 34 (4): 0567 doi: 10.7498/aps.34.567
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Some combinations of simultaneous equations for obtaining lattice constants of low-symmetry crystal systems can lead to a serious accumulation of errors and the formation of abnormal state equations. A method of solving the nermal state equations to obtain lattice constants by using the inverse matrix to discriminate the stability of simultaneous equations is given in this paper. Pratical example proves that the method is quite explicit and reliable and satisfactory results can be obtained.
CONTENT

THE CURRENT-VOLTAGE HYSTERISIS FOR THE SUPE-RCONDUCTING CROSSED-FILM TUNNELING JUNCTION

ZHANG YU-HENG, LIU HONG-BAO, CHEN GENG-HUA
Acta Physica Sinica. 1985, 34 (4): 0429 doi: 10.7498/aps.34.429
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We point out in this paper that for the superconducting crossed-film tunneling junction, the tunneling electrical current must raise the temperature in the junction area and also produce a nonomogeneous self-induced magnetic field simutaneously. It causes the superconducting film to transform into intermediate state. By means of this physical model we not only can explain the hysterisis in I-V curves of nonequilibrium superconducting Pb films and the existance of thresheid current I(t3) revealed in previous experiments, but also predict the existance of the hysterisis, a strange phenomenon, in the usual tunneling I-V curves.

THE IRVERSE SOURCE PROBLEM IN PARTIALLY COH-ERENT OPTICAL INFORMATION PROCESSING

ZHUANG SONG-LIN, ZHENG QUAN
Acta Physica Sinica. 1985, 34 (4): 0439 doi: 10.7498/aps.34.439
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In this paper, we established a mathematical model for describing a partially coherent optical processing, and the error transfer formulas are also derived. The mathematical model could be used not only for estimating the error of a restoration image, but also for predicting the optimum source distribution. The necessary and sufficient condition for achieving non-error restoration image is obtained. And we also proved that for a truncation signal, the restoration image could be obtained with arbitrary precision by using an appropriate light source.

A NEW MODEL FOR THE GROWTH OF SILICON DIOXIDE LAYERS

LU YU-ZENG, Y. C. CHENG
Acta Physica Sinica. 1985, 34 (4): 0447 doi: 10.7498/aps.34.447
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A new model of oxidation is proposed to describe the growth of both thin and thick silicon dioxide layers. The assumption of the model is the presence of an exponential distribution of total net charges during oxidation. In this paper, we take into account the influence of the oxide charges and derive a new thermal-oxidation relationship of silicon, which agrees reasonably well with experimental data covering both thin and thick oxides. The relationship can be reduced to the well-known formula of Deal and Grove in the limit of thick oxide. With this model, we can also explain the effect of an external field on the oxidation rates satisfactorily.

ELECTRONIC STRUCTURE OF THE DIVACANCY IN SEMICONDUCTORS (Ⅰ)——BASIC EQUATIONS

REN SHANG-YUAN, MAO DE-QIANG, LI MING-FU
Acta Physica Sinica. 1985, 34 (4): 0455 doi: 10.7498/aps.34.455
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A complete set of equations for determining the energy levels and the wavefunc-tions with different symmetry of electronic states of the ideal divacancy in cubic semiconductors is obtained using the Koster-Slater Green's function method. Using an empirical tight binding Hamiltonian for the band structure of the host and the on-site pertubation approximation for the defect, only the on-site and the off-site Green's functions of the host and their derivatives with respect to energy E are involved in these equations.

STUDIES OF FOURIER-TRANSFORM ANALYSIS METHOD FOR ENERGY-DEPENDENT PHOTOELEC-TRON-DIFFRACTION (Ⅰ)——THE SYSTEMS OF Se-Ni(001) AND S-Ni(001)

TANG JING-CHANG, HUANG YI
Acta Physica Sinica. 1985, 34 (4): 0464 doi: 10.7498/aps.34.464
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Direct Fourier-transform analysis method for energy-dependent photoelectron-dif-fraction curves of Se-Ni(001) and S-Ni(001) systems has been studied. The effect of different energy range in which Fourier-transformation was performed on △a (layer-spacing modification) was considered. The possibility that surface structure could be determined by using these △a value and FT of experimental EDPD data has been discussed.

A STUDY ON PHASE RELATIONS OF RAPIDLY QUENCHED ALLOYS IN Ag-Ge SYSTEMS

CHE GUANG-CAN, LIANG JING-KUI, JIN ZUO-WEN, ZHAO ZHONG-XIAN
Acta Physica Sinica. 1985, 34 (4): 0476 doi: 10.7498/aps.34.476
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The phase relations and thermodynamic stabillity of metastable phases in rapidly quenched Ag-Ge alloys have been studied by means of DTA, DSC and X-ray powder diffraction techniques. Solubillity of Ge in Ag is extended from 1.5 at% Ge to 8 at% Ge, when cooling speed of alloy is approximately 104 K/s. Except supersaturated solid solution of Ge in Ag and Ge, there also exists a metastable phase, which has the hexagonal close-packed structure (hep) with lattice parameters a=2.893±0.010 ?, c=4.720±0.010 ?, c/a=1.632. For 20 at% Ge alloy, the activation energy of hep phase transition and supersaturated solution desolvation are 93 kJ/mol and 102 kJ/mol respectively. The nature and transition mechanism of the metastable phases are discussed.

EXACT SOLUTION OF A DILUTE DOUBLE BOND POTTS MODEL ON THE DECORATED SQUARE LATTICE

YANG ZHAN-RU, F. Y. WU
Acta Physica Sinica. 1985, 34 (4): 0484 doi: 10.7498/aps.34.484
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The critical behavior of a dilute double bond Potts model on the decorated square lattice is investigated. The exact equations of critical surface and phase diagrams are obtained in some special cases. In particular, our results exhibited a distinctive low-temperature phase at q≤3 on two-dimension lattice for the dilute antiferromagnet Potts model, as expected.

THEORY OF N-COMPONENT DISORDER MATERIALS WITH SHORT-RANGE ORDER

FU ZHUO-WU
Acta Physica Sinica. 1985, 34 (4): 0493 doi: 10.7498/aps.34.493
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A theory for studying the properties of N-component disorder materials is developed. It takes into account the short-range correlation effect of nearest-neighbor atoms and includes various disorder arrangements of atoms from segregation to forming N-component compound within the same framework. The method to calculate the density of electronic states of disorder materials using extended Cluster-Bethe-Lattice Green function with a tight-binding Hamiltonian is present in detail. As an application, we calculated the densities of states of ternary disorder alloys AxByCz(x + y + z) =1 under various concentrations and different correlation parameters. The results show strikingly the effects of correlation among the atoms and of disorder on the densities of states.

BIFURCATION AND CHAOS IN FORCED VIBRATION SYSTEMS CONTAINING A SQUARE NONLINEAR TERM

NI WAN-SUN, WEI RONG-JUE
Acta Physica Sinica. 1985, 34 (4): 0503 doi: 10.7498/aps.34.503
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The phenomena of bifurcation and chaos in forced vibration systems containing a square nonlinear term x+kx+ω02x-ax2 =μcosωt have been investigated by using a 2-D iterated map and by integrating the differential equation. The critical values of control parameter μ are inversely proportional to a.

VARIATIONS OF INDUCED MAGNETIC ANISOTROPY,MAGNETOSTRICTION AND STRAIN IN A METALLIC GLASS WITH ANNEALING UNDER FIELD AND TENSION

CHEN DU-XING
Acta Physica Sinica. 1985, 34 (4): 0512 doi: 10.7498/aps.34.512
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Based on simultaneous measurements of magnetic anisotropy, magnetostriction, and strain in the same ribbon specimen of metallic glass Co65.2Fe4.2Ni3Nb1Al2Si9.8B14.8 after various anneals under a transverse field and a tension, an experimental comparison among the variations of these parameters has been made. The behaviours of strain-induced anisotropy and transient creep exhibits some sort of similarity, but there is not a corresponding or a causality relation between them. The variations of magnetization-induced anisotropy Kum, straininduced anisotropy Kus saturation magnetostriction constant λs, and annealing strain with isochronal anneals show that they behave different kinetics, so further separate studies seem to be needed.

ULTRASONIC ATTENUATION AND INTERNAL FRICTION DURING FERROELASTIC TRANSFORMATION OF Gd2(MoO4)3 CRYSTAL

WANG YA-GU, WANG YE-NING
Acta Physica Sinica. 1985, 34 (4): 0520 doi: 10.7498/aps.34.520
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The critical attenuation (as) of longitudinal ultrasonic propagation in the vicinity of the f erroelastic-f erroelectrie transformation of GMO has been measured at frequencies (f) 31, 50, 72 and 93 MHz. The proportional relation between as and f2 is established satisfactorily in so far as the shear type phase transition is concerned. In addition, the critical exponents for the attenuation is determined: ρ=1.52 for T-Tc>0.05 K and the crossover behavior is observed.Eesults are also reported on a internal friction investigation (at f=1 Hz, 150kHz) of the ferroelastic transition of GMO, which is suggested to be caused by the moving interphase boundary. The critical stress to move the boundary is determined and it is then confirmed that the mechanism of the ultrasonic attenuation of longitudinal wave in the 2-4°direction is just contributed by the fluctuation damping.

NONEQUILIBRIUM IONIZATION PROBLEM ANALYZED BY USING MULTIPLE-TIME-SCALE PERTURBATION THEORY

CHANG TIE-QIANG
Acta Physica Sinica. 1985, 34 (4): 0528 doi: 10.7498/aps.34.528
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This paper analyzes nonequilibrium ionization problem by using multiple-time-scale perpurbation theory. The processes which are responsible for electron's average occupation probabilities Pn generally have much different time scales. In this paper the transitions between two neighbouring bound energy levels are considered as fast, the others, including the ionization processes, as slow. It is especially suitable for lower levels of high Z elements. The theory presented here gives analytic expressions for Pn as functions of ne, the number of free electrons. As a result, instead of solving equitions of dPn/dt we just need solving the differential equation for ne. So the problem is much simplified with avoiding the strong stiff which exists in equations dPn/dt. When radiation field reaches the Planck distribution, the Pn obtained here can naturally change into the Fermi-Dirac distribution.
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