Forward Bias Conditions Research Articles

Comparison of SOI and Partial-SOI LDMOSFETs Using Electrical–Thermal–Stress Coupled-Field Effect

The requirement of electrical-thermal-stress (E-T-S) modeling of semiconductor devices as indicated by ITRS2006 demands the use of finite-element analysis (FEA) for device simulation. In this paper, we perform E-T-S coupled-field simulation from the first principle by considering the stress-induced modification of the Si band structures and employ FEA software COMSOL to apply the E-T-S model on lateral double-diffused MOS field-effect transistors (LDMOSFETs) as an example. From the comparison of the electrical characteristics computed using the models with and without the mechanical stress caused by material thermal mismatch in the device structures, we found that the effect of the mechanical stress is insignificant in the forward-bias condition but it does have impact in the reverse-bias condition, namely, the reverse leakage current is higher if the mechanical stress is considered. Simulations are performed on two types of LDMOSFETs, namely, silicon-on-insulator (SOI) and partial-SOI (PSOI) LDMOSFETs, because the temperature and mechanical stress distributions are very different in these LDMOSFETs even under the same operating conditions. From the comparison of the computational results of SOI and PSOI LDMOSFETs, the results indicate that PSOI power LDMOSFET structure enables efficient heat conduction from the hot junctions and offers higher breakdown voltage.

Flexible photodiodes constructed with CdTe nanoparticle thin films and single ZnOnanowires on plastics

We construct a flexible pn heterostructured photodiode using a CdTe nanoparticle thinfilm and a single ZnO nanowire (NW) on a plastic substrate. The photocurrentcharacteristics of the flexible photodiode are examined under illumination with325 nm wavelength light and the photocurrent efficiencies at bias voltages of ± 2.5 V are estimatedto be 8.0 and 2.1 µA W − 1 under forward and reverse bias conditions, respectively. The photocurrent generation of thepn heterostructured photodiode is dominantly associated with the transport of thephotogenerated charge carriers in the single ZnO NW. Furthermore, the operations of ourflexible photodiode are investigated in the upwardly and downwardly bent states, as well asin the flat state.

Bias current dependence of spin accumulation signals in a silicon channel detected by a Schottky tunnel contact

We study the electrical detection of spin accumulation at a ferromagnet-silicon interface, which can be verified by measuring a Hanle effect in three-terminal lateral devices. The device structures used consist of a semiconducting Si channel and a Schottky tunnel contact. In a low current-bias region, the Hanle-effect curves are observed only under forward bias conditions. This can be considered that the electrical detectability at the forward-biased contact is higher than that at the reverse-biased contact. This is possible evidence for the detection of spin-polarized electrons created in a Si channel.

Comparison of DC performance of Pt/Ti/Au- and Ni/Au-gated AlGaN/GaN high electron mobility transistors

We have demonstrated significant improvements of AlGaN/GaN high electron mobility transistors (HEMTs) dc performance by employing Pt/Ti/Au instead of the conventional Ni/Au gate metallization. During off-state bias stressing, the typical critical voltage for HEMTs with Ni/Au gate metallization was ∼−45 to −65 V. By sharp contrast, no critical voltage was observed for HEMTs with Pt/Ti/Au gate metallization, even up to −100 V, which was the instrumental limitation in this experiment. After the off-state stressing, the drain current of Ni/Au gated-HEMTs decreased by ∼15%. For the Pt-gate HEMTs, no degradation of the drain current occurred and there were minimal changes in the Schottky gate characteristics for both forward and reverse bias conditions. The HEMTs with Pt/Ti/Au metallization showed an excellent drain on/off current ratio of 1.56×108. The on/off drain current ratio of Ni-gated HEMTs was dependent on the drain bias voltage and ranged from 1.16×107 at VDS=5 V and 6.29×105 VDS=40 V due to the larger gate leakage current at higher drain bias voltage.

On the input common‐mode voltage range of CMOS bulk‐driven input stages

AbstractIn this paper the response of a bulk‐driven MOS Metal‐Oxide‐Semiconductor input stage over the input common‐mode voltage range is discussed and experimentally evaluated. In particular, the behavior of the effective input transconductance and the input current is studied for different gate bias voltages of the input transistors. A comparison between simulated and measured results, in standard 0.35‐µm CMOS Complementary Metal‐Oxide‐Semiconductor technology, demonstrates that the model of the MOS transistors is not sufficiently accurate for devices operating under forward bias conditions of their source‐bulk pn junction. Therefore, the fabrication and the experimental evaluation of any solution based on this approach are highly recommended. A technique to automatically control the gate bias voltage of a bulk‐driven differential pair is proposed to optimize the design tradeoff between the effective input transconductance and the input current. The proposed input stage was integrated as a standalone block and was also included in a 1.5‐V second‐order operational transconductance amplifier (OTA)‐C lowpass filter. Experimental results validate the effectiveness of the approach. Copyright © 2010 John Wiley & Sons, Ltd.

Fabrication and liquefied petroleum gas (LPG) sensing performance of p-polyaniline/n-PbS heterojunction at room temperature

In the present work, we report the fabrication and liquefied petroleum gas (LPG) sensing performance of p-polyaniline/n-PbS heterojunction at room. The p-polyaniline/n-PbS heterojunction was fabricated by electrodepositing polyaniline on predeposited PbS thin film by chemical bath deposition. The PbS and polyaniline films were characterized for their structural as well as surface morphological analyses. The XRD analyses revealed that PbS thin film is polycrystalline whereas polyaniline exhibited amorphous nature. The scanning electron micrographs of PbS film showed the formation of compact and well covered nanograins whereas, polyaniline has interconnected fuzzy nanofibrous architecture. Room temperature LPG response of heterojunction in forward biased condition showed the maximum response up to 70% at 0.06 vol.% of LPG.

Time-Domain Travelling-Wave Model for Quantum Dot Passively Mode-Locked Lasers

We present a time-domain travelling-wave model for the simulation of passive mode-locking in quantum dot (QD) lasers; accurate expressions for the time varying QD optical susceptibility and the QD spontaneous emission noise source are introduced in the 1-D wave equations and numerically described using a set of infinite-impulse response filters. The inhomogeneous broadening of the density of states of the whole QD ensemble as well as the homogeneous linewidth of each QD interband transition are properly taken into account in the model. Population dynamics in the QD, quantum well, and barrier states under both forward and reverse bias conditions are modeled via proper sets of multi-population rate equations coupled with the field propagation equations. The model is first applied to the study of gain and absorption recovery in a QD semiconductor optical amplifier under both forward and reverse bias conditions. Simulations of passive mode-locking in a two-section QD laser are then performed as a function of the bias parameters. Gain and absorption dynamics leading to the generation of mode-locking pulses is described. The onset of a trailing-edge instability at low currents is observed and fully explained in the framework of the described model.

Growth and properties of transparent p-NiO/n-ITO (In2O3:Sn) p–n junction thin film diode

We have grown “all oxide” transparent p–n junction thin film nanostructure device by using chemical solution deposition and E-beam evaporation onto SiO2 substrate. Combined grazing incidence X-ray diffraction and atomic force microscopy confirm phase pure, mono-disperse 30nm NiO and 2at. wt.% Sn doped In2O3 (ITO) nanocrystallites. Better than 70% optical transparency, at a wavelength of 600nm, is achieved across 160nm thick p–n junction. The optical band gap across the junction was found to decrease as compared to the intrinsic ITO and NiO. The current–voltage (I–V) characteristics show rectifying nature with dynamic transfer resistance ratio of the order of 103 in the forward bias condition. Very small reverse leakage current with appreciable breakdown was observed under the reverse bias condition. The observed optical and electrical properties of oxide transparent diode are attributed to the heteroepitaxial nature and carrier diffusion at the junction interface.

Enhancement of Electron Injection in Organic Light-Emitting Diodes with Photosensitive Charge Generation Layer

We describe the enhancement of electron injection by external light irradiation in organic light-emitting diodes (OLEDs) with a charge generation layer (CGL). Under He–Ne laser irradiation, photon-induced charge generation under electric field occurred in the CGL. Electrons and holes were generated in the CGL and the electrons were directly injected into adjacent electron transport layers. As a result, the enhancement of current density under light irradiation was observed. A thousand fold enhancement of current density was obtained for light irradiation under forward biased condition. Current density was determined by the intensity of light irradiation and was saturated under the higher voltage regions. Up-converted light emission was also observed under the light irradiation.

Ultraviolet electroluminescence from ZnO-based light-emitting diode with p-ZnO:N/n-GaN:Si heterojunction structure

A p-ZnO:N/n-GaN:Si structure heterojunction light-emitting diode (LED) is fabricated on c-plane sapphire by full metal organic chemical vapor deposition (MOCVD) technique. The p-type layer with hole concentration of 8.94×1016cm−3 is composed of nitrogen-doped ZnO using NH3 as the doping source with subsequent annealing in N2O plasma ambient. Silicon-doped GaN film with electron concentration of 1.15×1018cm−3 is used as the n-type layer. Desirable rectifying behavior is observed from the current–voltage (I–V) curve of the device. The forward turn on voltage is about 4V and the reverse breakdown voltage is more than 7V. A distinct ultraviolet (UV) electroluminescence (EL) with a dominant emission peak centered at 390nm is detected at room temperature from the heterojunction structure under forward bias conditions. The origins of the EL emissions are discussed in comparison with the photoluminescence (PL) spectra.

Impedance spectra under forward and reverse bias conditions in gold/porous silicon/p‐Si structures

AbstractAbstract – The AC electrical characterization of Au/porous silicon/p‐Si structure is presented. The low porosity porous silicon layers were prepared by electrochemical etching in p‐type silicon 〈100〉 with two resistivities. The AC electrical measurements capacitance–conductance–frequency were performed from 5 Hz to 10 MHz, at room temperature in the DC range of ±2 V. We studied two structures; first a conductor type Au/PS/Au and second diode type Au/PS/p‐Si/Al. We found the relationship between the bias voltage in the PS/p‐Si heterostructures with the depletion region formation and the conduction mechanism presents in these structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparative study of AlGaN/GaN HEMTs robustness versus buffer design variations by applying Electroluminescence and electrical measurements

By means of step stressing tests on AlGaN/GaN HEMTs the robustness properties of devices fabricated on wafers with different buffer designs have been compared to each other (standard UID GaN buffer and UID Al 0.05Ga 0.95N back-barrier in combination with GaN channel layer). The devices with GaN buffer showed an abrupt increase of gate leakage current after reaching drain bias values in the range of 30 V while devices with Al 0.05Ga 0.95N back-barrier did not show any degradation up to 120 V drain bias. All DC-Step-Stress tests have been accompanied by Electroluminescence (EL) analysis and electrical characterization techniques before, during and after stress. It has been shown that EL at forward and reverse bias conditions can be used as an indicator of potential device degradation. Devices comprising an AlGaN back-barrier design demonstrated superior robustness.

1.54 μ m emitters based on erbium doped InGaN p-i-n junctions

We present here on the growth, fabrication and electroluminescence (EL) characteristics of light emitting diodes (LEDs) based on Er-doped InGaN active layers. The p-i-n structures were grown using metal organic chemical vapor deposition and processed into 300×300 μm2 mesa devices. The LEDs exhibit strong emissions at 1.0 and 1.54 μm, due to Er intra-4f transitions, under forward bias conditions. The emitted EL intensity increases with applied input current without exhibiting saturation up to 70 mA. The integrated power over the near infrared emission, measured at room temperature from the top of a bare chip, is about 2 μW. The results represent a significant advance in the development of current injected, chip-scale emitters and waveguide amplifiers based on Er doped semiconductors.

Influence of Different Iodide Salts on the Performance of Dye-Sensitized Solar Cells Containing Phosphazene-Based Nonvolatile Electrolytes

Polyphosphazene-based electrolytes containing different iodide salts were studied as components of dye-sensitized solar cells (DSSCs). Electrolytes based on hexa[methoxyethoxyethoxycyclotriphosphazene] (MEE trimer) with dissolved LiI, NaI, NH4I, and 1-methyl-3-propylimidazolium (PMII) and I2 were examined by ac conductivity and steady-state voltammetry. These measurements gave the individual conductivities of I−, I3−, and cations in each electrolyte as a function of salt concentration. The anionic conductivities were highest in the PMII system and decreased in the order PMII > NH4I > NaI > LiI. Photovoltaic measurements of DSSCs containing these electrolytes showed the same order of performance, and electrochemical impedance spectra (EIS) under open circuit and forward bias conditions were used to study the separate impedance components of the cells. High polymeric polyphosphazene−plasticizer blends with a dissolved PMII/I2 electrolyte gave better performance in DSSCs than equivalent poly(ethylene oxide)−...

Optimization on Layout Style of ESD Protection Diode for Radio-Frequency Front-End and High-Speed I/O Interface Circuits

The diode operated in forward-biased condition has been widely used as an effective on-chip electrostatic discharge (ESD) protection device at radio-frequency (RF) front-end and high-speed input/output (I/O) pads due to the small parasitic loading effect and high ESD robustness in CMOS integrated circuits (ICs). This work presents new ESD protection diodes drawn in the octagon, waffle-hollow, and octagon-hollow layout styles to improve the efficiency of ESD current distribution and to reduce the parasitic capacitance. The measured results confirmed that they can achieve smaller parasitic capacitance under the same ESD robustness level as compared to the stripe and waffle diodes, especially for the diodes drawn in the hollow layout style. Therefore, the signal degradation of RF and high-speed transmission can be reduced because of smaller parasitic capacitance from the new proposed diodes.

Synthesis and Electrical Characterization of Multilayer Thin Films Designed by Layer-by-Layer Self Assembly of Nanoparticles

In this work, we report the directed self organization of multilayer thin film devices with colloidal nanoparticles through Layer-by-Layer (LbL) technique [1]. Self-organization of nanoparticles into assemblies to create novel nanostructures is getting increasing research attention in microelectronics, medical, energy and environmental applications. Directed self-organization of nanoparticles [2] into multilayer thin films were achieved by LbL growth through the interaction of oppositely charged of colloidal nanoparticles on substrates of any kind and shapes. Multilayer thin film devices were fabricated using multilayers of gold (conducting) nanoparticles separated by a dielectric nanoparticulate layer of zinc sulphide. The thin films obtained have been studied extensively and the changes in surface morphology, the optical absorption characteristics, thickness, uniformity, adhesion, and conduction behavior are reported. Current voltage (I-V) characteristics of multilayer devices with an increasing number of deposition cycles show an initial current blockade until an onset voltage value, which increases linearly upon the additional layers stacked in devices [3]. A conductive behavior of the device was observed upon exceeding the onset voltage. Moreover, I-V behavior showed that the conduction onset voltage increases linearly depending on the numbers of layers in the final device controlled by the deposition cycles. Systematic I-V characteristics in the forward and reverse biased conditions demonstrated rectifying behaviors in the onset of conduction voltage which makes these films attractive for future electronic device applications.

Study of C– V characteristics in thin n +-p-p + silicon solar cells and induced junction n-p-p + cell structures

Capacitance–voltage ( C– V) measurements were carried out on conventional n +-p-p + structure based silicon solar cells (SSC) of different thicknesses (40–300 μm) and on induced junction n +-p-p + structures (IJS) under dark at room temperature. The capacitance is determined from the best fit of the measured data. It is shown that the capacitance under reverse and forward bias condition can be divided into two distinct regions, which are correlated to the quality of the junction and effectiveness of back surface field (BSF). It is found that the IJS has shallow junction and better BSF than the conventional solar cells.

A‐Si:H temperature sensor integrated in a thin film heater

AbstractIn this work we present an hydrogenated amorphous silicon (a‐Si:H) temperature sensor integrated in a thin film heater to perform biomolecular treatments. The system is fabricated on a microscope glass slide and includes a PolyDiMethylSiloxane (PDMS) chamber to confine the solution containing the sample and to avoid its evaporation. The heater is a 200 nm‐thick titanium/tungsten sputtered film with a serpentine shaped geometry that has been designed by a finite element simulator in order to obtain a spatial‐uniform temperature distribution. A uniformity better than 3% has been achieved over the surface of the structure. The temperature sensor is a n‐type/intrinsic/p‐type a‐Si:H stacked structure deposited by plasma enhanced chemical vapor deposition. The top and bottom contacts of the diode are made by the same metal utilized to fabricate the heater. The characterization of the sensor response has been performed both under forward and reverse bias condition. In reverse bias condition, at fixed voltage, the current–temperature curve exhibits an exponential behavior. In forward bias condition, at constant bias current, the voltage across the diode is linearly dependent on the temperature in the range 30–90 °C. In particular, using a constant bias current of 10 nA, a sensitivity around −3.3 mV/°C has been achieved.

A Self-Consistent Model of the OCVD Behavior of Si and 4H-SiC $\hbox{p}^{+}\hbox{-n-n}^{+}$ Diodes

A comprehensive analytical model of the open-circuit voltage-decay (OCVD) response for a generic diode, switched from an arbitrary forward-bias condition, is proposed. To properly account for the steady-state conditions of the diode, the dynamic model incorporates an accurate description of the static <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> curves, which turns also useful for better understanding the influence of physical parameters on voltage transitory. As shown from comparisons with simulations and experiments, the model accurately describes the spatial-temporal variation of carriers and currents along the whole epilayer and allows one to resolve some ambiguities reported in the literature, such as the stated inapplicability of the OCVD method on thick epilayers, the reasons of the observed nonlinear decay of the voltage with time, and the effects of junction properties on voltage transient.

Reduction of I2/I3− by Titanium Dioxide

A photoelectrochemical cell was designed that allowed the reactivity of oxidized iodide species with mesoporous nanocrystalline (anatase) TiO2 thin films to be quantified spectroscopically on nanosecond and longer time scales in half molar iodide acetonitrile solutions. Under forward bias conditions, TiO2 did not react with photogenerated iodine radical anions, I2−•, that were found instead to disproportionate with a rate constant that was within experimental error the same as that measured in fluid acetonitrile solution, k = 3 × 109 M−1 s−1. The absence of reactivity with I2−• was unexpected. It appears that the reduction of I2−• by TiO2(e−) does not complete kinetically with rapid I2−• disproportionation. In contrast, TiO2(e−) was found to decrease the concentration of tri-iodide, I3−, and presumably molecular iodine, I2, that was expected to be present in low equilibrium concentrations. The findings have relevance to unwanted charge recombination processes in dye sensitized solar cells.