Negative Differential Conductance Devices Research Articles

Negative Differential Conductance in Polyporphyrin Oligomers with Nonlinear Backbones.

We study negative differential conductance (NDC) effects in polyporphyrin oligomers with nonlinear backbones. Using a low-temperature scanning tunneling microscope, we selectively controlled the charge transport path in single oligomer wires. We observed robust NDC when charge passed through a T-shape junction, bistable NDC when charge passed through a 90° kink and no NDC when charge passed through a 120° kink. Aided by density functional theory with nonequilibrium Green's functions simulations, we attributed this backbone-dependent NDC to bias-modulated hybridization of the electrode states with the resonant transport molecular orbital. We argue this mechanism is generic in molecular systems, which opens a new route of designing molecular NDC devices.

Negative differential conductance and super-Poissonian shot noise in a single quantum dot coupled to two noncollinear polarized ferromagnetic leads

We have theoretically studied the full counting statistics of electron transport through a single quantum dot (QD) weakly coupled to two noncollinearly polarized ferromagnetic leads. We found a strong robust bias-voltage-tunable negative differential conductance (NDC) region, in which the shot noise is dramatically enhanced and reaches up to a super-Poissonian value. In particular, the formed super-Poissonian shot noise can still occur in a wide bias voltage region where only the singly-occupied electronic states entering the bias voltage window. The underlying mechanisms of the observed NDC and super-Poissonian shot noise originate from the quantum coherence between the two singly-occupied electronic states. In addition, the skewness in the NDC regime can be significantly increased up to a large positive value, which is also attributed to the quantum coherence of the QD system, and the variation of the skewness value is more sensitive to the quantum coherence than the shot noise. Our findings suggest a QD-based tunable NDC device, and the predicted properties of high-order current cumulants can provide a deeper understanding of electron transport through the single QD.

Tunable super-Poissonian noise and negative differential conductance in two coherent strongly coupled quantum dots

The full counting statistics of electron transport through two coherent strongly serially coupled quantum dots (QDs) is theoretically studied based on an efficient particle-number-resolved master equation. When the coupling of the double-QD system with the incident-electrode is stronger than that with the outgoing-electrode, it is demonstrated that the super-Poissonian noise bias voltage range, which originates from the so-called dynamical channel blockade mechanism, depends sensitively on the types of energy-level detuning, which means that the super-Poissonian noise bias voltage range can be controlled by energy-level detuning and can be used to reveal the internal energy level structure of the considered double-QD system. For the on-site energy of the left QD coupled to incident-electrode is larger than that of the right QD coupled to out-electrode, i.e., ϵ L > ϵ R , a strong negative differential conductance (NDC) is observed in a certain energy-level detuning range and this level detuning range depends on the interdot Coulomb interaction, which suggests a tunable NDC device; whereas for ϵ L < ϵ R the magnitude of NDC is relatively very weak, and the corresponding shot noise is not always enhanced and even decreased at appropriate energy-level detuning. Moreover, the super-Poissonian behaviors of skewness and kurtosis are found to be more sensitive to the effective competition between the fast-and-slow transport channels than shot noise.

Shot noise in negative-differential-conductance devices

We have compared the shot-noise properties at T=4.2 K of a double-barrier resonant-tunneling diode and a superlattice tunnel diode, both of which exhibit negative differential-conductance (NDC) in their current–voltage characteristics. While the noise spectral density of the former device was greatly enhanced over the Poissonian value of 2eI in the NDC region, that of the latter device remained 2eI. This result implies that charge accumulation, not system instability, is responsible for shot-noise enhancement in NDC devices.

A microwave measurement technique for characterizing the I-V relationship for negative differential conductance devices

The practical procedures of a recently proposed technique to experimentally determine the I-V characteristics of negative differential conductance (NDC) devices are presented in this paper. The technique employs microwave reflection coefficients together with the measurable portions of the device's I-V characteristics to infer the I-V curve in the negative conductance region where oscillations tend to occur under normal DC bias conditions. The effects of higher harmonics at large signal levels are also taken into account in the calculation. The advantages of the method for high NDC devices have been pointed out in the stability analysis contained in a previously published work. The technique was demonstrated in the case of a low NDC tunnel diode where the agreement between the deduced I-V curve using the described method and the DC measured I-V curve is within 5%. The I-V curve in the negative conductance region for another tunnel diode with much higher negative conductance is also obtained and a self-consistent accuracy of 5% is found. >

Field-effect controlled resonant interband tunnelling in electron surface layers on InAs and In0.53Ga0.47As

The authors report on an experimental study of a novel three-terminal negative differential conductance device. Interband tunnelling from an electron inversion layer through the depletion barrier into resonant states of the bulk valence band is controlled by the gate voltage Vg at an InAs or InGaAs metal-insulator-semiconductor field-effect structure. Upon increasing Vg from the threshold voltage by up to 2 V the peak current can be varied by a factor of 5000 (500) with a peak-to-valley current ratio in excess of 2(16) for InAs (InGaAs). The effective tunnelling electric field and an areal electron density, as determined by measurements under high magnetic fields, are found to be only weakly dependent on Vg and on the tunnelling voltage. The mechanism of current control is discussed in terms of a variation of effective tunnelling area.

A new method of determination of the I-V characteristics of negative differential conductance devices

A method for mapping the complete I-V characteristic of a negative differential conductance (NDC) device has been investigated. This method employs the measurable positive differential conductance (PDC) portions of the DC I-V curve together with the measured conductances at a fixed DC bias voltage in the PDC region with different RF signal levels using a standard semiconductor analyzer. The NDC regime of the I-V curve is numerically constructed from the measured conductances at a fixed DC bias voltage in the PDC region with different signal levels using a large-signal nonlinear-circuit analysis. >

A new method of determination of the I-V characteristics of negative differential conductance devices by microwave reflection coefficient measurements

A technique to map out all of the I-V characteristics of negative differential conductance (NDC) devices is described. This method uses the DC measurable positive conductance portions of the I-V curve together with the measured microwave reflection coefficients at different RF signal levels and fixed DC bias voltage. The advantages of the method for high NDC devices are pointed out in a stability analysis. The complete I-V curve of a tunnel diode has been obtained with an accuracy within 5% in a proof-of-principal test of this method. >