Temperature Dependence Of Current-voltage Characteristics Research Articles

Compact and Distributed Modeling of Cryogenic Bulk MOSFET Operation

We have developed compact and physics-based distributed numerical models for cryogenic bulk MOSFET operation down to 20 K to advance simulation and first-pass design of device and circuit operation at low temperatures. To achieve this, we measured and simulated temperature-dependent current-voltage characteristics of 0.16- and 0.18- bulk MOSFETs. Our measurements indicate that these MOSFETs supply approximately 40% more current in the saturation and linear regions of operation when they are cooled from room temperature to 20 K. The threshold voltage monotonically increases as the temperature is lowered, but it saturates below 40 K. The subthreshold slope decreases with the temperature lowering but at a rate that is less than theoretically predicted. The extrapolation of the subthreshold slope indicates a finite value at near absolute zero. We show that the measured behavior can be well corroborated with distributed numerical simulations using the drift-diffusion transport model. In addition, to obtain a compact model for use in low-temperature circuit design, SPICE-type compact models need to be modified to incorporate the subtle temperature effects that are not part of the standard models. To this end, we use the analog behavioral language Verilog-A and the BSIM3 model equation set to include additional temperature dependences into the standard compact models to accurately reproduce measured characteristics.

Trap-free space-charge-limited electron transport in amorphous tin(IV) phthalocyanine dichloride thin film

The morphology and electrical properties of thin films of an n-type organic semiconductor tin(IV) phthalocyanine dichloride (SnCl2Pc) are investigated. An investigation of atomic force microscopy and x-ray diffraction shows that the vacuum-deposited SnCl2Pc films on room-temperature glass substrates exhibit a homogeneous amorphous state. The temperature-dependent current–voltage characteristics of the electron-only devices show that the electron transport in SnCl2Pc thin films is bulk-limited, from the Ohmic region (J ∼ V) at low voltages to the trap-free space-charge-limited current (TFSCLC) region (J ∼ V2) at high voltages. The linear dependence of current on voltage at low voltages yields the temperature-dependent conductivity, while the TFSCLC relationship provides a direct measurement of the free-electron mobility as a function of electric field and temperature. The zero-field electron mobility at 293 K is as high as (1.8 ± 0.3) × 10−4 cm2 V−1 s−1. It can be seen that the obtained mobility and conductivity obey well the Gaussian disorder model and the three-dimensional variable range hopping model, respectively.

Fabrication and Characterization of Low-Temperature Poly-Silicon Lateral p-i-n Diode

We have studied a lateral p-i-n photodiode made of excimer-laser-annealed poly-Si on glass. The diode quality factor, activation energy of diode currents at -3 V, and built-in potential were found to be 1.6, 0.5 eV, and 0.89 eV, respectively, which were achieved from temperature-dependent current-voltage characteristics. The 50-nm-thick p-i-n diode shows a high rectification ratio of > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> at ±1 V and a relatively high photoresponse at 500 lx. PACS: 81.05.Gc; 62.20.-x; 07.10.Lw; 07.10.Pz.

Bias and temperature dependent charge transport in high mobility cobalt-phthalocyanine thin films

The temperature dependent current-voltage (J-V) characteristics of highly-oriented cobalt phthalocyanine films (rocking-curve width=0.11°) deposited on (001) LaAlO3 substrates are investigated. In the temperature range 300–100 K, charge transport is governed by bulk-limited processes with a bias dependent crossover from Ohmic (J∼V) to trap-free space-charge-limited conduction (J∼V2). The mobility (μ) at 300 K has a value of ∼7 cm2 V−1 s−1 and obeys Arrhenius-type (ln μ∼1/T) behavior. However, at temperatures &amp;lt;100 K, the charge transport is electrode-limited, which undergoes a bias dependent transition from Schottky (ln J∼V1/2) to multistep-tunneling (conductivity varying exponentially on the inverse of the square-root of electric field).

Spin Filter Effect of La0.7Sr0.3MnO3/Bi1-xBaxFeO3 Junctions

Spin-filter devises were fabricated using multiferroic Bi1-xBaxFeO3 films. La1-xSrxMnO3/Bi1-xBaxFeO3/LaNiO3 junctions showed non-linear current-voltage characteristics with barrier height of 0.37eV and magnetoresistance (MR) of 2.3% at 4.2 K. These results indicate ultra-thin Bi1-xBaxFeO3 layers behaved as ferromagnetic tunnel barriers and showed spin-filter effects. From the analysis of the temperature dependence of current-voltage characteristics of the junctions and the leakage current of Bi1-xBaxFeO3 layers, one of possible reasons for low MR is suppression of spin-filter effects by tunneling through defect levels induced by O and/or Bi deficiency in Bi1-xBaxFeO3 tunnel barriers.

Analysis of Reverse-Bias Leakage Current Mechanisms in Metal/GaN Schottky Diodes

Temperature-dependent reverse-bias current-voltage characteristics obtained by other researchers for Schottky diodes fabricated on GaN are reinterpreted in terms of phonon-assisted tunneling (PhAT) model. Temperature dependence of reverse-bias leakage current is shown could be caused by the temperature dependence of electron tunneling rate from traps in the metal-semiconductor interface to the conduction band of semiconductor. A good fit of experimental data with the theory is received in a wide temperature range (from 80 K to 500 K) using for calculation the effective mass of 0.222 . and for the phonon energy the value of 70 meV. The temperature and bias voltages dependences of an apparent barrier height (activation energy) are also explicable in the framework of the PhAT model.

Electrical Properties of RF Sputtered CdTe/CdS Thin Film Solar Cells

The charge transport properties of CdTe/CdS solar cells deposited by radio frequency (RF) sputtering have been investigated and presented in this article. The temperature dependent current-voltage characteristics of the devices under dark condition were carried out in the temperature range 240-340 K. The capacitance of the devices at various frequencies was also investigated. procedures and both CdTe and CdS films were deposited using RF sputtering technique. The thickness of the films was approximately 2.0 μm for CdTe and 0.13 μm for the CdS film. The CdTe/CdS heterojunction was vapor chloride treated at 390 °C for 30 minutes under a flow of dry air. Pseudo ohmic contact to CdTe was obtained by vacuum evaporating 3 nm of Cu followed by 50 nm Au. The Cu diffusion was achieved by annealing the contacts at 150 °C for 35 minutes.

Temperature dependence of electrophysical characteristics of zinc oxide based varistors

ZnO-based varistors were fabricated by sintering zinc oxide micro crystals with several additives of metal oxides. To avoid the shortage of oxygen, the samples were annealed in a continuously oxygen injected oven at 400 °C for 3–6 h. Temperature dependence of current-voltage characteristics (CVC) and the electrical conductivity of these samples were investigated in the temperature range 25–190 °C. They exhibited high nonlinearity in their I-V characteristics. The nonlinear coefficient varied between 40 and 60 but the highest nonlinearity coefficient for an individual sample was β = 100. At high temperatures, nonlinearity in the I-V characteristics of samples disappeared and the conductivity became ohmic in nature. The observed nonlinearity, an exponential dependence of electric conductivity, and also reduction of samples opening voltage are related with zinc oxide grain boundaries. In all temperature intervals, the hysteresis on curves I = f ( U) was observed.

Nanograins dependent dielectric constant, tunability, phase transition, impedance spectroscopy and leakage current of (Pb 1 − xSr x)TiO 3 thin films

Nanostructured (Pb 1 − x Sr x )TiO 3 (PST) ( x = 0.1, 0.2 and 0.3) thin films have been prepared by chemical solution deposition process using spin coating technique. The solution as such was deposited on Pt/Ti/SiO 2/Si substrates and annealed at 650 °C/3h. Nanograins dependent dielectric properties of PST films show dielectric constant up to the higher frequency region, low losses, large tunability and phase transition at small temperature. The impedance data has been fitted by Cole–Cole model to study the effect of grain boundaries on the dielectric properties. The current–voltage characteristics have been measured to study leakage current in PST films and described by Poole–Frenkel emission model. It is suggested that the key carrier transport process in PST films is emission of electrons from a trap state near the metal–film interface into a continuum of states associated with each conductive dislocation. The activation energy value for carrier transport in PST films is obtained from temperature-dependent current–voltage characteristics.

Temperature dependence of current-voltage characteristics in highly doped Ag/p-GaN/In Schottky diodes

To obtain detailed information about the conduction process of the Ag/p-GaN Schottky diodes (SDs) fabricated by us, we measured the I-V characteristics over the temperature range of 80–360 K by the steps of 20 K. The slope of the linear portion of the forward bias I-V plot and nkT=E0 of the device remained almost unchanged as independent of temperature with an average of 25.71±0.90 V−1 and 41.44±1.38 meV, respectively. Therefore, it can be said that the experimental I-V data quite well obey the field emission model rather than the thermionic emission or thermionic field emission model. The study is a very good experimental example for the FE model. Furthermore, the reverse bias saturation current ranges from 8.34×10−8 A at 80 K to 2.10×10−7 A at 360 K, indicating that the charge transport mechanism in the Ag/p-GaN SD is tunneling due to the weak temperature dependence of the saturation current. The possible origin of high experimental characteristic tunneling energy of E00=39 meV, which is ten times larger than possible theoretical value of 3.89 meV, is attributed to the accumulation of a large amount of defect states near the GaN surface or to the deep level defect band induced by high doping or to any mechanism which enhances the electric field and the state density at the semiconductor surface.

High- k HfO 2–Ta 2O 5 mixed layers: Electrical characteristics and mechanisms of conductivity

Electrical properties of mixed HfO 2–Ta 2O 5 films (10;15 nm) deposited by rf sputtering on Si have been studied from the view point of their applications as high- k layers, by standard capacitance–voltage and temperature dependent current–voltage characteristics. The effect of HfO 2 addition to the Ta 2O 5 is thickness dependent and the thicker layers exhibit advantages over the pure Ta 2O 5 (higher dielectric constant, enhanced charge storage density and improved interface quality). The process of HfO 2 and Ta 2O 5 mixing introduces negative oxide charge, tends to creates shallow bulk traps and modifies the dominant conduction mechanisms in the stack capacitors as compared to the Ta 2O 5-based one (a contribution of tunneling processes through traps located below the conduction band of mixed layers to the leakage current in the HfO 2–Ta 2O 5 stacks is observed). The traps involved in both Poole–Frenkel and tunneling processes are identified.

Properties of Tl 4Se 3S single crystals and characterization of Ag/Tl 4Se 3S Schottky barrier diodes

The main physical properties of Tl 4Se 3S single crystals were investigated for the first time. Particularly, the crystal data, Debye temperature, dark electrical resistivity and Hall effect in addition to the temperature dependent current–voltage characteristics and photosensitivity of the Ag/Tl 4Se 3S Schottky barrier diode were studied. The X-ray diffraction patterns have revealed that the crystal exhibited a single phase of tetragonal structure belonging to the D 4 h 18 - I 4 mcm space group. A Debye temperature of 100 K was calculated using the results of the X-ray diffraction analysis. The dark electrical resistivity and Hall-effect measurements indicated that the samples exhibits p-type conduction with an electrical resistivity, carrier concentration and Hall mobility of 6.20 × 10 3 Ωcm, 1.16 × 10 12 cm −3 and 873 cm 2 V −1 s −1, respectively. The crystals were observed to have Schottky diode properties. The Ag/Tl 4Se 3S Schottky barrier device bias voltage was observed to depend on the crystal direction and on temperature. It was found that the calculated energy barrier height decreased and the diode ideality factor increased with temperature decreasing. The photosensitivity–light intensity dependence of this device was found to be linear reflecting the ability of using it in optoelectronics.

Temperature dependent current–voltage characteristics of the Cd/CdO/n–Si/Au–Sb structure

In this study, this is the first time, it has been employed Successive Ionic Layer Adsorption and Reaction (SILAR) method in order to prepare Cd/CdO/n–Si/Au–Sb sandwich structure. The sample temperature effect on the current–voltage ( I– V) characteristics of Cd/CdO/n–Si/Au–Sb structure has been investigated in a wide temperature range by steps of 20 K. The parameters such as barrier height, ideality factor and series resistance of this structure have been calculated from the forward bias I– V characteristics as a function of sample temperature. With a decreasing temperature, a decreasing in the apparent barrier height ( Φ b 0) , an increasing in the ideality factor ( n) and a nonlinearity in the activation energy plot have been seen. The experimental values of barrier height and ideality factor for this device have been calculated as 0.871 eV and 1.787 at 300 K and 0.436 eV and 2.221 at 80 K, respectively. These abnormal behaviors can be explain by the barrier inhomogeneities at the metal–semiconductor ( M– S) interface. From the temperature dependent I– V characteristics of the Cd/CdO/n–Si/Au–Sb sandwich structure, Φ ¯ b 0 and A ∗ are calculated as 0.790 and 1.160 eV, and 153.90 and 188.42 A/cm 2 K 2, respectively, by using ln ( I 0 / T 2 ) - q 2 σ s 2 / 2 k 2 T 2 vs . 1 /T plot for the two temperature regions. Deviation of experimental values of A ∗ from known value for n–Si has been attributed to the spatial inhomogeneous barrier heights and potential fluctuations at the interface that consist of low and high barrier areas.

Formation of the charge selective contact in solar cells with extremely thin absorber based on ZnO-nanorod/In2S3/CuSCN

Annealed and not-annealed solar cells with extremely thin absorber based on ZnO-nanorod /In2S3/CuSCN structures have been compared. Significantly higher external quantum efficiencies have been recorded on annealed devices. The temperature dependent current-voltage characteristics in the dark and under illumination were analyzed in detail. The short-circuit current density increased with the temperature and depended on the light intensity by a power law with a power coefficient of 0.85 that was independent of the annealing or measurement temperature. The temperature dependence of the ideality factor dominated the temperature dependencies of the diode saturation current density and of the open circuit voltage. The activation energies increased strongly after annealing. We propose that the limiting charge selective contact is driven away from the highly defective In2S3/CuSCN interface into the In2S3 layer due to stimulated by the annealing Cu diffusion.

Temperature-dependent current–voltage characteristics of the Au/n-InP diodes with inhomogeneous Schottky barrier height

Abstract The current–voltage (I–V) characteristics of Au/n-InP Schottky contacts have been measured in the temperature range of 70–300 K by steps of 10 K. Our data of the Au/n-InP Schottky contact strongly suggest that the temperature-dependent electron transport at the metal–semiconductor interface is significantly affected by the barrier inhomogeneity. The distribution of local effective SBHs has been modeled by a summation of existence of double Gaussian barrier heights which represents the high- and low-barrier of the full distribution in 170–300 and 70–170 K ranges.

Dislocation-governed current-transport mechanism in (Ni/Au)–AlGaN/AlN/GaN heterostructures

The current-transport mechanisms in (Ni/Au)–Al0,22Ga0,78N/AlN/GaN heterostructures were studied by using temperature dependent forward-bias current-voltage (I-V) characteristics in the temperature range of 80–410 K. In order to determine the current mechanisms for (Ni/Au)–Al0,22Ga0,78N/AlN/GaN heterostructures, we fitted the experimental I-V data to the analytical expressions given for the current-transport mechanisms in a wide range of applied biases and at different temperatures. The contributions of thermionic-emission, generation-recombination, tunneling, leakage currents that are caused by inhomogeneities, and defects at the metal-semiconductor interface current mechanisms were all taken into account. The best fitting results were obtained for the tunneling current mechanism. On the other hand, we did not observe sufficient agreement between the experimental data and the other current mechanisms. The temperature dependencies of the tunneling saturation current (It) and tunneling parameters (E0) were obtained from fitting results. We observed a weak temperature dependence of the saturation current and the absence of the temperature dependence of the tunneling parameters in this temperature range. The results indicate that in the temperature range of 80–410 K, the mechanism of charge transport in the (Ni/Au)−Al0.22Ga0.78N/AlN/GaN heterostructure is performed by tunneling among those dislocations intersecting the space charge region. The dislocation density (D) that was calculated from the I-V characteristics, according to a model of tunneling along the dislocation line, gives the value of 0.24×107 cm−2. This value is close in magnitude to the dislocation density that was obtained from the x-ray diffraction measurements.

Carrier transport mechanism in aluminum nanoparticle embedded AlQ 3 structures for organic bistable memory devices

Electrical bistability is demonstrated in organic memory devices based on tris-(8-hydroxyquinoline)aluminum (AlQ 3) and aluminum nanoparticles. The role of the thickness of middle aluminum layer and the size of the nanoparticles in device performance is investigated. Above a threshold voltage, the device suddenly switches from a low conductivity OFF state to a high conductivity ON state with a conductivity difference of several orders of magnitude. The OFF state of the device could be recovered by applying a relatively high voltage pulse. The electronic transition is attributed to an electric field induced transfer of charge between aluminum nanoparticles and AlQ 3. The type of charge carriers responsible for conductance switching is investigated. The charge carrier conduction mechanism through the device in ON and OFF states is studied by temperature dependent current–voltage characteristics and analyzed in the framework of existing theoretical models. The conduction mechanism in the OFF state is dominated by field-enhanced thermal excitation of charge carriers from localized centers, whereas it changes to Fowler–Nordheim tunneling of charge carriers in the ON state. The device exhibited excellent stability in either conductivity states. The results indicate the strong potential of the device towards its application as a nonvolatile electronic memory.

On a current mechanism in Ta2O5 thin films

Abstract Electrical conduction in the temperature range of 120–370 K has been studied in sandwiched structures of Al/Ta2O5/Si. The tantalum oxide films were prepared by evaporation of tantalum on a p-Si crystal substrate, followed by oxidation at a temperature of 600°C. The temperature-dependent current-voltage (I–V) characteristics are explained on the basis of a phonon-assisted tunnelling model. The same explanation is given for I–V data measured on Ta2O5 films by other investigators. From the comparison of experimental data with theory the density of states in the interface layer is derived and the electron-phonon interaction constant is assessed.

Electrical Characterization of ZnO Single Nanowire Device for Chemical Sensor Application

Vertically well-aligned high quality ZnO nanowires were grown on GaN epilayer on c-plane sapphire via a vapor-liquid-solid (VLS) process by introducing an Au thin film (3 nm) as a catalyst. ZnO single nanowire device was ingenuously fabricated by combining conventional optical lithography and high resolution electron beam lithography and its current-voltage characteristics were measured with doing the post process to acquire reproducible performance as a chemical gas sensor. And its temperature dependent current-voltage characteristics were measured to investigate temperature dependant electrical transport. The ZnO nanowire device showed slightly non-ohmic current-voltage characteristics which may be due to back-to-back configuration of the diodes with the insulating contact barriers and showed an relatively small activation energy of 0.2 eV. To test our device as a chemical sensor, the NO2 gas response was reported at the elevated temperature.

Current-voltage characteristics and transport mechanism of solar cells based on ZnO nanorods/In2S3∕CuSCN

Temperature dependent current-voltage characteristics in the dark and under illumination have been analyzed on up to 3.2% efficient solar cells with extremely thin absorber based on ZnO nanorods/In2S3∕CuSCN structures. The diode ideality factor and the open circuit voltage are strongly influenced on a thermal activation process. Significant enhancement of the devices efficiency by annealing at moderate temperatures has been demonstrated. After this annealing, the activation energy of the saturation current increased from 1.00to1.46eV (in the dark). Transport mechanisms at the In2S3∕CuSCN interface region are discussed.