Search

This paper represents a highly efficient bidirectional full bridge GaN based DC-DC buck converter. The devices are used for their several advantages, such as size, weight, and efficiency over silicon device. The power devices allow to upsurges the switching frequency and also helps in attaining high efficiency. This enhanced speed of GaN device switching is employed to accomplish very improved conversion efficiency. In this article design considerations of different types of losses, converter design and applications of this converters is also highlighted. The efficiency measurements of power converter are tested at different frequency and 98% efficiency has been obtained. The converter has been simulated in MATLAB and the results are validated using "OPAL-RT." Capitalizing on the potential of GaN technology, this DC-DC converter offers a significant step forward in achieving more sustainable and energy-efficient power conversion solutions. [ABSTRACT FROM AUTHOR]

The implementation of two optimization methodologies, Biharmonic and Thin Plate Spline, aims to improve the cut-off frequency of InAlGaN HEMT on SiC substrate. This is achieved by altering the aspect ratio of the gate length/width to 0.15nm. The study consists of two groups: Group 1 using Biharmonic optimization (BHO) and Group 2 using Thin Plate Spline optimization (TPSO). Each group has 7 samples, resulting in a total of 14 samples. The statistical analysis shows that there is enough statistical power (G power=0.84) to draw meaningful conclusions. The objective is to enhance the cut-off frequency by utilizing AI-driven optimization to adjust the gate length in HEMT. The SPSS analysis of the independent sample t-test shows a result that is not statistically significant (p>0.05) with a value of 0.216. The Biharmonic optimization obtains a cut-off frequency of 242 GHz, while the Thin Plate Spline optimization achieves 209 GHz within the gate length/width range of 0-35 nm. The highest cutoff frequency is observed at a temperature of 35nm, reaching a value of 242.24 GHz. This study highlights the improved performance of Biharmonic optimization (242 GHz) compared to Thin Plate Spline optimization (209 GHz) in improving the cut-off frequency of InAlGaN HEMT for various gate lengths, underlining its potential for power electronics devices. [ABSTRACT FROM AUTHOR]

High performance ultraviolet (UV) photodetectors are in great demand for strategic applications such as military, flameout protection, missile flame detection and many other applications based on different sub bands of UV detection. Conventional UV detectors are constrained by size, high dark current noise and cost. There is a need for high performance, compact size and less expensive UV detectors. In this paper, a ZnO quantum dot photo-doped graphene/hexagonal Boron Nitride (hBN)/ GaN substrate heterostructure based UV detector is designed, simulated and analyzed for its performance prediction. Electrical and optical characteristics of the device are obtained using a device simulator. The hBN layer at the graphene/GaN interface is used to decrease the dark current. ZnO quantum dot layer deposited on the graphene/hBN/GaN heterojunction help in increasing the responsivity of the device due to its long trapped-charge life time. This detector provides high responsivity in the deep UV to UVA region (100 nm-350 nm) compared to the devices without hBN and ZnO quantum dots layers. [ABSTRACT FROM AUTHOR]

New circuit techniques for increasing the performance of OAmps on Split-Length transistors in the input stage (IS) are considered. A promising architecture of high-speed micropower OAmps, which allows increasing SR by 1-2 orders of the magnitude, is proposed in the article. The computer simulation results of the input stages throughput characteristics and study of the OAmp Slew Rate in Cadence OrCAD 16.6 environment on low-temperature models of AGAMC_2.1 transistors (JSC "Integral", Minsk) are presented, which confirm a significant increase in Slew Rate without increasing power consumption in static mode. The developed architecture of the high-speed OAmp is also promising for implementation on wide-gap semiconductors (GaAs, GaN, SiC, Si technologies) and for designing high-speed ADC drivers operating in harsh operating conditions (exposure to penetrating radiation and low temperatures). [ABSTRACT FROM AUTHOR]

The gallium nitride (GaN) films are grown on molybdenum disulfide (MoS2) layers via plasma-assisted molecular beam epitaxy (PA-MBE). Investigating the surface structure and morphology of GaN film was performed by reflection high energy diffraction (RHEED), Scanning Electron Microscopic (SEM), and Atomic Force Mechanical (AFM). The spots patterns with high intensity were demonstrated by RHEED showing the structure of single crystal constructed in GaN films. The surface of GaN appears homogenous with a few bright spots. The surface texture formed on GaN films was the smooth surface with RMS of 1.96 nm and average roughness was 1.39 nm. The use of a 2D MoS2 layer as a template for GaN growth is beneficial because it has a similar lattice structure and thermal expansion coefficient to GaN, resulting in reduced lattice mismatches and defects at the interface. In addition, the hexagonal structure of GaN cluster was exhibited by GaN films on the surface. Based on the surface structure and morphology, GaN films was sucessfully grown on the MoS2 layers using PA-MBE system. [ABSTRACT FROM AUTHOR]

A cascade Class-F power amplifier (PA) is proposed for smart parking solutions. Input and output matching network are designed and analyzed using Microstrip line (MSL), suspended shielded lines (SSL) and shielded inverted line (SIL). Class-F PA design is based on the harmonic termination of an even and odd harmonic for improved efficiency. Class-F PA produces non-overlapping drain current of half sinusoidal form and voltage waveforms of half square form to reduce power dissipation. Suspended shielded (SSL) and shielded inverted lines (SIL) have low attenuation, low propagation loss, low insertion loss (S11) and low dielectric constant as compared to Microstrip line (MSL). The main objective of the work is to compare the transmission line like MSL, SSL and SIL for better performance of Class-F PA in terms of high efficiency and bandwidth. Design is based on even and odd harmonic termination to get non-overlapping current and voltage waveform. Simulation is performed using advanced design system (ADS) software using gallium nitride high electron mobility transistor (GaN HEMT) device from CREE. The results show improved power added efficiency (PAE) of 80 to 85%, gain of 15dB and output power (Pout) of 44dBm with suspended shielded (SSL) and shielded inverted (SIL) line as compared to Microstrip line (MSL) at 0 to 3GHz frequency. [ABSTRACT FROM AUTHOR]

This paper studies GaN device structure on silicon substrates. The fabricated device, with LG of 4-µm and WG of 100-µm, demonstrates a maximum drain current of 780mA/mm and a threshold voltage of - 4V. The two-dimensional Silvaco simulator tools are used to analyze and model the fabricated device. The simulation results closely match the experimental findings, validating the developed model's accuracy. These outcomes signify that the study can be a reference for modeling other GaN-based devices in future material growth and process development. [ABSTRACT FROM AUTHOR]

There is a rising demand for power MOSFET semiconductors with low power consumption and high energy efficiency. Wide band-gap semiconductor materials Gallium nitride (GaN) and Silicon Carbide (SiC) achieve the need of low power consumption and high energy efficiency. GaN and SiC based power devices with satisfying performance are commercially available now. These devices are found to be more efficient as compared to their Si counterpart because of their several advantages such as operated at faster switching speed, high temperature, high voltage, lower ON-resistance and smaller size. The paper shows the performance comparison between Si, SiC and GaN based power MOSFET/HEMT are performed with the help of LTSPICE simulation software by considering a DC-DC Boost converter. It can be observed that the efficiency of the converter primarily increases when GaN and SiC switches are used for switching. [ABSTRACT FROM AUTHOR]

Wedge-shaped c-GaN nanowall networks grown on c-sapphire substrates are found to show significant blue shift and broadening of the band-edge feature in photoluminescence (PL) spectra. Electron mobility in these structures has also been estimated to be much higher than the theoretical mobility limit in GaN for the same concentration of electrons. These findings suggest quantum confinement of the electrons in the system. Such a confinement has been theoretically explained in terms of the accumulation of negative polarization charges at the inclined facets of the nanowedges that force the free electrons in the conduction band to assemble at the central vertical plane of the structure. If such a triangular confining potential at all exists, the carrier recombination rate is expected to be reduced due to the movement of the photogenerated electrons and holes in opposite directions. Here, we have carried out time-resolved photoluminescence measurements at different transition energy points on a nanowedge-network and a continuous c-GaN epitaxial film grown on c-sapphire substrates. Our study reveals slower PL decay time for the network sample as compared to the continuous film that supports the theoretical model. [ABSTRACT FROM AUTHOR]

Interpreting certain story content and producing its corresponding set of images in a manner that is logically coherent is the sole purpose of story visualization. Methods and tools for the generation of an image from texts are in high demand because there are always new challenges for educators and students in presenting and understanding any tale material. On the other hand, finding images to picture uncommon characters and events in a story often requires a great deal of manual labor and is occasionally neglected. The proposed work tackles automatic scene sequence generation, a new multimedia task that makes it easier to do this and encourages teachers and students to effectively visualize stories. In order to achieve this, it is necessary to transform the story's words into a series of visuals. The series of images is an unbroken line of reliable images that all relate to the same narrative or incident. Hence, a novel phenomenon called Story Visualization is proposed. From a collective passage, a narrative story can be conceived by creating an image sequence, one for every sentence or phrase. Less emphasis is placed on the narrative's flow in story visualization, but more emphasis is placed on overall coherence among the story's dynamic scenes and characters. This is still a challenge that no conventional image or video generation methods have addressed. Henceforth, we presented an approach namely Logically Consistent Story Visualization (LoCoSV) to confront the issues. LoCoSV efficiently discovers how to represent the story visually through the use of three key modules: figure-ground segmentation (auxiliary task to provide information for maintaining character and story consistency), story and context encoder (learning of story and sentence representation), and figure-ground aware generation (using figure-ground information to generate the sequence of image). Various Evaluation Metrics and human evaluation studies were used to evaluate the performance and they demonstrated that LoCoSV improves generation over baseline models, especially in improving the Logical coherency and background consistency of the stories [ABSTRACT FROM AUTHOR]

In semiconductor electronics firms like Samsung, field effect transistor (FET) technology is the main design layout for high-performance applications. Gate-all-around (GAA) FETs, nanosheet FETs, complementary FETs, and so on are regarded as attractive prospects for the next-generation electronic devices following FinFETs because they have better gate controllability and scalability than FinFETs. Very few studies investigated the emerging trends in FET technology based on scaling, multi-gate structure, and substrate materials utilized. As a result, this paper presented a detailed survey on the latest advancements in FET technology for semiconductor industries like Samsung. We explained the latest FET technologies based on multi-gate and scaling, which include double-gate FET, Tri-gate FET, Gate-All-Around FET (GAAFET), Nano-sheet FET (NSFET), Nano-wire FET (NWFET), and complementary FET (CFET). In addition, this survey briefly describes the latest FET technologies based on substrate materials used, which involve Silicon-On-Insulator FET (SOIFET), Graphene FET (GFET), Carbon Nano Tube FET (CNTFET), Gallium Nitride FET (GaNFET), and Ferroelectric FET (FeFET). The limitations of the latest FET technologies and future directions in FET technologies for the improvement of electronic industries are illustrated in this survey. [ABSTRACT FROM AUTHOR]

The increase of power conversion stages has increased the power converter technology in various fields. The selection of switches for different applications is a tedious and challenging task as it involves the power level and switching frequency of the desired application. The recent technologies developed high power density semiconductor devices that not only operate at higher power levels but also at higher frequencies. This has given a wide variety of choices for the selection of switches for the desired application. This necessitates having knowledge of the dynamics of individual switches. In this regard, this paper presents a study of the switching characteristics of different semiconductor devices such as Si-based IGBT, Si, SiC, and GaN-based MOSFET. The standard double pulse test method has been used to characterize these semiconductor devices in LTspice software. Further, an attempt has been made to compare the switching parameters of the devices with similar test conditions. The comparison has been made with respect to different switching parameters like turn-on and turn-off times and energy loss. [ABSTRACT FROM AUTHOR]

Recent research has led to Gallium Nitride (GaN) as promising material, enhancing properties like higher operational temperature, smaller dimension, faster operation, and efficient performance. As metal contact on the semiconductor is essential to provide the HEMT's device external connection, no significant work has been found that focuses on physical modelling to analyze the contact resistance and implementation methods to reduce the contact resistivity. Hence, this work focuses on physical-based modelling using Silvaco ATLAS TCAD to model and further investigate the effect of the parameters and structures of GaN's on its Ohmic contact resistance. One of the crucial physical model which is Universal Schottky Tunneling (UST), was chosen to calibrate the thermionic (and field emission) between the metal contact and effective mass for various heavily doped n++ layer under the metal contact to obtain the best optimization for the low ohmic contact resistivity. The result revealed the reduction in contact resistivity by 100 % for doping layer thickness 18 nm and above with heavy doping n++ layer≥1E+19 cm−3. This work would be beneficial to reduce the cost of experimental trials by narrowing the optimization process windows to achieve low contact resistivity. [ABSTRACT FROM AUTHOR]

A nanopipe in a GaN crystal was nondestructively observed by X-ray ptychographic coherent diffraction imaging. A sharp-tipped nanopipe with a length of ∼3 µm and a width of ∼200 nm was identified at a depth of∼15 µm from the surface in a hexagonal pit with ∼6 µm per side. The position, length, thickness, and depth of the nanopipe can be used to efficiently perform detailed structural analysis by transmission electron microscopy and atom probe tomography. [ABSTRACT FROM AUTHOR]

The temperature significantly affects the performance of semiconductor devices. Therefore, it is mandatory to analyze its impact on the performance of these devices. GaN has fascinated as a material of choice for different semiconductor devices. The short channel effects are generated in the field effect transistors when the length of channel is comparable to the sum of depletion regions on the drain and source side. These short channel effects are more significant in the nanometer regime. It has been revealed that the drain current and transconductance reduces significantly with increase in temperature. It is also noticed that the apex value of the distortion parameters gm2 and gm3 occurs at lower value of temperature. The temperature is varied as 200, 250, 300, 350, and 400 ˚K. [ABSTRACT FROM AUTHOR]

The gallium nitride (GaN) nanostructure thin film was prepared and deposited on the quartz, silicon and porous silicon substrates by using pulsed laser ablation in liquid (PLAL) technique and drop-casting method for photoelectric detecting and NO2 gas sensor applications. Firstly, GaN nanoparticles have been ablated using the PLAL technique using Nd: YAG laser (Q-switching) at a wavelength of 532 nm with 500 pulses of different energies 1000, 1200, 1400, 1600, 1800, and 2000 mJ. The drop casting method has been adopted to deposit GaN on quartz substrates. The images characterization for the laser ablation energies 1400 mJ and 1600 mJ shows that in the XRD results there are enhancements in the thin film crystallization. This can be attributed to the increase in the peak intensity. Morphological analysis exhibits an increase in GaN grain size and roughness. [ABSTRACT FROM AUTHOR]

By analyzing the bibliographic information of natural science papers, we propose a method to discover the science that is the starting point of scientific innovation in the shortest period of time from its occurrence. Specifically, taking gallium nitride research in blue LED development research as an example, we attempt to discover the science that became the starting point by observing the change in the cumulative number of papers and the cooccurrence of author keywords. Based on the cumulative number of papers, we found that the science started around 1990. The co-occurrence of the author keywords during this period suggests that the MOCVD production method may have contributed to the growth of gallium nitride research. The co-occurrence pattern of MOCVD is also unique in that it bridges other keywords. The fact that this research was conducted by Nakamura, who was awarded the Nobel Prize in Physics, also confirms the certainty of this method. [ABSTRACT FROM AUTHOR]

Nanostructured surfaces with embedded noble metal nanoparticles is an attractive way for manipulation with the optical properties of wide bandgap semiconductors applied in optoelectronics, photocatalytic processes or for Surface-Enhanced Raman spectroscopy. Ion implantation offers an effective way for nanoparticle preparation without the use of additional chemicals that offers precise control of nanoparticle depth distribution. The aim of this study is a synthesis of the gold nanoparticles in GaN by implantation of 1.85 MeV Au ions with high fluences up to 7×1016 cm-2 and study of optical properties of Au implanted GaN. Implanted crystals were annealed at 800 °C in an ammonia atmosphere for 20 min to support Au nanoparticle creation and GaN recovery. The structure characterisation has been realized by Rutherford backscattering spectroscopy in channelling mode and it showed the formation of two separated disordered regions – the surface region and buried layer. The lower implantation fluences induce damage mainly in a buried layer; however, the increase of the Au-ion fluence leads to the increase of surface disorder as well. Further, the increase of the Au-ion fluence induces the Au dopant shift to the surface and multimodal Audepth profiles. TEM analyses confirmed the formation of Au nanoparticles in the implanted samples after annealing with sizes up to 14 nm. The increase of light absorption and modification of GaN bandgap of the Au modified GaN was deduced from the change in optical transmission spectra between 370 – 1400 nm. [ABSTRACT FROM AUTHOR]

This work represents a theoretical study of a GaN HEMT under the condition of electron velocity saturation. A simple current model is developed in order to find out the drain current of the device. The performance of the device has been studied with respect to mole fraction of AlGaN. It is observed that the choice of mole fraction of AlGaN has a significant role in controlling the drain current of the device. The device performance is also studied with doping concentration and thickness of the doped AlGaN layer. In addition, the impact of ambient thermal variation on the device performance has been studied and results are presented. [ABSTRACT FROM AUTHOR]

This paper presents a review of a Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) technology appropriate in high-power and high-frequency applications. GaN, as wide bandgap materials (WBG) has demonstrated superior material properties such as improved thermal conductivity and excellent electrical properties, has become an attractive candidate for the next generation of high-power and high-frequency applications. The occurrence of the two- dimensional electron gas (2DEG) channel at AlGaN/GaN heterostructures interface makes GaN HEMTs intrinsically Normally-on devices. However, the Normally-off operation is often desired in many power electronics applications. Several methods had been explained to obtain Normally-off devices. Therefore, Normally-off GaN-based HEMTs with a p-GaN gate method is among the most promising and the only commercially available today. First, this paper would summarize the physical properties and device performance of GaN material over Silicon (Si) and Gallium Arsenide (GaAs) and related to other WBG material. Then, a normally-on and normally-off configuration are explored. After that, the most relevant technological issues for normally-off HEMTs focusing on the p-GaN gate are discussed. Finally, the p-GaN interface's role and the impact of the thermal processes on the electrical characteristics are widely discussed. [ABSTRACT FROM AUTHOR]

Ab initio calculations within the density-functional theory (DFT) are carried out to investigate the electronics and magnetic properties of the p-block elements doped two-dimensional GaN (2D GaN). We have selected Al, Si, P and S dopants as the representative for Group III, IV, V and VI elements, respectively. Depending on the type of dopant and substitution site, the semiconducting characteristic of the 2D GaN can be changed into metallic. Similarly, magnetism can be induced on the 2D GaN with the total magnetization varied from 0.5 µB to 1.46 µB. [ABSTRACT FROM AUTHOR]

GaN is a wide bandgap semiconductor which is expected to withstand high radiation doses. Consequently, it is considered a promising material for new generation particle detectors in radiation related applications. We report on the fabrication and electrical characterization under proton irradiation of single microwire sensors based on a back-to-back Schottky contact configuration. The microwires are grown by metal-organic vapor phase epitaxy and processed into sensors by using optical lithography on dispersed wires. We investigate the impact of the contacts and the semiconductor bulk on the ion beam induced current (IBIC) by irradiating specific areas of the sensor and simultaneously measuring the change in conductivity. We observed that the contribution of the excess charge carriers generated in the depletion regions formed at the contact interfaces is of low influence when compared to the excess charge carriers generated in the microwire bulk. [ABSTRACT FROM AUTHOR]

The Gallium Nitride Ferrite-Polypyrrole nanocomposistes with different contents of (3%,10%,30%) by weight were prepared via impregnation technique, while the gallium nitride ferrite synthesized by Sol-Gel technique. The thermo gravimetric-differential thermal analysis used to study the thermal stability of the ferrites and their corresponding nano composites. The weight decomposition takes place above 500-550°C. The thermal stability of nanoferrites and nanocomposites was increased with increase in the concentration of Gallium nitride ferrite and with the increase in concentration of Polypyrrole. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) light emitting diode (LED) has been used as highly efficient solid-state light sources to radiate a wide range of wavelengths in the visible spectrum. Larger currents drive bright LEDs, causes reduced efficiency which known as LED droop. Insertion of strained-layer superlattice (SLS) in GaN LED gives uniform electron distribution, lead to high emission and efficiency. The primary aim of this work is to investigate the operation of LED with the inclusion of SLS by simulation. The GaN LED was designed in cylindrically symmetrical configuration with the insertion of the InGaN/GaN SLS of 3 nm thick. This work investigates the effect of different number of SLS layers, which is represented by 1, 2 and 3 periods of SLS, which represent the total SLS thicknesses of 3 nm, 6 nm and 9 nm respectively. A GaN cylindrical chip of 700 nm diameters was designed with p- and n-type doped active region. The results has shown that the efficient operation of the LED can occur within the lowest current of 0.1 mA for the 2 periods of SLS with the total emission rate displayed linearly increased. A sharp decline of internal quantum efficiency (IQE) droops close to zero despite the increasing current was significantly observed for the 2 periods of SLS, which has also resulted to operate at a low turn-on voltage of 2.5 V. However, it was found that higher than 3 periods with SLS total thickness of higher than 6 nm cause the pn junction failure with no emission. [ABSTRACT FROM AUTHOR]

Magnetism of Gadolinium-doped gallium nitride (GaGdN) depending on the Ga flux during crystal growth is investigated using magnetic Doppler broadening (MDB) measurements and M-H measurements. In Ga deficient condition, the matrix phase of GaGdN layer is regarded as GaN due to the precipitation of GdN nanoparticles. From the MDB measurements, magnetic moments at gallium vacancies (VGa) in GaN is detected, however, ferromagnetism derived from GdN nanoparticle is dominant. In Ga rich condition, pure GaGdN layer was formed and weak ferromagnetism was observed. The MDB measurements detect the magnetic moments at VGa in GaGdN, which might be a source of magnetism. [ABSTRACT FROM AUTHOR]

Compared to vacuum electron devices, solid-state RF technology for powering particle accelerators offers significant improvements in terms of operating lifetime (> 1 million hours), efficiency (>70%) and availability. However, commercially available 50 V RF Gallium Nitride (GaN) and Silicon LDMOS technology achieve only 1 - 1.5 kW building blocks in CW operation for VHF frequencies, and lower power levels at UHF and higher frequencies which are of interest to the particle accelerator community. Thus, power combining of hundreds to thousands of modules is required to achieve hundreds of kilo-watts to mega-watts power level; this approach adds complexity and degrades efficiency which limits its applicability in mega-watts class systems. This publication introduces an emerging solid-state technology based on RF GaN/SiC High Electron Mobility Transistors (HEMT) designed to operate at 100 VDC in CW mode and up to 150 V in pulse mode. More specifically, demonstration 50 mm single die devices are reported here which achieve 600 W CW at 100 V with 80% efficiency and 1-kW at 145 V bias with a pulse width of 100 µs and 10% duty cycle, also with 80% efficiency. A comparison between CW and pulse operation with 100 µs pulse width 10% duty cycle and 10 ms 10% signals is reported. The design employs harmonic tuning for class E, F or inverse F power amplifier topology to achieve >70% efficiency and assembly techniques that overcome heat dissipation in such high-power density systems. These devices and the respective circuits have been designed to operate at 325 MHz and 650 MHz, with potential applications at other UHF frequencies and L-band. The technology allows for single-ended transistors and small modules as building blocks with a power level of 5 - 10 kW and efficiency >70% which reduce the required number of combiners and related losses to achieve mega-watt power levels. The emerging technology developed for high efficiency high-power RF sources in particle accelerators can also be applied in other industrial, scientific and medical (ISM) applications, as well as in radars for aerospace and defense applications, whenever kilo-watts to mega-watts RF power is required. The high efficiency and longer lifetime of these solid-state devices translate into fewer replacements and reduced electrical power consumption for lower maintenance and operating cost. High modularity also ensures no down-time during maintenance. [ABSTRACT FROM AUTHOR]

The investigation of Electronic structure of pristine Gallium nitride homobilayer(GaNS2) sheet and the effect of doping with Mn has been done using the spin polarized density functional theory. Also the effect of external applied field on electronic band structure of these pristine and doped nanosheets has been studied. It is found that doping suppressesthe energy band gap(Eg) but the extent of suppression is highly dependent on the site of doping.Eg for GaNs2 is 1.857 eV whereas for doped sites i.e g, b, c and n, energy band gaps are 0.245eV, 1.134eV, 1.169eV, and 1.305eV respectively. On applying the external electric field across the bilayer also mutates the HOMO-LUMO gap of individual nanosheets and decrease in band gap is observed on increasing the electric field. Finally, semiconductor to metal transition takes place at critical electric field (EC). EC for GaNs2is investigated to be 0.8 V/ Å and for sites g, b, c, n values of EC is found to be 1.2 V/ Å, 1.3 V/ Å, 1.4 V/ Å,1.4 V/ Å, respectively. The electric field induced changes in electronic band structurecan be utilized in electrical sensor nanodevices and site of doping can be used in engineering desirable band gap according to the requirement. [ABSTRACT FROM AUTHOR]

Dislocation structure and cathodoluminescence (CL) of locally plastically deformed n-GaN is investigated in transmission electron microscope (TEM) and in scanning electron microscope (SEM). Multiple dense indentations of the samples with subsequent TEM foil preparation enables to study the same dislocation-rich region of the specimen with both TEM and CL-SEM and to establish direct correlation between the types of dislocations and their luminescent properties. It is shown that only straight segments of a-screw dislocations possess intrinsic luminescent band at 3.12 eV at room temperature confirming previous conclusion made from independent SEM and TEM results. [ABSTRACT FROM AUTHOR]

In this work the possibility of thick GaN layers growth by molecular epitaxy on a silicon substrate with nanoscale buffer layer of silicon carbide without any AlN buffer layers was demonstrated for the first time. Morphological and optical properties of the resulting structure are described. [ABSTRACT FROM AUTHOR]

InGaN/GaN QDs nanorod structure for the fabrication of light-emitting diodes by means of plasma-chemical etching is presented. Processes of the etching of nanorods and the defect passivation are studied. The obtained results can be used to create the light-emitting diode nanostructure with a greater efficiency compared to the classical planar technology. [ABSTRACT FROM AUTHOR]

In this study, the characterization of porous Gallium Nitrate (PG) for potential Ultra-violet (UV) light emission was examined by simulation. The simulation was carried out using SILVACO TCAD tools to fabricate the PG. By using DevEdit, the structure was constructed, and the device simulation was carried out using ATLAS provided by the SILVACO TCAD. Different pore width sizes of the PG structures were developed. The optical and electrical properties of the structural PG were measured by Current-Voltage (I-V), current gain, spectral response and energy band gap. It was discovered that the PG enhanced the current gain up to 88.98% compared to bulk GaN and exhibited photo emission in the UV spectrum by 24.35% higher compared to Bulk GaN. [ABSTRACT FROM AUTHOR]

The built-in-polarization (BIP) enhances Debye temperature, phonon mean free path and thermal conductivity of InN/GaN heterostructures at room temperature. The variation of thermal conductivity (k) with temperature for with and without BIP mechanism in heterostructures predicts the existence of a transition temperature (Tp) between primary and secondary pyroelectric coefficient. Below Tp,k with BIP field is lower than k without BIP field; while above this temperature k is significantly contributed by BIP mechanism due to thermal expansion. This study suggests that thermal conductivity measurement can reveal role of phonons and pyroelectricity in InN/GaN heterostructures. The primary pyroelectric transition temperature of InN has been predicted as 70K which is in line with prior studies. The result will be useful for designing of pyroelectric sensors from InN/GaN heterostructures. [ABSTRACT FROM AUTHOR]

The built-in-polarization (BIP) of Inx Ga1-x N/GaN heterostructure modifies phonon mean free path and thermal conductivity of heterostructures at room temperature. The variation of thermal conductivity (k) with temperature for including and excluding BIP mechanism of the heterostructures predicts the existence of a transition temperature between primary and secondary pyroelectric coefficient. Below this temperature, k with BIP field is lower than k without BIP field; while above this temperature k is significantly contributed by BIP mechanism due to thermal expansion. This study suggests that thermal conductivity measurement can reveal role of phonons and pyroelectricity in InxGa1-xN alloy. The primary pyroelectric transition temperature of InxGa1-xN alloy has been predicted for different x which are in line with prior studies. The result will be useful for designing of pyroelectric sensors from InxGa1-xN/GaN heterostructures. [ABSTRACT FROM AUTHOR]

In this invited talk, we present the effective mass representation (EMR) in the presence of spin-orbit interaction and an applied magnetic field. The resulting equation of motion in the k -space is then solved by using a Green's function formalism. The lack of lattice translational symmetry of the vector potential in the presence of the magnetic field is considered by redefining the Green's function in terms of the Peierls' phase factor. The equation of motion of the Green's function as a function of a magnetic wave vector was solved using perturbation theory, leading to expressions for the effective mass and the g-factor. We study the electronic structure of wurtzite Zinc Oxide and Gallium Nitride theoretically using the resulting k p method, where k is the electronic wave vector and ... is the relativistic momentum operator by considering the conduction band edge and three valence bands. The k p Hamiltonians for the conduction band edge and the valence bands are diagonalized, considering the conduction band and one valence band at a time. We obtain electron and hole dispersions. Effects of other bands are considered by using perturbation theory. Resulting dispersions agree with the results of other calculations. In order to study the effective mass and the g-factor, we use the eigenvalues and eigenfunctions obtained after the diagonalization. Our results for the effective masses and the g-factors agree fairly well with available theoretical and experimental results, Temperature dependence of both the electronic effective mass and g-factor in case of GaN is studied and trends obtained agree with the existing experimental data. [ABSTRACT FROM AUTHOR]

We report the maiden experimental observation of the formation of Wasp-waists in the Hysteresis loop, of PPY Nanocomposite with GaN doped Ferrite. Earlier this phenomenon was reported in paleo magnetic and environmental magnetic studies. It is probably the very first time we report it in our Synthesized Nanocomposites. Details supported by data are presented. Parameters like Exchange Anisotropy, Multi Domain formation, Variations in Coercivity are suspected to be prominent causes for this occurrence. Systematic analysis of our data provides substantial evidence for the existence of the phenomenon. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the mechanical strength of a semiconductor structure based on gallium nitride in terms of light-emitting diode crystal nearby a dislocation. The role of thermoplastic deformation in the expansion of defect areas during formation of new defects in the heterostructure was estimated. According to the calculation, the local stresses caused by local overheating are insufficient to form new defects, but these stresses can lead to the movement and accumulation of existing dislocations, which can lead to the formation of dislocation clusters, additional overheating and failure of the light-emitting diode. [ABSTRACT FROM AUTHOR]

In this research, the gallium nitride (GaN) thin films were deposited on aluminium nitride on sapphire (AlN/Al2O3) substrate by sol-gel spin coating method. Simple ethanol-based precursor with the addition of diethanolamine solution was used. The structural and morphology properties of synthesized GaN thin films were characterized by using X-ray Diffraction, Field-Emission Scanning Electron Microscopy and Atomic Force Microscopy. While the elemental compositions and the lattice vibrational properties of the films were investigated by means of the Energy Dispersive X-ray spectroscopy and Raman spectroscopy. All the results revealed that the wurtzite structure GaN thin films with GaN(002) preferred orientation and smooth surface morphology were successfully grown on AlN/Al2O3 substrate by using inexpensive and simplified sol-gel spin coating technique. The sol-gel spin coated GaN thin film with lowest oxygen content was also achieved.FESEM images show that GaN thin films with uniform and packed grains were formed. Based on the obtained results, it can be concluded that wurtzite structure GaN thin films were successfully deposited on AlN/Al2O3 substrate. [ABSTRACT FROM AUTHOR]

The optimal input voltage and spontaneous emission rate characteristics based on different material of a LED chip which is Gallium Nitride, Indium Nitride, Zinc Oxide, Zinc Selenide and Titanium Dioxide are simulated and successfully analyzed. These materials have been chosen as selected material due to highly potential being used in the next generation LED. To obtain a good emission state, the optimal voltage for Gallium Nitride, Zinc Oxide and Titanium Dioxide are fall in the range of 2.6V to 3V. Meanwhile, Indium Nitride and Zinc Selenide are produce lower optimal voltage in between 1.2V to 1.6V. Gallium Nitride and Indium Nitride has the ability to achieve a higher emission rate as only required the minimum current below than 0.05 mA as compared to other materials. Furthermore, the Titanium Dioxide has the lowest emission rate with ×1013 per second as compared to other materials the average emission rate can be up to ×1015~1027 per second. [ABSTRACT FROM AUTHOR]

Impact of 2 MGy and 10 MGy electron irradiation on gallium nitride (GaN) light emitting diodes (LEDs) has been studied. The device was a commercial product (Manufacturer: Vishay) type of GaN Blue LEDs (TLHB5400). The capacitance-voltage (C-V) characteristics of pre- and post-irradiation were measured. The result showed that the amount of capacitance and doping concentration decreases as the radiation dose increased. The deactivation of dopants atoms in the bulk increased due to higher irradiation dose hence increasing the radiation-induced defect which lead to the degradation of the device. [ABSTRACT FROM AUTHOR]

The article introduces the benefits and application features of Silvaco TCAD tools. The possibility of using Device Simulation Framework - ATLAS for GaN power transistor modeling demonstrated. The band diagram of the AlGaN/GaN heterostructure of power transistor built, taking into consideration the polarization processes and surface traps as a source of the electrons in two dimensional electron gas (2DEG). Furthermore, the self-consistent system of Schrödinger - Poisson equations solved to calculate the profile of carrier concentration in the transistor structure. Simulation allows prediction of basic device parameters before its fabrication. [ABSTRACT FROM AUTHOR]

Nowadays, the technology computer aided design (TCAD) software has become an important and powerful tool for improving the efficiency of GaN power devices design and its optimization. The paper attempts to describe the features, advantages and applications of such approach. The limitations and calibration problems of technology simulation are also discussed. Furthermore, the possibility of using Silvaco TCAD tools for 2D-numerical simulation of GaN HEMT T-gate formation is demonstrated. The paper represents the results of simulation of several technological operations like mask formation, resist reflow and metal deposition and varying of process parameters. The comparisons between simulated and experimental data revealed good agreement and proved the validity of the developed process models. [ABSTRACT FROM AUTHOR]

Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In0.25Ga0.75N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In0.25Ga0.75N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10% improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%. [ABSTRACT FROM AUTHOR]

Correlations between frequencies of the Raman-active A(TO) and E(LO) phonons and the layer thickness ratio in the AlN/GaN superlattices are determined. Theoretical frequency-structure relations are derived by using the dielectric continuum model. It is found that the elastic strains which inevitably arising in the layers upon SL growth affect frequencies of the most Raman-intense polar modes insignificantly. The obtained frequency-structure relations agree well with available experimental data. These results confirm efficiency of the Raman spectroscopy for a fast nondestructive structure characterization. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL), electron beam current (EBIC) and transmission electron microscopy (TEM) techniques have been applied to investigate recombination properties and structure of freshly introduced dislocations in low-ohmic GaN crystals. It was confirmed that the only a-screw dislocations exhibited an intense characteristic dislocation-related luminescence (DRL) which persisted up to room temperature and was red-shifted by about 0.3 eV with respect to the band gap energy not only in HVPE but also in MOCVD grown samples. EBIC contrast of the dislocations was found to be temperature independent indicating that the dislocation-related recombination level is situated below 200 meV with respect of conduction band minimum. With the increasing of the magnification of the dislocation TEM cross-sectional images they were found to disappear, probably, due to the recombination enhanced dislocation glide (REDG) under electron beam exposure which was immediately observed in CL investigations on a large scale. The stacking fault ribbon in the core of dissociated a-screw dislocation which form a quantum well for electrons was proposed to play an important role both in DRL spectrum formation and in REDG. [ABSTRACT FROM AUTHOR]

We report the synthesis and Characterization of III-V doped Nano ferrite Ga(2x+2)N Fe2(49-x)O3 for x=1 and x=5 by Sol-Gel method. The Morphological, structural and Thermal characterisation studies are done by using Transmission Electron Microscopy, Energy Dispersive X-ray Analysis, Selected Area Electron Diffraction, Thermo-Gravimetric Analysis and Differential Thermal Analysis. Using the Sci-Finder software we could not trace any reports related to GaNFe2O3 in the literature. It has been observed from our studies that the particles are in the Cylindrical and the Globular structure. The particle diameter values from the Histograms are in good agreement with the XRD values that were communicated by us earlier. The SAED and the EDAX studies reveal the confirmation of the composition and also that the synthesized Ferrite exhibits crystalline nature. The TG-DTA results show that the compound indicates constant sample weight. [ABSTRACT FROM AUTHOR]

We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surface with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface. [ABSTRACT FROM AUTHOR]

Gallium nitride nanowires (GaN-NWs) of diameters ranging from 20 to 80 nm were grown on the p-type Si substrate by Thermal Chemical Vapor Deposition (TCVD) using Iron (Fe) catalyst via VLS mechanism. Raman and FTIR spectra reveal the presence of broad transverse optic (TO) and longitudinal optic (LO) phonon peak spreads over 500-600 cm-1 and 720 cm-1 respectively. The detail deconvolution of integrated transverse and longitudinal phonon analysis reveals phonon confinement brought out by incorporation of hydrogen atom. The red shifts of TO and LO phonon peak position indicates nanosized effect. IA1(LO)/IA1(TO) increases from 0.073 to 1.0 and their respective fwhm A1(LO)/ fwhmA1(TO) also increases from 0.71 to 1.31 with increasing H2 flow rate. E1(LO) - E1(TO) and A1(LO) - A1(TO) increases from 173.83 to 190.73 and 184.89 to 193.22 respectively. Apart from this usual TO and LO phonon, we have found Surface Optic (SO) phonon at 671 cm-1 in FTIR spectra. The intensity of PL peak increases with increasing H2 dilution reveals efficient passivation of defect centre at surface of GaN-NWs. [ABSTRACT FROM AUTHOR]

Surface treatments of GaN in HCl-based solutions are studied by X-ray photoelectron spectroscopy (XPS) and electrical characterization of fabricated GaN surfaces. A dilute-HCl treatment (HCl:H2O=1:1) at room temperature and a boiled-HCl treatment (undiluted HCl) at 108°C are made on high-temperature annealed n-GaN. From the XPS study, removal of surface oxide by the dilute-HCl treatment was found, and more thoroughly oxide-removal was confirmed in the boiled-HCl treatment. Effect of the surface treatment on electrical characteristics on AlGaN/GaN transistor is also studied by applying treatment processes prior to the surface SiN deposition. Increase of drain current is found in boiled-HCl treated samples. The results suggest that the boiled-HCl treatment is effective for GaN device fabrication. [ABSTRACT FROM AUTHOR]

The article focuses on comparison between Gallium nitride (GaN) light emitting diodes (LEDs) for giga bit communication with plastic optical fiber (POF). Topics discussed include eye safe data transmission of laser diodes, attenuation of POF at green and blue window, sensitivity of red source power performance, advantages of using blue-green LEDs such as less influence of change in wavelength and its stability at higher temperature.

In this paper, we have been studied the optical properties such as refractive index n(ω), absorption coefficient α(ω), and dielectric constant of wurtzite (WZ) GaN semiconductor using the plane-wave pseudopotential method within density functional theory (DFT). We have also been calculated the optical phonon modes using phonon calculation on Cambridge Serial Total Energy Package (CASTEP) software at 0 GPa. The calculated values of all above parameters are compared with the available experimental values and the values reported by different workers. A fairly good agreement has been found between them. [ABSTRACT FROM AUTHOR]