Light-emitting Characteristics Research Articles

A methodical investigation on stilbazolium derivative substituted with 2,4-Dichlorobenzaldehyde as a donor: An effective crystal for optical device fabrication

For a couple of decades, nonlinear optics (NLO) has garnered significant attention due to its widespread application in optical systems. In this viewpoint, a new 2-[2(2,4-Dichloro-phenyl)vinyl]methyl-1-pyridinium iodide (DCPI) crystal was grown through slow evaporation process for NLO application. Single Crystal X-ray diffraction (SCXRD) study reveals that the DCPI crystallized centrosymmetric (P-1) space group. The CHN elemental analysis and NMR spectroscopy assess the purity of the material. The vinyl (CC) group formation in DCPI was asserted by the Fourier-transform infrared (FT-IR) spectrum. The Hirshfeld surface analysis confirms the presence of hydrogen bonds in the crystal structure through its contribution percentage (27 %) to the overall intermolecular interaction. DCPI crystal exhibits 80 % transparency in the visible region. Luminescence studies assess the green light-emitting characteristics of the DCPI crystal. The etching and Atomic Force Microscopy (AFM) studies confirm that the DCPI crystal has a flat surface with minimum dislocations. Z-scan studies found the third-order nonlinear characteristics of the crystal. Overall, the article illustrates the appropriateness of DCPI crystal in fabricating optical devices through its significant optical characteristics.

Biosynthesis, Structural, Spectroscopic, Photoluminescence, and Antifungal Activity of Ni-doped CeO2 Nanoparticles.

Pedalium Murex leaf extract was used in this study to create Nickel-doped Cerium oxide (Ni-CeO2) nanoparticles at 3mol% and 5mol% molar concentrations. The biosynthesized process was applied for the fabrication of Ni-CeO2 NPs. The X-ray diffraction method was used to identify their crystal structure. The XRD measurements showed that the Ni-CeO2 NPs crystallized into the face-centred cubic system. Fourier transform infrared spectral study was applied to explore the molecular vibrations and chemical bonding. The surface texture and chemical ingredients of Ni-CeO2 NPs were studied using field-emission scanning electron microscopy and energy-dispersive X-ray analysis. The EDX mapping spectra illustrate the uniform dispersal of Ce, Ni, and O atoms over the sample's surface. X-ray photoelectron spectroscopy (XPS) was conducted to confirm the chemical state of the Ni-CeO2 NPs. UV-Vis spectrum study was performed to ascertain the photon absorption, bandgap, and Urbach edge of Ni-CeO2 NPs. Photoluminescence (PL) research has been used to study the light-emitting characteristic of Ni-CeO2 NPs. The emissive intensity transition corresponding to Ni-CeO2 NPs was found to increase with the dopant level. The CIE 1931 chromaticity map was plotted to find the aptness of the samples for optical uses.The antifungal ability of Ni-CeO2 NPs was evaluated against the fungi candida albicans and candida krusein with the agar well-diffusion process. The fungicidal activity of the 3mol% Ni doped CeO2 nanoparticles has shown a maximum zone of inhibition. The experimental findings illustrate the utility of Ni-CeO2 NPs for optical and antifungal applications.

Effect of temperature on GaN-integrated optical transceiver chips.

The gallium nitride (GaN) integrated optical transceiver chip based on multiple quantum wells (MQW) structure exhibits great promise in the fields of communication and sensing. In this Letter, the effect of ambient temperature on the performance of GaN-integrated optical transceiver chips including a blue MQW light-emitting diode (LED) and a MQW photodiode (PD) is comprehensively studied. Temperature-dependent light-emitting and current-voltage characteristics of the blue MQW LEDs are measured with the ambient temperature ranging from -70°C to 120°C. The experimental results reveal a decline in the electroluminescent (EL) intensity and an obvious redshift in the emission peak wavelength of the LED with increasing ambient temperature. The light detection performance of MQW PD under different temperatures is also measured with the illumination of an external blue MQW LED, indicating an enhancement in the PD sensitivity as the temperature rises. Finally, the temperature effect on the MQW PD under the illumination of the MQW LED on the GaN-integrated optical transceiver chip is characterized, and the PD photocurrent increases with higher ambient temperature. Furthermore, the measured temperature characteristics indicate that the GaN-integrated optical transceiver chip offers a promising application potential for optoelectronic temperature sensor.

Design and spectroscopic study of samarium complexes with tunable photoluminescent properties

The synthesis and characterization of four octacoordinated complexes of [Sm(TFPB)3] with different neutral ligands have been successfully performed. This study aimed to evaluate the potential of neutral ligands in enhancing the emission intensity of Sm(III) ion by investigating their light-emitting characteristics. Dominance of hypersensitive transition 4G5/2 → 6H9/2 is observed which suggests the asymmetry in the vicinity of Sm(III) ion in these complexes, reinforced by asymmetry ratio. Stark-splitting in the magnetic dipole 4G5/2→6H5/2 transition was consistent across most complexes, but [Sm(TFPB)3(topo)2] displayed a different pattern due to monodentate auxiliary moiety, which does not provide as much structural rigidity and stability as found in the other complexes. Various analyses including IR, NMR, CV, TGA, UV and colorimetry, supported possible applications of synthesized complexes in devices based on photonics, sensors, magnets and other technological fields.

Effect of Thermal History During Device Fabrication on Quantum-Dot Light-Emitting Diode Characteristics

Effect of Thermal History During Device Fabrication on Quantum-Dot Light-Emitting Diode Characteristics

Aging and Recovery Effects of Quantum-Dot Light-Emitting Diode Characteristics

Aging and Recovery Effects of Quantum-Dot Light-Emitting Diode Characteristics

Characterization of YAG:Ce ceramics with graphene oxide

Yttrium-aluminum garnet (Y3Al5O12) is an optical material that shows great potential due to its favorable light-emitting and mechanical properties, as well as its chemical stability and thermal resistance. It is commonly utilized in laser technology, optical instruments, and solid-state light sources as a result of its activation by transition metal or rare earth element ions. In this work, experiments were carried out on the procedure for compacting samples of luminescent ceramics Y3Al5O12:Ce3+, by single-base pressing followed by sintering. Comprehensive studies of the influence of graphene oxide of variable concentration (x=0.1;0.5; 1 wt.%) on the radiative characteristics of ceramic samples. It was found that the addition of graphene oxide in an amount from 0.1 to 1 wt. % affects the density and luminescent properties of YAG:Ce ceramics. There is a decrease in the value of the density parameter at concentrations of graphene oxide 0.1-1 wt. % before annealing, after annealing, the relative density value increases to ~99 %. The luminescence spectrum when excited by a blue LED chip appears as a wide band in the spectral range 460-750, the nature of which is associated with radiative transitions in the cerium ion. It has been established that the light-emitting characteristics have a downward trend when activated by graphene oxide. The integral luminescence intensity decreases from 27.1 % to 19 % with an increase in the concentration of graphene oxide.

Far-Red Interlayer Excitons of Perovskite/Quantum-Dot Heterostructures.

Interlayer excitons (IXs) at the interface of heterostructures (HSs) with a staggered band alignment are fascinating quantum quasi-particles with light-emitting and long-lifetime characteristics. In this study, the energy band alignments (EBAs) of the HS of MAPbI3 perovskite thin sheets with CdSe-ZnS core-shell quantum dot (QD) layers are modulated by using different diameters of the QDs. Far-red IX emission is observed at 1.42eV from the HS of MAPbI3 /CdSe-ZnS-QD (λem =645nm) with type-II EBA owing to charge transfer. The lifetime of the far-red IXs is estimated to be 5.68µs, which is considerably longer than that (0.715ns) of the intralayer excitons from CdSe-ZnS-QD. With increasing incident excitation power, the PL peak and its intensity of IXs are blue-shifted and linearly increased, respectively, indicating a strong dipole alignment of far-red IXs at the heterojunction. Back focal plane imaging suggests that the directions of dipole moments of the IXs are relatively out-of-plane compared to those of the intralayer excitons (MAPbI3 and CdSe-ZnS-QD). Notably, the abnormal behavior of the optical characteristics is observed near the phase transition temperature (90K) of MAPbI3 . MAPbI3 /CdSe-ZnS-QD HS photodetectors show the increase in photocurrent and detectivity compared to MAPbI3 at IX excitation.

New Light-Green Thermally Activated Delayed Fluorescence Polymer Based on Dimethylacridine-Triphenyltriazine Light-Emitting Unit and Tetraphenylsilane Moiety as Non-Conjugated Backbone.

In the search for solution-processable TADF materials as a light emitting layer for OLED devices, polymers have attracted considerable attention due to their better thermal and morphological properties in the film state with respect to small molecules. In this work, a new polymer (p-TPS-DMAC-TRZ) with thermally activated delayed fluorescence (TADF) light-emitting characteristics was prepared from a conjugation-break unit (TPS) and a well-known TADF core (DAMC-TRZ). This material was designed to preserve the photophysical properties of DAMC-TRZ, while improving other properties, such as thermal stability, promoted by its polymerization with a TPS core. Along with excellent solubility in common organic solvents such as toluene, chloroform and THF, the polymer (Mn = 9500; Mw = 15200) showed high thermal stability (TDT5% = 481 °C), and a Tg value of 265 °C, parameters higher than the reference small molecule DMAC-TRZ (TDT5% = 305 °C; Tg = 91 °C). The photoluminescence maximum of the polymer was centered at 508 nm in the solid state, showing a low redshift compared to DMAC-TRZ (500 nm), while also showing a redshift in solution with solvents of increasing polarity. Time-resolved photoluminescence of p-TPS-DMAC-TRZ at 298 K, showed considerable delayed emission in solid state, with two relatively long lifetimes, 0.290 s (0.14) and 2.06 s (0.50), and a short lifetime of 23.6 ns, while at 77 K, the delayed emission was considerably quenched, and two lifetimes in total were observed, 24.6 ns (0.80) and 180 ns (0.20), which was expected from the slower RISC process at lower temperatures, decreasing the efficiency of the delayed emission and demonstrating that p-TPS-DMAC-TRZ has a TADF emission. This is in agreement with room temperature TRPL measurements in solution, where a decrease in both lifetime and delayed contribution to total photoluminescence was observed when oxygen was present. The PLQY of the mCP blend films with 1% p-TPS-DMAC-DMAC-TRZ as a dopant was determined to be equal to 0.62, while in the pure film, it was equal to 0.29, which is lower than that observed for DMAC-TRZ (0.81). Cyclic voltammetry experiments showed similarities between p-TPS-DMAC-TRZ and DAMC-TRZ with HOMO and LUMO energies of -5.14 eV and -2.76 eV, respectively, establishing an electrochemical bandgap value of 2.38 eV. The thin film morphology of p-TPS-DMAC-TRZ and DMAC-TRZ was compared by AFM and FE-SEM, and the results showed that p-TPS-DMAC-TRZ has a smoother surface with fewer defects, such as aggregations. These results show that the design strategy succeeded in improving the thermal and morphological properties in the polymeric material compared to the reference small molecule, while the photophysical properties were mostly maintained, except for the PLQY determined in the pure films. Still, these results show that p-TPS-DMAC-TRZ is a good candidate for use as a light-emitting layer in OLED devices, especially when used as a host-guest mixture in suitable materials such as mCP.

Ultra High Luminous Efficiency p-Type Surface Defect Structure GaN LED

In this paper, we propose a double-layer SiO2 photonic crystal LED with a linear defect structure in the [Formula: see text]-GaN layer, the purpose is to solve the problem of low light extraction efficiency caused by diffusion scattering effect. We used FDTD modeling to analyze the light-emitting characteristics of GaN LED, after optimizing the structural parameters of two-dimensional photonic crystals, the light extraction efficiency is improved from 19.4% to 35.2%, the light extraction efficiency is increased by 1.8 times, meanwhile the light output power is also increased by 1.86 times. The introduction of the defect structure does not affect the [Formula: see text]–[Formula: see text] characteristics of the LED, and the output power of the LED is increased by 11% under the current of 300[Formula: see text]mA.

Direct Visualization of UV-Light on Polymer Composite Films Consisting of Light Emitting Organic Micro Rods and Polydimethylsiloxane.

We experimentally demonstrate the direct visualization of ultraviolet (UV) light using flexible polymer composite films consisting of crystalline organic tris-(8-hydroxyquinoline) aluminum (Alq3) micro-rods and polydimethylsiloxane (PDMS). The representative organic mono-molecule Alq3, which is a core material of organic light-emitting diodes, was used to detect light in the invisible UV region and visualize photoluminescence (PL). Alq3 shows absorption in the UV region and light-emitting characteristics in the green region, making it an optimal material for UV visualization because of its large Stokes transition. Crystalline Alq3 micro-rods were fabricated in a deionized water solution through a sequential process of reprecipitation and self-assembly. Highly bright photoluminescence was observed on the highly crystalline Alq3 micro-rods under UV light excitation, indicating that the crystalline structures of Alq3 molecules affect the visible emission decay of excitons. The Alq3 micro-rods were manufactured as flexible polymer composite films using a PDMS solution to observe UV photodetector characteristics according to UV intensity, and it was confirmed that the intensity of the fine UV light reaching the earth’s surface can be visualized by making use of this UV photodetector.

Fabricated Flexible Composite for a UV-LED Color Filter and Anti-Counterfeiting Application of Calcium Molybdate Phosphor Synthesized at Room Temperature.

Crystalline CaMoO4 and rare-earth-doped CaMoO4:RE3+ (RE = Tb, Eu) phosphors were synthesized at room temperature using a co-precipitation method. The crystal structure of the synthesized powder was a tetragonal structure with a main diffraction peak (112) phase. When CaMoO4 was excited at 295 nm, it showed a central peak of 498 nm and light emission in a wide range of 420 to 700 nm. Rare-earth-ion-doped CaMoO4:Tb3+ was excited at 288 nm and a green light emission was observed at 544 nm, and CaMoO4:Eu3+ was excited at 292 nm and a red light emission was observed at 613 nm. To take advantage of the light-emitting characteristics, a flexible composite was manufactured and a color filter that could be used for UV-LEDs was manufactured. In addition, it was suggested that an ink that could be checked only by UV light could be produced and applied to banknotes so as to prevent counterfeiting.

Bimodal Tactile Sensor without Signal Fusion for User-Interactive Applications

Tactile sensors with multimode sensing ability are cornerstones of artificial skin for applications in humanoid robotics and smart prosthetics. However, the intuitive and interference-free reading of multiple tactile signals without involving complex algorithms and calculations remains a challenge. Herein a pressure-temperature bimodal tactile sensor without any interference is demonstrated by combining the fundamentally different sensing mechanisms of optics and electronics, enabling the simultaneous and independent sensing of pressure and temperature with the elimination of signal separation algorithms and calculations. The bimodal sensor comprises a mechanoluminescent hybrid of ZnS-CaZnOS and a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) thermoresistant material, endowing the unambiguous transduction of pressure and temperature into optical and electrical signals, respectively. This device exhibits the highest temperature sensitivity of -0.6% °C-1 in the range of 21-60 °C and visual sensing of the applied forces at a low limitation of 2 N. The interference-free and light-emitting characteristics of this device permit user-interactive applications in robotics for encrypted communication as well as temperature and pressure monitoring, along with wireless signal transmission. This work provides an unexplored solution to signal interference of multimodal tactile sensors, which can be extended to other multifunctional sensing devices.

Improving the efficiency of industrial samples of silicon solar elements

Possibilities of increasing the efficiency by more than 20 % for silicon photoelectric converters made in China have been investigated. It has been established by the method of computer simulation that the life-times of nonequilibrium charge carriers, which are 520 μs, realized in such photoelectric converters, do not limit the possibility of increasing their efficiency by more than 20 %. It is shown that an increase in the photocurrent density to 43.1 mA/cm2 leads to an increase in efficiency to 20.1 %, and a decrease in the diode saturation current density to 3.1∙10-14 A/cm2 leads to an increase in efficiency to 20.4 %. Simultaneous change of these diode characteristics leads to an increase in efficiency to 23.1 %. The paper proposes physical and technological approaches to increase the photocurrent density and reduce the diode saturation current density in ready-made photovoltaic converters. The study of the influence of operating temperature on the efficiency of crystalline silicon photoelectric converters is carried out in the article. It is shown that with increasing operating temperature the relative decrease in the efficiency of single-crystal devices is –0.7 relative %/C, which is significantly higher than in the instrument structures of European production and due to non-traditional decrease in short-circuit current density. Mathematical modeling of the influence of light-emitting diode characteristics on the efficiency of crystalline silicon solar cells showed that the decrease in the efficiency of instrument structures with increasing operating temperature is due not only to an increase in diode saturation current density from 10-13 A to 3·10-13 A, which is 300 %, but also by reducing the shunt resistance from 2.5 kOhm to 1.5 kOhm. A study of the effect of operating temperature on the diode saturation current showed that the height of the potential barrier in the studied silicon photovoltaic converters is 0.87 eV, due to the insufficient level of doping of the base material. The limited height of the potential barrier leads to an unconventional decrease in the shunt resistance with increasing operating temperature.

Amplified spontaneous emission and gain in highly concentrated Rhodamine-doped peptide derivative

Bioinspired fluorescence, being widely explored for imaging purposes, faces challenges in delivering bright biocompatible sources. While quite a few techniques have been developed to reach this goal, encapsulation of high-quantum yield fluorescent dyes in natural biological forms suggest achieving superior light-emitting characteristics, approaching amplified spontaneous emission and even lasing. Here we compare gain capabilities of highly concentrated Rhodamine B solutions with a newly synthesized biocompatible peptide derivative hybrid polymer/peptide material, RhoB-PEG1300-F6, which contains the fluorescent covalently bound dye. While concentration quenching effects limit the maximal achievable gain of dissolved Rhodamine B, biocompatible conjugation allows elevating amplification coefficients towards moderately high values. In particular, Rhodamine B, anchored to the peptide derivative material, demonstrates gain of 22–23 cm−1 for a 10−2 M solution, while a pure dye solution possesses 25% smaller values at the same concentration. New biocompatible fluorescent agents pave ways to demonstrate lasing in living organisms and can be further introduced to therapeutic applications, if proper solvents are found.

Stimuli responsive lanthanide ions doped layered piezophotonic microcrystals for optical multifunctional sensing applications

Multifunctional optical sensing devices are of decisive significance to the miniaturization and integration of optoelectronic devices. However, the development of stimuli responsive materials with multimode emission is still in the early stage, limiting the application of integrated optical sensing. Here, we report the multimode emission piezophotonic material fabricated by doping lanthanide ions into the quaternary piezoelectric semiconductor SrZnOS, achieving multimode emission under various stimulus/excitation sources (ultraviolet, near-infrared laser, X-ray, and force), due to its multifunctional optical properties. Particularly the mechanoluminescence has been realized covering both the visible and near-infrared spectral bands. Optical stress sensing was achieved by establishing a quantitative relationship between force and light conversion. Moreover, near-infrared mechanoluminescence can effectively resist the interference of ambient light. The temperature detection performance and the power-dependent color tunability of the sample were also evaluated for multifunctional applications. All the results indicate that the developed multifunctional optical materials with inherent multimode light-emitting characteristics have the potential in advanced optical sensing and anti-counterfeiting applications. The piezophotonic material with multimode emission has been developed by doping lanthanide ions into layered quaternary piezoelectric semiconductor SrZnOS. The materials can be responsive to external stimuli (X-ray, UV light, NIR laser, stress), which could be used for energy conversion and optical stress/temperature dual-sensing. • Lanthanide ions doped SrZnOS is synthesized for stress/temperature dual-sensing. • It can be responsive to multi-mode stimuli (X-ray, UV light, NIR laser, stress). • The material can generate mechanoluminescence covering visible and NIR region. • The developed flexible composite can be used for energy conversion and sensing.

Effect of Al3+ on the spectroscopic properties of Eu2+- and Tb3+-Doped high silica glass

In this study, Eu2+/Al3+-, Eu2+/Tb3+-, and Eu2+/Tb3+/Al3+-doped high silica glasses were prepared, and the effect of Al3+ on the spectroscopic properties of Eu2+ and Tb3+ and the energy transfer of Eu2+→Tb3+ was investigated. The results revealed that the addition of Al3+ increased the luminescent intensity of the Eu2+-doped glass by approximately 400 times. An obvious Eu2+→Tb3+ energy transfer occurred in the Eu2+/Tb3+-doped high silica glass, whose transfer efficiency can reached 66.9%. However, the efficiency continuously decreased as the Al3+ concentration increased, and eventually, it dropped to 7.2%. These phenomena can be explained by the following: Al3+ not only disperses Eu2+ but also changes the field strength and symmetry of its neighboring environment, thus increasing its emission intensity. Moreover, Al3+ destroys the strong dipole–dipole interactions between Eu2+ and Tb3+ in high silica glass due to its dispersive ability, which inhibits the energy transfer of Eu2+→Tb3+. This indicates that a small amount of Al3+ can significantly modify the neighboring environment of Eu2+ and change its light-emitting characteristics, potentially yielding efficient blue and green phosphors excited by near-ultraviolet light for use in white light-emitting diodes.

Optical Management of CQD/AgNP@SiNW Arrays with Highly Efficient Capability of Dye Degradation

The facile synthetic method for the preparation of incorporated carbon quantum dots (CQDs)/Ag nanoparticles (AgNPs) with well-aligned silicon nanowire (SiNW) arrays is demonstrated, offering the superior photodegradation capabilities covering UV to visible wavelength regions. By examining the morphology, microstructure, crystallinity, chemical feature, surface groups, light-emitting, and reflection characteristics, these hybrid heterostructures are systematically identified. Moreover, the involving degradation kinetics, band diagram, cycling capability, and underlying mechanism of photodegradation are investigated, validating their remarkable and reliable photocatalytic performances contributed from the strongly reduced light reflectivity, superior capability of charge separation, and sound wettability with dye solutions.

Resonance Coupling in an Individual Gold Nanorod-Monolayer WS2 Heterostructure: Photoluminescence Enhancement with Spectral Broadening.

Recently, resonance coupling between plasmonic nanocavity and two-dimensional semiconductors has attracted considerable attention. Most of the previous studies have focused on demonstrating this effect with light scattering or reflection spectroscopy, while the photoluminescence (PL) spectrum can help ascertain the underlying physics. Here, we report on the light-emitting characteristics of a monolayer WS2 flake coupled with a plasmonic gold nanorod. We construct a heterostructure by integrating an individual gold nanorod on top of a small piece of monolayer WS2, where the WS2 area is determined by the projected area of the nanorod. In such a heterostructure, the background PL from the uncoupled WS2 can be suppressed, which allows us to characterize the resonance coupling effect using correlated single-particle dark-field (DF) scattering and PL spectroscopies. Distinct mode splitting and anticrossing dispersion are observed in the scattering spectra, which originate from the resonance coupling between the excitons in the WS2 and plasmon resonance in the gold nanorod. In addition, a 1187-fold enhancement is obtained for the light emitted from the heterostructure relative to that of the pristine monolayer WS2. The emission spectra are broadened with mode-splitting features at room temperature, which can be further decomposed into two resonance modes using a coupled mode analysis. Moreover, two PL modes are polarized along the longitudinal axis of the gold nanorod. These findings show the potential of the designed individual gold nanorod-monolayer WS2 heterostructure as a platform for studying the resonance coupling effect between plasmon resonance and two-dimensional excitons.

Investigation of Pd/MoOx/n-Si diodes for bipolar transistor and light-emitting device applications

Sub-stoichiometric molybdenum oxide (MoOx) has recently been investigated for application in high efficiency Si solar cells as a “hole selective” contact. In this paper, we investigate the electrical and light-emitting properties of MoOx-based contacts on Si from the viewpoint of realizing functional bipolar devices such as light-emitting diodes (LEDs) and transistors without any impurity doping of the Si surface. We realized diodes on n-type Si substrates using e-beam physical vapor deposition of Pd/MoOx contacts and compared their behavior to implanted p+n-Si diodes as a reference. In contrast to majority-carrier dominated conduction that occurs in conventional Schottky diodes, Pd/MoOx/n-Si diodes show minority-carrier dominated charge transport with I–V, C–V, and light-emitting characteristics comparable to implanted counterparts. Utilizing such MoOx-based contacts, we also demonstrate a lateral bipolar transistor concept without employing any doped junctions. A detailed C–V analysis confirmed the excessive band-bending in Si corresponding to a high potential barrier (>0.90 V) at the MoOx/n-Si interface which, along with the observed amorphous SiOx(Mo) interlayer, plays a role in suppressing the majority-carrier current. An inversion layer at the n-Si surface was also identified comprising a sheet carrier density greater than 8.6×1011 cm−2, and the MoOx layer was found to be conductive though with a very high resistivity in the 104 Ω-cm range. We refer to these diodes as metal/non-insulator/semiconductor diodes and show with our device simulations that they can be mimicked as high-barrier Schottky diodes with an induced inversion layer at the interface.