Change In Electron Concentration Research Articles

On Correlations between Extended Defects Formation and Electron Concentration Changes Caused by Annealing of GaAs:Te

Extended type defects in heavily doped GaAs:Te (n 1 x 10 19 cm-3 ) after annealing at 700°C and 1150°C were studied by transmission electron microscopy, by high resolution technique and energy-dispersive X-ray analysis. Assuming, according to the literature that these defects are enriched in impurity atoms it is suggested that this solely is not sufficient to explain changes of electrical properties during annealing. Estimated amount of atoms involved in faulted dislocation loops seems to be too small, energy-dispersive X-ray microanalysis of precipitates did not show large differences in composition with the matrix. PACS numbers: 61.72.Nn, 61.72.Vv, 72.80.Ey

Reflection of finite-width edge channels.

We have studied experimentally the edge channels in an externally controlled inhomogeneous two-dimensional electron gas (2DEG) under quantum Hall conditions. The 2DEG is inhomogeneous in the sense that the electron concentration changes linearly across the width of the sample. In an impurity-free (or ideal) electron gas, these edge channels are wide compressible strips alternated with incompressible strips. However, when the presence of charged impurities (or disorder) is considered, localized compressible strips appear on both sides of the incompressible strips. We show that the width of the incompressible plus the localized compressible strips can be determined from resistance measurements. We further demonstrate that the macroscopically wide compressible strips in an inhomogeneous, disordered 2DEG act as if they are edge channels; they can be reflected at an interior potential and the values of the quantized resistances can be determined from the Landauer-B\"uttiker model. \textcopyright{} 1996 The American Physical Society.

Shallow donor impact ionization in n-InP and n-GaAs: influence of doping and compensation

The donor impact-ionization coefficient is calculated using the Boltzmann transport equation. It is shown that impact-ionizing collisions of free electrons with shallow donors induce strong cooling of the hot-electron distribution function. From the obtained results it is found that in the analysis of impurity breakdown or related processes the approach based on phenomenological equations is valid only for small changes of electron concentration. Corresponding graphs for the impact-ionization coefficient are presented for n-InP and n-GaAs.

Heavy doping of silicon into Ga 0.5In 0.5P at low temperatures in organometallic vapor phase epitaxy

High concentration doping of silicon into Ga 0.5In 0.5P layers using disilane as the doping precursor in organometallic vapor phase epitaxy is performed at growth temperatures between 620 and 700°C. The electron concentration changes linearly with disilane flow rate, reaching a maximum at 1 × 10 19 cm −3 and staturates thereafter, while the silicon concentration keeps increasing. Heavy doping raises the photoluminescence (PL) peak energy to 1.95 eV. The increment is 120 meV at lower growth temperatures on (100) substrates, but it remains 40 meV on (511)A. The former is due to the combined effect of electron concentration and atomic disordering, whereas the latter is due to electronic effects only.

Enhanced stability of potassium solutions in tetrahydrofuran containing 15-crown-5

The process of potassium metal dissolution in tetrahydrofuran containing 15-crown-5 and the properties of the solution were studied. The changes in concentration of potassium anions and electrons as a function of time were determined by means of 39 K NMR and ESR spectroscopie. Enhanced stability of the solution with 15-crown-5 relative to that containing 18-crown-6 or 12-crown-4 was revealed

Influence of annealing on the optical properties of indium tin oxide

The effect of annealing on the optical properties of indium tin oxide films prepared by d.c. magnetron sputtering was investigated. The influence of annealing can be described in terms of a change in free electron concentration. With an increase in carrier concentration the absorption edge due to the direct and the indirect transition shifts to the near UV. The intrinsic band gap is found to be 3.53 eV, the intrinsic indirect transition energy is 1.80 eV. The effective electron mass is 0.31 m 0 and 1.0 m 0 for electrons in the conduction and the valence band respectively.

Low-Temperature Growth and Characterization of InP Grown by Gas-Source Molecular-Beam Epitaxy

ABSTRACTLow-temperature (LT) growth of InP by gas-source molecular-beam epitaxy has been studied. Contrary to GaAs, InP grown at low temperature (from 200°C to 410°C) shows ntype, low-resistivity properties. The electron concentration changes dramatically with growth temperature. A model of P antisite defects formed during LT growth was used to explain this experimental result. Ex-situ annealing can increase the resistivity, but only by a factor of about 6. Heavily Be-doped LT InP also shows n-type property. We believe this is the first report of an extremely high concentration of donors formed in LT InP and n-type doping by Be in III–V compounds.

Magnetic order in new silver-based Heusler alloys

Neutron diffraction measurements made on intermetallic compounds in the new Heusler alloy series Pd 2- x Ag x MnIn show a sequence of magnetic structures that relate to the changes in electron concentration produced by altering the proportions of silver to palladium. The implications of the results are discussed and compared with related series.

Effect of pressure and alloying on antiferromagnetism of chromium: Insight from thermal expansion measurements

Change in volume or electron concentration strongly affects the antiferromagnetic properties of Cr through change in the gapped area A M of the Fermi surface. The mechanisms are however quite different, with decrease in volume increasing the kinetic energy associated with magnetic ordering and so reducing A M, without significant change in the nesting of the electron and hole surfaces.

Measurement of Plasma Conductivity Using Faraday Rotation of Submillimeter Waves

This paper examines the application of Faraday rotation to the measurement of electron concentration in combustion MHD plasmas. Details on the design of a working system are given, including the selection of operating wavelength. A theoretical comparison between the Faraday rotation technique and two-path interferometry shows Faraday rotation in its simplest form to be somewhat less sensitive to changes in electron concentration. This deficit can be balanced against greater immunity to vibration and thermal drift. Improved techniques of measuring the rotation angle promise greater sensitivity. A preliminary experiment has verified the technique.

Electron Concentration Changes in High Purity GaAs Grown by Liquid Phase Epitaxy

Electron Concentration Changes in High Purity GaAs Grown by Liquid Phase Epitaxy

Influence of Additives to V2O5 on the Rate of 1‐Butene Oxidation

AbstractThe deviation from stoichiometric composition of V2O5 due to doping with Al3+ and W6+ ions in the range of concentration of 0.001 to 0.01 mol was studied. The change of excess electron concentration caused by doping was small as can be concluded from electrical measurements. The electric microbalance results show a higher deviation from stoichiometry by Al3+ ion doping where the catalyst composition reached V2O4.01 structure compared with V2O4.7 for V2O5 doped with W6+ ions. In general, the nature of the surface as well as the catalyst bulk properties were affected even by small additions of foreign cations. These effects on the oxidative dehydrogenation of 1‐butene were studied in a microflow reactor. An oxidation mechanism was proposed, where the oxygen exchange seems to be rate‐determining while all electronic steps are fast.

Drain conductance of junction gate FET's in the hot electron range

A new model is proposed for the drain conductance of J-FET's in the hot electron range. The model is based on a physical picture revealed through two-dimensional numerical analysis. The two-dimensional analysis shows that the electron concentration changes gradually at the boundary of a depleted region which is defined by a conventional theory. Because of this gradual change, electrons can remain after the pinch-off and contribute to the drain current. Although the high electric field causes the electron velocity to saturate, the drift velocity vector rotates into the x axis (source-to-drain) with the increase in the drain voltage. The increase in the x component V x of the drift velocity gives rise to a small increase in drain current, that is, a finite drain conductance. The proposed model takes into account the above two essential features, gradual change in electron distribution, and the rotation of the velocity vector. This model is constructed in a single formulation which describes the current-voltage characteristics from the linear to the saturated drain-current region. Theoretical calculations agree quite well with the experiment on GaAs Schottky barrier gate FET's.

The Electrical Properties of Thin Films of TiNx and TiCx

Abstract Thin films of metallically conductive titanium mononitride and carbide were prepared by means of electron beam evaporation. The composition of the samples could be changed over appreciable ranges by introducing nitrogen in the system or adding carbon to the pure starting material, respectively. The transport properties of the resulting compounds were studied as a function of nonstoichiometry and defect structure. A plausible explanation for the different behavior of the films compared to corresponding bulk samples is given and a correlation between the change in electron concentration and the electron transfer theory is presented.

Magnetic interactions in intermetallic compounds

The magnetic interactions in intermetallic compounds containing 4 f or 3 d electrons are discussed. The magnetism of rare-earth intermetallic compounds can adequately be described by the RKKY model. An evaluation of the validity of this model is given by means of experimental data presented for the compounds Gd 2Al, Gd 3Al 2, GdAl 2, GdPdIn, and GdCuAl, together with the changes in the magnetic properties observed when Gd is gradually replaced by La, Y (no change in conduction electron concentration) or by Th (increase of the conduction electron concentration). In GdAl 2 it also proved possible to replace Gd by non-magnetic Yb, which decreases the conduction electron concentration. The magnetic properties and the magnetovolume effects of various intermetallic compounds of Fe, Co, and Ni, with the rare earth, Y or Th are discussed in terms of a model involving itinerant 3 d electrons.

Influence of heating of the ionosphere by high-power radio emission on the sporadic E layer

The way in which the sporadic E layer is influenced by heating of the ionospheric electron gas by high-power radio emission is investigated within the framework of the wind-shift theory with allowance for the redistribution of metal ions. The change in electron concentration in the regular E region and the E s layer is estimated for various degrees of electron-gas heating by high-power radio emission. It is shown that owing to heating by the radio-wave field electron concentration falls in the E s layer, while layer thickness increases.

Structural and magnetic properties of Co2Ga2-xTixalloys

An investigation of the structure of alloys from the series Co2Ga2-xTix (0<x<1) which have been quenched from 830 degrees C has been performed using neutron diffraction, X-ray, and density measurements. The alloys have been found to crystallize in the L21 (Heusler) structure, with a small amount of vacancy formation comparable to that observed in binary Co-Ga alloys, and some residual disorder. The onset of ferromagnetism near x=0.5 has been observed from magnetization measurements, and it is suggested that this is the result of a change in electron concentration. Some preliminary resistivity measurements on the paramagnetic alloys show minima in the resistivity versus temperature curves, arising it is thought from the small number of antistructure cobalt atoms present.

A neutron diffraction and magnetization study of Heusler alloys containing Co and Zr, Hf, V or Nb

Neutron diffraction, X-ray diffraction and saturation magnetization measurements have been made on a series of ferromagnetic alloys at the composition Co 2YZ, where Y is a group IVA or VA element and Z is a group IIIB or IVB element. The alloys are mainly ordered in the Heusler L2 1 type chemical structure, but some show the presence of a small amount of additional phase, or some preferential disorder. The magnetic results form two distinct groups in which the moments are confined to the Co sites but their magnitude depends on the electron concentration determined by the Y and Z atoms. Although the magnetic moments and Curie temperatures of the alloys in the same group are similar, their lattice parameters differ according to whether Z is a group IIIB or IVB element. Such behaviour indicates that, as in other alloy series with the Heusler structure, a change in lattice parameter has little effect on the magnetic properties in comparison with the effect of a change in electron concentration.

The Effect of Alloying on the Fermi Surface of Copper. II. Electron-scattering and Neck Cross Sections with Dilute Heterovalent and Transition Metal Solutes

The Fermi surface neck size and the scattering cross sections for the neck and [Formula: see text] belly orbits have been measured in dilute alloys of Zn, Al, Ge, Si, Ni, Co, Fe, Mn, and Cr in Cu. Earlier observations of rigid-band behavior for the neck size in Cu(Zn) and Cu(Al), while essentially substantiated by the present measurements, are now believed to be fortuitous; Cu(Ge) and Cu(Si) do not agree with a rigid-band prediction. The changes (generally reductions) of neck size in the transition metal alloys do not appear to be related directly to changes of electron concentration. The scattering anisotropy is rather small in the heterovalent alloys, the scattering being somewhat greater on the necks, but is large and in the opposite sense in the transition metal alloys. The magnitude and anisotropy of scattering is interpreted in terms of phase shifts associated with the impurities and the wave functions over the Fermi surface. There is evidence for additional scattering anisotropy in alloys exhibiting the Kondo effect.

A spin echo study of the 59Co hyperfine field in GdCo2 and several related series of substitutional compounds

The hyperfine fields at the 59Co nucleus have been observed in GdCo2 (GdY)Co2, (GdDy)Co2 and Gd(CoNi)2 using a spin echo technique. The field strength in the basic compound GdCo2 was found to be 607 kOe. The results can be interpreted in terms of contributions to the hyperfine field arising from the transition metal sublattice and from the rare earth sublattice. The former appears to be proportional to the magnetic moment associated with the transition metal ion while the rare earth contribution is taken to arise predominantly from conduction electron polarization. With yttrium substitution this second term is found to be directly proportional to the gadolinium concentration. In the nickel substituted compounds the hyperfine field due to the rare earth sublattice is observed to decrease. This is believed to be the result of a change in conduction electron concentration.