Negative Conductance Effect Research Articles

Preparation and Characterization of Orthorhombic AgMn Alloys by the Pulsed Laser Welding Technique

AbstractHerein, AgMn alloys are prepared by the pulsed laser welding technique in an argon atmosphere. The effect of the laser pulses width and stoichiometric composition of the alloys on the structural, compositional, morphological, and electrical properties are investigated. In contrast to the traditional preparation techniques which reveal cubic structure of AgMn alloys, the pulsed laser welding technique reveals the orthorhombic phase of the alloys. The lattice parameters of the orthorhombic phase of AgMn are . It is observed that pulse widths of 50 ms are the optimum from preparing these alloys. From an electrical point of view, the AgMn alloys exhibit negative dielectric constant and negative conductance effect in the microwave frequency domain. The impedance spectroscopy analyses in the frequency domain of 0.01–1.80 GHz have shown that AgMn alloys can be employed as band filters with return loss value of ≈16 dB. The features of the AgMn alloys which are achieved by the pulsed laser welding technique nominate them for use as negative capacitance and negative conductance transistors. These devices are suitable for noise reduction and parasitic capacitance cancellation.

Ag/SeO2/C Avalanche Type Resonant Tunneling Schottky Barriers

Herein, the design and characterization of Ag/SeO2/C avalanche type resonant tunneling devices are reported. Thin pellets of SeO2 nano-powders pressed under hydraulic pressure of 1.0 MPa which is used as the active material are characterized. They showed tetragonal structure refereeing to space group of P42mbc and lattice parameters of a=b= 7.866 Å and c=5.336 Å. The current-voltage characteristic curves have shown that SeO2 can perform as active media to produce resonant tunneling diodes when forward biased and as avalanche type diode when reverse biased. The peak to valley current ratios of these diodes reached 18.3. In addition, the impedance spectroscopy measurements have shown that the device works in the low impedance mode when operated in the microwave range of frequency near 1.50 GHz. Negative conductance effect is observed in that frequency domain. The features of the Ag/SeO2/C nominate them for use as signal amplifiers and microwave oscillators.

Magnetoconductivity oscillations induced by intersubband excitation in a degenerate 2D electron gas

Magnetoconductivity oscillations and absolute negative conductivity induced by nonequilibrium populations of excited subbands in a degenerate multisubband two-dimensional electron system are studied theoretically. The displacement from equilibrium, which can be caused by resonant microwave excitation or by any other reason, is assumed to be such that electron distributions can no longer be described by a single Fermi level. In this case, in addition to the well-known conductivity peaks occurring at the Shubnikov-de Haas conditions and small peaks of normal intersubband scattering, sign-changing oscillations with a different shape are shown to be possible. We found also that even a small fraction of electrons transferred to the excited subband can lead to negative conductivity effects.

Formation, negative capacitance and negative conductance effects in Selenium stacked layers sandwiched with Ag nanosheets

In this work, we report the nature of formation in the presence and absence of Ag nanosheets being inserted between of two stacked layers of Se thin films which are grown onto Au substrates. The Se/Se and Se/Ag/Se films which are prepared by the thermal evaporation technique under vacuum pressure of 10−5 mbar are studied by means of x-ray diffraction, conductance and capacitance spectroscopy techniques in the frequency domain of 0.01–1.80 GHz. Metal inducted crystallization processes from amorphous to hexagonal phases are achieved by using the Au substrate. The presence of Ag nanosheets of thicknesses of 50 nm between two 500 nm thick stacked layers of Se strongly affects the structural parameters through increasing the lattice constants, the microstrain and the defect density and decreasing the crystallite size. While the two stacked layers of Se sandwiched between Au and In metals displayed negative conductance effect associated with resonance in the capacitance and maximum microwave cutoff frequency () of 0.68 GHz near 1.31 GHz, the insertion of Ag nanosheets forced the two stacked layers to exhibit higher positive conductance values and increased the values to 17.4 GHz. Ag nanosheets also caused negative capacitance (NC) effect in all the studied frequency domain. NC effect is associated with resonance-anti-resonance phenomena in the region of 1.33–1.37 GHz. The features of the selenium stacked layers make them attractive for use in microwave circuits as cavities, noise reducers, parasitic capacitance cancellers and bandpass filters.

Transient Magnetoresponse of Photoexcited Electrons: Oscillating Conductivity and Negative Cyclotron Absorption

The nonlinear transient magnetoresponse of two-dimensional (2D) electrons is studied theoretically. Transient conductivity is calculated under exact cyclotron resonance condition. Two cases are considered: (a) the electrons excited by an ultrashort optical pulse, and isotropy of the initial distribution is expected; (b) dc electric field impose strongly anisotropic initial distribution. In case (b), evolution is strongly dependent on the initial phase of a circularly polarized wave. After the streaming distribution is formed, the magnetoresponse demonstrates periodically oscillating conductivity for both cases. The negative cyclotron absorption caused by the transient absolute negative conductivity effect is predicted for a certain range of parameters.

Calculations of transient magnetoconductivity of photoexcited electrons

Transient magnetotransport of two-dimensional electrons with partially inverted distribution excited by an ultrashort optical pulse is studied theoretically. The time-dependent photoconductivity is calculated for GaAs-based quantum wells by taking into account the relaxation of the electron distribution caused by nonelastic electron-phonon interactions and the retardation of the response due to momentum relaxation and due to a finite capacitance of the sample. We predict large-amplitude transient oscillations of the current density and Hall field (Hall oscillations) with frequencies corresponding to the magnetoplasmon range, which are initiated by the instability owing to the absolute negative conductivity effect.

Negative photoconductivity of illuminated α-Se layers

The investigation results of the negative conductivity effect of α-Se layers illuminated by white light are presented in this paper. It is shown that with illumination of the α-Se layer the value of the current can decrease several times as compared with the dark value of the current. This effect is observed only in the case when the voltage–current characteristic changes into the function dependence ( J vs V n ), the exponent index of which n=7.7. This effect is caused by recharge of deep states when the sample is illuminated.

Static N-Type Negative Differential Conductivity in Semiconductors Induced by Thermal Quenching of Photoconductivity

Current-voltage characteristic with static N-type negative differential conductivity arising from thermal quenching of photoconductivity by Joule self-heating is observed in a highly photoconductive semiconductor below room temperature. The characteristic can be controlled by changing illumination intensity. The static differential conductivity is examined in terms of the physics of a bulk negative conductivity effect.

Negative Conductivity Effects and Related Phenomena in Germanium. Part II

This paper is the second part of a two-part review of recent work on current instabilities and related properties of germanium in high electric fields. In this part the transferred carrier mechanism for producing bulk negative differential conductivity (BNDC) in a semiconductor is discussed. Experimental work on instabilities related to three realizations of this effect, in uniaxially compressed n and p-type Ge, and in n-type Ge at low temperatures with field and current in a 〈111〉 direction, is reviewed. Theoretical understanding of these effects, which is largely qualitative at this time, is discussed. In an appendix a list of materials in which BNDC effects have been observed is presented, with some of the relevant properties of these materials.

Negative Conductivity Effects and Related Phenomena in Germanium. Part I

This paper is the first part of a two-part review of recent work on current instabilities and related properties of germanium in high electric fields. In this part we discuss the general subject of high field transport in n-Ge with emphasis on the concept of saturated drift velocity. The oscillations which result from bulk negative differential conductivity (BNDC) in [100] and [110] directions at low temperatures are discussed and related to the saturation effects. A discussion of theoretical and experimental evidence with regard to the BNDC effects is presented. Finally, the anisotropy of the high-field conductivity is discussed and related to the Erlbach instability.

Monte Carlo simulation of oscillatory photoconductivity

Abstract Results of a detailed Monte Carlo simulation of oscillatory photoconductivity, utilising a “secondary self-scattering” device, are described. The negative conductivity effect predicted by an earlier approximate analytical approach is confirmed.

Stable Space-Charge Layers in Two-Valley Semiconductors

When electric fields of several thousand volts are applied to certain samples of n-type GaAs and InP, space-charge layers have been observed which are stable until they drift into the anode. Calculations of the possible stable configurations have been made using the two-valley model of McCumber and Chynoweth for GaAs. Under various voltage and sample length conditions, four types of configurations are possible: a high-field domain (or dipole layer), a low-field domain, an accumulation layer, and a depletion layer. Only in the limit of very high voltages do the domain configurations resemble the superposition of a stable accumulation layer and a stable depletion layer. The calculations show that the high-field domain is the only type that should have been observed under past experimental conditions. When a device contains a high-field domain, an increase in voltage reduces the current. This negative conductance effect is most pronounced in samples of GaAs where the value of doping density times sample length squared (NL2) is about 109 cm−1. The minimum field for sustaining a high-field domain decreases rapidly from the critical field for samples 30 μ long to about one-half the critical field for longer samples.