GaN Structures Research Articles

Red light-emitting diode with full InGaN structure on ScAlMgO4 substrate

Abstract Here, we report the first demonstration of full InGaN-based red light-emitting diode (LED) grown on a c-plane ScAlMgO4 substrate. This work represents a potential approach for achieving red emissions from an InGaN quantum well grown on InGaN underlying layers. The LED device exhibits a peak wavelength of 617 nm at a current injection of 40 mA (10.5 A/cm2). The light output power and external quantum efficiency were 12.6 µW and 0.016% at 40 mA (10.5 A/cm2), respectively. These results are expected to contribute to the development of longer-wavelength emission LEDs and laser diodes.

CRASA: Chili Pepper Disease Diagnosis via Image Reconstruction Using Background Removal and Generative Adversarial Serial Autoencoder

With the recent development of smart farms, researchers are very interested in such fields. In particular, the field of disease diagnosis is the most important factor. Disease diagnosis belongs to the field of anomaly detection and aims to distinguish whether plants or fruits are normal or abnormal. The problem can be solved by binary or multi-classification based on a Convolutional Neural Network (CNN), but it can also be solved by image reconstruction. However, due to the limitation of the performance of image generation, SOTA’s methods propose a score calculation method using a latent vector error. In this paper, we propose a network that focuses on chili peppers and proceeds with background removal through GrabCut. It shows a high performance through an image-based score calculation method. Due to the difficulty of reconstructing the input image, the difference between the input and output images is large. However, the serial autoencoder proposed in this paper uses the difference between the two fake images, instead of the actual input, as a score. We propose a method of generating meaningful images using the GAN structure and classifying three results simultaneously by one discriminator. The proposed method showed a higher performance than previous research, and image-based scores showed the best performance.

Mechanistic study of β-Ga2O3 nitridation by RF nitrogen plasma for GaN heteroepitaxy

The transformation of 2¯01β-Ga2O3 to h-GaN under exposure to RF nitrogen plasma was monitored in situ by reflection high-energy electron diffraction. Analysis of the reaction kinetics reveals that the nitridation process is initiated by the formation of an oxynitride phase and proceeds via two-dimensional nucleation and growth of wurtzite GaN grains. X-ray photoelectron spectra suggest a Ga−(NxO1−x) type configuration dominates the surface early in the nitridation process. The surface restructuring is followed by a diffusion-fed phase transformation, which propagates the wurzite GaN structure into the substrate upon reaching 70% nitrogen anion site occupation, corresponding to the oxygen solubility in h-GaN. A direct correlation is observed between the nitridated film morphology and the epitaxial film crystallinity, demonstrating control of the residual strain, lateral coherence, and mosaicity in subsequent GaN epitaxy by the nitridation conditions. This study provides mechanistic details of the nitridation reaction of 2¯01β-Ga2O3 facilitating the optimization of the nitridation process toward improving GaN-2¯01β-Ga2O3 heterojunctions.

First principles study of point defects and Li doping on the electronic structure and photovoltaic performance of single-layer GaN

The preparation of single-layer GaN by chemical vapor deposition inevitably generates H interstitials. In this study, the optical properties of single-layer Ga36N36, Ga34LiN36 and Ga34HiLiN36 (0 0 1) surfaces were investigated by using the first-principles method. In the presence of Li doping and H interstitial, the dielectric function and reflectivity red-shifted in the low-energy range and the dielectric function and reflectivity of the Ga36N36 improved. In the visible range of the absorption spectrum, the impurity-containing surfaces red-shifted, and the light absorption on the Ga36N36 improved. The Ga34HiLiN36 (0 0 1) surface performed better as a photovoltaic material than other surfaces.

Dodecagonal GaN Microrods: Chemical Stability of a‐, m‐, and c‐Plane Walls and Their Application to Water‐Splitting

AbstractPhotoelectrolysis of water is a sustainable option for the production of hydrogen fuel. GaN nano‐ or microstructures are considered for water‐splitting due to their general high chemical stability and high surface‐to‐volume ratio enhancing the process effectiveness. In this study GaN structures with dodecagonal microrods are used as a working electrode for the water‐splitting process. Microrods are grown using a plasma‐assisted molecular beam epitaxy process allowing tailoring of microrod height and density. Their unique property is the of presence twelve sidewalls with alternating a‐ and m‐plane orientations. This enables a simultaneous study of the chemical stability of c‐, a‐, and m‐plane walls of GaN. The water‐splitting process is performed using a 1 mol l−1 NaOH electrolyte solution. Non‐zero current measured at zero bias under illumination indicates that the process takes place. A degradation of the GaN structure is observed after a prolonged process time. In short‐term exposures, etching of microrod sidewalls is observed. Roughening of the a‐plane walls studied by transmission electron microscopy indicates that this orientation is etched with a fastest rate. The internal crystalline structure is not influenced by the etching and remains stable as shown by the X‐ray absorption spectroscopy study.

GaN Nano Air Channel Diodes: Enabling High Rectification Ratio and Neutron Robust Radiation Operation.

Nano air channel transistors (NACTs) provide numerous advantages over traditional silicon devices, including faster switching speeds, higher operating frequencies, and enhanced radiation hardness attributable to the ballistic transport of electrons. In the development of field-emission-based integrated circuits, low-power consumption rectifying nano air channel diodes (NACDs) play a crucial role. However, achieving rectification characteristics in NACDs is challenging due to their structural and material symmetry. This paper proposes a vertical GaN NACD with a consistent nano air channel fabricated using IC-compatible processes. The GaN NACD exhibits an exceptionally low turn-on voltage of 0.3 V while delivering a high output current of 5.02 mA at 3 V. Notably, it demonstrates a high rectification ratio of up to 2.2 × 105, attributing to significant work function disparities within the GaN-Au structure, coupled with the reduction of Au surface roughness to minimize reverse current. Furthermore, the junction-free structure and superior material properties of GaN enable the NACD to be suitable for use in radiation-rich environments. With its potential as a fundamental component of ultrafast and ultrahigh-frequency integrated circuits, this intriguing and cost-effective rectifying diode is anticipated to garner widespread interest within the electronics community.

Cathodoluminescence studies of the optical properties of a zincblende InGaN/GaN single quantum well

Zincblende GaN has the potential to improve the efficiency of green- and amber-emitting nitride light emitting diodes due to the absence of internal polarisation fields. However, high densities of stacking faults are found in current zincblende GaN structures. This study presents a cathodoluminescence spectroscopy investigation into the low-temperature optical behaviour of a zincblende GaN/InGaN single quantum well structure. In panchromatic cathodoluminescence maps, stacking faults are observed as dark stripes, and are associated with non-radiative recombination centres. Furthermore, power dependent studies were performed to address whether the zincblende single quantum well exhibited a reduction in emission efficiency at higher carrier densities—the phenomenon known as efficiency droop. The single quantum well structure was observed to exhibit droop, and regions with high densities of stacking faults were seen to exacerbate this phenomenon. Overall, this study suggests that achieving efficient emission from zinc-blende GaN/InGaN quantum wells will require reduction in the stacking fault density.

Tuning the active plane and crystallinity of GaN microcrystals for high-performance supercapacitors through potassium nitrate-mediated synthesis

The surface atomic structure and crystallinity have an important effect on the electrochemical energy storage of electrode materials, in addition to the surface chemistry and textural properties. We report here for the first time that the surface atomic structure and crystallinity of GaN, a renowned electrode material for energy storage, can be tuned by controlling the annealing time via potassium nitrate-mediated synthesis. The underlying mechanism for GaN microcrystals with enhanced intensity ratios of I(002)/(100) and I(101)/(100) manifesting excellent rate performance has been revealed by theoretical computations. The energy storage mechanism and electrode kinetics of the GaN electrodes have been clarified. In addition, the GaN microcrystals-based symmetric supercapacitors empowered by 52 wt% H3PO4 can deliver an output voltage of 1.5 V and volumetric specific energy of 11.6 and 40.2 W h L−1 at a specific power of 392.2 W L−1 when operating at −60 and 60 °C, respectively, with electrode material on a commercial loading level.

Two‐Dimensional Characterization of Au/Ni/Thin Heavily‐Mg‐Doped p‐/n‐GaN Structure under Applied Voltage by Scanning Internal Photoemission Microscopy

The two‐dimensional characterization of the Au/Ni/thin p+‐GaN/n−‐GaN structure, which is a part of a junction barrier Schottky structure, is demonstrated by scanning internal photoemission microscopy (SIPM) method. In the SIPM photoyield image using a blue laser, small photocurrents based on the internal photoemission effect by electron injection across the metal/semiconductor interface (from Ni to GaN) are detected in the center of the electrode. On the periphery, large photocurrents in the opposite direction are detected. These currents are caused by the hole injection from Ni into p+‐GaN layer and the electrical field in the laterally extended depletion layer at the edge. By using a violet laser, large photocurrents based on the fundamental absorption generated in the depletion layer of the n−‐GaN layer are uniformly detected over the electrode. It is conformed that SIPM can be available for quasi‐three‐dimensional characterization of this structure.

Effect of strain on the electronic structure and optical spectra of two-dimensional monolayer GaN

The effect of compressive strain and tensile strain on the band structure and optical spectra of two-dimensional monolayer GaN has been investigated. Computations were performed within density functional-theory. The results show that tensile two-dimensional monolayer-GaN undergoes an indirect-to-direct transition, which makes the material suitable for light-emitting and laser diodes. The material of interest is found to exhibit different optical properties dependent on the strain. Besides, the absorption band becomes wider and the optical absorption coefficient is reduced negligibly by strain, making two-dimensional-GaN a good candidate for application in photovoltaics and flexible optoelectronics.

Fundus Image Enhancement via Semi-Supervised GAN and Anatomical Structure Preservation

Fundus Image Enhancement via Semi-Supervised GAN and Anatomical Structure Preservation

Intelligent enhancement of ancient Chinese murals based on multi-scale parallel structure

Ancient mural artwork preserves the historical background and cultural customs of that time through intricate details and bright colors. However, after the natural environment and man-made damage, these works of art are damaged in color, texture and content and lose their quality. In order to identify and enhance murals with large areas of color damage, we propose a multi-scale parallel GAN and parallel Unet structure, which can extract features from multiple scales or images to adapt to the changing scale of the target and provide a more diverse set of features. This structure can reduce the risk of overfitting the training data by learning more general features. The verification results of indicators such as PSNR on the ancient mural data set show that the method has a certain performance improvement effect.

A Modeling Study of Electron Transport in GaN/AlGaN Superlattices Using Monte Carlo Simulation

Electron transport in superlattices (SLs) is analyzed using a single‐particle Monte Carlo (MC) method. This study includes the band structure of GaN, AlN, and their alloys, utilizing a single‐electron MC approach and a three‐band model. It explores how intervalley (IV) and electron–polar longitudinal optical phonon (PLOP) scatterings influence electron velocity. A single non‐parabolic band approximation is effectively used in SL modeling, as the miniband's energy width limits electron kinetic energy, reducing IV scattering. The energy band structure of the SL is calculated using the Schrödinger equation and a Poisson solver, incorporating a single‐band model to determine the Fermi energy and characteristics of the SL miniband. Miniband dispersion is evaluated using an effective mass approximation at low energies and a non‐parabolicity factor at higher energies. The MC method is then applied to study electron transport within the miniband, revealing that for SLs with low Al content and short periods, electron behavior resembles that in bulk GaN. It is observed that negative differential mobility can occur, attributed to electron–PLOP scattering and non‐parabolicity. This approach offers a quick and effective way to research high‐field electron transport in n‐doped SLs, aiding in device design.

Scalable nano-integration strategy: Controllable three-dimensional monocrystalline GaN nanostructures from nanobelts to nanonetwork

The effective and scalable assembly of 1D nano-units into ordered 3D monocrystalline networks remains a challenge. Based on the crystal structure and growth characteristics of GaN, we have designed a specific epitaxy strategy and successfully achieved large area self-networking of 3D monocrystalline nanostructure on Au-coated β-LiGaO2 (100) substrate formed by the interconnection of GaN nanobelts grown along three equivalent directions of the m-axis [011̅0], [101̅0] and [11̅00]. This well-aligned 3D GaN nanostructure grown by simple CVD method has good reproducibility and the yield of cross-linked junctions are quite high. The mono-crystallinity of this structure were proved by X-ray diffraction (XRD) and transmission electron microscope (TEM) results, especially at the crosslinked junctions. The overall epitaxial relationships between GaN and LiGaO2 was analyzed and the defect-mediated anisotropic VS growth mechanism was deduced from thorough characterization of individual nanobelts. Besides, the morphology of 3D GaN nanostructure including length, width and height was found to be controllable. The E2 (high) phonon peak at 567.4 cm−1 in the Raman spectrum and the strong ultraviolet emission peak centered at 363.3 nm (3.41 eV) in the photoluminescence (PL) spectrum indicate that the 3D GaN nanostructures are nearly strain-less and have high crystalline quality. This large-scale 3D monocrystalline network not only retains the advantage of 1D nanomaterials, but also become easier to operate compared with individual nanowire. The epitaxy assembly strategy is expected to ensure the property homogeneity of chip-scale devices for their real applications and provide a reference for further growth of tunable 3D structures of other materials.

Electrochemistry in Photonic Devices Processing: a Disruptive Approach in GaN Technology

Electrochemistry, except the electrodeposition of metal for making contacts, is rarely represented in microelectronics, despite the many possibilities it may offer like “soft” surface treatments (no surface bombardment, low damage), very sensitive methods (femtoampers sensitivity) and its large compatibility with high aspect ratio structures (TSV Cu filling). Nowadays, the More than Moore law compels researchers to look for other solutions than standard microelectronic processes to reach disruptive solutions: electrochemical processes may provide this new pathway. In that context, our study focuses on III-N material, specifically on GaN porosification through electrochemical anodization for photonic applications. After a study to understand GaN electrochemistry, we will see how new photonic device architectures may arise from the controlled porosification of GaN.Before going towards photonic applications, the understanding of the GaN electrochemical system is required. First we show that the variation of the main electrochemical and material parameters like GaN doping level, anodization potential, and electrolyte composition enables the fine-tuning of the porosity level, pore density, pore size and pore morphology. Then nano-indentation, ellipsometry and reflectometry measurements give us access to a good knowledge of the variation of the Young modulus and refractive index versus porosity level and pore morphology. The measured physico-chemical properties, mechanical as well as optical, of porous GaN eventually paves the way for new device developments.In our talk, we will show how electrochemistry requirements have an impact on the design of the final structure. We will focus on two porous GaN structures built from the previous electrochemical systemic study on GaN thin layers: i) a LED on porous GaN Bragg mirror (DBR) and ii) a relaxed InGaN pseudo-substrate for RGB micro-display applications. LED on DBR: Specifically designed epitaxial stack and technology allow the fabrication of a blue GaN/InGaN based LED structure on a DBR made of alternating porous and dense GaN layers. The optimized one-step electrochemical process results in a very efficient DBR with 99,99% reflectance and a large stop band centered on 460-520 nm. The presence of the porous GaN DBR below the LED stack exalts the photoluminescence and the cathodoluminescence signals compared with standard LEDs grown on bulk substrates. These results open a new field of research regarding the capability of tuning GaN refractive index. Fully relaxed InGaN structure for red light emission: Results on partially or totally relaxed InGaN pseudo-substrate will be presented. The InGaN pseudo-substrate relaxation helps indium incorporation in the overgrown quantum wells and enables light emission in long wavelength towards red. The control of the electrochemical and semi-conductor parameters shows that the relaxation of the III-N structure measured by HR-DRX clearly depends on the porosity level and pore morphology. This means that relaxation can be fine-tuned: that will allow an epitaxial regrowth of micro-LED structures compatible with high indium concentration in the quantum wells and possibly RGB micro-LED fabrication for micro-display applications. In that part, we will demonstrate how electrochemistry associated with microelectronic technology brings a new way of controlling relaxation of InGaN on GaN and how the obtained experimental results are promising for the fabrication of high indium content relaxed structure. Through these two examples, we put in evidence how electrochemistry allows inventing solutions unimaginable with the standard microelectronics processes.

3D Carbonate Digital Rock Reconstruction by Self-Attention Network and GAN Structure

Amidst the rapid advancements in digital technology, the pursuit of simulating geologic and mineralogic samples in a digital domain has garnered considerable attention, becoming a linchpin in modern earth science and petrological research. This manuscript intricately explores the deployment of state-of-the-art generative models for the meticulous reconstruction of digital rock core samples. Central to this investigation was the innovative incorporation of the self-attention mechanism—a pioneering endeavor in the domain of digital rock core studies. By harnessing the prowess of this sophisticated model, we endeavored to produce samples that echo the nuanced geological and mineralogical attributes emblematic of authentic rock specimens. Distinguishing our approach, the generative architecture, bolstered by the self-attention mechanism, demonstrated unparalleled proficiency in replicating quintessential rock features, ranging from porosity and granular texture to contiguous core sequences. Additionally, the idiosyncrasies of carbonate rocks were meticulously captured, highlighting phenomena like dissolution. Empirical evaluations, rooted in stringent statistical analyses, attested to the model’s capability to generate outputs that resonate closely with genuine samples. This exploration not only amplifies the potential applications of our proposed model in geoscientific endeavors but also signals a transformative stride in digital rock physics, emphasizing the harmonious amalgamation of innovative computational models with profound geological insights.

Surface roughness-controlled foam-like GaN fabricated by the change H2O concentration in ionic liquid etchant solution via photoelectrochemical etching

The structure and morphology of foam-like GaN (F-GaN) was significant to the performances of nanodevices, especially optoelectronic devices. Here we present a reasonable way to regulate the surface roughness on F-GaN, by the change of H2O concentration in the etching system. Ionic liquid (ILs) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTF]) was used as the etchant for the photoelectrochemical etching (PECE) process. With the H2O concentration changed from 0 to 5 % in the etchant solution, the surface roughness of F-GaN was reduced from 57.6 to 34.6 nm. In addition, to describe the role of H2O in the etching procedure, a physical impact etching mechanism was proposed. These results further promoted the potential value of F-GaN in the optical field.

Reshaping of 3D GaN Structures during Annealing: Phenomenological Description and Mathematical Model

Reshaping of 3D GaN Structures during Annealing: Phenomenological Description and Mathematical Model

193 nm laser annealing on p-GaN with enhanced hole concentration and wall-plug-efficiency in deep ultraviolet LED

The high acceptor ionization energy and, thus, low carrier concentration in p-type III-nitride have widely been recognized as the bottleneck preventing the development of high-efficiency light-emitting-diodes (LEDs). In this contribution, the influences of 193 nm pulsed laser annealing on the structure, electrical, and optical properties of p-type GaN were systematically analyzed. The hole concentration of p-GaN first increases and then decreases with increasing laser fluence, regardless of post-growth thermal annealing. The effective dopant activation due to laser annealing can be attributed to the dissociation of Mg–H complexes during the treatment. Laser-annealed p-GaN was utilized in a 280 nm deep ultraviolet LED. A maximum of 1.47 times higher wall-plug-efficiency enhancement factor was obtained compared to that without laser annealing, demonstrating that 193 nm laser annealing plays a decisive role in the boosting of quantum efficiency of optoelectronic devices.

Mid-infrared thermal radiation resonating with longitudinal-optical like phonon from n++-doped GaN–semi-insulating GaN grating structure

The mid-infrared emission mechanism of line-and-space structures of metallic plates on dielectric materials is substantiated using high conductive n-doped (n++-) GaN–semi-insulating (SI-) GaN microstripe structures on an SI-GaN epitaxial layer, which was veiled when using line-and-space structures of Au plates. The present structure exhibits a few thermal emission lines originating from electric dipoles resonating with the coherent longitudinal optical (LO) phonon-like lattice vibration, which are formed by the local depolarization electric field in the surface n++-GaN/SI-GaN/n++-GaN regions. The energies of the LO-phonon-like modes shift from the original LO-phonon energy of GaN to the lower energy region, which contrasts with the LO-phonon resonant emission from the microstructures on GaAs. These emission lines have another notable feature, i.e. the observed peak energies are independent of the polar emission angle for both s- and p-polarizations, unlike the emissions by surface phonon polaritons showing a significant directive nature of peak energies. The results show that each peak energy of the present emission lines is positioned at the zero-point of the real part of the electric permittivity comprising the components of the transverse optical phonon and other electric dipoles induced by the LO-like modes, excluding the target mode. The significant peak-energy shift of the LO-like phonons is applicable to materials with wide Reststrahlen bands, which contrasts with that of the nearly LO-phonon resonating feature of materials with narrow Reststrahlen bands, such as GaAs. The peak energy shift depending on the emission direction is observed for Au–GaN stripe structures. This property is ascribed to the imperfect Au/GaN interface with surface states through the theoretical analysis of the modified electric permittivity in the surface region, numerical simulation of the local electric field via finite-difference time-domain calculation, and experimental studies on a Ti–GaN structure and emission peaks originating from an LO-like phonon of the α-Al2O3 substrate.