Y. Schlesinger

Electric-field-effect thermoelectrics

A significantly large thermoelectric “figure of merit” in a bipolar semiconductor is achieved by converting it, by doping, into an essentially monopolar semiconductor. We show here, that for a bipolar semiconductor film, having a thickness smaller than the screening length, there is an alternative to doping to obtain a practically monopolar semiconductor. The electric-field effect (EFE) or the ferroelectric-field effect can be used to quench the concentration of one type of charge carriers. We show that this method is particularly suited for narrow-gap semiconductors and for semimetals, having sufficiently high dielectric permittivity. We also show that this “EFE doping” is free from the drawbacks of conventional doping. Our analysis demonstrates that increased values of the figure of merit are feasible. We present here the theory and the figure-of-merit calculation for typical cases of the bipolar semiconductor thermoelectric film under EFE doping. Numerical results for a film of the PbTe type are presented.

High-temperature PbTe diodes

We describe the preparation of high-temperature PbTe diodes. Satisfactory rectification was observed up to 180-200 K. Two types of diodes, based on a p-PbTe single crystal, were prepared: (1) by In ion-implantation, and (2) by thermodiffusion of In. Measurements were carried-out from ∼10 K to -200 K. The ion-implanted diodes exhibit a satisfactorily low saturation current up to a reverse bias of ∼400 mV, and the thermally diffused junctions up to ∼ 1 V. The junctions are linearly graded. The current-voltage characteristics have been fitted using the Shockley model. Photosensor parameters: zero-bias-resistance × area product, the R 0 C 0 -time constant and the detectivity D* are presented.

Characterization of high-temperature PbTe p-n junctions prepared by thermal diffusion and by ion implantation

Two types of high-quality PbTe p-n junctions, prepared by thermal diffusion of In4Te3 gas [thermally diffused junction (TDJ)] and by ion implantation [implanted junction (IJ)] of indium (In-IJ) and zinc (Zn-IJ), have been characterized. Capacitance-voltage and current-voltage characteristics have been measured over a temperature range from ∼10to∼180K. The saturation current density J0 in both diode types was ∼10−5A∕cm2 at 80K, while at 180K, J0∼10−1A∕cm2 in TDJ and ∼1A∕cm2 in both IJ diodes. At 80K, the reverse current started to increase markedly at a bias of ∼400mV for TDJ and at ∼550mV for IJ. The ideality factor was about 1.5–2 for both diode types at 80K. Both diode types were linearly graded. The height of the junction barrier, the concentration and the concentration gradient of the impurities, and the temperature dependence of the static dielectric constant have been determined. The zero-bias resistance times area product (R0Ae) at 80K is 850Ωcm2 for TDJ, 250Ωcm2 for In-IJ, and ∼80Ωcm2 for Zn-IJ, w...

The edge electric field of a pyroelectric and its applications

Following a change of temperature of a pyroelectric (PE), a depolarizing electric field appears both inside the PE as well as outside its edges, the edge depolarizing electric field (EDEF). The EDEF extends outwards up to a distance of the order of magnitude of the PE width. The mapping and the strength of the EDEF have been here calculated and analyzed for the case of a semi-infinite pyroelectric plate. We propose here the idea of utilizing the EDEF of the pyroelectric solely as the source of an electrical field. This strong EDEF (104–105V∕cm), when penetrating into the surrounding medium, creates a variety of physical effects: inducing electrical current in a semiconductor and affecting its resistance, accelerating charged and neutral particles in vacuum or in a gas, generating electromagnetic waves, modifying optical characteristics by electro-optical and photoelasic effects, generating piezoelectric deformation, and more. We discuss a number of possible applications and devices based on these EDEF ind...

Analysis of the excess resistivity induced by a low magnetic field in YBCO and BSCCO compounds

The results of a (weak) DC magnetic field induced excess resistivity in granular high-temperature superconductors are analyzed. Assuming a random mixture of superconducting and normal regions, the two characteristic excess resistivity peaks are interpreted as originating from two different mechanisms: the higher temperature peak in excess resistivity is attributed to a distribution of the critical temperature in individual grains affected by the applied magnetic field, this results in a quasi-percolative normal current energy dissipation. The lower temperature wide peak is attributed to an interplay between strong pinning due to the spatial inhomogeneity of the condensation energy on one hand and to the onset of proximity effect with decreasing temperature, on the other. The results obtained with various concentrations of Ag admixture and under varying magnetic field are consistent with the predictions of this model.

Quantum-size oscillations of the electric field effect (EFE) in thin Bi films

Abstract The quantum-size state (QSS) of semimetal Bi films has been studied by electric field effect (EFE), namely, the change of the conductance at the electrical charging of the film. The ratio of the electron and hole density of states g n / g p has been measured by EFE . The thickness dependence of this ratio exhibits a characteristic oscillation pattern, which is an unique label of QSS. This method allows a rather precise determination of the film thickness period of the oscillations. The result is in excellent agreement with the value derived from the dispersion law of bulk Bi.

Anomalous quenching of the remanent resistivity in YBCO ceramics

Abstract We report an anomalous reduction of the resistivity in certain YBCO ceramics, upon applying and consequently removing a low DC magnetic field. This phenomenon is observed just below Tc, while at lower temperatures the observed remanent resistivity is higher than the pristine, similar to the characteristic “field-on” resistivity hump. We show that this effect can be interpreted as originating in an intricate interplay of the frozen-in screening currents and the superconducting percolating current in the presence of the complex intergranular boundary system.

The effect of Ag concentration on the vortex pinning at the grain boundaries in the Ag/BSSCO composites

Abstract The BSSCO/Ag compounds prepared via the AgNO 3 route exhibit a complex magnetic field induced excess resistance. We argue that this is related to several different types of pinning centers. The pinning strength depends strongly on the Ag content and on its distribution in the BSSCO matrix.

Thermal wave induced edge electrical field of pyroelectric: Spatial pattern mapping and effect of ambient conditions

We have recently analyzed theoretically the main characteristics of the edge depolarizing electric field (EDEF), in the vicinity of a nonpolar face of a pyroelectric. In this work, we measured and characterized the EDEF, excited by a harmonical thermal wave. We present here experimental results obtained on a pyroelectric crystal LiTaO3, confirming our theoretical predictions. The interpretation assumes an equivalent circuit of a pyroelectric capacitive current source. The effect of the air pressure at the pyroelectric/air interface, on the EDEF, was determined in the interval 103–10−5 torr. We found that EDEF increases significantly with decreasing air pressure, presumably due to diminishing of adsorption screening at the polar faces. Teflon plates, covering the polar faces, prevent accumulation of screening charged particles, resulting in a significant increase in EDEF. Our experimental results highlight the feasibility of EDEF application in micro- and nanotechnology as a contactless controlled electric...

Electric field effect controlled thermoelectricity in thin Bi films

Abstract We demonstrate here, for the first time, the feasibility of enhancing the thermoelectric properties, by electric field effect controlled doping. The experimental data, on thin Bi films reported here, confirm the considerable enhancement of the Seebeck voltage. It should be noted that Bi may not be the most effective thermoelectric to use in this context. Some of the narrow-gap semiconductor thermoelectrics, presently investigated, carry an even larger potential of improved thermoelectric properties.