Fabrication Of Diodes Research Articles

Atomic Mechanism of Strain Alleviation and Dislocation Reduction in Highly Mismatched Remote Heteroepitaxy Using a Graphene Interlayer.

Remote heteroepitaxy is known to yield semiconductor films with better quality. However, the atomic mechanisms in systems with large mismatches are still unclear. Herein, low-strain single-crystalline nitride films are achieved on highly mismatched (∼16.3%) sapphire via graphene-assisted remote heteroepitaxy. Because of a weaker interface potential, the in-plane compressive strain at the interface releases by 30%, and dislocations are prevented. Meanwhile, the lattice distortions in the epilayer disappear when the structure climbs over the atomic steps on substrates because graphene renders the steps smooth. In this way, the density of edge dislocations in as-grown nitride films reduces to the same level as that of the screw dislocations, which is rarely observed in heteroepitaxy. Further, the indium composition in InxGa1-xN/GaN multiquantum wells increases to ∼32%, enabling the fabrication of a yellow light-emitting diode. This study demonstrates the advantages of remote heteroepitaxy for bandgap tuning and opens opportunities for photoelectronic and electronic applications.

Fully Vacuum-Free Fabrication of Bi-Directional Polymer Light-Emitting Diodes Based on a Hybrid Lamination Top Electrode

This study investigates a hybrid lamination electrode based on a silver nanowire and a conductive polymer for the top electrode of bi-directional polymer light-emitting diodes (PLEDs). Through a vacuum-free hot-press lamination step, the proposed hybrid electrode employed a complete and concrete electrical contact with the underlying emissive polymer layer. In addition, by inserting a hole injecting poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) layer to increase the level of work function, the bi-directional PLED device with a laminated top electrode showed a more competitive device performance such as an operating voltage, a current efficiency, and a total external quantum efficiency compared to the counterpart device with a multilayered electrode of MoO3/Ag/MoO3 by the vacuum thermal evaporation method. An analysis carried out on the angular characteristics of bi-directional PLEDs including the variation of color coordinates and change in luminance values according to emission angles confirmed that the hybrid lamination electrode provided a more uniform angular distribution regardless of the direction of emission without any optical micro-cavity effect. Detailed optical and electrical analyses were also performed to evaluate the compatibility of the hybrid lamination electrode for the low-cost fabrication of efficient PLEDs.

Fabrication of vertical AlGaN-based deep-ultraviolet light-emitting diodes operating at high current density (∼43 kA cm−2) using a laser liftoff method

We have successfully fabricated vertical LEDs by separating a 1 × 1 cm2 wafer composed of deep-ultraviolet LED on a sapphire substrate from the substrate using a laser liftoff (LLO) method. Reproducible substrate separation was achieved by the LLO method using an Al0.68Ga0.32N underlayer film on an AlN template with periodic pillars. The fabricated vertical LED successfully demonstrated notable luminescence (peak wavelength: 298 nm) characteristics up to a current density of ∼43 kA cm−2 at room temperature and in pulsed drive, which is expected to be used in high-power LEDs and laser diodes.

Direct GaAs Nanowire Growth and Monolithic Light‐Emitting Diode Fabrication on Flexible Plastic Substrates

The growth of self‐catalyzed GaAs nanowires (NWs) and monolithic light‐emitting diode (LED) directly on flexible plastic substrates is reported. Dense GaAs NW forest is attained in self‐catalyzed mode using metalorganic vapor phase epitaxy. The NWs are shown to be crystalline with a zinc‐blende phase. The optical properties of the GaAs NWs are found to be promising in both photoluminescence emission and light‐trapping based on reflectance and transmittance measurements. The LED is fabricated from p‐type NWs by depositing Au as Ohmic contact and TiO2/ITO as an electron‐selective contact. The demonstrated NW growth and LED fabrication represent a significant step toward low‐cost, industrially feasible flexible III–V NW optoelectronic applications, as plastic is inexpensive, and the fabrication steps are compatible with roll‐to‐roll processing.

Full-spectrum solid-state white lighting with high color rendering index exceeding 96 based on a bright broadband green-emitting phosphor

Developing blue-light-excited high-efficiency phosphor remains challenging for the fabrication of warm-white light-emitting diodes (LEDs) with an ultra-high color rending index (CRI). Here, the co-substitution of Ca2+-Hf4+ ion-pairs into a Y3Al5O12:Ce3+ phosphor, affords a novel, broadband, green-emitting CaY2HfAl4O12:2%Ce3+ garnet-type phosphor amenable to efficient blue light excitation. The structure, luminescent properties and blue-shift of this new material relative to a Y3Al5O12:2%Ce3+ phosphor have been extensively studied. Under 450 nm excitation, the optimum material exhibits high internal quantum efficiency (73.3%) and excellent thermal stability. Incorporation of the CaY2HfAl4O12:2%Ce3+ green phosphor into a prototype LED device delivers full-spectrum lighting with a high CRI (Ra = 97.2, R9 = 98.3) and low correlated color temperature (CCT = 3508 K). The resulting insight should aid the development of novel high-efficiency phosphors for full-spectrum warm-white LEDs with high-CRI value.

Room‐Temperature Processed Lateral Trench‐Metal–Insulator–Semiconductor Schottky Barrier Diodes with Amorphous Gallium Oxide (a‐Ga2O3) Thin Films on Single‐Crystal Silicon <100>

This article proposes a novel design approach for the fabrication of lateral Schottky barrier diodes (SBD) using a wide bandgap oxide semiconductor on silicon. Structural and electrical properties of the fabricated device are reported and compared with published data. The metal–insulator–semiconductor (MIS) Schottky barrier is realized between the room‐temperature sputtered Al/a‐Ga2O3 on single‐crystal <100> boron‐doped silicon substrate (p‐type). The device fabrication process is implemented entirely at room temperature. The proposed trench diode yields an ideality factor of 1.65 and a rectification ratio of ≈1 × 106 at ±5.0 V. The extracted specific ON resistance is 78 mΩ cm2, and the breakdown voltage is not observed for 180 V for a 200‐nm‐thin layer of a‐Ga2O3. Due to such low‐temperature process, simple fabrication steps, and notably high Baliga's figure‐of‐merit (BFOM), the proposed diode is, therefore, promising for power electronics applications.

A rectifying Al/ZnO/pSi/Al heterojunction as a photodiode

The investigation reports on fabrication and measurements of heterojunction diode based on ZnO layer. The layers are ultrasonic sprayed onto p-type silicon substrates at 350 ​°C and the front contacts made from aluminum have been thermally evaporated in low pressure vacuum. The Al/ZnO/p-Si/Al device is then made-up and characterized by current-voltage and capacitance-voltage under dark, light and temperature environments. The ideality factor exceeds the unity which confirms the non-ideal comportment of such device based on nZnO layer. An interesting rectifying sketch around 2544 in dark and 4082 in light is recorded as shown by I–V curve. The electrical parameters of such device are determined in dark and light (60–150 ​mW/cm2) conditions displaying the values of ideality factor (ni) of 3.5 (1.6), barrier height ΦB of 0.74 (0.89) V, series resistance Rs of 5 (1.6) kΩ. Influence of temperature on the current-voltage curve is evidenced within the 22–107 ​°C range. To boost this study, the measurement of C–V-f characteristics are measured and interface state densities of ZnO/p-Si diode in dark, light and temperature environments are investigated. Richardson plot evidences numerous parameters of ZnO/pSi heterojunction diode.

Metal Inorganic–Organic Complex Glass and Fiber for Photonic Applications

The vitrification of hybrid materials (e.g., metal–organic frameworks and coordination polymers) is considered as the fourth generation of glass. To extend the hybrid glass family with photonic functionalities, we report a crystalline metal inorganic–organic complex (MIOC) (i.e., ZnCl2(HbIm)2, HbIm = benzimidazole) with a one-dimensional hydrogen bonded chain that can be melted to a stable liquid at elevated temperatures and subsequently quenched to form a large-sized bulk glass under ambient atmosphere with excellent thermal and chemical stability. Benefiting from the moderate glass-forming ability of the MIOC, we succeeded in the fabrication of the first MIOC glass fibers with diameters of 7–200 μm. The doping of the MIOC fibers by organic dyes results in anisotropic photoluminescence. Furthermore, the as-prepared MIOC bulk glass can be employed as the stable and inert host for inorganic phosphors, which leads to the development of a novel phosphor-in-MIOC glass composite and enables the fabrication of high-power white light-emitting diodes. Our findings make the ZnCl2(HbIm)2-based MIOC glass a promising material for photonic applications.

Asymmetric Chemical Functionalization of Top-Contact Electrodes: Tuning the Charge Injection for High-Performance MoS2 Field-Effect Transistors and Schottky Diodes.

The fabrication of high-performance (opto-)electronic devices based on 2D channel materials requires the optimization of the charge injection at electrode-semiconductor interfaces. While chemical functionalization with chemisorbed self-assembled monolayers has been extensively exploited to adjust the work function of metallic electrodes in bottom-contact devices, such a strategy has not been demonstrated for the top-contact configuration, despite the latter being known to offer enhanced charge-injection characteristics. Here, a novel contact engineering method is developed to functionalize gold electrodes in top-contact field-effect transistors (FETs) via the transfer of chemically pre-modified electrodes. The source and drain Au electrodes of the molybdenum disulfide (MoS2 ) FETs are functionalized with thiolated molecules possessing different dipole moments. While the modification of the electrodes with electron-donating molecules yields a marked improvement of device performance, the asymmetric functionalization of the source and drain electrodes with different molecules with opposed dipole moment enables the fabrication of a high-performance Schottky diode with a rectification ratio of ≈103 . This unprecedented strategy to tune the charge injection in top-contact MoS2 FETs is of general applicability for the fabrication of high-performance (opto-)electronic devices, in which asymmetric charge injection is required, enabling tailoring of the device characteristics on demand.

Coinage Metal Complexes of Germylene and Stannylene.

Group 11 metal (M = Cu, Ag, Au) complexes of heavier tetrylenes (namely, germylene and stannylene) have been studied for several years now. However, the field is mainly unexplored for their potential application either in homogeneous catalysis or in photophysical properties regardless of how the current reports allude to the rich and fascinating chemistry of group 14 elements. In this mini-review, we attempted to summarize the recent advances of heavier tetrylene-stabilized coinage metal complexes, which are majorly dominated by structure elucidation studies. This comprehensive summary intends to help researchers design and fine-tune the tetrylene ligand framework that can lead to coinage metal complexes for future applications as photoemitters in organic light-emitting diode fabrication and efficient catalysts in homogeneous catalysis.

Effects of deposition temperature on Mo/SiC Schottky contacts

We report on the results of our investigation of the effect of deposition temperature on molybdenum (Mo) used as Schottky contacts to fabricate silicon carbide (SiC) Schottky barrier diodes. The contacts were deposited using magnetron sputtering on n-type 4H-SiC at temperatures ranging from 25 to 900 °C. The fabricated diodes were characterized by current–voltage, current–voltage–temperature, and capacitance–voltage measurements. The diodes showed average Schottky barrier heights that decreased from 1.54 to 1.00 eV with increasing deposition temperature of the contacts. The average values of the ideality factors similarly decreased from 1.21 to 1.06 with increasing deposition temperature. However, the diodes with contacts deposited at 400–900 °C nearly maintained a constant ideality factor value of 1.06. The x-ray diffraction analysis indicated that silicides were formed at the interface for contacts deposited at or above 400 °C. The improved properties of the diodes with contacts deposited at higher temperatures are correlated with the formation of the interfacial alloys possessing improved electrical properties. This work demonstrates that high temperature deposition is another method for optimizing the properties of Mo contacts for the fabrication of 4H-SiC Schottky diodes for electronic applications in high power and high temperature environments.

Monomeric carbazolylcyanobenzenes as thermally activated delayed fluorescence emitters: effect of substitution position on photoluminescent and electroluminescent properties

In this study, two new donor-acceptor type thermally activated delayed fluorescence materials using carbazole as a donor and cyano substituted benzene as an acceptor were synthesized. Structural parameters, molecular orbital densities, photophysical characteristics were determined. By changing the substitution position of the cyano groups on the phenyl rings, the relationship between structure and properties was also be disclosed. These materials were tested as emissive species for the fabrication of organic light-emitting diodes. The blue devices showed EL emission peaks at 464 and 488 nm with the CIE coordinates of (0.17, 0.18) and (0.21, 0.31), respectively.

Solution-Processed Smooth Copper Thiocyanate Layer with Improved Hole Injection Ability for the Fabrication of Quantum Dot Light-Emitting Diodes.

Copper thiocyanate (CuSCN) has been gradually utilized as the hole injection layer (HIL) within optoelectronic devices, owing to its high transparency in the visible range, moderate hole mobility, and desirable environmental stability. In this research, we demonstrate quantum dot light-emitting diodes (QLEDs) with high brightness and current efficiency by doping 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) in CuSCN as the HIL. The experimental results indicated a smoother surface of CuSCN upon F4TCNQ doping. The augmentation in hole mobility of CuSCN and carrier injection to reach balanced charge transport in QLEDs were confirmed. A maximum brightness of 169,230 cd m−2 and a current efficiency of 35.1 cd A−1 from the optimized device were received by adding 0.02 wt% of F4TCNQ in CuSCN, revealing promising use in light-emitting applications.

Fabrication and optical characterization of erbium-doped silicon diode for quantum communication applications

Quantum Key Distribution allows two users to exchange secret keys and it is based on the transmission of single photons or attenuated laser pulses. Recently, sources based on multiple single-photon emitters were demonstrated to be suitable for QKD. Here, we present a CMOS compatible multiple single-photon emitters source realized on a SOI wafer by a standard silicon diode doped with erbium ions. Particular emphasis is placed on the fabrication of such a device enhancing the erbium electroluminescence signal by adopting a proper oxygen co-doping. Finally, electroluminescence characterization at room temperature of the device is presented.

Fabrication and characterization of high performance InAlZnO Schottky barrier diode and its application in ultraviolet photodetection

High-performance InAlZnO (IAZO) Schottky barrier diodes (SBDs) with top Pd/IAZO Schottky contact were fabricated, and the influence of sputtering power used to prepare IAZO films on the device performance was investigated. The 50 W-fabricated IAZO SBD exhibited the relatively best electrical properties, including a close-to-unity ideality factor (1.03), a high rectification ratio (1.83 × 107), a low series resistance (237.5 mΩ cm2), large barrier heights (0.87 and 0.82 eV), and a small barrier inhomogeneity (0.05 eV), which was mainly due to the least background doping density (8.43 × 1015/cm3) and interface state density (4.30 × 1010/eV cm2) at 50 W. Meanwhile, the IAZO SBDs prepared at 50 W also displayed the best device uniformity and highest reverse breakdown voltage (−15.23 ± 0.405 V). A 50 W-fabricated IAZO SBD with a horizontal structure was then applied to the ultraviolet photodetector, and it showed good detection effect, especially the fast response with an average rise time of 0.208 s and an average decay time of 0.094 s. Our study indicates the great research value and development potential of IAZO SBDs in future integrated circuits and other fields.

Structures and Materials in Stretchable Electroluminescent Devices.

Stretchable electroluminescent (EL) devices are obtained by partitioning a large emission area into areas specifically for stretching and light-emission (island-bridge structure). Buckled and textile structures are also shown effective to combine the conventional light emitting diode fabrication with elastic substrates for structure-enabled stretchable EL devices. Meanwhile, intrinsically stretchable EL devices which are characterized with uniform stretchability down to microscopic scale are relatively less developed but promise simpler device structure and higher impact resistance. The challenges in fabricating intrinsically stretchable EL devices with high and robust performance are in many facets, including stretchable conductors, emissive materials, and compatible processes. For the stretchable transparent electrode, ionically conductive gel, conductive polymer coating, and conductor network in surface of elastomer are all proven useful. The stretchable EL materials are currently limited to conjugated polymers, conjugated polymers with surfactants and ionic conductors added to boost stretchability, and phosphor particles embedded in elastomer matrices. These emissive materials operate under different mechanisms, require different electrode materials and fabrication processes, and the corresponding EL devices face distinctive challenges. This review aims to provide a basic understanding of the materials meeting both the mechanical and electronic requirements and important techniques to fabricate the stretchable EL devices.

Synthesis of n-type ZrO2 doped ε-Ga2O3 thin films by PLD and fabrication of Schottky diode

Tin-assisted pure phase n-type ZrO2-doped ε-Ga2O3 films were synthesized by pulsed laser deposition (PLD) and deposited on (0001) epi-GaN/sapphire substrates. The characterization of n-type ZrO2-doped ε-Ga2O3 thin films and the electrical properties of SBD based on that film were investigated in details. From XRD, the pure Zr-doped ε-Ga2O3 without diffraction peaks of zirconia suggested the formation of ε-(ZrxGa1−x)2O3 solid solution. The surface morphology and chemical content of the ε-Ga2O3 thin film were studied by AFM and XPS. The electrical resistivity and related free carrier concentration at room temperature were measured to be 108 Ω·cm and 5.5 × 1015 cm−3, respectively, and mobility up to 10.3 cm2/V·s. The Schottky barrier diode possessed a rectification ratio up to 106~107, breakdown voltage of 392 V, and the interface states density from 2.4 × 1013 cm-2 eV-1 to 6.4 × 1014 cm-2 eV-1 with the trap energy level from 0.89 eV to 0.94 eV below the bottom of the conduction band.

Ambient fabrication of efficient triple cation perovskite-based near-infrared light-emitting diodes

In addition to their widespread use as an outstanding light-harvesting material, solution-based organometallic halide perovskites have also recently emerged as a promising material for light-emitting diode (LED) applications. However, their stability under an ambient environment remains a challenge. Triple cation perovskites offer an appealing solution as it reduces the sensitivity to the processing conditions and improves the purity of the perovskite films. This work describes a facile ambient-processed thiocyanate-doped triple-cation perovskite Csx(MA0.17FA0.83)Pb(100-x)(I0.83Br0.17)3 used for high-performance perovskite-based LEDs with peak emission at 750 nm. Using the perovskite film tailoring technique by mixing DMF (N,N-Dimethylmethanamide) with perovskite precursor, we are able to reduce the perovskite grain size and optimize the film thickness while preserving its crystalline structure. With optimized processing techniques, we achieve a ∼90% improvement of the perovskite LEDs external quantum efficiency (EQE) from ∼3.1% to ∼5.9%. We believe this triple cation perovskite synthesis approach and film tailoring technique yields excellent device performances and constitutes a significant step towards low-cost and efficient LEDs.

Investigation of I-V-T Charactersitics of Cr/Indigo Carmine/p-Si/Al Heterojunction Diode

The subject of this study is the use of Indigo Carmine (IC) material in Schottky diode application. The p-Si crystal was chosen as the base material for diode fabrication. One surface of the p-Si metal was coated with Al metal by thermal evaporation method. Indigo carmine interface material was coated on the other surface of p-Si by spin coating method. Finally, Cr metal was coated on this material with DC sputtering method. So we obtained refence Cr/p-Si/Al diode and Cr/IC/p-Si/Al heterojunctions diode. When the current-voltage (I-V) measurements of these diodes at room temperature were examined, it was determined that the Indigo Carmine material improved the diode parameters. It was determined from the I-V measurements of the Cr/IC/p-Si/Al diode for different temperatures that the ideality factor (n) decreased and the barrier height (Φb) value increased with the increasing temperature. These changes with temperature have been attributed to the inhomogeneous distribution in the potential barrier. In addition, the change of diode parameters with temperature showed that the diode has a double Gaussian distribution.

Status of the growth and fabrication of AlGaN-based UV laser diodes for near and mid-UV wavelength

Status of the growth and fabrication of AlGaN-based UV laser diodes for near and mid-UV wavelength