High resolution potentiometry of planar electroformed MIM structures

Many attempts have been made to detect the current carrying filaments in electroformed metal-insulator-metal (MIM) structures (Pagnia and Sotnik 1988, Pagnia 1990). Transmission and scanning electron microscopes have been used without real success. Even experiments with the scanning tunnelling microscope (STM) could not definitely detect the filaments. We have mapped the potential distribution on an electroformed planar MIM diode (gold on quartz glass) with an STM and found usually only one (sometimes a few) sharp potential drop(s) in the microslit.     

Energy distribution of emitted electrons from electroformed MIM structures: the carbon island model

The electrons emitted from an electroformed metal island metal (MIM) device have a broad energy distribution with an FWHM of more than 2eV. The emission is thermionic from potentials somewhere between the electrodes. Islands, as detected by potentiography in an STM, are assumed to be the emitting spots. This model is able to describe all features of electron and photon emission, as well as electrical properties of electroformed MIM devices. It involves hot electrons in the lattice of small carbon islands embedded between carbon electrodes.     

Electrical properties of carbon and carbon-compounds compared with electroformed MIM characteristics

MIM diodes consisting of a vacuum gap between glassy carbon tips show the same electroforming behaviour as MIM diodes with arbitrary types of metals and insulators. It is shown that the current conducting filaments consist of carbon, as assumed for electroformed MIM structures (Pagnia and Sotnik 1988).     

Simulation of a microprofile and electric field distribution in MIM structures

Simulation of etching of a microtip’s lower electrode and deposition of a dielectric film has shown that the film undergoes a strong thinning at lateral surfaces and at the microtip’s bases. It is demonstrated that, at a microtip density of 5 × 10⁸ cm⁻², the electric field’s strength at the base of the tip is 3.5 times that at its apex, which gives rise to additional emission centers.     

Features of the current-voltage characteristics of long semiconductor structures under ultrahigh-level double-injection conditions

The widespread use of low-resistivity materials in modern solid-state electronics calls for an analysis of the current-voltage characteristics of long semiconductor structures under ultrahighlevel double-injection conditions. It is shown that the pure plasma model of semiconductors is not applicable in such an analysis, since the concentration dependence of the carrier mobility μ(n) must be taken into account. The conditions for the appearance of highly superlinear current-voltage characteristics in the region of the initial variation of μ(n) due only to the rate of variation of the mobility of the majority carriers (the λ effect) are analyzed. The λ effect is manifested on the experimental current-voltage characteristics in the form of sharp current jumps and corresponding high values of the differential order of the current-voltage (J-V) characteristic (a=d log J/d log V), which are determined by the variation of the differential order of the concentration dependence of the carrier mobility λ(n)=d log μ/d log n. A calculation shows that the mechanism for the appearance of the λ effect can be determined at injection levels as high as ∼10¹⁷ cm⁻³. Fiz. Tekh. Poluprovodn. 32, 1476–1481 (December 1998)     

Sodium-peak splitting in dynamic current-voltage characteristics of convective ion currents in metal-oxide-semiconductor structures

The results of simultaneous measurements of dynamic current-voltage and capacitance-voltage characteristics are presented for metal-oxide-semiconductor structures in the temperature range T = 420–470 K and voltage-sweep rates β _v = 0.5–1000 mV/s. The convective currents I _con (V) in oxide are extracted from usual ion currents in the I-V characteristics. In I _con (V) curves, the Na⁺-ion peaks are split. In addition, an envelope curve is seen in initial portions of “fast” I _con(V) curves with β _V ? 10 mV/s that indicates to the presence of a certain quasi-steady ion-transport mode. A more equilibrium mode at slow rates β _V < 1 mV/s manifests itself in the form of stabilization of convective-current peak shapes. The nature of efficient neutralization of the second peaks in the I _con(V) dependences is discussed.     

Simulation of current-voltage characteristics of a ferroelectric field-effect transistor

Current-voltage (I-V) characteristics of an all-perovskite ferroelectric-semiconductor field-effect transistor (FET) were simulated. The modeling is based on an analysis of an experimental hysteresis loop of a metal-ferroelectric-metal structure. The charge in the semiconductor, electric fields in the semiconductor and ferroelectric (FE), and FE polarization at the FE-semiconductor interface are calculated at a given semiconductor surface potential. The Poisson equation is solved numerically across the FE thickness. The semiconductor surface potential, semiconductor charge, FE polarization, electric field and voltage drop in the FE are calculated as functions of the applied voltage. By using appropriate semiconductor thickness and built-in voltage between the FE and the gate, it is possible to provide a remanent polarization necessary for the opening and blocking of the FET channel in the ascending and descending portions of the hysteresis loop, respectively. The I-V characteristics and the voltage drop along the FET channel are calculated and analyzed for both polarities of the drain bias. The results make it possible to predict I-V characteristics of an all-perovskite ferroelectric FET.     

Inverted bistability in the current-voltage characteristics of a resonant tunneling device

The current-voltage characteristics of an asymmetric double barrier resonant tunneling device show a butterfly-shaped hysteresis loop in which, for a range of voltage, the off-resonant current exceeds the resonant current. This “inverted bistability” is due to the effects of space charge buildup in the quantum well. Magnetoquantum oscillations in the tunnel current with | are used to investigate the distribution of charge within the device and the intersubband scattering processes which control the charge buildup.     

Effect of hydrogen on the current-voltage characteristics of Pd/p-InGaAsP and Pd/n-InGaAs barrier structures

The effect of hydrogen on the current-voltage characteristics of palladium-semiconductor barrier structures based on the solid solutions In_0.92Ga_0.08As_0.17P_0.83 and In_0.53Ga_0.47As is investigated. The hydrogen-induced kinetics of the change in the current in the structures is studied. It is shown that the response time of the structures decreases with increasing hydrogen concentration in the gas mixture. The results obtained are discussed from the standpoint of the adsorption of hydrogen atoms on the semiconductor surface. Fiz. Tekh. Poluprovodn. 33, 1220–1223 (October 1999)     

The role of impact ionization in the formation of reverse current-voltage characteristics of Al-SiO2-n-Si tunnel structures

Physical processes responsible for the reverse current-voltage (I-V) characteristics of Al-SiO₂-n-Si structures with 1.2–3.2-nm-thick SiO₂ and a silicon doping level of 10¹⁴-10¹⁸ cm^?3 were analyzed. A new model describing the evolution of the hot-electron energy in structures of this kind is suggested. The roles played by Auger ionization and impact ionization are differentiated. The turn-on voltages of a tunnel MOS structure are studied both theoretically and experimentally. The turn-on voltage is shown to decrease with increasing oxide layer thickness.     

Modeling of current-voltage characteristics for dual-gate amorphous silicon thin-film transistors considering deep Gaussian density-of-state distribution

Considering combination of the deep Gaussian and tail exponential distribution of DOS (density of states) instead of double exponentials empirically, a physics-based approximation has been developed to describe the behavior of the surface and centric potential as a function of applied voltage for DG a-Si:H TFT (amorphous silicon thin film transistor with dual gate). The resulting scheme provides a novel method for quickly evaluation of the inter-related potentials and is proved to offer better computational efficiency than other numerical alternatives. Based on these potentials, a compact drain current model accounting for the interaction factor has been proposed that followed. We show what parameters are truly required for accurately describing the I-V characteristic of DG a-Si:H TFT and just how qualitatively these parameters affect TFTs current. Model derivation also demonstrated an intuitive physical explanation for the gate-voltage dependent mobility as usually observed experimentally in these devices. Terms of potentials and current calculation are successively verified by comparison with numerical and the published experimental data.     

On the current-voltage characteristics of epitaxial Schottky barrier diodes

The J-V characteristics of epitaxial Schottky barrier diodes are analyzed. Based on the assumption of negligible recombination in the epitaxial layer, formal solution from which the J-V characteristics can be calculated is derived. The solution is valid for all injection levels and reduces to the form I = I_s[exp (q(V?IR)/kT) ? 1], where R is the series resistance of the epitaxial layer, under C12 C12V low-injection conditions. The analysis is justified by very close correspondence with exact numerical calculations using the Finite Element Device Analysis Program (FIELDAY) in which thermionic emission boundary conditions are implemented for both electrons and holes. It is shown that for low barrier Schottky diodes the minority carrier injection is negligible and the expression I = I_s[exp (q(V?IR)/kT) ? 1] describes the I-V characteristics over large bias range. For high barrier C12 C12 V Schottky diodes the exact solution must be used as minority carriers are injected and the series resistance is decreased due to conductivity modulation effect.     

Numerical simulation of the current-voltage characteristics ofheteroepitaxial Schottky-barrier diodes

A numerical model resulting in the current-voltage characteristics of standard and heteroepitaxial Schottky-barrier diodes is presented. Simulations of GaAs diodes, as well as InGaAs diodes grown on GaAs and InP substrates, are presented. The model considers quantum-mechanical tunneling, and is therefore applicable to highly doped devices. A self-consistent drifted-Maxwellian distribution is used to model the electron energy distribution at high current densities. The assumption of a drifted-Maxwellian distribution is shown to lead to higher current at high bias than predicted with the assumption of a Maxwell-Boltzmann or Fermi-Dirac distribution. The presence of a heterojunction at the InGaAs-substrate interface is predicted to lead to an additional series resistance component     

基于双结模型非理想太阳能电池伏安特性参数数值分析

提出了一种对于太阳电池光照条件和暗特性条件下对其伏安特性全段进行拟合提取参数的改进方法.对太阳电池J-V曲线进行分段, 提取每段的4个关键参数: 串联电阻(Rs)、并联电阻(Rsh)、品质因子(n)、反向饱和电流密度(J0).这种方法采用了双结电路模型法, 并以CdS/CdTe薄膜电池为例进行了光照下和暗特性分析, 得到了比单结电流模型更多的参数, 并且具有较高的拟合精度(误差<0.7%).     

Resistive switching characteristics of MIM structures based on oxygen-variable ultra-thin HfO2 and fabricated at low temperature

We report the resistive switching characteristics of Metal-Insulator-Metal (MIM) structures fabricated at low temperature and having different concentrations of oxygen vacancies in the insulator. The oxygen modulation in HfO₂ is promoted by a very simple variation of standard thermal Atomic-Layer Deposition (ALD), so that different exposure times to H₂O during each half-cycle of the hafnium oxide deposition are used (being Tetrakis Dimethylamino Hafnium–TDMAH the other precursor). We show the correlation of the stoichiometry with the forming voltage, conduction mechanisms and resistance windows of memory devices. All structures present a bipolar operation mode in which the resistive switching mechanism is related to the migration of oxygen vacancies inside the dielectric. These MIM devices have a simple structure, low power consumption and they are fabricated using a very low thermal budget of only 250 °C, thus enabling their integration at the Back-End of Line (BEOL) stage of an integrated circuit in order to increase the density of memory arrays in at least one order of magnitude.     

Refined model for the current-voltage characteristics of quantum-well infrared photodetectors

The temperature dependences of the dark current of quantum-well infrared photodetectors are investigated experimentally. It is established that the pre-exponential factor in the analytical expression for the photodetector current-voltage characteristics varies linearly with temperature. On the basis of the results obtained, it is suggested that the temperature dependence of the photodetector??s dark current is determined by the thermal excitation of charge carriers to a band characterized by a two-dimensional density of states. In the context of this suggestion, a refined model for the current-voltage characteristics is proposed. The model takes into account the thermal generation of charge carriers in a band with a two-dimensional density of states and the electric field dependence of the thermal activation energy for the quantum-well ground state and of the drift velocity of the carriers in the barrier conduction band.     

Causes of variation in the static current-voltage characteristics of the structures with the Me/n-n +-GaAs Schottky barrier on hydrogenation

Causes of a decrease in the ideality factor n and an increase in the reverse voltage U _r for the structures with the Schottky barrier (SB) Au/n-n ⁺-GaAs due to treatment in atomic H were investigated. It was found that the treatment of n-n ⁺-GaAs in atomic hydrogen induces two processes, which lead to an increase in the reverse voltage U _r and a decrease in the ideality factor n for SB structures. On the one hand, U _r increases and n decreases due to lowering the concentration profile and formation of the inverse concentration gradient of an ionized shallow-level donor impurity in the n layer. This is caused by the passivation of the impurity with H. On the other hand, U _r increases and n decreases due to the formation of a thin (～8 nm) semi-insulating surface layer. In both cases, U _r increases and n decreases owing to an increase in the effective width of the potential barrier at the metal-semiconductor contact as a result of variation in the shape of the concentration profile for the ionized shallow-level donor impurity.     

N-type negative differential resistance, hysteresis, and oscillations in the current-voltage characteristics of microwave diodes

The dc current-voltage characteristics of microwave diodes are experimentally studied on simultaneous exposure of the diodes to a high-frequency (100 MHz) high-amplitude harmonic signal. In the current-voltage characteristics of the microwave diodes, regions of N-type negative differential resistance, hysteresis, and current oscillations are observed depending on the amplitude and frequency of the high-frequency signal. A comparative analysis of the experimentally observed effects is performed, and possible mechanisms for the effects are discussed.