Quantitative Analysis of Current–Voltage Characteristics of Semiconducting Nanowires: Decoupling of Contact Effects

A metal‐semiconductor‐metal (M‐S‐M) model for quantitative analysis of current–voltage (I–V) characteristics of semiconducting nanowires is described and applied to fit experimental I–V curves of Bi₂S₃ nanowire transistors. The I–V characteristics of semiconducting nanowires are found to depend sensitively on the contacts, in particular on the Schottky barrier height and contact area, and the M‐S‐M model is shown to be able to reproduce all experimentally observed I–V characteristics using only few fitting variables. A procedure for decoupling contact effects from that of the intrinsic parameters of the semiconducting nanowires, such as conductivity, carrier mobility and doping concentration is proposed, demonstrated using experimental I–V curves obtained from Bi₂S₃ nanowires and compared with the field‐effect based method.     

Monitoring plasma nitridation of HfSiOx by corona charge measurements

In this work we present an evaluation and understanding of corona charge measurements on decoupled plasma nitrided (DPN) HfSiOx. Typical corona charge parameters such as equivalent oxide thickness (EOT), density of interface states (D_it) and saturated surface voltage (V_sat) are evaluated. It is shown that especially D_it and V_sat are promising parameters for nitiridation monitoring as they show correlation to DPN parameters within good accuracy. Fundamental explanation is given for the observed behaviour of V_sat by use of a direct tunneling model.     

Leakage current by Frenkel–Poole emission on benzotriazole and benzothiadiazole based organic devices

In this study three different organic semiconductors were used in the fabrication of ITO/PEDOT:PSS/Polymer:PCBM/LiF/Al configuration. Reverse current density–voltage (J_r–V) measurements of the samples were investigated to define the reverse-bias leakage current mechanisms on benzotriazole and benzothiadiazole based organic devices. Our results indicate that the J_r–V plot behaviors are given by linear dependence between In ( J_r) and V^1/2, where J_r is the reverse current density, and V is the applied voltage. This behavior is well known as the Poole–Frenkel (PF) effect where it is found to be dominating in the reverse-bias leakage current.     

Single-parameter model for the post-breakdown conduction characteristics of HoTiOx-based MIM capacitors

The post-breakdown conduction characteristics of holmium titanium oxide (HoTiO_x)-based metal–insulator–metal capacitors fabricated by the atomic layer deposition technique on Si substrates were investigated. Diode-like and power-law models were fitted to the experimental current–voltage (I–V) curves and the results assessed with the aim of detecting any possible correlation among the model parameters. It was found that the number of parameters involved can be reduced in both cases and that for the power-law model a single parameter is solely required to approximate the I–V curves in a wide current range (from 10⁻¹¹ to 10⁻⁴ A). This property, which has also been observed in a variety of material systems, was used to simulate the bipolar switching behavior exhibited by the I–V characteristics. The connection with the physics of electron transport through atom-sized constrictions is discussed.     

A prognostic approach for non-punch through and field stop IGBTs

Development of prognostic approaches for insulated gate bipolar transistors (IGBTs) is of interest in order to improve availability, reduce downtime, and prevent failures of power electronics. In this study, a prognostic approach was developed to identify anomalous behavior in non-punch through (NPT) and field stop (FS) IGBTs and predict their remaining useful life. NPT and FS IGBTs were subjected to electrical–thermal stresses until their failure. X-ray analysis performed before and after the stress tests revealed degradation in the die attach. The gate–emitter voltage (V_GE), collector–emitter voltage (V_CE), collector–emitter current (I_CE), and case temperature were monitored in situ during the experiment. The on-state collector–emitter voltage (V_CE(ON)) increased and the on-state collector–emitter current (I_CE(ON)) decreased during the test. A Mahalanobis distance (MD) approach was implemented using the V_CE(ON) and I_CE(ON) parameters for anomaly detection. Upon anomaly detection, the particle filter algorithm was triggered to predict the remaining useful life of the IGBT. The system model for the particle filter was obtained by a least squares regression of the V_CE(ON) at the mean test temperature. The failure threshold was defined as a 20% increase in V_CE(ON). The particle filter approach, developed using the system model based on the V_CE(ON), was demonstrated to provide mean time to failure estimates of IGBT remaining useful life with an error of approximately 20% at the time of anomaly detection.     

The temperature dependent analysis of Au/TiO2 (rutile)/n-Si (MIS) SBDs using current–voltage–temperature (I–V–T) characteristics

In this study, the main electrical parameters of Au/TiO₂(rutile)/n-Si Schottky barrier diodes (SBDs) were analyzed by using current–voltage–temperature (I–V–T) characteristics in the temperature range 200–380 K. Titanium dioxide (TiO₂) thin film was deposited on a polycrystalline n-type Silicon (Si) substrate using the DC magnetron sputtering system at 200 °C. In order to improve the crystal quality deposited film was annealed at 900 °C in air atmosphere for phase transition from amorphous to rutile phase. The barrier height (Φ_b) and ideality factor (n) were calculated from I–V characteristics. An increase in the value of Φ_b and a decrease in n with increasing temperature were observed. The values of Φ_b and n for Au/TiO₂(rutile)/n-Si SBDs ranged from 0.57 eV and 3.50 (at 200 K) to 0.82 eV and 1.90 (at 380 K), respectively. In addition, series resistance (R_s) and Φ_b values of MIS SBDs were determined by using Cheung's and Norde's functions. Cheung's plots are obtained from the donward concave curvature region in the forward bias semi-logarithmic I–V curves originated from series resistance. Norde's function is easily used to obtain series resistance as a function of temperature due to current counduction mechanism which is dominated by thermionic emission (TE). The obtained results have been compared with each other and experimental results show that R_s values exhibit an unusual behavior that it increases with increasing temperature.     

The effects of thermal annealing on the electrical characteristics of Au/n–InP/In diode

An Au/n–InP/In diode has been fabricated in the laboratory conditions and the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the diode have been measured in room temperature. In order to observe the effect of the thermal annealing, this diode has been annealed at temperatures 100 and 200 °C for 3 min in N₂ atmosphere. The characteristic parameters such as leakage current, barrier height and ideality factor of this diode have been calculated from the forward bias I–V and reverse bias C–V characteristics as a function of annealing temperature. Also the rectifying ratio of the diode is evaluated for as-deposited and annealed diode.     

Quantum supercurrent and Andreev reflection in silicon nanostructures

The tunneling spectroscopy is used for studying the hole transport in a sandwich nanostructure of the superconductor-ultra-narrow-self-assembled-p-silicon-quantum-well (Si-QW)-superconductor type on the n-Si (100) surface; the quantum well’s width is less than the coherence length and the Fermi wave-length. The high-resolution tunneling I–V characteristics display the supercurrent quantization, the characteristics of which depend on the positions of the dimensional-quantization levels for holes in the Si-QW. The correlation in the tunneling of single holes and Cooper pairs manifests itself in identical oscillations of the I–V characteristics for the supercurrent at T < T _c and the conductivity at T > T _c . In addition to the Josephson effect, the forward and reverse I–V characteristics for the first time reveal the processes of multiple Andreev reflection of two-dimensional holes in the Si-QW, which cause the microscopic mechanism responsible for the superconducting proximity effect. The investigation of the two-dimensional hole’s conductivity in the Si-QW plane indicates the presence of coherent tunneling under conditions of the spin-dependent multiple Andreev reflection between the superconducting δ] barriers confining it.     

MISFET structures with barium titanate as a dielectric layer for application in memory cells

This work shows investigations of La₂O₃ containing BaTiO₃ thin films deposited on Si substrates by Radio Frequency Plasma Sputtering (RF PS) of sintered BaTiO₃ + La₂O₃ (2 wt.%) target. Round, aluminum (Al) electrodes were evaporated on top of the deposited layers. Thus, metal–insulator–semiconductor (MIS) structures were created with barium titanate thin films playing the role of an insulator. The MIS structures enabled a subsequent electrical characterization of the studied film by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements. Several electronic parameters, i.e., ε_ri, ρ, V_FB, ΔV_H were extracted from the obtained characteristics. Moreover, the paper describes technology process of MISFETs fabrication and possibility of their application as memory cells. The influence of voltage stress on transfer and output I–V characteristics of the transistors are presented and discussed.     

Analysis of the persistent photoresponse of C8BTBT transistors in the near-bandgap spectral region

The variations in physical parameters of an organic field-effect transistor having dioctylbenzothieno[2,3-b]benzothiophene (C8BTBT) as the channel semiconductor were investigated under different light irradiation conditions at wavelengths of 350 nm, 370 nm, 400 nm and by increasing exposure doses. The progress of the electro-optical history of the transistor was evaluated by repeating I–V scan cycles both in the dark and under light exposure. The information recorded upon different exposure times was used to detect the photoactivated charge-trapping effects. The device showed a stable I–V response in the dark bias (V_DS = −10 V, −10 V ≤ V_GS ≤ +10 V) conditions and a persistent threshold voltage (V_T) shift under illumination at all irradiation wavelengths. We suggested that the observed dose-dependent V_T drifts were due to charge retention in trap sites within the organic semiconductor. The threshold voltage was recognized as the main parameter affected by charge retention. V_T variations were modelled versus time through a single exponential revealing a maximum in charge relaxation times for irradiations at wavelengths of 370 nm, in proximity of the C8BTBT bandgap energy. Furthermore, bias-stress effects and persistent photoinduced V_T drifts were found to depend on comparable characteristic times. Therefore, a common nature for both the bias-stress decay and relaxation from photoexcitation mechanisms is likely.     

Frenkel thermal-field effect in MnGaInS<Subscript>4</Subscript> layered single crystals

The I–V characteristics are investigated in the region of high electric fields in MnGaInS₄ single crystals. It is shown that the current in the nonlinear portion of the I–V characteristic is caused by the Frenkel thermal-field effect. The permittivity, trap concentration, and potential-well shape are determined.     

On current spreading in solar cells: a two-parameter tube model

The phenomenon of current spreading is essential for concentrator solar cells since it limits the conversion efficiency at high sunlight-concentration ratios. A model, which describes the regularities of the above phenomenon, is proposed and developed. The model uses a stylized representation of current lines and, respectively, of current tubes; it includes two resistive parameters accounting for the variable lateral (horizontal) component and the constant vertical component of the resistance of each tube. In the model the fact that the thickness of the spreading region is much less than the distance between the contact grid strips is taken into account. The calculated current—voltage (I–V) characteristics of a solar cell in the resistive and a nonresistive cases are obtained. The spreading-resistance I–V characteristic obtained by the voltage subtraction of these characteristics is nonlinear and depends on the photogenerated current. Thus, the equivalent electrical circuit of a solar cell includes a lumped nonlinear resistance, which depends parametrically on the photogenerated current. The comparison of experimental and calculated I–V characteristics by the example of Ge, GaAs, and GaInP solar cells is performed and both resistive parameters of the model are determined. The model describes correctly the regularities of spreading in single-junction solar cells and can be extended to multijunction solar cells.     

Current conduction mechanism of MIS devices using multidimensional minimization system program

The present work presents an evaluation approach which enables the in-depth analysis of current–voltage (I–V) characteristics of MIS devices to determine their current transport mechanisms using a multidimensional minimization system program.Exemplarily, the current transport mechanisms were determined for a TiN/SiO₂/p-Si MOS and a TaN/HfSiO/SiO₂/p-Si MIS structure by fitting the analytical expressions for different current transport mechanisms to experimental I–V data in a wide range of applied biases and temperatures. The considered mechanisms for the investigated samples include temperature dependent Fowler–Nordheim (FN) tunneling and Poole–Frenkel (PF) emission as well as ohmic conduction. The presented approach can easily be extended to account for additional mechanisms such as trap assisted tunneling (TAT) if relevant for different samples. In contrast to typical extraction procedures which determine current conduction mechanism parameters sequentially, in this work, the adjustable fit parameters are extracted in a single operation using the Levenberg–Marquardt algorithm (Nash, 1990) to obtain a least-square fit of the model to measured I–V characteristics. Thus, simultaneously occurring current mechanisms can properly be evaluated which allows to determine the fraction of each conduction mechanism quantitatively for each voltage.     

The effect of Mo-doped PVC+TCNQ interfacial layer on the electrical properties of Au/PVC+TCNQ/p-Si structures at room temperature

The effect of Mo-doped and undoped PVC+TCNQ interfacial layer on electrical characteristics of a Au/PVC+TCNQ/p-Si structure was investigated using current–voltage (I–V), capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements at room temperature. The energy dependent interface states density (N_ss) was obtained from the forward bias I–V data by taking into account voltage dependent effective barrier height (Φ_e) for two diodes, i.e. with and without Mo doping. The voltage dependent resistance (R_i) of structures was also obtained using Ohm׳s law and the method of Nicollian and Brews for the diodes. In order to eliminate the effect of series resistance (R_s), C and G/ω at high frequency values were corrected. N_ss and R_s values were compared between the diodes and experimental results showed that N_ss and R_s values of the Mo-doped PVC+TCNQ structure are considerably lower than those of the undoped PVC+TCNQ structure. The other important parameters such as ideality factor (n), reverse saturation current (I_s), zero-bias barrier heights (Φ_Bo) and R_s were obtained from forward bias I–V data by using I–V, Cheung and Norde methods. Experimental results confirmed that the Mo-doped (PVC+TCNQ) layer considerably improved the performance of the Au/PVC+TCNQ/p-Si structure.     

Fabrication and electrical properties of Al/aniline green/n-Si/AuSb structure

The current–voltage (I–V), capacitance–voltage (C–V) and capacitance–frequency (C–f) characteristics of Al/aniline green(AG)/n-Si/AuSb structure were investigated at room temperature. A modified Norde's function combined with conventional forward I–V method was used to extract the parameters including barrier height (BH) and the series resistance. The barrier height and series resistance obtained from Norde's function was compared with those from Cheung functions, and it was seen that there was a good agreement between the BH values and series resistances from both methods. The C–V characteristics were performed at 10 and 500 kHz frequencies, and C–f characteristics were performed 0.0, +0.4 and −0.4 V.     

Schottky-Barrier Model Nonlinear in Surface-State Concentration and Calculation of the <Emphasis Type="Italic">I–V</Emphasis> Characteristics of Diodes Based on SiC and Its Solid Solutions in the Composite Charge-Transport Model

A modified Schottky-barrier model, which is nonlinear in terms of the surface-state concentration and contains a local quasi-Fermi level at the interface induced by excess surface charge, is proposed. Such an approach makes it possible to explain the observed similarity of the I–V characteristics of diodes with the Schottky barrier M/(SiC)_1–x(AlN) _x and those of heterojunctions based on SiC and its solid solutions taking into account Φ_g ≈ Φ_B. The results of calculations of the Schottky-barrier heights are consistent with the experimental data obtained from measurements of the photocurrent for metals (M): Al, Ti, Cr, and Ni. The I–V characteristics in the composite–additive model of charge transport agree with the experimental data for the n-M/p-(SiC)_1–x(AlN) _x and n-6H-SiC/p-(SiC)_0.85(AlN)_0.15 systems.     

Effect of passivation of the p-CdTe surface in (NH4)2Sx on the current-voltage characteristics of contacts

The current-voltage (I–V) characteristics of contacts to CdTe are studied at 300 and 77 K. The contacts were obtained by chemical deposition of Au on the (111) surface of polycrystalline p-CdTe after etching in bromine methanol and after passivation in (NH₄)₂S_x. It is shown that passivation of the surface noticeably linearizes the I–V characteristics at 300 K and only slightly at 77 K. The measurements of the low-temperature photoconductivity of the samples showed that the passivation of the surface in (NH₄)₂S_x decreases the surface-state density at the metal-semiconductor interface.     

Model of V Hg Incorporation in Arsenic-Doped HgCdTe: First-Principles Calculations

Following the suggestion that the As_Hg–V _Hg and As_Hg–2V _Hg defect complexes are potential sources of carrier compensation observed in As-doped HgCdTe, we have studied the electronic properties and formation energies of these complexes. We find that these complexes are electrically active acceptors but have exceedingly high formation energies, meaning that they play no role in carrier compensation except at low temperatures. V _Hg will thus likely remain as an isolated defect. Such a model of V _Hg incorporation allows us to further predict the postgrowth As activation. Our prediction emphasizes the As_Hg–2V _Hg complex as the starting defect for As activation, rather than the As_Hg–V _Hg pair as previously suggested.     

Consideration of the “island” background charge in single-electron transistor simulation

Three approximations of the “island” background charge are described within the proposed 2D numerical model of the metal single-electron transistor. These approximations fit the experimental data well when calculating I–V characteristics of single-electron transistors according to the model developed in many cases. The validity of these approximations is exemplified by specific calculations of I–V characteristics.