Diode Structure Research Articles

Growth of (101¯1) Semipolar GaN‐Based Light‐Emitting Diode Structures on Silicon‐on‐Insulator

The growth and characterization of semipolar GaN buffer, InGaN multiple quantum wells (MQWs), and light‐emitting diode (LED) structure on patterned silicon‐on‐insulator (SOI) substrates, implementing the aspect ratio technique (ART), are reported. The early growth stages of GaN result in continuous and uniform stripes with small height variations that cause the formation of chevrons. Three coalescence strategies are tested to improve surface morphology and optical quality. Scanning electron microscopy identifies no crack formation but undulations of the surface. A roughness of ≈10 nm is measured by atomic force microscopy on large areas. The impact of MQW growth temperature shows similar surface morphology in terms of undulations and roughness. Room temperature photoluminescence spectra show wavelength emission redshifting when decreasing the MQW growth temperature. Room‐temperature cathodoluminescence (CL) highlights first the presence of threading dislocations (TDs) in between the coalescence boundary despite the use of the ART technique. Second, CL shows a spatially homogeneous emission wavelength of around 485 nm only perturbed by lower‐wavelength emission (455 nm) arising from the chevrons. Blue LED structures exhibit uniform emission wavelength at 450 nm, having a crack‐free surface, and roughness of ≈5 nm. These results pave the way for the fabrication of semipolar micro‐LEDs on SOI substrates.

Recombination in Polar InGaN/GaN LED Structures with Wide Quantum Wells

The analysis of the photoluminescence of polar light emitting diode (LED) structures with a 25 nm In0.17Ga0.83N quantum well is reported. The observed emission most likely originates from a set of energetically close excited states (ES), while the ground state decays only extremely slowly on a μs‐to‐ms timescale, that is, long‐living charge accumulates there. However, this population can also be quantified spectroscopically by applying short reverse voltage pulses. The emission from ES is effective and nearly exponential with decay time constants of 1.5 and 8 ns at 6 and 300 K, respectively, and is likely dominated by radiative processes. These findings point to a possible route to improved polar device architectures.

Numerical simulations of heterojunction GaN nanopillar light emitting diodes

The paper deals with numerical modeling of electrothermal phenomena in 3D GaN core-shell light-emitting diode (LED) structures that were developed in the frame of GECCO project.1 The simulations investigate the influence of pillar dimensions on the LED work conditions. The inherent feature of such a design is the discrepancy between the internal contact footprint current density JFP and the current density on the junction active area JAA, which, at the same contact current, decreases when the pillar is taller. The simulations indicate that the decrease of JAA results in significant changes in the LED parameters. At the same diode current, i.e., constant light emission, it leads to the voltage decrease leading to the reduction of power delivered to the diode and, consequently, to the increase of its efficiency.

Freestanding High-Power GaN Multi-Fin Camel Diode Varactors for Wideband Telecom Tunable Filters

The quality, resolution, and quantity of information transmitted in RF front end modules favor compact tunable filters with varactor elements that can handle high power and that are highly linear. Gallium nitride (GaN) varactors can theoretically reach the highest quality factor figure of merit (QFOM), owing to the GaN outstanding breakdown electric field and good electron mobility. Popularly pursued GaN Schottky diode varactors suffer from leakage currents at high reverse voltage biases at their junctions and because of GaN inherent threading dislocations in thin GaN layers on foreign substrates. We devised a novel device architecture to overcome these limitations. First, we employ an interdigitated anti-series multi-Fin camel diode structure composed of a thin <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{p}^{+}$ </tex-math></inline-formula> GaN top layer situated between the Schottky metal and an n-type GaN drift layer. The anti-series symmetric Fin structure leads to excellent linearity and minimizes device parasitics to achieve measured record high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> factors. The p-GaN layer raises the barrier height to suppress reverse leakage current to maintain a high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> factor at higher reverse biases than Schottky diodes. Second, we utilize GaN on Qromis Substrate Technology (QST) wafers that permit the growth of thick GaN layers with lower dislocation densities and lower leakage currents than GaN-on-Si and that are comparable to GaN-on-GaN. We report in this work the fabrication and dc, RF <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}$ </tex-math></inline-formula> -parameters of these diodes, and assess their potential with empirical models. Breakdown voltage of 146 V and extrapolated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> factor of 84, 33, and 9 at 2, 5, and 18 GHz, respectively, are obtained in multi-Fin back-to-back varactor device configuration.

Performance simulation of an InGaSb/GaSb based quantum well structure for laser diode applications

The present study reports the impact of structural parameters on optoelectronic properties of InGasb/GaSb based quantum well structures (Qws). The laser diodes are designed to operate at 2.3 μm at 300 K. Numerical calculations of the emission wavelength, optical and modal gain of TE mode in InGaSb/GaSb laser diode structure have been carried out for various well material compositions, well thickness, number of quantum wells and temperature. The optical confinement factor and threshold current density are also simulated and reported. The calculations were performed using the 8-bands k.p model. For an injected carrier concentration of 1.56 × 1018 cm−3 at 300 K, peak gain value of the order of 1400 cm−1 is reached and a modal gain of 94 cm−1 can be obtained. A threshold current density around 3 kA/cm2, is expected to be obtained through optical losses of about 50 cm−1. The results show that InGaSb/GaSb quantum wells are appropriate for mid-infrared lasers operating at 300 K.

Electroluminescence of negatively charged single NV centers in diamond

The realization of electroluminescence (EL) of negatively charged nitrogen vacancy (NV−) centers is important toward all-electrical control of diamond quantum devices. In this study, we demonstrated electrical excitation and detection of EL of single NV− centers by using lateral diamond p+–i(n−)–n+ diodes. It had been grown by homoepitaxy using the plasma enhanced chemical vapor deposition technique. We introduced a lightly phosphorus doped i(n−) layer to stabilize the negative state of NV centers. It was estimated that the efficiency of the electrical excitation rate of the NV center was more than 30 times enhanced by introducing lateral diamond p+–i(n−)–n+ diodes structure compared with the previous vertical diode. Furthermore, the EL of a single NV− center embedded in the i(n−) layer region was characterized. The results show that the charge state of the single NV centers can be manipulated by the voltage applied to the p+–i(n−)–n+ diode, where the emission of EL is increasingly dominated by NV− in the range of 30 to 50 V.

Efficient optimization approach for designing power device structure using machine learning

Low power-loss semiconductor devices are necessary to achieve a carbon-neutral society. The optimization of device structures is known as a time-consuming process. In this work, we investigated an optimization approach with the help of machine learning. We applied an active learning scheme to optimize a gallium oxide Schottky barrier diode structure and demonstrated how this approach helps to reduce the number of time-consuming simulations for the optimization process. For the investigated work, the active learning strategy almost reduced the number of simulations by a factor of 2 in contrast to the conventional genetic optimization. In addition, we also demonstrated that machine learning models can be used to estimate the performance variations caused by process variations. This approach can also contribute to reducing the number of simulations and speeding up the structure design process.

Two‐step novel aromatic polyimide synthesis and characterization: Survey of energy calculations and diode applications

AbstractHerein, aromatic polyimides (API) synthesis was carried out by polycondensation of the original diamine (new synthesis) and commercial dianhydride. The original diamine and API were characterized by different analysis techniques. In addition, experimental and quantum chemical calculations of the synthesized API were analyzed by density functional theory method. Quantum theory analysis of atoms in molecules was performed for a structural unit of the compound. Here, the proton transfer phenomenon was investigated. The main purpose of synthesizing API1 was diode application. Therefore, the Au/API‐p‐Si/Al diode was produced accomplishedly. When the electrical characterization of the obtained diode structure was made, electrical parameter values such as ideality factor (n) (between 1.9 and 3.8), barrier height (ΦB) (0.73–0.28 eV), and series resistance (Rs) (1270–40,187 kΩ) were calculated.

Over-67-GHz-Bandwidth Membrane InGaAlAs Electro-Absorption Modulator Integrated With DFB Laser on Si Platform

We fabricate a membrane InGaAlAs electro-absorption modulator (EAM) integrated with a distributed feedback (DFB) laser combining direct wafer bonding and epitaxial regrowth of InP-based layers on a silicon-on-insulator wafer. Heterogeneous integration of an InP-based multiple-quantum-well (MQW) layer into the Si photonics simplifies the integration of the O-band EAMs and laser diodes (LDs). EAMs and LDs can be fabricated using the same MQW layer because of the wide operating range and the direct bandgap of the MQWs. A compact and high-speed lumped-electrode EAM can be made because the membrane lateral p-i-n diode structure has low capacitance and a large optical confinement factor. The effective-refractive-index matching between the membrane InP and Si layers enables the DFB laser to be fabricated with a low-loss supermode waveguide whose MQW core was optically coupled to the Si core. The fabricated 100-μm-long membrane EAM has a high modulation efficiency of about 3 dB/V at 1260 nm and E-O bandwidth of over 67 GHz even without a 50-ohm termination. The EAM-integrated DFB laser has a fiber coupled output power of about −2 dBm and clear eye openings with an extinction ratio of 3.8 and 3.2 dB for 100- and 112-Gbit/s non-return-to-zero signals, respectively.

Improving Charge Carrier Transport Properties in AlGaN Deep Ultraviolet Light Emitters Using Al-Content Engineered Superlattice Electron Blocking Layer

In this study, we investigate a unique Al-content engineered superlattice electron blocking layer (AESL-EBL) for improving the charge carrier transport properties of AlGaN quantum well (QW) deep ultraviolet (DUV) light-emitting diode (LED) structures. LED structures without EBL, with conventional bulk EBL (BEBL), and superlattice EBL (SL-EBL) are used for comparison. It is found that the LED structure with the AESL-EBL can exhibit superior electron blocking and hole injection, leading to reduced efficiency droop and improved light output power, compared to LED structures without EBL and with BEBL. Notably, the LED structure with AESL-EBL also outperforms the LED structure with SL-EBL, benefitting from the Al-content engineered SL. In the end, such an ASEL-EBL is applied to a DUV laser diode structure, and by optimizing the device structure low Mg-induced internal loss of around 1 cm−1 can be obtained.

Post-processing of real-time quantum event measurements for an optimal bandwidth

Single electron tunneling and its transport statistics have been studied for some time using high precision charge detectors. However, this type of detection requires advanced lithography, optimized material systems and low temperatures (mK). A promising alternative, recently demonstrated, is to exploit an optical transition that is turned on or off when a tunnel event occurs. High bandwidths should be achievable with this approach, although this has not been adequately investigated so far. We have studied low temperature resonance fluorescence from a self-assembled quantum dot embedded in a diode structure. We detect single photons from the dot in real time and evaluate the recorded data only after the experiment, using post-processing to obtain the random telegraph signal of the electron transport. This is a significant difference from commonly used charge detectors and allows us to determine the optimal time resolution for analyzing our data. We show how this post-processing affects both the determination of tunneling rates using waiting-time distributions and statistical analysis using full-counting statistics. We also demonstrate, as an example, that we can analyze our data with bandwidths as high as 175 kHz. Using a simple model, we discuss the limiting factors for achieving the optimal bandwidth and propose how a time resolution of more than 1 MHz could be achieved.

Enhanced light output from deep ultraviolet light-emitting diodes enabled by high-order modes on a photonic crystal surface.

The authors demonstrate the enhanced light output from 275-nm AlGaN-based deep ultraviolet (DUV) light-emitting diode (LED) structures via the in-plane modulation of shallow photonic crystal (PC) patterns that were fabricated on the p-AlGaN contact layer surface. The employed PC lattice constants are in the range of 270-780 nm, much larger than the fundamental Bragg order lattice constant (∼95 nm). As compared to the unpatterned sample, the intensity of the top (or bottom) emission can be enhanced by up to 331% (or 246%), attributed to the high-order coherent diffraction of the internal trapped light and also the Purcell enhancement of spontaneous emission. The findings in this Letter suggest an easier way for the realization of more energy-efficient DUV LEDs which offer the advantage of high emission for various applications in disinfection and sterilization.

Tuning the luminescence of thin nanocrystalline CsPbBr-=SUB=-3-=/SUB=- perovskite films during the in situ anion exchange reaction

Inorganic perovskite CsPbX3 nanocrystals (PNCs), where X is a halide anion, are currently promising materials for a wide range of optoelectronic devices. One of the key tasks to be solved before they are used in practice is to obtain stable thin PNC films whose luminescence wavelength could be finely tuned. The chemical composition of CsPbX3 PNCs is the main parameter determining their band gap width and, hence, the position of their photoluminescence maximum. Variation of the PNC composition in the course of their synthesis or postsynthetic treatment in solution makes it possible to obtain CsPbBr(3-x)Ix and CsPbBr(3-y)Cly materials emitting in the entire visible spectral range. In addition, these PNCs are more structurally stable than CsPbCl3 and CsPbI3 ones. However, most exchange reactions in solution reported in published studies are spontaneous and poorly controllable. In this study, the anion exchange reaction is proposed to be carried out directly on the formed thin film of CsPbBr3 incorporated in the matrix of a copolymer of methyl and lauryl methacrylates. The exchange reactions with octadecylammonium iodide and PbI2 leading to a shift of the photoluminescence maxima to longer wavelengths by 130 and 137 nm within 15 and 6 min, respectively. The study also shows the possibility of carrying out an ion exchange reaction on a substrate mimicking the real structure of a light-emitting diode. Keywords: inorganic perovskite nanocrystals, anion exchange, thin films, photoluminescence.

Изменение люминесценции тонких нанокристаллических пленок перовскита CsPbBr-=SUB=-3-=/SUB=- в ходе реакции анионного обмена in situ

Inorganic perovskite CsPbX3 nanocrystals (PNCs), where X is a halide anion, are currently promising materials for a wide range of optoelectronic devices. One of the key tasks to be solved before they are used in practice is to obtain stable thin PNC films whose luminescence wavelength could be finely tuned. The chemical composition of CsPbX3 PNCs is the main parameter determining their band gap width and, hence, the position of their photoluminescence maximum. Variation of the PNC composition in the course of their synthesis or postsynthetic treatment in solution makes it possible to obtain CsPbBr(3–x)Ix and CsPbBr(3–y)Cly materials emitting in the entire visible spectral range. In addition, these PNCs are more structurally stable than CsPbCl3 and CsPbI3 ones. However, most exchange reactions in solution reported in published studies are spontaneous and poorly controllable. In this study, the anion exchange reaction is proposed to be carried out directly on the formed thin film of CsPbBr3 incorporated in the matrix of a copolymer of methyl and lauryl methacrylates. The exchange reactions with octadecylammonium iodide and PbI2 leading to a shift of the photoluminescence maxima to longer wavelengths by 130 and 137 nm within 15 and 6 min, respectively. The study also shows the possibility of carrying out an ion exchange reaction on a substrate mimicking the real structure of a light-emitting diode.

Metal Oxide Films as Charge Transport Layers for Solution-Processed Polymer Light-Emitting Diodes

Here, we discuss the use of metal oxide films as charge transport layers in polymer light-emitting diodes containing poly(9,9-dioctyl-9H-fluorene-2,7-diyl) (PFO) as emissive layer. A simple device architecture consisting of glass-ITO | poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) | poly(9-vinylcarbazole) (PVK) | PFO | Ca | Al was used as starting point. This device assembly allows the investigation of basic properties of polymeric emitting layers, but does not provide stable devices with high performances. Thus, a more complex, multilayered diode structure is needed. We pursuit that goal with focus on the use of low-cost, easily processed materials. At one side, solution-processed non-stoichiometric MoOx films were used to replace the PEDOT:PSS as hole transport layer. At the other interface, solution-processed ZnO films containing either the bare oxide or a ZnO/carbon dots composite were introduced as electron transport layer. By tunning the characteristics of the metal oxide films, the performance of the blue-emitting PFO-based polymer light-emitting diodes (PLEDs) was massively enhanced.

Nonlinear Properties of an Inhomogeneous Diode Structure in a Strong Microwave Field

Results of experimental investigation of detection (rectification) of high power X-band microwave signal in diodes of various design (semiconductor p-n-junction, point-contact, Schottky, Metal-Isolator-Metal—MIM) are reported. The maximum of the detected direct voltage V vs. power P of microwave signal and subsequent polarity reversal, previously found in MIM diodes in the optical and microwave bands, have found to be characteristic of all investigated diodes as well. After the reversal of polarity, this dependence comes linear, and the sign of the voltage corresponds to thermoEMF. In some diodes, the hysteresis on V(P) was observed. All 5 types of V(P) of MIM diodes (have made from different pairs of metals), reported earlier, were reproduced on same p-n-junction diode by variable external DC bias. These results joined with abnormal frequency cutoff forced to suggest that there is an unknown mechanism for direct flow of charge carriers (and for generate direct current) in the high-frequency electrical field, which differs from the conventional rectification.

Effect of conversion efficiency of electroluminescence and solar cell with change of perovskite thickness

Evidence suggests that the combination of a diode structure with a hybrid organic-inorganic perovskite may give rise to multifunctional device phenomena, such as the high power conversion efficiency of a solar cell and the strong electroluminescence efficiency of a light-emitting diode. This might open the door for the creation of a device with several uses. These multifunctional devices have a limited ability to approach the Shockley-Queisser efficiency limit due to the nonradiative losses that lower the open circuit voltage (Voc) . Here, we investigate and quantify the radiative limit of current carrying capacity in a perovskite solar cell as a function of absorber thickness. We seek to get a deeper understanding of the limiting elements that contribute to a low Voc by developing a link between PCE and EL efficiency over a variety of thicknesses. The efficiency of power conversion increases with increasing perovskite thickness, whereas the efficiency of energy conversion declines. To control light while also minimisingnonradiative losses, it is necessary to consider both of these figures of merit of a solar cell and tie them together. The findings suggest that increasing the efficiency of absorption and emission is critical for enhancing device performance.

Study on Working Principle, Structure, Enhancement Technology, and Applications of Organic Light-emitting Diodes

Nowadays OLEDs outperform normal LEDs in terms of ease-processing, flexibility, skinniness, lightweight, and manufacturing cost. However, there is still much room to improve in terms of materials, efficiency, and longevity. Improving the performance of OLEDs has become the most popular research area. In order to make full use of excitons after recombination of carriers, phosphorescent OLED has been proposed. Recently, there is a gradual trend for phosphorescent OLEDs to be replaced by TADF OLEDs, as these TADF OLEDs can not only exhibit 100% internal quantum efficiency and are cheap to produce because they do not contain precious metals. At the same time, TADF OLEDs are considered to have more room for development especially in the aspect of longevity and color. Therefore, more researches are still needed to solve the blue OLED problem because compared to other colors, such as red and green OLEDs, blue OLEDs still have a big gap in stability and efficiency. In this work, the history of OLEDs, their working principle, the technologies that have been improved, and the cross-border derivative applications were studied.

Investigation into the temperature dependence of electron leakage in GaN-based blue laser diode structures by numerical simulation

Investigation into the temperature dependence of electron leakage in GaN-based blue laser diode structures by numerical simulation

Effects of Thermal Treatment on DC Voltage-Driven Color Conversion in Organic Light-Emitting Diode.

A DC voltage-dependent color-tunable organic light-emitting diode (CTOLED) was proposed for lighting applications. The CTOLED consists of six consecutive organic layers: the hole injection layer, the hole transport layer (HTL), two emission layers (EMLs), a hole blocking layer (HBL), and an electron transport layer (ETL). Only one metal-free phthalocyanine (H2Pc) layer with a thickness of 5 nm was employed as the EML in the CTOLED on a green organic light-emitting diode (OLED) structure using tris (8-hydroxyquinoline) aluminum (III) (Alq3). The current density-voltage-luminance characteristics of the CTOLEDs before and after thermal treatment were characterized and analyzed. Several Gaussian peaks were also extracted by multipeak fitting analysis of the electroluminescent spectra. In the CTOLED before thermal treatment, green emission was dominant in the entire voltage range from low to high voltages, and blue and infrared were emitted simultaneously and at relatively low intensities at low and high voltages, respectively. In the CTOLED after thermal treatment, the dominant color conversion from blue to green was observed as the applied voltage increased, and the infrared emission was relatively low over the entire voltage range. By simulating the CTOLED with and without traps at the H2Pc interface using a technology computer-aided design simulator, we observed the following: 1. After thermal treatment, the CTOLED emitted blue light by exciton generation at the H2Pc-HBL interface because of the small electron transport through the H2Pc thin film due to the dramatic reduction of traps in the low-voltage regime. 2. In the high-voltage regime, electrons reaching the HBL were transferred to Alq3 by resonant tunneling in two quantum wells; thus, green light was emitted by exciton generation at the HTL-Alq3 interface.