Semi-insulating electrical properties of undoped inp after heat treatment in a phosphorus atmosphere

Nominally undoped InP wafers have been annealed in a phosphorus atmosphere under a pressure of about 5 bar at temperatures of 900 °C for about 80 h. It was found that the electrical properties of the samples changed considerably after this treatment. A room temperature resistivity of up to 2×10⁷cm (semi-insulating behaviour) was obtained in the bulk of the samples. The resistivity finally obtained depends on the starting carrier concentration of the untreated samples. The Hall coefficient and Hall mobility have been measured up to 600 °C. The results can be interpreted in terms of a deep electronic level (E _A=0.63 ... 0.65 eV below the conduction band). The Hall coefficient was always found to be negative resulting in a Hall mobility of 1.4 to 4.9×10³ cm²/Vs. The highest resistivity in nominally undoped bulk InP so far reported in the literature [1] was =3.6 × 10⁵cm. Therefore, this paper demonstrates for the first time that a really semi-insulating behaviour of >10⁷ cm can be achieved for bulk InP with the purity of nominally undoped material (10¹⁵ to 10¹⁶cm^–3).     

A Study on Hall Voltage and Electrical Resistivity of Doped Conducting Polyaniline

We report the electrical resistivity of HCl doped polyaniline in the temperature range 77 T 300 K. A maximum is obtained in the conductivity versus concentration of HCl curve at 3(N) HCl. The resistivity of the sample has been observed to show a decreasing trend with increase in temperature. The resistivity obeys the Mott variable range hopping theory. The Mott characteristic temperature (T _Mott) is very low in this sample compared to other studies. The Hall voltages have been found to be negative. The Hall coefficient, carrier concentration, and density of states have been determined from Hall measurement. From the conductivity versus temperature plot, different physical quantities such as localisation length and molecular vibrational frequency have been determined.     

The hall coefficient of YBa2Cu3O7-x thin films with (100) orientation

The Hall coefficientR _H and the resistivity of an (100) orientated YBa₂Cu₃O_7-x thin film was measured. A very smallR _H was obtained. The resulting carrier density is very different from the widely accepted value of the order of 10²¹ cm^–3 for the bulk sample. The result is explained with the influence of grain boundaries and the anisotropy of the thin films.     

Spatially-resolved characterization of HTSC-films near T c by laser raster microscopy with thermal excitation

A method (laser raster microscopy with thermal excitation, LRMTE) for characterizing high-T _c thin-film superconductors (HTSC) with microscopic resolution is described. By means of spatially resolved laser excitation and subsequent monitoring of the time dependence of the film resistivity at a base temperature near the transition temperature T _c, spatial variations of the transition temperature (T _c), of the temperature coefficient of the resistivity (dQ/dT), of the heat conductivity and heat capacity of the film and of the heat conductivity between film and substrate can be detected with high spatial resolution (15 m have been achieved so far).     

Dc electrical conductivity of Ge2S3Agx glasses at high hydrostatic pressure

The paper deals with the influence of hydrostatic pressure on d.c. electrical conductivity in Ge₂S₃Ag _x glasses forx10%. The initial material exhibits high resistivity and the presence of Ag impurity yields strong increase in electrical conductivity. The experimental results suggest that there is a non-linear decrease of electrical resistivity at pressure ranging from 0·1 to 10³ MPa. The pressure coefficient of resistivity is a function ofx. All measurements were performed on bulk samples using graphite contacts. The experimental results are interpreted by means of ionic conductivity.     

Ferromagnetic resonance in a gallium substitued garnet film

The ferromagnetic resonance at X, K and Q-band has been studied on LPE₁₁₁ films of composition Y₃Fe_4.2Ga_0.8O₁₂. From the in-plane measurement and measurement in a 11¯2 plane theg-factor,g=2-02 (K, Q),g=2·05 (X band), the total uniaxial anisotropy fieldB _A (80 K)=750 G (75 mT),B _A (300 K)=250 G (25 mT) and the cubic field 2K ₁/M have been dstermined. Besides of the main resonance with the linewidth B =15 G (1·5 mT), B =50 G (5 mT), B _min=10·5 G (1·05 mT) a linear spin-wave spectrum and some high-field modes were observed. A new approximate method of crystal orientation in the plane of the film has been used based on the analysis of the in-plane dependence of the resonance field.The authors wish to express their thanks to Dr. S.Krupika for helpful discussions.     

The low energy scattering for slowly decreasing potentials

For the radial Schrödinger equation with a potentialq(x) decreasing at infinity asq ₀ q ^–, (0, 2), the low energy asymptotics of spectral and scattering data is found. In particular, it is shown that forq ₀>0 the spectral function vanishes exponentially as the energyk ² tends to zero. On the contrary, there is always a zero-energy resonance forq ₀<0. These results determine the local asymptotics of solutions of the time-dependent Schrödinger equation for large timest. Specifically, for positive potentials its solutions decay as exp(–₀ t ^(2–)/(2+), ₀>0,t. In the case (1, 2) it is shown that for ±q ₀>0 the phase shift tends to ± ask0 and its asymptotics is evaluated.     

Temperature- and magnetic field dependence of the Hall effect in the heavy fermion system CeCu6

The temperature dependence of the Hall coefficient and the magnetic field dependence of the Hall resistivity of CeCu₆ have been determined in the temperature range 80 mK<T<10 K and in magnetic fields up to 10T. The Hall coefficientR _H shows a very strong temperature dependence with two extrema and a change of sign, and the Hall resistivity _xy has a strong field dependence with up to two changes of sign. The observed behavior can partially be explained by the field- and temperature dependence of the skew scattering contribution to the Hall coefficient.     

Magnetic susceptibility and electrical conductivity of the highest chromium germanide

Results are given of measurements over the temperature range 80–1000 ° K of the magnetic susceptibility () and the electrical resistivity () of the highest chromium germanide Cr₁₁Ge₁₉. A ferromagnetic spin ordering is indicated at T < 86 ° K. From the (T) dependence and the values of the resistivity, thermo-emf and Hall constant, it is concluded that the compound studied is a semimetal with p-type conductivity.     

Properties of RF sputtered ZnxCd1−xS thin films

Zn _x Cd_1–x S thin films (0x0.20) were prepared using rf sputtering in argon atmosphere and characterized using X-ray diffraction, optical transmission, electrical resistivity and photoconductive decay measurements. The films were found to possess hexagonal structure. The crystallite size and degree of preferential orientation were found to decrease with the increase ofx and to improve upon annealing in vacuum at 250 °C. The transmission edge shifted towards shorter wavelengths with the increase ofx in agreement with the expected shift in the energy band gap. The films were found to exhibit room temperature resistivity in the range 100–1000 cm. The obtained values of long wavelength transmission (70–80%) and minority carrier diffusion length (30 m) are high enough for the application of these films in the field of solar cells.     

Giant Hall effect in (GaAs)Fe granular films

A series of (GaAs)_1 − xFe_x (x: volume fraction) films with Fe granules embedded in GaAs matrix were prepared by magnetron sputtering. Hall Effect of the films was characterized. The largest saturated Hall resistivity of was observed in (GaAs)₃₀Fe₇₀ film at room temperature, which is over 2 orders larger than that of pure Fe, about 1 order larger than that of (NiFe)–(Al₂O₃) and (NiCo)–(SiO₂) granular films prepared under the same preparation conditions, and 150% larger than that of Ge₃₀Fe₇₀.     

Room temperature diluted magnetic semiconductor synthesized by dual beam laser deposition

Diluted magnetic semiconductor Co-doped ZnO film has been synthesized by a dual beam pulsed laser deposition method. The magnetic, electrical, and optical properties of the Zn_0.985Co_0.015O_0.67 film are studied in this paper. The film shows ferromagnetic behavior with a coercivity of about 300 Oe at room temperature, and semiconductor behavior with carrier concentration of 2.2×10¹⁸ cm^-3, and a resistivity of 102 mcm. Structural investigations indicated that the film has similar lattice constants to that of ZnO. It is shown that the film exhibits excellent optical properties with a band gap energy of 3.31 eV, which is close to that of ZnO. The origins of the magnetism are also discussed. PACS 81.15.Fg; 75.50 Pp; 61.72.Vv     

Surface and bulk electrical properties of the hematite phase Fe2O3

Electrical properties of Fe₂O₃ were studied by using several electrical methods such as electrical conductivity, thermopower (Seebeck effect) and work function. The studies were performed at elevated temperatures (1053–1153 K) and under controlled oxygen activity (10²10⁵ Pa). Samples of different thickness varying between 10³ nm and 1 mm were taken for the measurements of both electrical conductivity and thermopower. It has been found that the exponent of the po₂ dependence resulting from the work function measurements (1/n ) is about 1/2. Both thermopower and electrical conductivity data are well consistent with work function data for the thin film (1000 nm) of Fe₂O₃. The charge transport in Fe₂O₃ has been interpreted in terms of small polaron mechanism. Analysis of measured electrical parameters, regarding the thickness of studied specimens, indicates that the near-surface layer of Fe₂O₃ exhibits much higher deviation from stoichiometry than the bulk phase and resulting strong interaction between charge carriers. This effect has been interpreted in terms of segregation of intrinsic lattice defects to the surface, and presumably also to grain boundaries, of Fe₂O₃.     

Space-charge capacitance in thin semiconductor monocrystalline films

The paper describes the solution for the space-charge capacitance in thin semiconductor films under general boundary conditions. The influence of both surfaces and film thickness on this capacitance is discussed in more detail and it is shown that cases exist in which the space-charge capacitance depends on the properties of one surface or on the film thickness only.Notation E _s2 dimensionless surface field intensity - F ₁, F₂, F₃ space-charge functions - k Boltzmann's constant - n bulk electron density - p _b bulk hole density - q electron charge - T absolute temperature - _o permittivity of free space - _s relative permittivity of semiconductor - dimensionless thicknessd/L _D - dimensionless coordinate perpendicular to the surfacez/L _D - dimensionless potential (multiples ofkT/q).     

Stochastic modeling of a billiard in a gravitational field: Power law behavior of Lyapunov exponents

We consider the motion of a point particle (billiard) in a uniform gravitational field constrained to move in a symmetric wedge-shaped region. The billiard is reflected at the wedge boundary. The phase space of the system naturally divides itself into two regions in which the tangent maps are respectively parabolic and hyperbolic. It is known that the system is integrable for two values of the wedge half-angle ₁ and ₂ and chaotic for ₁<< ₂. We study the system at three levels of approximation: first, where the deterministic dynamics is replaced by a random evolution; second, where, in addition, the tangent map in each region is, replaced by its average; and third, where the tangent map is replaced by a single global average. We show that at all three levels the Lyapunov exponent exhibits power law behavior near ₁ and ₂ with exponents 1/2 and 1, respectively. We indicate the origin of the exponent 1, which has not been observed in unaccelerated billiards.     

Hall-Koeffizient und spezifischer elektrischer Widerstand flüssiger Metallegierungen

The Hall coefficient and the electrical resistivity of liquid alloys has been measured with an ac current — ac magnetic field method. The experimental Hall coefficients are in agreement with the values given by the free-electron model. If for alloys of the Ag-In type the Fermi wave numbers 2k _F deduced from the experimental Hall coefficients agree with the wave numbersK _p of the first maximum of the partial or total correlation functionsa _AB ora(K), negative temperature coefficients and a maximum of the electrical resistivity are observed for the corresponding concentrations. For alloys of the In-Sn type,K _p is allways smaller than 2k _F, and these alloys do not show any anomalies of the electrical resistivity. The behavior of the electrical resistivity can be explained using the formula for liquid alloys due toFaber andZiman.     

Ideals and solutions of nonlinear field equations

Families of horizontal ideals of contact manifolds of finite order are studied. Each horizontal ideal is shown to admit ann-dimensional module of Cauchy characteristic vectors that is also a module of annihilators (in the sense of Cartan) of the contact ideal. Since horizontal ideals are generated by 1-forms, any completely integrable horizontal ideal in the family leads to a foliation of the contact manifold by submanifolds of dimensionn on which the horizontal ideal vanishes. Explicit conditions are obtained under which an open subset of a leaf of this foliation is the graph of a solution map of the fundamental ideal that characterizes a given system of partial differential equations of finite order withn independent variables. The solution maps are obtained by sequential integration of systems of autonomous ordinary differential equations that are determined by the Cauchy characteristic vector fields for the problem. We show that every smooth solution map can be obtained in this manner. Let {_Vi¦1in} be a basis for the module of Cauchy characteristic vector fields that are in Jacobi normal form. If a subsidiary balance ideal admits each of then vector fieldsV _i as a smooth isovector field, then certain leaves of the foliation generated by the corresponding closed horizontal ideal are shown to be graphs of solution maps of the fundamental ideal. A subclass of these constructions agree with those of the Cartan-Kähler theorem. Conditions are also obtained under which every leaf of the foliation is the graph of a solution map. Solving a given system ofr partial differential equations withn independent variables on a first-order contact manifold is shown to be equivalent to the problem of constructing a complete system of independent first integrals. Properties of systems of first integrals are analyzed by studying the collection ISO[A _ij ] of all isovectors of the horizontal ideal. We show that ISO[A _ij ] admits the direct sum decomposition ^*[A _ij ]W[A _ij ] as a vector space, where ^*[A _ij ] is the module of Cauchy characteristics of the horizontal ideal. ISO[A _ij ] also forms a Lie algebra under the standard Lie product,^*[A _ij ] andW[A _ij ] are Lie subalgebras of ISO[A _ij ], and [A _ij ] is an ideal. A change of coordinates that resolves (straightens out) the canonical basis for ^*[A _ij ] is constructed. This change of coordinates is used to reduce the problem of solving the given system of PDE to the problem of root extraction of a system ofr functions ofn variables, and to establish the existence of solutions to a second-order system of overdetermined PDE that generate the subspaceW[A _ij ]. Similar results are obtained for second-order contact manifolds. Extended canonical transformations are studied. They are shown to provide algorithms for calculating large classes of closed horizontal ideals and a partial analog of classical Hamilton-Jacobi theory.     

Hall effect in the ternary ordered alloys Ni3(Mn,Fe) and Ni3(Mn,Co) 1. Disordered solution solutions

The normal and anomalous Hall constants R₀ and R_s, respectively, and the resistivity have been measured for the quasibinary alloys Ni₃Mn-Ni₃Fe and Ni₃Mn-Ni₃Co. The results imply that in ternary alloys of Ni₃Mn containing slight Fe and Co impurities the hole regions of the Fermi surface make an important contribution to R₀ and that the primary scattering mechanism for the carriers corresponding to the anomalous Hall current in the alloys with Fe at room temperature is phonon scattering. It is concluded that the Fermi surface of the Ni₃Mn-Ni₃Fe alloys is closed.Translated from Izvestiya VUZ. Fizika, No. 3, pp. 21–29, March, 1970.     

Ground state energies of doubly even nuclei

Ground state energies of doubly even nuclei which are assumed to be composed of rigid and structureless alpha-particles are calculated. The alpha-particles are assumed to be interacting through a potential composed of a hard core followed by a square well potential in one set of calculations and a Gaussian potential in another set of calculations. Our calculations support the existence of the hard core in the alpha-alpha potential, and suggest the existence of the alphaclustering in doubly even light nuclei.From the graph betweenE ₀/N and we find thatE ₀/N is minimum at =2·57×10³⁷ particles cm^–3. This means that in the surface region an assembly of alpha-particles with = = 2·57×10³⁷ particles cm^–3 is the most stable one.We are greatly indebted to Professors R. Tamagaki, M. Harada and F. Iwamote for making very useful suggestions and for making a few points clear to us. Thanks are also due to Professors P. C. Sood, S. Duttamazumdar and M. K. Pal for many helpful discussinos, and to the Indian National Science Academy, New Delhi for giving financial assistance. Thanks are also due to Shri A. N. Phukan for drawing the graphs.     

Microwave heating of electrons of a dense plasma column at frequencies higher than electron cyclotron frequency

In this experimental study the absorption of plasma waves, excited in a dense plasma column, was investigated and the localization of the regions of efficient heating of electrons were determined in a broad range of parameters: 1>_ce/>0·1, 0·3<n/n _UH <25, 10^–5<v/< <10^–3. The heating of electrons near the second electron cyclotron harmonic was investigated in greater detail.We are grateful to the members of the Staff of the Institute of Plasma Physics Drs. P.unka, R.Klí'ma, V.Kopecký, J.Musil for discussion of the results. We also thank Drs. J.Musil, F.áek for the help and advice in the early stages of experimental work during construction of different diagnostic devices. Our thanks are due to the director of the Institute Dr. J.Váa for encouraging support of this experimental program.