A single-molecule diode with significant rectification and negative differential resistance behavior

A series of ferrocenylalkanethiol (HSCnFc) single molecular junctions are modeled and their rectification ratios (RRs) are up to 100 (for HSC11Fc), which agrees with the experiments of Whitesides et al. Not only explanation to the origin of the remarkable large RR is given, but also the reason why one order deviation of RR between HSC11Fc and HSC9Fc is discussed and depicted, which was not pointed out by previous researchers. The single asymmetric accessible molecular orbital (MO) model is evaluated, which is different from the Donor (D)–Acceptor (A) models reported before and a clear negative differential resistance (NDR) behavior is found and explained in the HSC11Fc based device.     

Conditions for negative differential resistance and switching in a tunnel diode under the effect of an external microwave signal

Experimentally observed phenomenon of the origination of the mode of negative differential resistance and switching in a tunnel diode under the effect of external microwave signal is theoretically interpreted. The reasons for the existence of the ranges of bias voltages applied to the diode and the power levels of microwave signal for which the phenomenon is observed are clarified.     

A field-effect transistor with a negative differential resistance

We report the effect of negative differential resistance (NDR) in the drain circuit of a new type of selectively doped AlGaAs/ GaAs heterojunction transistor. The key new element of our structure is the presence of a subsidiary GaAs conducting layer, separated from the FET channel by an AlGaAs graded barrier. In this work the subsidiary layer is realized by the conducting substrate. The NDR effect arises due to the heating of channel electrons by the source-to-drain field, and the subsequent charge injection over the barrier. This effect is strongly influenced by the gate and substrate voltages. In a floating-substrate arrangement the current-voltage characteristics exhibit memory effects associated with retention of injected charge in the substrate. In this mode, the NDR is seen only at low temperatures with the peak-to-valley ratios in current at 77 K reaching values as high as 30. On the other hand, when the substrate is biased positively, the NDR results from a peculiar effect of dynamical channel depletion by the injected space charge which drifts on the downhill slope of the graded barrier. In this case, the NDR is observed even at room temperature.     

New cut of a quartz resonator with a linear temperature/frequency characteristic

The letter describes a new cut of quartz resonator with a linear temperature/frequency characteristic used as a sensor for precise temperature measurements. The newly developed thermosensitive quartz resonator has some important advantages: obtaining comparatively easily and reproducibly a precise orientation of the piezoelement, good linearity of the temperature/frequency characteristic and a clear frequency spectrum in a wide temperature interval. The first-order temperature coefficient is 38 parts in 106/deg C and the frequency of operation on the third overtone is about 26.5 MHz at 10°C. That leads to an increase of approximately 1000Hz/deg C, with a sensitivity of 0.0001 deg C. These qualities of the thermosensitive quartz resonator make possible its use in devices for precise temperature measurements.     

Tunnel Diodes Based on n+-Ge/p+-Si(001) Epitaxial Structures Grown by the Hot-Wire Chemical Vapor Deposition

Semiconductors - n+-Ge/p+-Si(001) epitaxial structures are grown by hot-wire chemical vapor deposition from GeH4 at a low substrate temperature (~325°C). Prototype tunnel diodes allowing for...     

The p+n−n+ diode pulsed at extreme current densities—I: Numerical techniques and reverse pulsed case

The anomalous voltage transient response of the p⁺n^?n⁺ diode structure to a single non-repetitive intense current pulse is presented for current densities up to and greater than 10⁴ amp/cm². A very general device model and an accurate numerical iterative method are used to solve the basic transport equations leaving the selection of pulse wave form, generation-recombination laws, avalanching, doping profiles, mobility, and injection levels arbitrary. The boundary conditions are applied solely to the external contacts. In order to achieve numerical convergence to such a nonlinear problem, due to the extreme currents, it was determined that a very accurate thermal equilibrium solution was necessary. Two examples for the reverse pulse case, reach-through and avalanche, are presented to show the effects of large current densities on the reverse voltage response.     

Measurement of J/V characteristics of a GaAs submicron n+-n?-n+ diode

The J/V characteristics of a GaAs 0.24 ?m channel length n+-n?-n+ diode have been measured at 8 K, 77 K and 300 K. Good agreement is observed with the J/V predictions recently reported by Awano et al. using a Monte-Carlo simulation of a similar device. This verifies the accuracy of their model, and substantiates their findings that electron transport in a 0.25 ?m channel is near-ballistic at 77 K, with a peak ensemble-average electron velocity approaching 108 cm s?1 for an ensemble-average energy just under 0.36 eV. An effective time-average velocity of about half this value can be expected for the total channel transit.     

The p+n−n+ pulsed diode at extreme current densities—II: The forward pulsed case and its anomalous voltage response

The voltage transient response of the p⁺n^?n⁺ diode structure to a single intense current pulse in the forward direction is presented for current densities up to 10⁴ A/cm². The anomalous voltage response is studied by computer simulation of the device and compared with the experimental results. The response at these current densities becomes very dependent upon the carrier lifetimes and the recombination law chosen for the n⁺ region. At the larger current densities Avalanche generation and Auger recombination can exist simultaneously, yielding a larger than expected voltage across the device even as steady state is approached.     

Development of a high-resolution quartz resonator force and weight sensor with increased reliability

Test-analyze-and-redesign method is employed to develop a quartz crystal resonator (QCR) force and weight sensor with increased reliability for batch production. The sensor, which mainly consists of a QCR and a metal diaphragm structure, has the advantages of high resolution, digital output, and low cost. The failure mechanism of the single-diaphragm QCR sensor has been uncovered by experiments aiming at providing insight into the failure factors. In order to eliminate the failure stress and improve reliability, the sensor has been redesigned based on failure analysis results by designing a double-diaphragm structure. Life testing experiments for validating the effect of the corrective action show that reliability has been improved five times, and after redesign, the reliability satisfies the requirement of practical use. Accelerated life testing is performed to find acceleration factors and development stresses for batch production.     

Electrical phenomena in a metal/nanooxide/p +-silicon structure during its transformation to a resonant-tunneling diode

To investigate and develop novel silicon-based electronic components, the electro-physical effects in a metal-insulator-semiconductor (MIS) structure with nanometer size parameters, gained by enhancement of the silicon doping level up to N _A ～ 10¹⁹ cm^?3 and reduction of the oxide thickness down to 0.4–4.0 nm, have been studied. As a result of such changes, the MIS nanostructure satisfies necessary and sufficient conditions for the electron resonant tunneling that can be observed at relatively low (some volts) reverse biases. Thereby a MIS capacitor can be transformed into a resonant-tunneling diode with substantial extension of its properties and functions.     

Charge effects controlling the current hysteresis and negative differential resistance in periodic nanodimensional structures Si/CaF2

A kinetic model for charge carrier transport in periodic nanodimensional Si/CaF₂ structures via localized states in the insulator was suggested. The appearance of the built-in electric charge in the insulator due to the polarization of the charge trapped by localized charge centers and the subsequent discharge of these centers were investigated. It was demonstrated that these phenomena explain the hysteresis of current-voltage (I–V) characteristics with a change of polarity of the applied external voltage. These phenomena bring about the portion of negative differential resistance (NDR) in these characteristics. Major factors ensuring the NDR appearance for the structures under investigation are the charge carrier density at the contacts and the charge voltage. At temperatures below 250 K, the NDR portion disappears. It was demonstrated that, in the course of recording the experimental I–V characteristics, the effect of the charging-discharging of localized centers should decrease. This decrease is in accordance with an increase in the time interval of measuring the current at a constant voltage and with an increase in the step of the applied voltage. This effect actually disappears for the measurement time of 20 s and the voltage step of 0.6 V.     

Shallow,small area,TiSi2 contacts to n+ and p+ silicon

Shallown ⁺ andp ⁺ doped source/drain contacts to silicon as small as 300 × 200 nm have been fabricated using an optimized silicided (TiSi₂) contact technology. Well behaved structural and electrical characteristics were found. The electrical series resistance through two of such contacts from metal to metal through the semiconductor contacts increases rapidly for contact sizes below the transfer length of the contact (about 0.5 μm). This resistance increase is critically dependent on the contact resistivity and three-dimensional current flow patterns.     

Carrier-Transport Processes in n+-GaAs/n0-GaAs/n+-GaAs Isotype Heterostructures with a Thin Wide-Gap AlGaAs Barrier

Semiconductors - Experimental studies of n+-GaAs/n0-GaAs/n+-GaAs isotype heterostructures with a 100-nm-thick wide-gap N0-AlGaAs barrier situated in the n0-GaAs region are carried out. It is shown...     

Charge transport mechanism and photoelectric characteristics of n +-Si-n-Si-Al2O3-Pd diode structures

Current-voltage characteristics at T=100 and 300 K, the temperature dependence of the forward current and photocurrent, the influence of a magnetic field on the photocurrent, and the influence of hydrogen on the photovoltage and dark current were investigated. It was found that the mechanism of the charge transport is controlled by double injection in the diffusion approximation at both T=100 K (I ∝ exp(qV/4kT)) and T=300 K (I ∝ V ^m , m=4–5.6). Diode structures enhance the photocurrent at a reverse bias. It was found that an increase in the photocurrent in the magnetic field H (ΔI _ph=αexpβH) can be explained by tunneling of the photocarriers during resonance impurity scattering in terms of their exponential energy distribution.     

Organic quantum wells with multiple negative differential resistance peaks and its photoswitch effect

Organic optoelectronic devices have experienced great progress in recent decades. However, quantum well has long been a challenge for organic semiconductors due to the weak intermolecular interactions, the difficulty of realizing high quality alternate crystalline films. Here, we construct a type II organic crystalline quantum well, in which both electron quantum well and hole quantum well show symmetrical and multiple negative differential resistance peaks, respectively. The blueshifts of absorption spectra and the peak voltage decreasing under illumination conditions are observed. Due to high absorption coefficient of organic semiconductors, photoswitch effect by taking advantage of negative differential resistance of organic quantum well, which owns very thin device structure is demonstrated. Our results prove the promising applications of organic quantum wells, which broaden the types of organic optoelectronic devices.     

Existence of a 2n FFT algorithm with a number of multiplications lower than 2n+1

First we give a decomposition of an FFT of length 2n into a number of one-dimensional polynomial products. If these products are computed with minimum multiplication algorithms, we show that the 2n FFT can be computed with less than 2n+1 nontrivial complex multiplications. A variation of this algorithm is also shown to give the same multiplication count as the `split-radix? FFT.     

Resistive switching properties of a thin SiO2 layer with CeOx buffer layer on n+ and p+ Si bottom electrodes

Resistive switching properties of a 2-nm-thick SiO₂ with a CeO_x buffer layer on p⁺ and n⁺ Si bottom electrodes were characterized. The distribution of set voltage (V_set) with the p⁺ Si bottom electrode devices reveals a Gaussian distribution centered in 4.5 V, which reflects a stochastic nature of the breakdown of the thin SiO₂. Capacitance–voltage (C–V) measurements indicate the trapping of electrons by positively shifting the C–V curve by 0.2 V during the first switching cycle. On the other hand, devices with the n⁺ Si bottom electrodes showed a broad distribution in V_set with a mean value higher than that of p⁺ Si bottom electrode devices by 0.9 V. Although no charge trapping was observed with n⁺ Si bottom electrode devices, a degradation in interface states was confirmed, causing a tail in the lower side of the V_set distribution. Based on the above measurements, the difference in the V_set can be understood by the work function difference and the contribution of electron trapping.     

Reverse recovery and rectification effeciency of a p?n junction diode simulated by an analogue model

A method of simulating the large-signal transient response of p?n junction diodes by means of an RC analogue network is presented. Simulated and computed results for the storage time and the rectification efficiency of a halfwave rectifier with an ohmic load are shown.     

Simultaneous Formation of Ohmic Contacts on p +- and n +-4H-SiC Using a Ti/Ni Bilayer

In this work, Ti/Ni bilayer contacts were fabricated on both p ⁺- and n ⁺-4H-SiC formed by ion implantation, and the effects of the Ti interlayer on the contact resistance and interfacial microstructure were studied. Adoption of a thin (10 nm) Ti interlayer resulted in specific contact resistance of 4.8 μΩ cm² and 1.3 mΩ cm² on n ⁺- and p ⁺-4H-SiC, respectively, comparable to the values for contacts using only Ni. Moreover, contacts using Ti/Ni provide a flat and uniform interface between Ni₂Si and SiC, whereas discontinuous, agglomerated Ni₂Si islands are formed without the use of a Ti interlayer. In addition, the Ti interlayer was demonstrated to effectively dissociate the thin oxide film on SiC, which is advantageous for low-resistance, reliable ohmic contact formation. In summary, use of a Ti/Ni bilayer is a promising solution for one-step formation of ohmic contacts on both p ⁺- and n ⁺-4H-SiC, being especially suitable for SiC n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) fabrication.