Simple Diode Structure Research Articles

Experimental study of single-phase change material thermal diode based on calcium chloride hexahydrate

Phase change material thermal diodes designed on the basis of different heat transfer forms and coefficients caused by different phase transition degrees in opposite heat transfer directions are considered as potential thermal management devices. However, the use of a variety of materials or only relying on numerical simulation research makes its structure complex or idealized, which reduces the possibility of practical application. Therefore, in this work, a simple thermal diode structure containing only CaCl<sub>2</sub>·6H<sub>2</sub>O single-phase variable material is proposed in combination with changes in heat transfer form and heat transfer coefficient in solid-liquid phase change and natural convection process. The corresponding device is prepared, and a steady-state heat flux test system is set up for experimental study, the measured results are close to those recorded in the literature with good accuracy. The influence of the temperature difference between hot end and cold end and the direction of positive heat transfer and negative heat transfer on the thermal rectification effect of the thermal diode are studied experimentally. The results show that the heat flux of the thermal diode decreases with the decrease of the difference in temperature between the cold source and hot source, and the thermal rectification ratio reaches to 1.58 when the forward and reverse along the antigravity direction and gravity direction, respectively. The optimal cold source temperature range is 20–25 ℃, which is close to room temperature. The proposed phase change material thermal diode structure has a certain application potential in energy saving and thermal management of building.

Effect of Substrates on Structural, Morphological, Optical and Electrical Characteristics on Poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) Thin Films

Polymer light-emitting diodes using organic-inorganic heterojunctions have a lot of benefits such as excellent blue-light emission, simple fabrication procedure, and low processing cost. We report on the effect of substrates on the fabrication of poly (9,9-di-n-octylfluorenyl-2,7-diyl) or (PFO) thin films and their characterization as a simple light-emitting diode (LED) structure. The structural properties of the thin films were characterized using X-ray Diffraction (XRD). The morphological properties of the thin films were studied using Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscopy (AFM). The XRD results demonstrated the formation of amorphous PFO structure, with no presence of the crystalline phase of PFO. The FESEM images showed the formation of cracks due to evaporation from annealing. Optical characteristics were studied using ultraviolet-visible (UV-Vis) spectroscopy, Photoluminescence (PL) and reflectance measurements showing the presence of β phase of PFO, important for charge carrier mobility. Thin films deposited on ITO-coated glass, FTO-coated glass and Silicon n-type (110) and (111) orientation substrates were used to fabricate a simple LED structure. The devices fabricated using Si n-type substrates showed p-n junction characteristics and was a better substrate choice than ITO or FTO coated glass.

Electrical properties of Cs3Sb photocathode emitters in panel device applications

Nonvacuum process technology was used to produce Cs3Sb photocathodes on substrates, and in situ panel devices were fabricated. The performance of the devices was characterized by measuring anode current as functions of the devices' operation times. An excitation light source with 475 nm wavelength was used for the photocathodes. The device has a simple diode structure, providing unique characteristics such as a large gap, vertical electron beam directionality, and resistance to surface contamination from ion bombardment and poisoning by outgassing species. Accordingly, Cs3Sb photocathodes function as flat emitters, and the emission properties of the photocathode emitters depend on the vacuum level of the devices. Improvement of current stability has been observed after conducting the electrical conditioning process to remove possible adsorbates on Cs3Sb flat emitters.

Fabrication and electrical characterization of planar lighting devices with Cs3Sb photocathode emitters

Non-vacuum process technology was used to produce Cs3Sb photocathodes on substrates, and in-situ panel devices were fabricated. The performance of the devices was characterized by measuring the anode current as functions of the devices’ operation times. An excitation light source with a 475-nm wavelength was used for the photocathodes. The device has a simple diode structure, providing unique characteristics such as a large gap, vertical electron beam directionality, and resistance to surface contamination from ion bombardment and poisoning by outgassing species. Accordingly, Cs3Sb photocathodes function as flat emitters, and the emission properties of the photocathode emitters depend on the vacuum level of the devices. An improved current stability has been observed after conducting an electrical conditioning process to remove possible adsorbates on the Cs3Sb flat emitters.

Photocurrent response enhanced by spin-orbit coupling on ruthenium(II) complexes with heavy atom ligands

This work presents a simple and efficient method for synthesis of ruthenium complexes with organic ligands derivative from 1,10-phenanthroline containing S and Se. An octahedral geometry of the ligands around the metallic center was determined by single-crystal X-ray diffraction. Processed in solution into a simple diode structure, the compounds with S and Se presented higher photocurrent response, probably due to increased spin-orbit coupling caused by the heavy S and Se atoms.

A stand-alone flat-plane lighting device in a diode structure employing highly crystalline SWCNTs as field emitters

We have developed and fabricated a visible-light flat plane-emission device in a simple diode structure composed of a cathode containing high crystallized single-walled carbon nanotubes (SWCNTs) dispersed in an organic In2O3–SnO2 precursor solution and a non-ionic surfactant. The SWCNTs were annealed at a high temperature of 1300K in a low-vacuum atmosphere of 10−1Pa to obtain highly crystalline SWCNTs as field emitters. The anode, on the other hand, was fabricated with phosphors coated by ITO film and assembled with the cathode in a cavity separated by glass plates by a stable assembling process to produce a stand-alone flat plane-emission panel, with a stable and high vacuum of under 10−4Pa. This device with its diode structure has a low driving voltage, stable current fluctuation, and low energy loss with electron emission in the cathode electrode. Furthermore, the brightness for power consumption, which is an important factor when comparing luminescent devices, was over 10,000cd/m2 with low power consumption of under 1.0W when using a white phosphor in the simple diode panel. This cathode device in a flat plane-emission panel has the potential to provide a new means of everyday lighting in daily life.

Plannar light source using a phosphor screen with single-walled carbon nanotubes as field emitters.

We developed and successfully fabricated a plannar light source device using a phosphor screen with single-walled carbon nanotubes (SWCNTs) as field emitters in a simple diode structure composed of the cathode containing the highly purified and crystalline SWCNTs dispersed into an organic In2O3-SnO2 precursor solution and a non-ionic surfactant. The cathode was activated by scratching process with sandpaper to obtain a large field emission current with low power consumption. The nicks by scratching were treated with Fourier analysis to determine the periodicity of the surface morphology and designed with controlling the count number of sandpapers. The anode, on the other hand, was made with phosphor deliberately optimized by coverage of ITO nanoparticles and assembled together with the cathode by the new stable assembling process resulting to stand-alone flat plane-emission panel. The device in a diode structure has a low driving voltage and good brightness homogeneity in that plane. Furthermore, field emission current fluctuation, which is an important factor in comparing luminance devices too, has a good stability in a simple diode panel. The flat plane-emission device employing the highly purified and crystalline SWCNTs has the potential to provide a new approach to lighting in our life style.

A simple organic diode structure with strong rectifying characteristics

A simple organic diode structure has been made based on N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB)/Fullerene (C60) heterojunction. Ultraviolet photoelectron spectroscopy measurements show an energy level alignment at the heterojunction as such that no potential barrier near this heterojunction to hinder the formation of charge transfer excitons, which recombines at a very fast rate. This fast exciton recombination at this heterojunction makes NPB/C60 behave like an ideal Ohmic contact and thus leads to an extremely high 7.8×104 rectifying ratio from the electrode/organic contacts.

Characterisation of electrically active defects

AbstractDefects may arise in the semiconductor substrate and at interfaces due to the processing used to fabricate transistors and circuits. The development of low‐thermal‐budget processes, which is advantageous in many ways, unfortunately reduces the likelihood of annealing out these electrically active defects. Electrical characterisation using simple diode structures yields valuable information; not only the absolute leakage current density value, but also carrier lifetimes, leakage activation energies, and diode ideality factor. Coupled with material analysis techniques, they can provide a detailed picture of the problems associated with process‐induced defects, and supply insight that can target optimised processes. In this paper the technological relevance of electrically active defects, their impact on device performance and power supplies, as well as their electrical and material characterisation, will be discussed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Field Emission Light Source Using Reflective Metal Groove Anode and Long Narrow Stripe Cathode

A novel reflective metal anode with different groove structures and a set of parallel long narrow stripe Carbon nanotube (CNT) cathodes to fabricate a 7 inches field emission backlight unit (CNT-FEBLU) has been carried out in this paper. In comparison with a simple diode structure, which has the same stripe cathode unit with screen printing phosphor layer on ITO glass surface as the anode, the reflective metal anode has some advantages such as sustaining high field emission current, no unexpected arcing, and high illumination and uniformity without phosphor degradation. The results show that a reflective metal anode not only conducts the residual charges and heat from the phosphor surface effectively, but also reflects the light to one side of the panel through the cathode end and exhibits high illumination without obvious obstacle by the narrow stripe cathodes. The luminance of the reflective metal groove anode we proposed is 11530 cd/m2, with the emission current density of 1.52 mA/cm2 under the electric field about 1.07 V/μm.

Planar PbS quantum dot/C60 heterojunction photovoltaic devices with 5.2% power conversion efficiency

Of interest for both photovoltaic and photodetector applications is the ability of colloidal quantum dot (CQD) devices to provide response further into the infrared than is typical for other solution-processable materials. Here, we present a simple heterojunction diode structure that utilizes the extended infrared absorption of PbS CQDs. We show that device performance benefits from a discontinuous exciton blocking layer which improves charge separation without limiting charge extraction. By enhancing charge carrier mobility in the CQD layer, we demonstrate a planar heterostructure device with a power conversion efficiency of 5.2% under 1 sun illumination.

Determination of the Transmission Coefficients for Quantum Structures Using FDTD Method

The purpose of this work is to develop a simple method to incorporate quantum effect in traditional finite-difference time-domain (FDTD) simulators. Witch could make it possible to co-simulate systems include quantum structures and traditional components. In this paper, tunneling transmission coefficient is calculated by solving time-domain Schrödinger equation with a developed FDTD technique, called FDTD-S method. To validate the feasibility of the method, a simple resonant tunneling diode (RTD) structure model has been simulated using the proposed method. The good agreement between the numerical and analytical results proves its accuracy. The effectness and accuracy of this approach makes it a potential method for analysis and design of hybrid systems includes quantum structures and traditional components.

Hybrid films based on silicon nanowires dispersed in a semiconducting polymer for thin film solar cells: Opportunities and new challenges

Hybrid devices based on silicon nanowires dispersed in poly(hexylthiophene: P3HT) thin films have been realized. The different steps, starting from the production of n type silicon nanowire, dispersion of the organic–inorganic components in solution to produce hybrid thin films, which have been integrated in simple photovoltaic diode structures, have been developed. The n type doping of the nanowires is indicated by Raman spectroscopy whereas their crystalline structure is shown by HRTEM. A broadening of the silicon absorption spectrum towards the near infrared is induced by an electronic confinement effect for nanowire diameters of the order of 10nm. Effective dissociation of the photogenerated charge pairs is shown by a partial quenching of P3HT photoluminescence with increasing SiNWs content, whereas an open circuit voltage of 0.68V is deduced from the electrical characteristics under visible light illumination. However photocurrents remain low for the investigated material combinations. The high series resistance appears the most critical point limiting the device performances. The high densities of SiNWs electronic surface states acting as trapping centers can account for the large reverse current. To confirm the high potential of this new type of hybrid films for energy conversion, improvements are needed for a better control of the silicon nanowire/polymer interface, which appears the critical point.

Fabrication of Simple Diode Structure FED Device with Connecting Plate

By using the thick soda-lime glass plate and the flat thin glass, the connecting plates were formed easily. The carbon nanotube materials were prepared to form the field emitters. The simple small diode structure field emission display device with connecting plate was developed. The detailed fabrication technology for the whole device was also presented. The sealing of the vacuum room was performed by means of glass frit and the gas in the vacuum room could be evacuated out through the exhaust tube. The developed diode structure FED sample exhibited large field emission current, better field emission properties and image display performance.

Bias frequency dependence of pn junction charging damage induced by plasma processing

Plasma-induced charging damage to pn junction in metal-oxide-semiconductor field-effect transistors (MOSFETs) was studied by using an inductively coupled plasma (ICP) reactor with Ar gas. The junction leakage current ( I leak) was measured for various source/drain to well in MOSFETs and simple diode structures. Two different rf bias frequencies, 13.56 MHz and 400 kHz, were utilized to investigate the effect of frequency on an increase in I leak. The I leak of n +/p and p +/n junctions was found to increase by a plasma treatment. In particular, more severe damage was observed for n +/p junction in both n-channel MOSFETs and the diodes. These observed results imply that plasma plays a role primarily as a positive current source. With regard to the rf bias frequency effects, samples exposed to the 400-kHz plasma were found to suffer from larger I leak than those to the 13.56 MHz. From capacitance–voltage ( C– V) measurement of junction capacitance changes, we also clarified that the observed increase in I leak was attributed to the defect density at pn junction created by the plasma charging damage.

Examining Dislocations in SiC Epitaxy by Light Emission from Simple Diode Structures

With a simple processing sequence using only patterned aluminum (Al), dislocations and stacking faults were examined in thick n- epitaxial layers including a grown p+ layer on top. The thicknesses of the n- layers were 100 and 150 μm, values that are typical for fabricating 10 kV PiN diodes. High temperature sintering of the metal film was avoided making this a potentially nondestructive scheme for evaluating SiC epitaxy. Faulting of basal plane dislocations (BPDs) and the resulting forward voltage, Vf, increase were examined at current densities up to 20 A/cm2. A simple guard ring structure defined in the Al pattern was successfully used to confine the current through the epitaxial layers to the area inside of the ring. Kelvin contacts compensated for voltage drops at the Al/SiC interfaces. As a result, current-voltage characteristics and electroluminescent imaging were obtained across a known area of the PiN layer at currents densities ranging from 20 A/cm2 to 7 × 10-3 A/cm2.

Electron field emission from nitrogen-containing diamond-like carbon films deposited by filtered arc deposition

In this paper, electron field emission properties and fluorescent displays of 300 nm thick nitrogen-containing diamond-like carbon (DLC:N) films are reported. The films were deposited on to highly n-doped Si (111) substrates by filtered arc deposition (FAD) with different N 2 partial pressures (0.01, 0.05, 0.1 Pa) in the deposition chamber. Their electron field emission properties were studied using a simple diode structure. It was shown that the DLC:N film possessed enhanced field emission properties when a N 2 pressure of 0.05 Pa was used. Emission current of 0.1 μA was detected under the electric field of 8.1 V/μm. An emission current density of 0.204 mA/cm 2 was obtained under 17.8 V/μm.

Synthesis and characterization of Si/Cs/O nanocluster thin films with negative electron affinity

Patterned and unpatterned thin films of Si/Cs/O nanoclusters have been synthesized by the technique of supersaturated thermal vaporization of Si and Cs in an oxygen background gas. These films, which were deposited onto conducting or semiconducting substrates, exhibit negative electron affinity (NEA) as evidenced by ultraviolet photoemission spectroscopy. Photo, secondary, and field electron emission properties of these nanocluster films were investigated with photoelectron emission microscopy, field electron emission microscopy, secondary electron microscopy, and current-voltage measurements. Flat cathodes covered with thin films of Si/Cs/O nanoclusters exhibited high current outputs and lower turn-on fields ({lt}8.7 V/{mu}m) than most NEA diamond surfaces and gated Si or Mo tip arrays. The films{close_quote} NEA is unaffected by air exposure and is stable to high-temperature annealing (550h{degree}C). The electron emission property of the NEA nanocluster films can be best explained by a subband gap abundant surface-state nanocluster model. A field-emission display unit with a simple diode structure containing a flat cathode coated with a thin film of Si/Cs/O nanoclusters has also been built to demonstrate the potential application of this material in cold cathode electron emitting devices, particularly field-emission flat panel displays. {copyright} {ital 1999} {ital The American Physical Society}

Electron field emission from a patterned diamondlike carbon flat cathode

A 300-nm-thick diamondlike carbon (DLC) film was deposited on to a heavily doped n-type Si (111) wafer by filtered arc deposition. A flat thin film cylindrical emitter array was then fabricated by reactive-ion etching the DLC film. Its electron field emission properties were studied using a simple diode structure. A field emission current of 0.1 μA was detected under an electric field of 5.2 V/μm. As large as 64.1 mA/cm2 of field emission current density was achieved after an activation process under a 39 V/μm field. An image formed on the anode screen showed that electron field emission from the DLC flat emitter array is rather uniform. The field emission behavior is also consistent with Fowler–Nordheim theory. Hydrogen plasma surface treatments were found to enhance the field emission properties.

Electron Field Emission from Different sp3 Content Diamond-Like Carbon Films

Different sp3 content diamond-like carbon films are deposited on to highly n-doped Si(111) substrates by a new plasma deposition technique-filtered arc deposition. Their electron field emission properties are studied by using a simple diode structure. It is showed that the turn-on field is decreased and field emission current density is increased with the increasing sp3 content (75-80%, 80-83%, and 88-90%) of the films. Field emission current of 0.1 μA from the three samples was detected under the electric field of 10.1, 5.6, and 2.9 V/μm and emission current density of 4.4, 15.2, and 43.2 μA/cm2, respectively, under 14.3 V/μm. Fowler-Nordheim (F-N) plots of the three samples nearly show of lineaity indicating that electron field emission obeys F-N theory.