Use Of Diodes Research Articles

Effect of fiber properties and dispersion management on distortions associated with two subcarriers modulation of laser diode in radio over fiber systems

We present numerical modeling and simulation on the effects of standard single-mode fiber (SSMF) properties and different dispersion management approaches on the distortions of laser diode. These distortions are associated with the two-tone modulation of laser diode for use in radio over fiber systems. The fiber properties include attenuation and dispersion. The dispersion management approaches include the use of nonzero dispersion-shifted fiber (NZ-DSF), fiber Brag grating (FBG), and dispersion-compensating fiber (DCF). The laser is directly modulated with two analog frequencies of 25 and 25.1 GHz at different modulation depths (m). The modulated laser signals are then propagated through SSMF at different lengths (L). The investigated laser signal distortions include the 2nd harmonic distortion (HD2), and the 2nd and 3rd intermodulation distortions (IMD2 and IMD3, respectively). The results reveal that all laser distortions are exacerbated as the fiber length increases, which is mainly due to the chromatic dispersion, while fiber attenuation has no effect. The use of dispersion management approaches gives almost similar effects on the reduction of IMD3 when L = 1 km, regardless of the value of m. Up to m = 0.3, DCF is the most effective approach for reducing all distortions over the entire fiber length range, while NZ-DSF is the least. When L = 2 km, FBG is the most effective approach for reducing both IMD2 and HD2 when m ≥ 0.4, whereas when L is increased to 6 km, DCF is the most effective approach up to m = 0.5.Graphical abstractSimulation setup of RoF system for two-tone direct modulation of laser diode using different dispersion management approaches

Temperature Sensors Based on AlN/4H-SiC Diodes

ABSTRACTThis study report on the formation of AlN/SiC heterostructure Schottky diodes for use of temperature sensing applications enhance the sensitivity. We analyzed the sensitivity of the AlN/SiC Schottky diode sensor depending on the annealing temperature. AlN/4H-SiC Schottky diodes were fabricated by depositing aluminum nitride (AlN) thin film on 4H/SiC by radio frequency sputtering. The forward bias electrical characteristics were determined under DC bias (in the voltage range of 0–1.5 V). The ideality factor, barrier height, and sensitivity were derived through current–voltage–temperature (I–V–T) measurements in the temperature range of 300–500 K. The sensitivity of the AlN/4H-SiC Schottky barrier diode ranged from 2.5–5.0 mV/K.

Highly Fast Response of Pd/Ta2O5/SiC and Pd/Ta2O5/Si Schottky Diode-Based Hydrogen Sensors.

Herein, the fabrication of a novel highly sensitive and fast hydrogen (H2) gas sensor, based on the Ta2O5 Schottky diode, is described. First, Ta2O5 thin films are deposited on silicon carbide (SiC) and silicon (Si) substrates via a radio frequency (RF) sputtering method. Then, Pd and Ni are respectively deposited on the front and back of the device. The deposited Pd serves as a H2 catalyst, while the Ni functions as an Ohmic contact. The devices are then tested under various concentrations of H2 gas at operating temperatures of 300, 500, and 700 °C. The results indicate that the Pd/Ta2O5 Schottky diode on the SiC substrate exhibits larger concentration and temperature sensitivities than those of the device based on the Si substrate. In addition, the optimum operating temperature of the Pd/Ta2O5 Schottky diode for use in H2 sensing is shown to be about 300 °C. At this optimum temperature, the dynamic responses of the sensors towards various concentrations of H2 gas are then examined under a constant bias current of 1 mA. The results indicate a fast rise time of 7.1 s, and a decay of 18 s, for the sensor based on the SiC substrate.

Diode Evaluation and Series Diode Balancing for High-Voltage High-Frequency Power Converters

Miniaturization of high-voltage power converters is severely limited by the availability of fast switching, low-loss high-voltage diodes. This article explores techniques for using discrete low-voltage diodes in series as one high-voltage diode in high-frequency applications (e.g., hundreds of kHz and above). We identify that when series connecting diodes, the parasitic capacitance from the physical diode interconnections to common can result in voltage and temperature imbalance among the diodes, along with increased loss. We quantify the imbalance and propose two related compensation techniques. To validate the approaches, a full-bridge rectifier is tested with each branch consisting of four 3.3 kV SiC diodes in series. Experimental results showcase the imbalance and demonstrate the effectiveness of the compensation techniques. Additionally, we characterize the performance of a range of diodes for use in high-frequency, high-voltage converters. The proposed technique and evaluation results will be valuable for the design of lightweight and miniaturized high-voltage power converters.

Band-to-Band Tunneling Diode for Ultralow-Voltage Applications

This paper presents a band-to-band tunneling (BTBT) diode for use in ultralow-voltage (ULV) applications. The BTBT diode is shown to have nearly zero turn-on voltage, because it does not operate using diffusion current like a typical p-n junction diode. A simple analytical model was developed to better understand the BTBT diode and to help optimize the design. Simulations were designed and implemented in Silvaco ATLAS to accurately define the BTBT diode. The current-density versus voltage characteristics from the simulations were found to have large on/off current ratio, demonstrating that the BTBT diode has potential applications for circuits utilizing ULVs.

Fabrication and characterization of silicon nanowire p-i-n MOS gated diode for use as p-type tunnel FET

In this paper, we present the fabrication and electrical characterization of a MOS gated diode based on axially doped silicon nanowire (NW) p-i-n junctions. These nanowires are grown by chemical vapour deposition (CVD) using the vapour–liquid–solid (VLS) mechanism. NWs have a length of about $$7\,\upmu \hbox {m}$$ with $$3\,\upmu \hbox {m}$$ of doped regions (p-type and n-type) and $$1\,\upmu \hbox {m}$$ of intrinsic region. The gate stack is composed of 15 nm of hafnium dioxide ( $$\text {HfO}_{2}$$ ), 80 nm of nickel and 120 nm of aluminium. At room temperature, $$I_{\text {on}} =-52\,\hbox {nA}/\upmu \hbox {m}\, (V_{\text {DS}}=-0.5\,\text {V}, V_{\text {GS}}=-4\,\text {V})$$ , and an $$I_{\text {on}}/I_{\text {off}}$$ ratio of about $$10^{4}$$ with a very low $$I_{\text {off}}$$ current has been obtained. Electrical measurements are carried out between 90 and 390 K, and we show that the I on current is less temperature dependent below 250 K. We also observe that the ON current is increasing between 250 and 390 K. These transfer characteristics at low and high temperature confirm the tunnelling transport mechanisms in our devices.

Computed tomography dosimetry with high-resolution detectors commonly used in radiotherapy - an energy dependence study.

New methods of dosimetry in computed tomography (CT) X‐ray fields require the use of high‐resolution detectors instead of pencil‐type ionization chambers typically used for CT dose index (CTDI) measurements. This paper presents a study on the suitability of a wide range of ionization chambers, diodes, and a two‐dimensional detector array, used primarily in radiation therapy, for CT and cone‐beam CT dosimetry. Specifically, the energy dependence of these detectors from 50 kVp up to 125 kVp is reported. All measurements were performed in reference to a calibrated diode for use in this energy region. The radiation quality correction factors provided by the manufacturer were used, depending on the measured half‐value layer (HVL) for the particular X‐ray beam. Our study demonstrated the general usability of thimble ionization chambers. These thimble ionization chambers showed a maximum variation in energy response of 5%. Ionization chambers with even smaller sensitive volume, and which exhibit similar variation in energy dependence, can be used if higher spatial resolution is required. Furthermore, the investigated detectors are better suited for dosimetry at CT and CBCT units than conventional large volume or flat detectors, due to their rotational symmetry. Nevertheless, a flat detector can be used for certain measurement tasks, such as the acquisition of percent depth‐dose curves or beam profiles for nonrotating beams, which are important for beam characterization.PACS numbers: 87.57.uq, 87.56.Da, 87.57.Q‐

Improved Design of UV- and Blue-Light-Inhibited White Light-Emitting Diode

This paper proposes the improved design of an ultraviolet (UV)- and-blue-light-inhibited white light-emitting diode for use as a safe and practical light source. Covered with a glass substrate coated with a photocatalyst resin on one side and a reflectance film on the other side, wavelengths below 400 nm are reflected back to re-excite the red–green–blue phosphors and, consequently, enhance luminous efficiency. The absorption spectrum of bismuth oxide photocatalysts is below 521 nm, and the leaked UV and blue light can be absorbed, thereby exciting electron–hole pairs and producing the photocatalytic effect. Thus, blue light and UV leakage can be suppressed appreciably, and the luminous efficiency can be increased markedly. Experimental results showed a UV suppression ratio of 88.43% and a visible light increasing ratio of 21.66%. The Commission International de L'Eclairage chromaticity coordinates $(x,y)$ were (0.343, 0.404), the correlated color temperature and the deviation from de Blackbody locus were (5201 K, 0.0250), and the color rendering index was 93.16. In addition, the photocatalyst coating layer can act as a diffuser to provide a comfortable visual experience and facilitate environmental purification.

Nanomorphology of Polymer Blends for a Light-Scattering Thermosetting Plate Based on Self-Assembly

An approach to optical plate production using the nanomorphology of polymer blends in light-scattering thermosetting plates based on self-assembly was investigated without using the conventional approach of blending nanoparticles such as silica sol, zirconia sol, phosphor, or chromophore into the polymer matrix. For this purpose, two specified polymers having carboxylic acid and epoxy groups were blended using a light-emitting diode for use in liquid crystal displays. The developed light-scattering thermosetting plate containing poly(acrylic acid) with the carboxylic acid at four different weight average molecular weights in a cycloaliphatic epoxy polymer was shown to achieve regular nanoparticles of 30–350 nm for light-scattering, light-scattering rates of over 10% at a wavelength of 300 nm, a thermal stability up to 230 °C, O2 gas barrier properties approximately 50 times smaller than that of polyethylene, and solvent resistance after polymerizing.

Design of polarization-dipole-induced isotype heterojunction diodes for use in III–N hot electron transistors

The design of III–nitride-based hot electron transistors (HETs) is investigated using different diode design methodologies. Barrier-limited forward bias current and low reverse leakage current are demonstrated for the emitter-base diode using a barrier formed by a high-Al% AlGaN layer as a polarization-dipole layer. Two different base-collector diode designs are compared, one using 30% AlGaN as the barrier and the other using 10% InGaN as a polarization-dipole barrier. The InGaN polarization-dipole approach is shown to exhibit much lower reverse leakage currents. The impact of threading dislocation density on diode characteristics is also discussed.

Hybrid photodiodes based on 6,13-bis(triisopropylsilylethynyl) pentacene:poly[2-methoxy-5-(2-ethyl) hexoxy-phenylenevinylene]/p-silicon

6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS) and poly[2-methoxy-5-(2-ethyl) hexoxy-phenylenevinylene] (MEH-PPV) blends with different ratios were deposited onto a p-type silicon (p-Si) single crystal wafer using spin coating technique. The dark current–voltage characteristics of the fabricated diodes were studied at room temperature. This study was carried out to predict the best blend composite to obtain a qualified diode for use in potential application. The obtained results suggest that the diode with 10:4 ratio between TIPS and MEH-PPV has the highest values for both the rectification factor (r=1.7×103) and the ratio between shunt resistance, Rsh, and series resistance, Rs, (Rsh/Rs=1.23×104) among the investigated diodes. Accordingly, the capacitance–voltage–frequency and conductance–voltage–frequency measurements were carried out for this diode in the frequency range between 10kHz and 1MHz at room temperature. Moreover, the I–V characteristics of such a diode were studied under different illumination intensities (P=20:100mW/cm2). The obtained results show a highly optoelectric response; i.e., the diode can be operated as a heterojunction photodiode.

Low-cost 13.56MHz Rectifier Based on Organic Diode

ABSTRACTIn this paper, low-cost rectifier based on an organic diode for use in organic radio frequency identification (RFID) tags is proposed. Pentacene is the electroactive layer, with 7,7,8,8-tetracyanoquinodimethane (TCNQ) modified low-cost copper (Cu) and aluminum (Al) as the Ohmic and Schottky contacts, respectively. Hole injection barrier between Cu and pentacene can be decreased by forming the self-assembled layers of Cu-TCNQ. The diode shows a high rectification ratio of approximately 2×106 at 5V and the organic diode based rectifier circuit generated a dc output voltage of approximately 2V at 13.56MHz, using an input ac signal with zero-to-peak voltage amplitude of 5 V. The results indicate that chemical modification of the low-cost electrodes could be an efficient way toward low-cost high performance organic electronics devices.

Förster resonance energy transfer enhanced color-conversion using colloidal semiconductor quantum dots for solid state lighting

In this paper, we present Förster resonance energy transfer (FRET)-enhanced color-conversion using colloidal semiconductor quantum dot nanocrystals (NCs) to make reddish-orange light-emitting diodes for use in ultraefficient solid state lighting. To achieve FRET enhancement at 614 nm, we use an energy gradient hybrid structure made of cyan- and orange-emitting CdSe/ZnS NCs (λPL=492 and 588 nm in solution, respectively). This enables recycling of trapped excitons using FRET and achieves a relative quantum efficiency enhancement of 15.1% in reddish-orange full color-conversion for the integrated hybrid cyan-orange NC layer with respect to the case of full color-conversion using only orange NCs without FRET.

Experimental characterization and numerical analysis of the 4H-SiC p–i–n diodes static and transient behaviour

Steady-state and turn-off switching characteristics of aluminium-implanted 4H-SiC p–i–n diodes designed for high-current density operation, are investigated experimentally and by mean of numerical simulations in the 298–523K temperature range. The diodes present circular structure with a diameter of 350μm and employ an anode region with an aluminium depth profile peaking at 6×1019cm−3 at the surface. The profile edge and the junction depth are located at 0.2 and 1.35μm, respectively. At room temperature the measured forward current density is close to 370A/cm2 at 5V with an ideality factor always less than 2 before high-current injection or device-series resistance became dominant. The transient analysis reveals a strong potential of this diodes for use in high-speed, high-power applications, especially at high temperature, with a very low turn-off recovery time (<80ns) in the whole range of test conditions. The simulated results match the experimental data, showing that the switching performance is mainly due to the poor minority charge carrier lifetime estimated to be 15ns for these implanted devices.

Fabrication and Characterization of Thin-Film Metal-Insulator-Metal Diode for use in Rectenna as Infrared Detector

ABSTRACTUncooled Infrared detectors with high sensitivity and shorter response times are preferred as through the wall detection device. An alternate approach for making these sensors, being pursued by us is to use the concept of rectenna with tunnel diodes. Successful fabrication of such high frequency switching diodes with antenna as detectors, offer a much faster response time than existing bolometer. This paper presents the fabrication and characterization of thin-film MIM diode for use in rectenna as an Infrared detector. MIM diodes operate on the basis of quantum mechanical phenomenon, i.e., when a sufficiently thin barrier (&lt;5nm) is sandwiched between two electrodes, current can flow between them by means of tunnelling. This tunnelling probability increases with a decrease in the dielectric barrier height and the separation distance. The MIM diodes were fabricated with asymmetric electrodes with 1μm2 contact areas with cut-off frequency ∼0.1THz. The electrodes of the Ni-NiO-Cr MIM diodes have been fabricated through Photolithography, e-beam lithography, followed by conventional lift-off process. The dielectric layer (NiO) was deposited through plasma oxidation to obtain 2nm thin films. The composition and the thickness of the insulator layer are characterized by metrological tools like SEM and Spectroscopic Ellipsometer. The diode characteristics presented in this paper have been found to be stable and reproducible with the established fabrication conditions. Electrical behaviour (I-V) of the MIM junctions were investigated and compared with the theoretical tunnelling characteristics of the Ni-NiO-Cr MIM diodes. For devices with such non-linear electrodes, excellent agreement is obtained between the measured and the calculated result with the forward bias current as 0.8mA at 0.2V and the reverse bias current as −0.2mA at −0.2V.

An assessment of the characteristics of n-type diodes for use in electron beam radiotherapy

Diodes are now commercially available for use in electron beams. This paper aims to assess their response and limitations under different clinical conditions. Parameters considered were applicator factors, focus skin distance (FSD), angle of incidence, and temperature dependence. The beam perturbation was also measured. The beam energies used varied from 5 to 17 MeV. Applicator factors, measured at the surface of a phantom, differed by up to 7% compared with ion chamber measurements at D max. Similarly, large differences were found in FSD dependence. The temperature dependence was found to be approximately double the manufacturer’s specification at 0.7% per degree Centigrade and the angular dependence was within the specification of ± 2% for angles of ± 30°. The beam perturbation was measured as a maximum of 25% for 5-MeV electrons. The measurements were compared to other published data but this is highly dependent on the methodology employed. It was concluded that the diodes could be used in some circumstances, but only if used with extreme caution. An extensive set of commissioning measurements would be required before introducing the diodes into use clinically.

Response corrections for solid-state detectors in megavoltage photon dosimetry

Solid-state detectors offer high sensitivity, stability and resolution and are frequently the dosimeter of choice for on-line dosimetry and small field therapies such as stereotactic radiosurgery. The departure from tissue equivalence of many solid-state devices, including diodes and MOSFETs, has to be carefully considered at lower energies and for Compton scattered radiation where the strongly Z-dependent photoelectric effect is significant. A modification of Burlin cavity theory is proposed that treats primary and scatter photon spectra separately and this has been applied to determine the correction factors for diode detector measurements of 6 and 15 MV linear accelerator beams. Uncorrected, an unshielded diode overestimates the dose at depth by as much as 15% for the 6 MV beam. The model predicts the effect to within 1% for both energies offering a basis for the correction of diodes for use in routine dosimetry.

A multichannel photometer based on an array of light emitting diodes for use in multivariate calibration

The development of a multichannel photometer based on an array of eight light emitting diodes (LED) as light sources is described. Optical fibre bundles were employed to guide the light radiation of the LED to the measuring cell and from the cell to the photodiode detector. The instrument was controlled by a microcomputer and was designed to perform absorbance measurements in a single wavelength continuously as well as in all wavelengths (470, 500, 562, 590, 612, 636 and 654 nm) sequentially, allowing its application in multivariate analysis methods. The photometer presented a drift lower than 2 μV h −1, allowing absorbance measurements with a precision better than 0.003 units. The instrument was applied for the simultaneous determination of Zn(II) and Cu(II) in pharmaceutical and metallic alloy samples, whose pH adjustment followed by the addition of xylenol orange complexing agent were accomplished by employing a monosegmented flow system. Solutions containing both metal ions in the concentration range from 1.0 to 4.0 mg L −1 were employed to constructed the calibration model based on multiple linear regression (MLR), providing root mean square errors of prediction of 0.06 and 0.12 mg L −1 for Zn(II) and Cu(II), respectively. The results obtained by employing the photometer were compared with those obtained by flame atomic absorption spectrometry, showing no significant differences at the 95 % confidence level.

Cross-section analysis of organic light-emitting diodes

The ‘lift-out’ technique using a focused ion beam microscope was applied to prepare cross-sectional specimens of organic light-emitting diodes for use in transmission electron microscopy. The focused ion beam equally thins the organic/inorganic hybrid devices despite the difference in material hardness of the compounds. This allowed to overcome preparation difficulties of conventional techniques such as ion thinning or ultra-microtomy. Two different samples were prepared and studied by both conventional transmission electron microscopy and analytical electron microscopy to display some of the investigation possibilities which become available with this sample preparation method.

Modulation speed and leakage current in 650 nm resonant-cavity light emitting diodes

The authors have investigated red-emitting (650 nm) resonant-cavity light emitting diodes for use with polymer optical fibres. The small signal modulation response is characterised by a single order roll-off. The -3 dB bandwidth is found to be determined solely by the differential carrier lifetime, /spl tau/, in the active region and hence dependent on current density, J, alone with no intrinsic size effects. The /spl tau/(J) relation allows the calculation of the active region carrier density and hence the recombination parameters (mono- and bimolecular) in the regime where the leakage is small. It is shown that the leakage is insignificant for currents below 200 A/cm/sup 2/ at 20/spl deg/C. Above 40/spl deg/C the leakage rises rapidly with temperature, and is evident from a dramatic fall in /spl tau/ and an accelerated rise in the current required to maintain constant light output.