Properties Of Diodes Research Articles

Dependence of Molecular Diode Behaviors on Aromaticity.

A molecule-scale diode is an essential component for the concept of molecular electronics. Here we report on heterogeneous contact-mediated rectifying behavior in single-molecule junctions. We performed massive current versus voltage characteristics measurements of metal-molecule-metal structures under stretching by a mechanical break junction method. In-situ deformations of the molecular bridges were revealed to induce stochastic switching of the rectifying direction to varying rectification ratio derived from the induced asymmetry in the contact motifs at the molecule termini. Aromatic molecules were found to enable stronger rectifications via the more pronounced Fermi pinning effect to shift the molecular orbital levels by the applied voltage. Dissimilar anchoring groups also served to stabilize the single-molecule diode properties by bestowing a chemically defined difference in the electronic coupling strengths at the electrode-molecule links. The present findings provide a guide to design diodes with the smallest and simplest structures.

Improved Ultraviolet-B Light-Emitting Diodes with Graded All Quaternary Layers in the Active Region

We employ quaternary graded AlInGaN layers numerically in the active region to study the effect on the optoelectronic properties of AlGaN-based ultraviolet light-emitting diodes (UV LEDs). We evaluated the device performance by analyzing carriers concentrations, carrier flux, radiative recombination rate, energy band diagrams and internal quantum efficiency (IQE). We compare the results with the reference device structure and found that the device with quaternary graded AlInGaN layers has high peak efficiency as well as low efficiency droop.

Influence of the a-directed off-cut on the opto-electrical properties of the laser diodes grown on the 0.3° misoriented m-directed GaN substrate: erratum

This erratum corrects the funding of [Opt. Mater. Express 12, 991 (2022)10.1364/OME.445695].

Performance Analysis of n-ZnO/p-Si Heterojunction Diode as Function of Zinc Oxide Thin Films Thickness

The n-type Zinc oxide (n-ZnO) nanostructured thin films (TFs) with different thicknesses (211, 325, 433 and 552 nm) were grown onto glass substrates employing the CVD technique at atmospheric pressure. Deposited films were characterized by EDX spectroscopy attached with FE-SEM and XRD techniques to determine the influence of thickness on elemental compositions and crystalline structure of ZnO films, respectively. Also, ZnO TFs were deposited on the p-Si(111) substrates to form different structures of n-ZnO/p-Si heterojunction diodes and then I-V characteristics were studied in the dark. The electrical parameters of the diodes such as rectification ratio (RR), reverse saturation current (Is), ideality factor (), barrier height (b) and series resistance (Rs) were calculated from the I-V measurements. EDX spectra showed that these films were only made from Zn and O elements. XRD patterns presented that the ZnO films possess hexagonal wurtzite structure with preferred orientation along [002] direction. I-V characteristics of the heterojunction diodes revealed rectification behavior and depend on ZnO TFs thickness. Also, electrical parameters of diodes were affected by the prepared film's thickness. It was found that the crystalline structure of the films and electrical properties of diodes were improved with increasing the thickness of ZnO films. It is noted that the best heterojunction diodes were that prepared with thickness (552 nm), where possess lowest value of ideality factor (3.38) and a series resistance (0.84 k) with a highest rectification ratio (1517), compared with other structures. This study offers a simple model for fabricating diodes from semiconductor films.

Radiation effect of X-ray with 100 kGy dose on the electrical properties of MESFET based on hydrogen-terminated diamond surface conductivity

The irradiation effect of X-ray on the electrical properties of Schottky-barrier diode (SBD) and metal-semiconductor field-effect transistors (MESFET) based on the surface conductivity of hydrogen-terminated single-crystal diamond (SCD) epilayers was investigated. The Ohmic contact was formed by a Pd/Ti/Au multilayer and the Schottky metal was Al thin film for the fabrication of the diamond SBDs and MESFETs. The X-ray irradiation was performed with a dose of 100 kGy. It was observed that both the forward current of the SBDs and the drain current of the MESFETs experienced a reduction after the X-ray irradiation. The type of the single-crystal diamond substrate had an obvious effect on the radiation properties. For the MESFETs on the type-Ib SCD substrate, the variation of the drain currents as the irradiation was inhomogeneous across the devices. For the MESFETs on the type-IIa SCD substrate, the reduction of the drain currents is more uniform and the threshold voltage changed little upon X-ray irradiation. The partial oxidation in the air of the exposure area in the device and the edge of the Al gate may be responsible for the degradation of the device performance under X-ray irradiation. The passivation technique with radiation-robustness is needed for diamond devices based on the surface conductivity of diamond.

Ultra-bright green InGaN micro-LEDs with brightness over 10M nits.

An investigation of electrical and optical properties of InGaN micro-scale light-emitting diodes (micro-LEDs) emitting at ∼530 nm is carried out, with sizes of 80, 150, and 200 µm. The ITO as a current spreading layer (CSL) provides excellent device performance. Over 10% external quantum efficiency (EQE) and wall-plug efficiency (WPE), and ultra-high brightness (> 10M nits) green micro-LEDs are realized. In addition, it is observed that better current spreading in smaller devices results in higher EQE and brightness. Superior green micro-LEDs can provide an essential guarantee for a variety of applications.

Comparison of electrical characteristics of Schottky junctions based on CdS nanowires and thin film

CdS nanowires and film Schottky diodes are fabricated and diode properties are compared. Effect of SnO2 on CdS film diode properties is investigated. CdS film/Au on 100 nm SnO2 substrate demonstrates like-resistor characteristics and increase in SnO2 thickness corrects resistor behavior, however the effective reverse saturation current density J o is significantly high and shunt resistance are considerably low, implying that SnO2 slightly prevents impurities migration from CdS films into ITO but cause additional issues. Thickness of CdS film on diode properties is further investigated and increasing CdS film thickness improved J o by one order of magnitude, however shunt resistance is obviously low, suggesting intrinsic issues in CdS film. 100 nm CdS nanowire/Au diodes reduce J o by three orders of magnitude in the dark and two orders of magnitude in the light respectively and their shunt resistance is significantly enhanced by 70 times when comparing with those of the CdS film diodes. The wide difference can be attributed to the fact that CdS nanowires overcome intrinsic issues in CdS film and thus demonstrate significantly well- defined diode behavior. Simulation found that CdS nanowire diodes have low compensating acceptor type traps and interface state density of 5.0 × 109 cm−2, indicating that interface recombination is not a dominated current transport mechanism in the nanowire diodes. CdS film diodes are simulated with acceptor traps and interface state density increased by two order of magnitude and shunt resistance reduced by one order of magnitude, indicating that high density of interface states and shunt paths occur in the CdS film diodes.

Numerical investigation of Tesla valves with a variable angle

A Tesla valve is a passive check valve but with no-moving parts. The unique diode nature of Tesla valves makes them attractive for fluid control in many engineering fields, such as microfluidic systems and hydrogen fuel systems. The effectiveness of a single-stage Tesla valve can be modified by changing its geometric parameters. In this study, four groups of Tesla valves by changing the angle between 45° and 90° are examined. Numerical and mathematical methods are used to compare the diode characteristics of the four groups of Tesla valves, and proper orthogonal decomposition is applied to analyze the main flow fields. Of particular interest is that the diode property is induced by separation bubbles, with those near the left junction of the Tesla valve providing the main control mechanism for the fluid flow. For the forward flow, the main bubble pushes the fluid into the straight channel, while for the reverse flow, the main bubble blocks the outlet of the Tesla valve, making it difficult for fluid to flow out. Notably, our findings suggest that the diode performance of Tesla valves is optimal at θ = 70–80°. The results presented in this paper identify the functional relationship between the angle of the Tesla valve, Reynolds number, and diodicity, and suggest strategies for the optimal design and performance predictions of Tesla valves.

Development of lidar for remote methane sensing using an optimal configuration of high-power laser diodes

A broadband differential absorption lidar (DIAL) is developed making us of the properties of high-power pulsed laser diodes for the purpose of monitoring methane, a major atmospheric greenhouse biogas. The detection range is optimized for the CH4 Q-branch 2v3 overtone spectrum centered at 1.667 μm and mixed with water-vapor absorption bands of. The resonance absorption evaluated of the DIAL signal is an integral sum of the multiple CH4 resonance absorption lines modulating the characteristic broad laser line and simultaneously compensating the interfering water-vapor absorption. A compact DIAL scheme is developed using an optimal configuration of high-power laser diodes matching the selected spectral parameters.

Perovskite nanocrystals-polymer composites with a micro/nano structured superhydrophobic surface for stable and efficient white light-emitting diodes

Metal halide perovskite nanocrystals (PNCs) offer excellent optoelectronic properties for light-emitting diodes (LEDs). However, the low chemical stability against water hinders their practical application. Herein, we develop a phase separation strategy to realize highly luminescent PNC-polymer composites with a superhydrophobic micro/nano structured surface. Ethyl α-cyanoacrylate (ECA) monomers and octavinyloctasilasesquioxane (OVS) are added into the PNC toluene solution together. Due to high reactivity of ECA toward H2O, the poly (ethyl α-cyanoacrylate) (PECA) polymer matrix (first phase) is initially formed via a rapid anion polymerization reaction in a humid environment. As the evaporation of toluene, the OVS is then condensed into the micro/nano-scale protrusions (second phase) on the PECA substrate because of the strong Si-O bonds between OVS molecules, and the PNCs are uniformly encapsulated within the two polymers. We find that besides the increased quantum efficiency, the chemical stability of the resulting PNC-PECA-OVS composites is remarkably enhanced. Immersing the superhydrophobic composites into water, the PL intensity still maintains ∼ 60% even after 1000 h. In contrast, the PL emission of pristine PNCs is completely quenched after only 10 min. By curing the green PNC-polymer composites with commercially available red-emitting phosphors on a blue-emitting InGaN chip, we demonstrate a long-term stable and efficient white LED with a high power efficiency of ∼ 93 lm/W and almost constant color-correlated temperature (CCT).

Transport and spectral properties of the XX+XXZ diode and stability to dephasing

We study the transport and spectral property of a segmented diode formed by an XX+XXZ spin chain. This system has been shown to become an ideal rectifier for spin current for large enough anisotropy. Here we show numerical evidence that the system in reverse bias has signatures pointing toward the existence of three different transport regimes depending on the value of the anisotropy: ballistic, diffusive, and insulating. In forward bias we observe two regimes, ballistic and diffusive. The system in forward and reverse bias shows significantly different spectral properties, with distribution of rapidities converging toward different functions. In the presence of dephasing the system becomes diffusive, rectification is significantly reduced, the relaxation gap increases, and the spectral properties in forward and reverse bias tend to converge. For large dephasing the relaxation gap decreases again as a result of quantum Zeno physics.

Influence of the a-directed off-cut on the opto-electrical properties of laser diodes grown on the 0.3° misoriented m-directed GaN substrate

We report on the results of the investigation of the influence of an additional a-directed off-cut of the substrate on the opto-electrical properties of the laser diodes grown on bulk GaN with initial misorientation 0.3° towards the m-direction. The investigated a-directed off-cut is varied from 0° up to 1° by means of multilevel laser lithography and dry etching. The results show that the increase of the a-directed off-cut causes the decrease of internal optical losses and increase of injection efficiency. In consequence, the devices fabricated on the wafer areas characterized by higher a-directed off cut are characterized by the lower threshold current, and higher slope and wall-plug efficiencies.

Design of a Structure for Optimized Optical Performance of a Full Colored Organic Light-Emitting Diode on a Parameter Space Map.

In general, optical properties of a top-emitting organic light-emitting diode (OLED) are dependent on the cavity effect of the OLED structure. Therefore, the optical path length of the many thin solid films in the OLED, which is strongly affected by the refractive index and thickness of each material, controls the cavity effect of the cell. In previous research, a parameter space method for optimizing the inorganic layer thickness of a red OLED structure was introduced to achieve the required bandwidth and peak wavelength. This is a simple method with high accuracy and can also be applied to red, green, and blue OLED structures. To design an OLED cell with a practical approach, however, the RGB OLED device requires the thickness of each inorganic layer and organic layer in all three R, G, and B OLED structures to be same. In this study, we applied the parameter space method to an RGB OLED device to find out and optimize the thickness of three inorganic parameters: Indium Tin Oxide (ITO), cathode, and capping layer (CPL) using the finite-difference time-domain (FDTD) method. The parameters ITO, cathode, and CPL were scanned from 18 to 21 nm, 5 to 100 nm, and 10 to 200 nm, respectively. The peak wavelength and bandwidth lines of the three spectral colors were placed on a map of the three inorganic layer thickness parameters to find the optimized points that can provide the desired optical characteristics with the same film thickness in the cell.

Numerical Model of Current Flow and Thermal Phenomena in Lateral GaN/InGaN LEDs

GaN-based light-emitting diodes (LEDs) became one of the most widely used light sources. One of their key factors is power conversion efficiency; hence, a lot of effort is placed on research to improve this parameter, either experimentally or numerically. Standard approaches involve device-oriented or system-oriented methods. Combining them is possible only with the aid of compact, lumped parameter models. In the paper, we present a new electro-thermal model that covers all the complex opto-electro-thermal phenomena occurring within the operating LED. It is a simple and low computational cost solution that can be integrated with package- or system-oriented numerical analysis. It allows a parametric analysis of the diode structure and properties under steady-state operating conditions. Its usefulness has been proved by conducting simulations of a sample lateral GaN/InGaN LED with the aid of ANSYS software. The results presented illustrate the current density and temperature fields. They allow the identification of ‘hot spots’ resulting from the current crowding effect and can be used to optimise the structure.

Electrical and Photoelectric Properties of Organic-Inorganic Heterojunctions PEDOT:PSS/n-CdTe

PEDOT: PSS thin films are widely used as transparent coatings in flexible semiconductor devices including solar cells. However, they are not widely used as transparent coatings in combination with crystal substrates. This work shows the possibility of using PEDOT:PSS thin films as a frontal transparent conducting layer in hybrid organic-inorganic Schottky type heterojunctions of the PEDOT:PSS/n‑CdTe, which were prepared by deposition of PEDOT:PSS thin films (using the spin-coating method) on crystalline cadmium telluride substrates. The current-voltage (in a wide temperature range) and capacitance-voltage (at room temperature) characteristics of heterojunctions were measurement and analyzed. It has been established that PEDOT:PSS/n-CdTe heterojunctions have good diode properties with a high rectification ratio RR≈105, a potential barrier height φ0 = 0.95 eV, and series Rs = 91 Ohm and shunt Rsh = 5.7 × 107 Ohm resistances. Analysis of the forward branches of the I–V characteristics of heterojunctions showed that the dominant charge transfer mechanisms are determined by the processes of radiative recombination at low biases (3kT/e <V <0.3 V) and tunneling through a thin depleted layer at high biases (0.3 V <V <0.6 V). Capacity-voltage characteristics are plotted in the Mott-Schottky coordinate, taking into account the influence of series resistance, measured at a frequency of 1 MHz. Used the C-V characteristic was determined the value of the built-in potential Vc = 1.32 V (it correlates well with the cutoff voltage determined from the current-voltage characteristics) and the concentration of uncompensated donors in the n-CdTe substrate ND-NA = 8.79 × 1014 cm-3. Although the photoelectric parameters of unoptimized PEDOT:PSS/n-CdTe heterojunctions are low, their photodiode characteristics (Detectivity D*> 1013 Jones) are very promising for further detailed analysis and improvement. The proposed concept of a hybrid organic-inorganic heterojunction also has potential for use in inexpensive γ- and X-ray detectors.

Schottky Diode with Asymmetric Metal Contacts on WS2

AbstractDiode characteristics of transition metal dichalcogenides are studied extensively owing to their electrical and optical properties. In particular, the Schottky barrier diode (SBD) structure has advantages, such as its small leakage current and power consumption, over conventional p–n diodes. This study develops an SBD system using n‐type tungsten disulfide (WS2). By depositing a low work function In (ΦIn = 4.1 eV) and high work function Au (ΦAu = 5.1 eV) on n‐type WS2, the diode characteristics are demonstrated to be close to an ideal diode. The In–Au contacts are measured, and SBD characteristics are confirmed with a 1.02 ideality factor at a zero back‐gate voltage at room temperature and a rectification ratio up to 5 × 102, even at a low temperature (77 K), indicating almost ideal diode properties. In addition, the In electrodes exhibited improved electrical properties, with a high on/off ratio of 107, mobility that is 100 times higher, and Schottky barrier height that is 20 times lower than that of Au electrodes.

Optical Properties of GaN-Based Green Light-Emitting Diodes Influenced by Low-Temperature p-GaN Layer.

GaN-based green light-emitting diodes (LEDs) with different thicknesses of the low-temperature (LT) p-GaN layer between the last GaN barriers and p-AlGaN electron blocking layer were characterized by photoluminescence (PL) and electroluminescence (EL) spectroscopic methods in the temperature range of 6–300 K and injection current range of 0.01–350 mA. Based on the results, we suggest that a 20 nm-thick LT p-GaN layer can effectively prevent indium (In) re-evaporation, improve the quantum-confined Stark effect in the last quantum well (QW) of the active region, and finally reduce the efficiency droop by about 7%.

The Effects of Optical Power of Semiconductor Laser on the Characteristics of Si-diode in an Exposed Device

In this paper, we experimentally studied the effects of optical power of semiconductor laser on the electrical properties of silicon diode of an exposed device. The experimental results showed that the laser diode light of different optical powers (2, 3, and 4 mW) had effects on the silicon diode that are somewhat similar to those of thermal treatment. A shift in the current-voltage curve to the left side was also noticed, which led to a non-linear decrease of the barrier voltage of the diode by the effect of laser light. We also reveal a decrease by 344.8 nA/mW in the reverse saturation current of the silicon diode as a result of exposure to laser light. The forward resistance of the silicon diode decreased with increased incident optical power. The value of the maximum current of diode increased by 0.5 A/W with increasing the optical power incident on the diode.

Research implementing different dopants (M = Al, Sn, and Eu) on the properties of Schottky diodes with structure TCO/CdS/C and TCO/CdS:M/C

A metal-semiconductor interface is an integral part of numerous electronic devices such as Schottky barrier diodes, photodetectors, photovoltaic detectors, photoelectric converters for UV radiation, among others. On the other hand, semiconductor thin films of cadmium sulfide have been applied to several electronic devices. This study presents the synthesis of semiconductor thin films of pure cadmium sulfide and those doped with Al, Sn, and Eu by a chemical bath deposition technique. XRD, SEM, EDS, XPS, UV-Vis spectroscopy, I-V, and photocurrent measurement analyzed these semiconductor thin films. Afterwards, the doped and undoped CdS thin films were applied to the manufacture of Schottky diodes. The doped CdS thin films reveals differences in the size of the crystallites, which decreased by 5.7%, 11.5%, and 60.1% after doping with aluminum, tin, and europium, respectively. The CdS thin films show morphological differences, decreasing grain size by 5.3% in the case of tin doping and increasing by 21.9% with aluminum and 32.6% after being doped with europium. Additionally, the energy bandgap of the doped CdS thin films show a blue shift, except when doped with Eu, which shows a red shift. This enables the design of window layers by choosing the suitable dopant of CdS. The effect of the CdS doping on the electrical photoresponse of the Schottky diodes was also analyzed. Due to the incorporation of dopants, the photoresponse of the aluminum-doped CdS Schottky diodes improved by 176% compared to its undoped counterpart and by up to 493% with other reports in the literature. The Schottky diodes manufactured in this work show variation in height of the potential barrier, increasing by 6% in the case of aluminum doping and decreasing by 5% and 25% after being doped with europium and tin respectively. These results demonstrated the beneficial impact of dopants on the characteristics of the CdS-based Schottky diodes and elaborated photodiodes, exhibiting an impressive enhancement in their photoresponse, in the potential barrier reached for photosensitivity and in the energy band gap value. Overall, our extensive study reveals that there is great potential in the design of affordable multifunctional optoelectronic devices.

Remarkable efficiency improvement in AlGaN-based ultraviolet light-emitting diodes using graded last quantum barrier

The optical properties of AlGaN-based deep ultraviolet light-emitting diodes (DUV LED) with step-graded AlInGaN last quantum barrier (LQB) are numerically studied. In contrast to conventional LQB, step-quaternary-graded last quantum barrier (QGLQB) exhibits enhancement in the internal quantum efficiency (IQE). This is attributed to the reduction in lattice mismatch, leading to suppressed leakage of electrons and enhanced hole transportation into the multiquantum well (MQW). Electrons are enhanced by ~124% whereas holes are enhanced by ~22% in the QGLQB structure. Moreover, the efficiency droop is also reduced from ~77% (conventional structure) to ~8% (proposed structure).