Performance Of Diodes Research Articles

Investigation of improving organic light-emitting diodes efficiency using an ultra-thin ultraviolet-ozone-treated Nb-doped ZnO film as anode buffer layer

In this study, ultraviolet (UV)-ozone treated ultrathin Nb-doped ZnO (NZO) films are developed as an efficient anode buffer layer to improve the overall performance of organic light-emitting diodes (OLEDs). The results show that the UV-ozone treated NZO buffer layer containing 1 mol% of Nb2O5 possesses a higher oxygen content and a greater work function (5.22 eV) as compared to that of an indium tin oxide (ITO) film (~4.7 eV) signifying a reduction in hole injection barrier and thus an improvement in the injection efficiency. In addition, UV-ozone treatment can increase the surface energy of NZO films while reducing their surface roughness. Importantly, the UV-ozone treated 1 nm-thick NZO film with a Nb2O5 doping concentration of 1 mol% can help to lower the turn-on voltage from 3.2 V to 2.8 V, increase the luminance from 10,450 cd/m2 to 25370 cd/m2, and improve the current efficiency from 3.46 cd/A to 5.26 cd/A, (~52 % enhancement as compared to the standard OLED device). Moreover, OLEDs with the developed buffer layer reveal a significant improvement in the roll-off phenomenon under high current densities, indicating a key role of the optimized NZO film in enhancing the carrier balance of the devices. When applied to the p-i-n structure, the NZO film also lead to a superior device performance as compared to the conventional p-i-n structure using NPB:MoO3 as a hole injection layer, suggesting a widespread use of the developed thin film. These findings therefore show a promising use of the UV-ozone treated NZO ultrathin film as an effective anode buffer material for enhancing OLED overall performance.

Direct Modulation Performance of Quantum Well Semiconductor Laser Diodes Operating in Multimode

A theoretical investigation has been carried out for both the direct sinusoidal modulation and associated noise performance of InGaN based quantum well (QW) semiconductor laser diodes (LDs) operating in multimode. The study is based on the QW lasers with two separate quantum wells with different carrier injection ratios. A model of multimode rate equations is developed by taking into account both symmetric and asymmetric cross-gain saturation. Numerical simulation shows that the mode partition effect exists in both the modulated and unmodulated LDs. From modulation at microwave frequency, highly synchronized oscillation of the modes resulting periodic pulse-like output is observed that contains peaks at modulation frequency and its harmonics. Associated total RIN and modal RIN values suppress with the modulation index. The simulation results have well correspondence with the previously reported theoretical and experimental findings. DUJASE Vol. 6 (2) 94-98, 2021 (July)

Slow recombination of the de-trapped carriers from doped OLEDs induced by spontaneous orientation polarization

The spontaneous orientation polarization (SOP) induced by molecular permanent dipole moment has recently been discovered and plays an important role in the photoelectric performances of small molecular organic light-emitting diodes (OLEDs). However, the effect of SOP on the transient electroluminescence (TEL) dynamics of OLEDs is still vague. Herein, we find that the generation of the spike at the TEL falling edge in doped OLEDs depends remarkably on the SOP in the devices. That is, SOP is a disadvantage for spike formation and even causes the spike to disappear totally. In addition, a long-lived EL decay was observed in the OLEDs with strong SOP. Through a series of control experiments, it has been confirmed that the SOP-induced internal electric field in doped OLEDs would slow down the recombination process of the de-trapped carriers, leading to a suppression of the TEL spike and a long-lived EL decay. Accordingly, our findings not only supplement the prerequisites for the generation of the TEL spike, i.e., with weak SOP effects in an emissive layer, but also deepen the fundamental understanding of the SOP role in the TEL dynamics process of OLEDs.

Trade-off between the Performance and Stability of Perovskite Light-Emitting Diodes with Excess Halides.

Incorporation of excess bulky organoammonium halides as additives is an efficient way to enhance the performance of perovskite light-emitting diodes (PeLEDs). The excess organoammonium halides can decrease the grain size and minimize the trap density to enhance radiative recombination. In this work, we reveal that the halides in excess additives also play a critical role in the operation stability of PeLEDs. With an increasing excess halide ratio, perovskite films gradually change from being rich in halide vacancies (VI) to being rich in halide interstitials (Ii), both of which can promote halide migration and reduce the operation stability. By using mixed 4-fluorophenylmethylammonium iodide and 4-fluorophenylmethylamine as additives, the excess halide ratio can be controlled and both VI and Ii can be minimized. Therefore, the operation stability of methylammonium lead iodide-based PeLEDs is enhanced significantly from 40 to 520 min. This work emphasizes the importance of controlling excess halide concentrations in terms of device performance and operation stability.

Reduced On-Resistance and Improved 4H-SiC Junction Barrier Schottky Diodes Performance by Laser Annealing on C-Face Ohmic Regions in Thin Structures

In this study, we investigated the characteristics of the n-type Ni/SiC ohmic contact using the laser annealing process on thin wafers. The electrical behavior of the ohmic contacts was tested in 4H-SiC JBS diode devices. As a result, a wafer thickness of 100 μm in the 4H-SiC JBS diode achieved a forward voltage of 1.33 V at 20 A with a laser annealing process using Ni silicide. Using a laser annealing process on a wafer thickness of 100 μm, an on-resistance decrease of almost 22% was demonstrated. Based on our experimental results, we suggest an alternative laser annealing fabrication scheme to obtain low on-resistance SiC power devices with thin structures after SiC grinding.

Study of SnO/ɛ-Ga2O3 p–n diodes in planar geometry

SnO/ε-Ga2O3 vertical p–n diodes with planar geometry have been fabricated on c-plane Al2O3 and investigated by current–voltage measurements. The effects of the in-plane conduction through the Si-doped ε-Ga2O3 layer on the diode performance and their relevance have been evaluated. A significant series resistance is observed, which shows typical features of the variable range hopping transport observed in Si-doped ε-Ga2O3; this in-plane transport mechanism is probably induced by the columnar domain structure of this polymorph. The dependence of the series resistance on the geometry of the diode supports the interpretation. A simple equivalent model is presented to describe the experimental behavior of the diode, supported by preliminary impedance spectroscopy investigation.

Applying bias voltage to improve rectification performance of molecular junction through side gate-group

Molecular diode is one of the most significant molecular devices for it being promised as electronic component in the molecular logic circuit. Controlling electronic transport to improve the rectification ratio of molecular diode is a crucial target for researchers. Here, based on the density functional theory and non-equilibrium Green's function method, the rectification performances of diblock co-oligomer molecules are investigated systematically. The numerical results show that, side gate-group can slightly enhance rectification ratios of diblock-molecule diodes, but it produces evident hindering effects on the electronic transports of the molecular junctions. Using electrode protrusion to contact with the side gate-group, the bias voltage is introduced to modulate the electronic transports of molecular junctions. By this strategy, the voltage at which the lowest unoccupied molecular orbital (LUMO) enters bias window is lowered evidently in the positive bias regime, which further significantly enhances the rectification ratios of the molecular diodes. The calculations additionally show that the LUMO is less delocalized under positive bias than it under negative bias, which is disadvantageous for enhancing the rectification performances of diblock co-oligomer molecular diode, thus very large rectification ratios are difficult to be achieved when one fabricates diblock co-oligomer molecular diodes in experimental fabrications.

71‐2: Invited Paper: High Power Red Laser Diodes for Display Applications

The AlGaInP red laser diodes were developed at the end of the 1980s, and since then we have been improving performance of laser diodes. Along with the improvement of laser performance, laser diodes has been used various applications such as optical discs and sensors. Recently, research and practical use of display applications and AR / VR devices are remarkable. In this paper, we mainly report on red laser diodes developed for display applications.

Influence of Phosphor Particle Size on Visual and Non-Visual Performances of White Light-Emitting Diodes for General Lighting

Influence of Phosphor Particle Size on Visual and Non-Visual Performances of White Light-Emitting Diodes for General Lighting

P‐137: High Performance Coplanar IGZO TFT Image Sensor with Partial Passivation‐less Structure for Digital X‐ray Detector

Recently, digital X‐ray detector (DXD) technology is needed to implement high‐resolution and high‐definition images, and low‐dose exposure of X‐ray imaging systems. This technology requires the IGZO TFT structure with better mobility and lower leakage current than the a‐Si backplane. In order to supplement stability and improve PIN diode (photodiode) performance, when SiNx‐based insulating layers and thick photodiodes are applied, continuous damage due to high concentration impurities occurs in the plasma environment, and thus the threshold voltage (Vth) shift problem of the IGZO TFT transistor occurs. To solve this problem, a high performance partial passivation‐less structure (PPLS) was applied to prevent damage using 43×43 centimeter flat panel X‐ray detector, and we investigated the improvement of the IGZO TFT characteristics. Before PIN diode deposition, Vth was +0.24V and after PIN diode & SiNx deposition, it moved slightly to Vth ‐0.17V, but the same characteristics as initial performance were guaranteed after TFT was completed.

Radiofrequency Schottky Diodes Based on p-Doped Copper(I) Thiocyanate (CuSCN).

Schottky diodes based on inexpensive materials that can be processed using simple manufacturing methods are of particular importance for the next generation of flexible electronics. Although a number of high-frequency n-type diodes and rectifiers have been demonstrated, the progress with p-type diodes is lagging behind, mainly due to the intrinsically low conductivities of existing p-type semiconducting materials that are compatible with low-temperature, flexible, substrate-friendly processes. Herein, we report on CuSCN Schottky diodes, where the semiconductor is processed from solution, featuring coplanar Al–Au nanogap electrodes (<15 nm), patterned via adhesion lithography. The abundant CuSCN material is doped with the molecular p-type dopant fluorofullerene C60F48 to improve the diode’s operating characteristics. Rectifier circuits fabricated with the doped CuSCN/C60F48 diodes exhibit a 30-fold increase in the cutoff frequency as compared to pristine CuSCN diodes (from 140 kHz to 4 MHz), while they are able to deliver output voltages of >100 mV for a VIN = ±5 V at the commercially relevant frequency of 13.56 MHz. The enhanced diode and circuit performance is attributed to the improved charge transport across CuSCN induced by C60F48. The ensuing diode technology can be used in flexible complementary circuits targeting low-energy-budget applications for the emerging internet of things device ecosystem.

Performance Comparison of 6.5 kV SiC PiN Diode with 6.5 kV SiC JBS and Si Diodes

6.5 kV SiC PiN diode with JTE and p+ rings termination was fabricated and characterized. The static and dynamic performance of SiC PiN diode were compared with that of SiC JBS diode and silicon diode, while switched in combination with a silicon IGBT. SiC PiN provides clear advantage while operating at higher current densities (above 100 A/cm2) and had lower leakage current. When switched together with a silicon IGBT, they contribute to losses similar to that of a SiC JBS diode.

Near‐Direct Band Alignment of MoTe2/ReSe2 Type‐II p‐n Heterojunction for Efficient VNIR Photodetection

AbstractVisible near infrared (VNIR) transition‐metal dichalcogenides (TMDs) photodetectors have attracted attention due to their unique electronic and optoelectronic properties. Herein, the photodetection performance of a novel MoTe2/ReSe2 van der Waals heterojunction (vdW HJ) diode is studied in the VNIR region. Density functional theory calculations reveal the formation of type‐II band alignment, which is beneficial for the design of a MoTe2/ReSe2 HJ diode with better optoelectronic properties. A superb rectification ratio of ≈1 × 104 is obtained via gate engineering, in which the ambipolar nature of MoTe2 enables a transition from p+–i to n–n+ state. In addition, the diode exhibits an excellent figure of merit for photodetection. The excellent diode performance is demonstrated by a high responsivity of 5.6 × 102 A W−1, an excellent detectivity of 8.1 × 1013 jones, and an external quantum efficiency of 9.5 × 102. Moreover, fast rise and decay times of 2 and 4 ms, respectively, are observed under illumination. The significant improvement is attributed to the combination of an intra‐TMD band‐to‐band transition and an inter‐TMD charge transfer process in the MoTe2/ReSe2 vdW HJ. This study provides an opportunity for advancing the prospects of TMDs in next generation optoelectronics.

Enhanced ultraviolet electroluminescence performance from p-NiO/n-GaN heterojunctions by using i-Ga2O3 as electron blocking layer

In recent years, GaN materials have been applied to the field of optoelectronic devices due to their excellent photoelectric properties, especially in the field of light-emitting diodes, which has attracted considerable attention. In this article, we use structural engineering methods to further improve the performance of GaN-based ultraviolet light-emitting diodes. The magnetron sputtering and annealing treatment were used to prepare ultraviolet light-emitting diodes based on p-NiO/i-Ga2O3/n-GaN and p-NiO/n-GaN heterojunction structure. X-ray diffractometer, field emission scanning electron microscope and ultraviolet-visible spectrophotometer were used to study the crystal quality, surface morphology, and optical properties of Ga2O3 film. Compared with the p-NiO/n-GaN heterojunction diode, the p-NiO/i-Ga2O3/n-GaN heterojunction diode exhibits better rectification characteristics and more excellent electroluminescence characteristics. Under the injection voltage of 35 V, the EL spectrum intensity of p-NiO/i-Ga2O3/n-GaN heterojunction diode is nearly 37 times higher than that of p-NiO/n-GaN heterojunction diode. Finally, the working mechanism of the electroluminescence is analyzed in detail through the energy band diagram of the two diodes.

Comparison of cross couple MOS based and Schottky diode based RF energy harvesting circuits using Wilkinson power combiner

Abstract This paper presents a new but simple RF energy harvesting circuit with the combination of Wilkinson power combiner and voltage multiplier circuits to enhance the output voltage level. Author has proposed a new Schottky diode-based voltage multiplier circuit which is the combination of existing conventional Greinacher voltage multiplier and Villard voltage multiplier circuits. In this proposed circuit first stage is a Greinacher circuit which provides a comparatively higher voltage and the later stages are followed by Villard Multiplier circuits to avoid the design complexities of multistage Greinacher circuits. A Wilkinson power combiner is connected with proposed circuit to combine RF receiving power from multiple receiving antennas. The insertion of Wilkinson power combiner increases the output voltages significantly for proposed circuits. A Cross couple of MOS-based RF energy harvesting circuit is also proposed and studied in RF energy harvesting applications. The performance of Schottky diode and MOS-based RF energy harvesting circuits has been studied and compared. Experimental performance of diode-based circuits has been carried out. The Experimental efficiency for proposed Schottky diode-based RF energy harvesting circuits is obtained as 58.6%. Insertion of Wilkinson power combiner in the proposed circuit increases output voltage level 84 and 90% for three stages Schottky diode-based circuit and MOS based circuit respectively that is a significant improvement of the proposed circuit. RF energy harvesting has various applications like low-power medical and remote healthcare electronics systems, providing wireless power to IoT devices for smart home automation and monitoring, and directly powering Wireless Sensor Nodes Networks (WSN) from ambient RF energy sources in a remote area.

Enhancing device performance of CsPbBr3 perovskite light-emitting diodes with Cs2CO3 modification layer and dual additives

This study presents the performance of CsPbBr3 perovskite light-emitting diodes (PeLEDs) with a cesium carbonate (CsCO3) modification layer and dual additives. With the Cs2CO3 modification layer, the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) hole transport layer was recrystallized to flatten the grains, reduce the series resistance, lower the impedance, and operate at a low level. It also has the lowest starting voltage at 3 V, which can release equivalent energy from electrons and holes. At 6 V, it has a maximum luminance of 16440 cd/m2 and an external quantum efficiency (EQE) of 1.56%.

Achieving High-Performance Molecular Rectification through Fast Screening Alkanethiol Carboxylate-Metal Complexes Electroactive Units

Achieving High-Performance Molecular Rectification through Fast Screening Alkanethiol Carboxylate-Metal Complexes Electroactive Units

Characterization of a thin photodiode as a routine dosimeter for low-dose radiation processing applications

The characterization of a dosimetry system based on a commercial PIN photodiode as a routine dosimeter in a 60Co industrial facility is reported. The main parameters of the dose rate response (repeatability, reproducibility, and angular dependence) and the dose response (dependence on both dose rate and accumulated dose) are investigated. The results obtained, within a dose rate range of 3.7–52.8 Gy/h and doses up to 200 Gy, fully adhere to the standard protocols established for radiation processing dosimetry. The diode performance as a routine dosimeter is validated by the good overall agreement with radiochromic films and alanine dosimetry.

Large cooperative effects in tunneling rates across van der Waals coupled binary self-assembled monolayers

This paper describes large positive cooperative effects of two orders of magnitude in the tunneling rates across molecular junctions of mixed self-assembled monolayers (SAMs) of rectifying (ferrocenyl undecanethiol HS(CH2)11Fc) and non-rectifying molecules with different terminal groups (11-undecanethiol and its derivatives, denoted as HS(CH2)11X, where X = -H, -NH2 or -NO2). By gradually diluting the surface fraction of HS(CH2)11Fc in the mixed SAM, it is found that the large positive cooperative effect is only important in the coherent tunneling regime but not in the incoherent tunneling regime. Density functional theory (DFT) shows that the measured cooperative effects in the tunneling rates in these binary systems are caused by Fc---X van der Waals interactions which increase in the order of -H< -NH2< -NO2. These strong cooperative effects dramatically alter the operation of a molecular diode, further highlighting the importance of taking cooperative effects into account, in this case driven by van der Waals interactions, in the rational design of electronic devices working at tunneling regime.

10-nanosecond dead time and low afterpulsing with a free-running reach-through single-photon avalanche diode.

The reduction of detector dead time represents an enabling factor in several photon counting applications. In this work, we investigate the free-running operation of reach-through single-photon avalanche diodes (SPADs) at ultra-low dead times. By employing a fast active quenching circuit with direct bonding to the detector, we are able to achieve a 10ns dead time with a thick SPAD by Excelitas, still maintaining extremely low afterpulsing probabilities (below 1.5%).