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.
We describe here the characteristics of two types of high-quality PbTe p-njunctions, prepared in this work: (1) by thermal diffusion of In 4 Te 3 gas (TDJ), and (2) by ion implantation (implanted junction, IJ) of In (In-IJ) and Zn (Zn-IJ).The results, as presented here, demonstrate the high quality of these PbTe diodes.Capacitance-voltage (C-V) and current-voltage (I-V) characteristics have been measured.The measurements were carried out over a temperature range from ~ 10 K to ~ 180 K.The latter was the highest temperature, where the diode still demonstrated rectifying properties. This maximum operating temperature is higher than any of the earlier reported results.The saturation current density, J 0 , in both diode types, was ~ 10 -5 A/cm 2 at 80 K, while at 180 K J 0 ∼ 10 -1 A/cm 2 in TDJ and ~ 1 A/cm 2 in both ion-implanted junctions. At 80 K the reverse current started to increase markedly at a bias of ~ 400 mV for TDJ, and at ∼ 550 mV for IJ. The ideality factor n was about 1.5 -2 for both diode types at 80 K. 2The analysis of the C-V plots shows that the junctions in both diode types are linearly graded. The analysis of the C-V plots allows also determining the height of the junction barrier, the concentrations and the concentration gradient of the impurities, and the temperature dependence of the static dielectric constant.The zero-bias-resistance×area products (R 0 A e ) at 80 K are: 850 Ω⋅cm 2 for TDJ,
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 x area product, the R0C time constant and the detectivity D* are presented
We discuss the possibility of a pyroelectric effect in a nonpolar solid. The built-in electrical field of a p–n junction barrier creates a polar axis in the solid. The electric dipole moment, due to the charge separation at the junction, depends on temperature mainly via the temperature dependence of the dielectric constant, giving rise to the pyroelectric effect. Illustrative estimates have been calculated for two quantum paraelectrics, PbTe and SrTiO3.
Measurements of the electric field effect (EFE) in thin films of Bi exhibit an unexpectedly small effect. Even though the additional charge density is comparable with the intrinsic carrier concentration, the measured EFE is minute. We show that this can be attributed to the following facts: (1) The additional charge due to EFE is divided between the electron and hole bands correspondingly to the density-of-states (DOS). The Bi film is in the quantum-size regime, thus the carriers DOS depend linearly on the corresponding effective masses of DOS. (2) The nature of the scattering mechanism is such that the ratio of the carrier mobilities is almost equal to the inverse ratio of the corresponding effective masses. This near equality is the cause of the anomalous EFE in Bi films.
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