Thermoelectric power of the n-InSb in a transverse quantizing magnetic field at a large temperature gradient

The thermoelectric power of the n-type indium antimonide was studied in the transverse magnetic field (0–80 kOe) at T _aV =160 K and different temperature gradients. It was found that the electron component of the thermoelectric power at a small temperature gradient is consistent with the theory that takes into account the electron spin, whereas, for a large temperature gradient, the value determined by the variation of the Benedicks thermoelectric power in the magnetic field is added to this component.     

On the temperature and field dependences of the effective surface mobility in MIS structures

A physical model establishing a relation between the surface density of the free electronic charge in an inversion layer and the surface density of stationary (localized) electrons trapped in surface states at a semiconductor-insulator interface is constructed. It is established that at moderately low temperatures this relation is close to a direct proportionality. The presence of surface states, which localize some of the surface electronic charge, is manifested as a decrease in the effective electron mobility in the channel of a MIS transistor. The well-known decrease of the surface mobility with increasing transverse electric field is attributed to field-induced variations in the position of the percolation level that separates bound electronic states from free states. Fiz. Tekh. Poluprovodn. 32, 748–751 (June 1998)     

Relaxation of photoinduced metastable states in a-Si:H films deposited at high temperatures

The results of an experimental study of dark-conductivity kinetics in a-Si:H after short-term and long-term illumination, are presented. The films were deposited at temperatures in the range T _s=300–390 °C. Data on relaxation of the photoinduced metastable states were found to correlate with the Fermi-level position. Fiz. Tekh. Poluprovodn. 32, 1269–1271 (October 1998)     

Drain noise in MOSFETs at zero drain bias as a function of temperature

The noise in MOSFETs at zero drain bias is found to be somewhat larger than the thermal noise of the output conductance g_do at that bias. The effect is most pronounced at 300°K and has practically disappeared at 77°K. The effect is attributed to the large transverse field at the surface of the channel; the temperature dependence of the effect is as yet unexplained.     

A study of flicker noise in MOS transistors operated at room and liquid helium temperatures

A study of flicker noise in MOS transistors operated in the linear and non linear regions at room and liquid helium temperatures is proposed. Besides, a theoretical analysis of the drain current noise characteristics is developed in the framework of the mobility fluctuation model as well as of the carrier number fluctuation model. It is shown experimentally that a close correlation between the drain current spectral density and the transconductance squared dependencies with gate voltage (or drain current) and drain voltage is observed in our devices both at room and liquid helium temperatures. Therefore, it is concluded that the carrier number fluctuation model is not only applicable to MOS devices operated at room temperature but also at liquid helium temperature in ohmic and non ohmic regimes. In addition, peculiarities of the drain current noise related to the appearance of a kink effect at liquid helium temperature in the saturation current characteristics are also discussed.     

8C9--Observation of cooperative effects and determination of the electron and ion temperatures in a plasma from the scattering of a ruby laser beam

Observations have been made on the forward scattering of aQ-spoiled ruby laser beam from a hydrogen plasma which show clearly both the central ion peak and the satellites due to cooperative interaction between the ions and electrons. In a separate experiment on a large θ-pinch producing a high temperature deuterium plasma, the ion peak has been resolved and values obtained for both the electron and ion temperatures in the plasma. Preliminary values of the ion temperature are consistent with a thermonuclear origin for the neutron emission observed.     

The staebler-wronski effect and temperature dependences of photoconductivity in p-type a-Si:H

Temperature dependences of the photoconductivity of boron doped a-Si:H films both prior to and after prolonged illumination were studied. It was found that the photoconductivity of films under study in the temperature range 200–300 K (intermediate temperatures) is independent of the doping level and the concentration of deep recombination centers (dangling bonds). A model of recombination is used to explain the experimental results; according to this model, the occupancy function of neutral dangling bonds in p-type a-Si:H (and, consequently, also the photoconductivity) is determined by the parameters of the states of the valence band tail and is independent of the doping level and of the total concentration of dangling bonds.     

Effect of temperature on the thermodynamic density of states in a quantizing magnetic field

The dependence of the density of energy states (N _s ) on temperature in quantizing magnetic fields is studied. It is shown that, as temperature is increased, the Landau levels are blurred as a result of thermal widening and the quantities N _s are transformed into the density of states as in the absence of a magnetic field. The temperature dependence of the distribution of the density of energy states in high magnetic fields for semiconductors is considered using a mathematical model. It is shown that the continuous spectrum of density of states measured at liquid-nitrogen temperature is transformed into discrete Landau levels at lower temperatures. Mathematical simulation of the processes with the use of experimental data for the continuous spectrum of the density of states makes it possible to calculate the discrete Landau levels. Experimental results obtained for PbS are analyzed using the suggested model. The density of states at low temperatures is calculated from data on high-temperature N _s .     

The temperature dependence of the thermopower of the InSb Corbino disc in a quantizing magnetic field

Thermopower of the Corbino disc made of InSb with n ₇₇ = 2 × 10¹⁴ cm^?3 in a transverse magnetic field as high as 30 kOe at temperatures of 60, 67, and 80 K is studied. It is established that the diffusion fraction of thermopower in a quantizing magnetic field rises according to the power law H ^2.2 at all mentioned temperatures. By the magnitude of saturation thermopower α_xx(∞) in a high field, the scattering mechanism of charge carriers is determined. It is established that in a temperature region of 60–80 K, the electrons are scattered by acoustic phonons.     

Resonant response of a FET to an AC signal: influence of magnetic field, device length, and temperature

A theoretical investigation is made of the response of a field-effect transistor (FET) to an incoming electromagnetic radiation in the presence of a perpendicular, weak magnetic field. The influence of an external friction due to electron scattering by impurities and/or phonons, and of the internal friction due to electron-electron scattering, is taken into account. The treatment is valid for a nondegenerate electron gas in which the mean-free path for electron-electron scattering /spl lambda//sub ee/ is much smaller than the device length L and than the mean-free path due to collisions with impurities and/or phonons /spl lambda//sub coll/. These requirements, written as /spl lambda//sub ee//spl Lt/L/spl Lt//spl lambda//sub coll/, are fulfilled for magnetic fields sufficiently weak that Landau quantization is absent and the electron motion is described within the framework of hydrodynamics. It is demonstrated that a high-electron mobility transistor (HEMT), with a short (long) channel, yields a resonant (nonresonant) response to an ac signal induced by the incoming electromagnetic radiation at the plasma oscillation frequencies of the two-dimensional electrons in the device. Keeping the device length and temperature at control, an applied magnetic field can be tuned to achieve the desired effect on the response of the device. It is observed that the lower the temperature, i.e., the higher the mobility, the higher the responsivity of the device. Such response makes the FET a promising device for new types of sources, detectors, mixers, and multipliers. The HEMT-based devices should, in principle, operate at much higher frequencies than the conventional transit time-limited devices, since the plasma waves propagate much faster than electrons.     

Magnetoresistance of layered semiconductors upon the scattering of charge carriers at impurity ions in a parallel magnetic field

The magnetoresistance of a semiconductor superlattice in a magnetic field directed perpendicular to its axis for the case of the scattering of charge carriers at impurity ions is calculated. It is demonstrated that the sign of the transverse magnetoresistance strongly depends on the band filling factor, the value of the magnetic field, and the ratios between the screening radius, cyclotron orbital radius, and superlattice constant. In a parallel magnetic field, the transverse magnetoresistance of a two-dimensional electron gas is positive in a strong field and negative in a weak field. The transverse magnetoresistance of a quasi-two-dimensional electron gas changes its sign due to the presence of a negative effective mass region in the miniband.     

Circular polarization of the magnetic field in the WG modes ofresonance of a dielectric disc at microwave frequencies

The circular polarization of the magnetic field of the whispering-gallery (WG) modes of resonance of a dielectric disk resonator was tested in the evanescent-field region outside the dielectric material. Microwaves in the frequency range from 18 to 26.5 GHz (K-band) and the techniques of electron spin response (ESR) were used. The distribution of the electromagnetic fields was obtained with a finite element method, and it was found to be in agreement with the experimental results     

A quantitative evaluation of the magnetic field generated by a CA3 pyramidal cell at EPSP and action potential stages

We evaluate quantitatively which behavioral stage dominantly generates magnetic field adjacent to a CA3 pyramidal cell by using a compartmental model with dendrites and an axon. Generally speaking, there are four stages in the potential behavior, i.e., excitatory and inhibitory postsynaptic potential, firing action potential, bursting action potential, if any, and after hyperpolarization potential stages. Calculated magnetic field also consists of corresponding four stages. We find, first, the dominant origin of the peaks of the magnetic field is counter propagating pulses at the firing and bursting stage at basal and apical dendrites. Second, the amplitude of the magnetic field changes to a great extent by the cancellation timing of the apical- and basal-originating fields depending on the calcium ionic channel spikes. Third, the field generated by the current flowing through the axon is significant enough when the temporal resolution of the measurement system becomes high. The results predict that the magnetic-field waveform measured in physiological experiments represents the dendritic configurations, channel density distributions, and bursting characteristics. These facts enable new investigations of neuronal activities in more detail through the observation of the magnetic-field waveform.     

Influence of a strong longitudinal static electric field on free carrier faraday effect in an n-type InSb at room temperature at submillimeter wave frequencies

The expression for free carrier Faraday rotation θ and for ellipticity Δ, as the function of the applied parallel static electric field \(\mathop {E_0 }\limits_ \to \) and static magnetic field \(\mathop {B_0 }\limits_ \to \) for a given value of wave angular frequency and electron concentration N₀, are obtained and theoretically analyzed with the aid of one-dimensional linearized wave theory and Kane's non-parabolic isotropic dispersion law. It is shown that the maximum Faraday rotation occurs near the cyclotron resonance condition, which can be expressed as \(\chi \omega = \omega _{ce} \) , where \(\chi = 1{1 \mathord{\left/ {\vphantom {1 {\sqrt {1 - ({{v_0 } \mathord{\left/ {\vphantom {{v_0 } {v_c }}} \right. \kern-0em} {v_c }})^2 } }}} \right. \kern-0em} {\sqrt {1 - ({{v_0 } \mathord{\left/ {\vphantom {{v_0 } {v_c }}} \right. \kern-0em} {v_c }})^2 } }}\) , \(v_c = \sqrt {{{\varepsilon _g } \mathord{\left/ {\vphantom {{\varepsilon _g } {2m}}} \right. \kern-0em} {2m}}} *\) , and \(\omega _{ce} = ({{eB_0 } \mathord{\left/ {\vphantom {{eB_0 } {m*}}} \right. \kern-0em} {m*}})\) . Here m^* and e denote the effective mass and charge of electron, respectively. ?_g is the forbidden bandgap of semiconductor. v₀ is the carrier drift velocity, which is a non-linear function of E₀ in high field condition. A possibility of a simple way of determining the non-linear “v₀ vs E₀” characteristics of semiconductors by the measurement of Faraday rotation is also discussed.     

Electric field and temperature dependence of the hole mobility in a bis-fluorene cored dendrimer

Time-of-flight mobility measurements on a first generation, bis(fluorene)-cored dendrimer are reported. A charge generation layer was used enabling measurements to be performed on spin-coated films, comparable to those used in devices such as organic light-emitting diodes. The results are compared with spin-coated polyfluorene films. The temperature and electric field dependence of the mobility of the dendrimer was studied and found to be in excellent agreement with the Gaussian disorder model, with an energetic disorder parameter, σ, of 74 meV and a positional disorder parameter, Σ, of 2.6.     

Holes localized in nanostructures in an external magnetic field: g-factor and mixing of states

Semiconductors - The energy spectrum and wave functions of holes in the valence band in semiconductor nanosystems, including quantum wells, quantum wires, and quantum dots, in an external magnetic...     

The short and long term properties of a liquid crystalline polymer at elevated temperatures: Characterization and modeling

Tensile and short term (24 h) creep tests were performed on Xydar G930, a liquid crystalline polymer (LCP) with 30 wt.% glass filler, at temperatures and stress levels ranging from room temperature to 175°C and 0.3 fraction ultimate tensile strength (UTS) to 0.8 fraction UTS, respectively. Temperature was found to have an affect on the short term tensile properties. The resulting strain vs time creep curves showed the expected dependence of creep strain on temperature and stress level. Creep compliance curves were derived from the creep curves and showed distinctively nonlinear viscoelastic behavior at all stress levels and temperatures. Creep compliance was found to follow a power law in time. The power law was used to model the stress dependence of creep and the Arrhenius equation was employed to model the temperature dependence up to 120°C. A significant reduction in creep resistance was observed at 175°C. Time-temperature-stress-superposition was used to show that the material followed power law behavior up to 1000 h.     

A two-beam interferometer for dispersive reflection spectroscopy of solids in the far infrared at temperatures between 4 and 300K

A Fourier spectrometer has been developed for determining the optical constants of highly absorbing solids in the far infrared at temperatures down to 4.2K from measurements of their amplitude and phase reflection spectra. The spectrometer has been constructed almost entirely from commercially available components, and its performance is illustrated with measurements of the optical constants of NaCl at 6K.