Showing papers on "Diode published in 2005"

Semiconductor Detector Systems

Abstract: 0. Preface 1. Detector systems overview 2. Signal formation and acquisition 3. Electronic noise 4. Signal processing 5. Elements of digital electronics and signal processing 6. Transistors and amplifiers 7. Radiation effects 8. Detector systems 9. Why things don't work A. Semiconductor device technology B. Phasors and complex algebra in electrical circuits C. Equivalent circuits D. Feedback amplifiers E. The diode equation F. Electrical effects of impurities and defects G. Bipolar transistor equations

A single-molecule diode

Abstract: We have designed and synthesized a molecular rod that consists of two weakly coupled electronic π -systems with mutually shifted energy levels. The asymmetry thus implied manifests itself in a current–voltage characteristic with pronounced dependence on the sign of the bias voltage, which makes the molecule a prototype for a molecular diode. The individual molecules were immobilized by sulfur–gold bonds between both electrodes of a mechanically controlled break junction, and their electronic transport properties have been investigated. The results indeed show diode-like current–voltage characteristics. In contrast to that, control experiments with symmetric molecular rods consisting of two identical π -systems did not show significant asymmetries in the transport properties. To investigate the underlying transport mechanism, phenomenological arguments are combined with calculations based on density functional theory. The theoretical analysis suggests that the bias dependence of the polarizability of the molecule feeds back into the current leading to an asymmetric shape of the current–voltage characteristics, similar to the phenomena in a semiconductor diode.

Enhanced light extraction from GaN-based light-emitting diodes with holographically generated two-dimensional photonic crystal patterns

Abstract: We observed a significant enhancement in light output from GaN-based light-emitting diodes (LEDs) in which two-dimensional photonic crystal (PC) patterns were integrated. Two-dimensional square-lattice air-hole array patterns with a period that varied from 300 to 700 nm were generated by laser holography. Unlike the commonly utilized electron-beam lithographic technique, the holographic method can make patterns over a large area with high throughput. The resultant PC-LED devices with a pattern period of ∼500nm had more than double the output power, as measured from the top of the device. The experimental observations are qualitatively consistent with the results of three-dimensional finite-difference-time-domain simulation.

Photovoltaic effect in ideal carbon nanotube diodes

Abstract: We demonstrate that individual single-walled carbon nanotubes (SWNTs) can form ideal p-n junction diodes. An ideal behavior is the theoretical limit of performance for any diode, a highly sought after goal in all electronic materials development. We further elaborate on their properties by examining photovoltaic effects, an application where its performance is intimately related to the quality of the diode. Under illumination, SWNT diodes show significant power conversion efficiencies owing to enhanced properties of an ideal diode.

Electro-tunable optical diode based on photonic bandgap liquid-crystal heterojunctions.

Abstract: Manipulation of light is in strong demand in information technologies. Among the wide range of linear and nonlinear optical devices that have been used, growing attention has been paid to photonic crystals that possess a periodic modulation of dielectric function. Among many photonic bandgap (PBG) structures, liquid crystals with periodic structures are very attractive as self-assembled photonic crystals, leading to optical devices such as dye lasers. Here we report a new hetero-PBG structure consisting of an anisotropic nematic layer sandwiched between two cholesteric liquid-crystal layers with different helical pitches. We optically visualized the dispersion relation of this structure, displaying the optical diode performance: that is, the non-reciprocal transmission of circular polarized light at the photonic-bandgap regions. Transmittance spectra with circularly polarized light also reveal the diode performance, which is well simulated in calculations that include an electro-tunable diode effect. Lasing action was also confirmed to show the diode effect with a particular directionality.

50 MHz rectifier based on an organic diode

Abstract: Amain focus of research on organic semiconductors is their potential application in passive organic radio-frequency identification (RF-ID) tags. First prototypes working at 125 kHz have been shown by industrial research groups1. However, to be commercially viable, the organic RF-ID tag would need to be compatible with the base-carrier frequency of 13.56 MHz (ref. 2). High-frequency operation has been out of reach for devices based on organic semiconducting material, because of the intrinsically low mobility of those materials. Here, we report on a rectifier based on a pentacene diode that can rectify an incoming a.c. signal at 50 MHz. At 14 MHz, a rectified voltage of 11 V for an a.c. voltage with a peak-to-peak amplitude of 36 V has been achieved. On the basis of those results, we estimate the frequency limits of an organic diode showing that even the ultra-high-frequency band at around 800 MHz is within reach.

Demonstration of Nonpolar m-Plane InGaN/GaN Light-Emitting Diodes on Free-Standing m-Plane GaN Substrates

Abstract: We report the fabrication of nonpolar m-plane InGaN/GaN multiple-quantum well light-emitting diodes (LEDs) on free-standing m-plane GaN substrates. On-wafer continuous wave output power of 240 µW was measured at 20 mA for a 300×300 µm2 device, and output power as high as 2.95 mW was measured at 300 mA. There was no sign of saturation of the output power at high drive currents. An emission peak at 450 nm was obtained on electroluminescence measurements with high drive currents. The current-voltage characteristics of these LEDs showed rectifying behavior with a turn-on voltage of 3–4 V.

Rewriteable memory cell comprising a diode and a resistance-switching material

Abstract: In a novel rewriteable nonvolatile memory cell formed above a substrate, a diode is paired with a reversible resistance-switching material, preferably a metal oxide or nitride such as, for example, NiO, Nb 2 O 5 , TiO 2 , HfO 2 , Al 2 O 3 , MgO x , CrO 2 , VO, BN, and AlN. In preferred embodiments, the diode is formed as a vertical pillar disposed between conductors. Multiple memory levels can be stacked to form a monolithic three dimensional memory array. In some embodiments, the diode comprises germanium or a germanium alloy, which can be deposited and crystallized at relatively low temperatures, allowing use of aluminum or copper in the conductors.

Carbon nanotube Schottky diodes using Ti-Schottky and Pt-ohmic contacts for high frequency applications

Abstract: We have demonstrated Schottky diodes using semiconducting single-walled nanotubes (s-SWNTs) with titanium Schottky and platinum Ohmic contacts for high-frequency applications. The diodes are fabricated using angled evaporation of dissimilar metal contacts over an s-SWNT. The devices demonstrate rectifying behavior with large reverse bias breakdown voltages of greater than 15 V. To decrease the series resistance, multiple SWNTs are grown in parallel in a single device, and the metallic tubes are burnt-out selectively. At low biases these diodes showed ideality factors in the range of 1.5 to 1.9. Modeling of these diodes as direct detectors at room temperature at 2.5 terahertz (THz) frequency indicates noise equivalent powers (NEP) potentially comparable to that of the state-of-the-art gallium arsenide solid-state Schottky diodes, in the range of 10-13 W(square root)xHz.

Junction and carrier temperature measurements in deep-ultraviolet light-emitting diodes using three different methods

Abstract: The junction temperature of AlGaN ultraviolet light-emitting diodes emitting at 295nm is measured by using the temperature coefficients of the diode forward voltage and emission peak energy. The high-energy slope of the spectrum is explored to measure the carrier temperature. A linear relation between junction temperature and current is found. Analysis of the experimental methods reveals that the diode-forward voltage is the most accurate (±3°C). A theoretical model for the dependence of the diode forward voltage (Vf) on junction temperature (Tj) is developed that takes into account the temperature dependence of the energy gap. A thermal resistance of 87.6K∕W is obtained with the device mounted with thermal paste on a heat sink.

A model for /spl mu/-power rectifier analysis and design

Abstract: This paper proposes a linear two-port model for an N-stage modified-Greinacher full-wave rectifier. It predicts the overall conversion efficiency at low power levels where the diodes are operating near their threshold voltage. The output electrical behavior of the rectifier is calculated as a function of the received power and the antenna parameters. Moreover, the two-port parameter values are computed for particular input voltages and output currents for the complete N-stage rectifier circuit using only the measured I-V and C-V characteristics of a single diode. To validate the model a three-stage modified-Greinacher full-wave rectifier was realized in an silicon-on-sapphire (SOS) CMOS 0.5-/spl mu/m technology. The measurements are in excellent agreement with the values calculated using the presented model.

Organic homojunction diodes with a high built-in potential: interpretation of the current-voltage characteristics by a generalized Einstein relation.

Abstract: We realize $p$- and $n$-type doping of the organic semiconductor zinc-phthalocyanine using a novel strong organic donor. This allows us to demonstrate the first stable and reproducible organic $p$-$n$ homojunctions. The diodes show very high built-in potentials, attractive, e.g., for organic solar cells. However, the diode characteristics cannot be described by the standard Shockley theory of the $p$-$n$ junction since the ideality factor strongly increases with decreasing temperature. We show that this behavior can be explained by deviations from the Einstein relation for disordered materials.

Single-crystalline diluted magnetic semiconductor GaN:Mn nanowires

Abstract: Single-crystalline diluted magnetic semiconductor GaN:Mn nanowires with controlled Mn concentrations have been successfully synthesized and incorporated into devices. These nanowires exhibit Curie temperatures above room temperature, magnetoresistances near room temperature, and spin-dependent transport. The nanowires are used as building blocks for the fabrication of GaN:Mn/n-SiC based light-emitting diodes.

Phase-change recording medium that enables ultrahigh-density electron-beam data storage

Abstract: An ultrahigh-density electron-beam-based data storage medium is described that consists of a diode formed by growing an InSe/GaSe phase-change bilayer film epitaxially on silicon. Bits are recorded as amorphous regions in the InSe layer and are detected via the current induced in the diode by a scanned electron beam. This signal current is modulated by differences in the electrical properties of the amorphous and crystalline states. The success of this recording scheme results from the remarkable ability of layered III-VI materials, such as InSe, to maintain useful electrical properties at their surfaces after repeated cycles of amorphization and recrystallization.

One THz harmonic oscillation of resonant tunneling diodes

Abstract: One THz harmonic oscillation was observed in a sub-THz oscillating GaInAs∕AlAs resonant tunneling diode integrated with a slot antenna. The fundamental and third-harmonic frequencies were 342GHz and 1.02THz, respectively, for a 50μm long antenna. The maximum output power of the fundamental mode was around 23μW, and that of the third-harmonic component was 2.6% of the fundamental. Theoretical analysis with the van der Pole equation qualitatively explained the measured results.

Vrms and rectified current sense full-bridge synchronous-rectification integrated with PFC

Abstract: A synchronous full bridge rectifier is controlled to provide a power factor near unity The full bridge rectifiers are transistors each with a controlling input The AC input signal and currents within the circuit are sensed and sent to a controller In response, the controller output control signals to turn on/off the rectifying MOSFETS on a timely basis to form a power factor of near one with respect to the AC input signal The full wave rectifier is made of N-channel MOSFET's, some with fast body diodes The MOSFET's are rectifiers and PFC control elements The result is a one stage synchronous rectifier with PFC A solid state precision analog differential amplifier senses the AC line waveform and high frequency current transformers sense the currents The controller accepts the inputs of the amplifier and the sensed currents and outputs control signals that turn on and off the four MOSFET's The timing of turning on/off is arranged so that the current drawn from the AC source is sinusoidal and matches the phase of the sinusoidal AC source

Novel passivation process for the mirror facets of Al-free active-region high-power semiconductor diode lasers

Abstract: A novel process for the passivation of mirror facets of Al-free active-region high-power semiconductor diode lasers is presented. Designed for technological simplicity and minimum damage generated within the facet region, it combines laser bar cleaving in air with a two-step process consisting of 1) removal of thermodynamically unstable species and 2) facet sealing with a passivation layer. Impurity removal is achieved by irradiation with beams of atomic hydrogen, while zinc selenide is used as the passivating medium. The effectiveness of the process is demonstrated by operation of 808-nm GaAsP-active ridge-waveguide diode lasers at record optical powers of 500 mW for several thousand hours limited only by bulk degradation.

Development of a fast temperature sensor for combustion gases using a single tunable diode laser

Abstract: The 12 best NIR water transition line pairs for temperature measurements with a single DFB laser in flames are determined by systematic analysis of the HITRAN simulation of the water spectra in the 1–2 μm spectral region. A specific line pair near 1.4 μm was targeted for non-intrusive measurements of gas temperature in combustion systems using a scanned-wavelength technique with wavelength modulation and 2f detection. This sensor uses a single diode laser (distributed-feedback), operating near 1.4 μm and is wavelength scanned over a pair of H2O absorption transitions (7154.354 cm-1 & 7153.748 cm-1) at a 2 kHz repetition rate. The wavelength is modulated (f=500 kHz) with modulation amplitude a=0.056 cm-1. Gas temperature is inferred from the ratio of the second harmonic signals of the two selected H2O transitions. The fiber-coupled-single-laser design makes the system compact, rugged, low cost and simple to assemble. As part of the sensor development effort, design rules were applied to optimize the line selection, and fundamental spectroscopic parameters of the selected transitions were determined via laboratory measurements including the temperature-dependent line strength, self-broadening coefficients, and air-broadening coefficients. The new sensor design includes considerations of hardware and software to enable fast data acquisition and analysis; a temperature readout rate of 2 kHz was demonstrated for measurements in a laboratory flame at atmospheric pressure. The combination of scanned-wavelength and wavelength-modulation minimizes interference from emission and beam steering, resulting in a robust temperature sensor that is promising for combustion control applications.

Schottky barrier diodes for millimeter wave detection in a foundry CMOS process

Abstract: CoSi/sub 2/-Si Schottky barrier diodes on an n-well and on a p-well/substrate are fabricated without a guard ring in a 130-nm foundry CMOS process. The nand p-type diodes with an area of 16/spl times/0.32/spl times/0.32 /spl mu/m/sup 2/ achieve cutoff frequencies of /spl sim/1.5 and /spl sim/1.2 THz at 0-V bias, respectively. These are the highest cutoff frequencies for Schottky diodes fabricated in foundry silicon processes. The leakage currents at 1.0-V reverse bias vary between 0.4 to 10 nA for the n-type diodes. The break down voltage for these diodes is around 15 V. It should be possible to use these in millimeter wave and far infrared detection.

Light-emitting diode arrangement

Abstract: A light-emitting diode arrangement is disclosed, comprising at least one light-emitting diode (LED) chip with a radiation decoupling surface through which a large portion of the electromagnetic radiation generated in the LED chip exits in a main direction of emission; a housing laterally surrounding the LED chip; and a reflective optic disposed after the radiation decoupling surface in the main direction of emission. The LED arrangement is particularly well suited for use in devices such as camera-equipped cell phones, digital cameras or video cameras.

Semiconductor device including a vertical field effect transistor, having trenches, and a diode

Abstract: A semiconductor device includes (a) a vertical field effect transistor, the vertical field effect transistor including a drain electrode formed on a first surface of a first conductivity type of a semiconductor, a pair of first trenches formed from a second surface of the semiconductor, control regions of a second conductivity type formed respectively along the first trenches, a source region of the first conductivity type formed along the second surface of the semiconductor between the first trenches, a source electrode joined to the source region, and a gate electrode adjacent to the control regions, (b) a pair of second trenches formed from the second surface of the semiconductor independently of the field effect transistor, (c) control regions of the second conductivity type formed along the second trenches, and (d) a diode having a junction formed on the second surface between the second trenches.

Photoresponse of n-ZnO∕p-SiC heterojunction diodes grown by plasma-assisted molecular-beam epitaxy

Abstract: High quality n-ZnO films on commercial p-type 6H–SiC substrates have been grown by plasma-assisted molecular-beam epitaxy, and n-ZnO∕p-SiC heterojunction mesa structures have been fabricated. Current-voltage characteristics of the structures had a very good rectifying diode-like behavior with a leakage current less than 2×10−4A∕cm2 at −10V, a breakdown voltage greater than 20V, a forward turn on voltage of ∼5V, and a forward current of ∼2A∕cm2 at 8V. Photosensitivity of the diodes was studied at room temperature and a photoresponsivity of as high as 0.045A∕W at −7.5V reverse bias was observed for photon energies higher than 3.0eV.

Modification of GaAs Schottky diodes by thin organic interlayers

Abstract: Control of the interfacial potential barrier for metal∕n‐GaAs diodes has been achieved using thin interlayers of the organic semiconductor, tin phthalocyanine (SnPc). The current–voltage (I–V) characteristics for organic-modified Ag∕S:GaAs diodes indicate a change from rectifying to almost ohmic behavior as the thickness of the SnPc interlayer is increased. Modeling reveals thermionic emission to be the dominant transport mechanisms for all diodes (ideality factors, n<1.3). Unlike other organic interlayers in similar device structures, SnPc reduces the effective barrier height by influencing the space charge region of the GaAs. The change in barrier height deduced from the I–V characteristics [(0.26±0.02)V] is similar to the band-bending measured using core-level photoelectron spectroscopy for SnPc growth on the S-passivated n‐GaAs(001) surface [(0.22±0.04)eV] and is much larger than previously reported for other similar systems.

Inversion of the rectifying effect in diblock molecular diodes by protonation

Abstract: A new molecular diode based on biphenyl-co-bispyrimidine was synthesized and showed a pronounced rectifying effect. Further studies indicate that protonation on the nitrogen atoms of the diode molecule by strong acids can reversibly alter the rectifying direction. This phenomenon can be envisioned as a starting point for single molecule detection devices.

Dosimetric characteristics of a new unshielded silicon diode and its application in clinical photon and electron beams.

Abstract: Shielded p-silicon diodes, frequently applied in general photon-beam dosimetry, show certain imperfections when applied in the small photon fields occurring in stereotactic or intensity modulated radiotherapy (IMRT), in electron beams and in the buildup region of photon beam dose distributions. Using as a study object the shielded p-silicon diode PTW 60008, well known for its reliable performance in general photon dosimetry, we have identified these imperfections as effects of electron scattering at the metallic parts of the shielding. In order to overcome these difficulties a new, unshielded diode PTW 60012 has been designed and manufactured by PTW Freiburg. By comparison with reference detectors, such as thimble and plane-parallel ionization chambers and a diamond detector, we could show the absence of these imperfections. An excellent performance of the new unshielded diode for the special dosimetric tasks in small photon fields, electron beams and build-up regions of photon beams has been observed. The new diode also has an improved angular response. However, due to its over-response to low-energy scattered photons, its recommended range of use does not include output factor measurements in large photon fields, although this effect can be compensated by a thin auxiliary lead shield.

Capacitance–voltage characterization of polymer light-emitting diodes

Abstract: The capacitance–voltage (C–V) characterization of polymer light-emitting diodes (PLEDs) employing poly[5-(2′-ethylhexyloxy)-2-methoxy-1,4-phenylene vinylene], as the light-emitting layer are reported. Several metals, such as calcium (Ca), aluminum (Al), and gold (Cu) were used as the cathode in order to investigate the influence of the charge injection on the C–V characteristics. Under forward bias, the capacitance increases with majority charge carrier injection into the polymer layer, and, afterwards, decreases upon minority charge carrier injection which results in recombination of electrons and holes in the active polymer layer. The increase in the value of capacitance follows the same dependence as the increase in the value of current density through the device, which suggests that the capacitance depends not only on the amount of charge trapped in the polymer near the interface, but also, and mainly, on the amount of charge injection into the polymer layer from the electrodes. The C–V behavior of PL...

Polarized‐Light‐Emitting Quantum‐Rod Diodes

Abstract: For the first time, polarized-light-emitting quantum-rod diodes have been successfully produced, using thin layers of quantum rods oriented by a rubbing technique. Diode emission at 620 nm with a luminance efficiency of 0.65 Cd A-1 and an external quantum efficiency of 0.49 % is obtained.

Semiconductor light-emitting device

Abstract: A semiconductor light-emitting diode, and method of fabricating same, wherein an indium (In)-containing light-emitting layer, as well as subsequent device layers, is deposited on a textured surface The resulting device is a phosphor-free white light source