Gallium Nitride Processing for Electronics, Sensors and Spintronics (Engineering Materials and Processes). Manufacturer: Springer. Part Number: Price.
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- Gallium Nitride Processing for Electronics, Sensors and Spintronics | MRAM-Info
- GaN and ZnO-based Materials and Devices
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The versatility extends to the degree of conductivity. Affordable versions of these materials open up the potential for use in a range of new-generation concepts: They can be used in rubber-like electronic devices that, unlike paper-like electronic devices, can stretch as well as bend. They can also be attached to topologically complex curved surfaces, serving as real skin-like sensing devices, Associate Professor Cheng said. An international collaboration of researchers led by a scientist with the U.
The recorded charge transfer time clocked in at under 50 femtoseconds, comparable to the fastest times recorded for organic photovoltaics. The resulting heterostructure is bound by the relatively weak intermolecular attraction known as the van der Waals force. This facilitates their application in transistors and other electronic devices because, unlike graphene, their electrical conductance can be switched off.
The separation of photoexcited electrons and holes is essential for driving an electrical current in a photodetector or solar cell. University of California, Davis researchers sponsored by Semiconductor Research Corporation SRC , a university-research consortium for semiconductors and related technologies, are exploring new materials and device structures to develop next-generation memory technologies. Existing magnetic hard disk drive and solid state RAM solutions store data either based on the magnetic or electronic state of the storage medium.
Hard disk drives provide a lower cost solution for ultra-dense storage, but are relatively slow and suffer reliability issues due to the movement of mechanical parts. Solid state solutions, such as Flash memory for long-term storage and DRAM for short-term storage, offer higher access speeds, but can store fewer bits per unit area and are significantly more costly per bit of data stored. An alternative technology that may address both of these shortcomings is based on the manipulation of magnetic domain walls, regions that separate two magnetic regions.
The research was conducted at the Notre Dame Radiation Laboratory by Joseph Manser, a doctoral student in chemical and biomolecular engineering, under the direction of Prashant Kamat, Rev. Zahm Professor of Science. The findings appear in a paper in the August 10 edition of the journal Nature Photonics.
More importantly, these materials are extremely easy and cheap to process, with much of the device fabrication carried out using coating and or printing techniques that are amenable to mass production. This is in stark contrast to most commercial photovoltaic technologies that require extremely high purity materials, especially for silicon solar cells, and energy-intensive, high-temperature processing.
Manser points out that although the performance of perovskite solar cells has risen dramatically in only a few short years, the scientific community does not yet fully know how these unique materials interact with light on a fundamental level. This separation process siphons energy within the light absorbing layer and restricts the device architecture to one of highly interfacial surface area. As a result, the overall effectiveness of the solar cell is reduced.
UCL scientists have discovered a new method to efficiently generate and control currents based on the magnetic nature of electrons in semiconducting materials, offering a radical way to develop a new generation of electronic devices. One way to achieve this is by the spin-Hall effect, which is being researched by scientists who are keen to understand the mechanisms of the effect, but also which materials optimise its efficiency. If research into this effect is successful, it will open the door to new technologies.
Unlike other concepts that harness electrons, spin current can transfer information without causing heat from the electric charge, which is a serious problem for current semiconductor devices. Effective use of spins generated by the spin-Hall effect can also revolutionise spin-based memory applications. The study published in Nature Materials shows how applying an electric field in a common semiconductor material can dramatically increase the efficiency of the spin-Hall effect which is key for generating and detecting spin from an electrical input.
The scientists reported a times-larger effect than previously achieved in semiconductor materials, with the largest value measured comparable to a record high value of the spin-Hall effect observed in heavy metals such as Platinum. This demonstrates that future spintronics might not need to rely on expensive, rare, heavy metals for efficiency, but relatively cheap materials can be used to process spin information with low-power consumption.
Gallium Nitride Processing for Electronics, Sensors and Spintronics | MRAM-Info
As there are limited amounts of natural resources in the earth and prices of materials are progressively going up, scientists are looking for more accessible materials with which to develop future sustainable technologies, potentially based on electron spin rather than charge. To address this, fundamentally new concepts for electronics will be needed to produce commercially viable alternatives which meet demands for ever-growing computing power. Georgia Tech research develops physics-based spintronic interconnect modeling for beyond-CMOS computing.
Georgia Institute of Technology researchers collaborating with and sponsored by Intel Corporation through the Semiconductor Research Corporation SRC have developed a physics-based modeling platform that advances spintronics interconnect research for beyond-CMOS computing. Spin-logic aims at reducing power consumption of electronic devices, thereby improving battery life and reducing energy consumption in computing for a whole range of electronic product applications from portable devices to data centers. Young, a collaborator and co-author of the research and a Senior Fellow at Intel Corporation.
The added functionality of this option includes the non-volatility of information on-chip, which is in essence a combination of logic and memory functions. However, to benefit from the increase in density of the on-chip devices, there has to be adequate connectivity among the switches—which is the focus of the Georgia Tech research. Among the potential alternatives, devices based on nanoscale magnets in the field of spintronics have received special attention thanks to their advantages in terms of robustness and enhanced functionality.
Thus, the circuits do not consume power when not used—a very desirable property for modern tablets and smart phones. One of the most important aspects of any new information processing element is how fast and power efficient they can communicate over an interconnect system with one another. The Georgia Tech research has therefore focused on this important aspect of communicating between spin-logic devices and demonstrates that interconnects are an even more important challenge for beyond-CMOS switches.
To analyze spintronic interconnects, the Georgia Tech team and their Intel collaborators have developed compact models for spin transport in copper and aluminum—taking into account the scattering at wire surfaces and grain boundaries that become quite dominant at nanoscale dimensions. The research team has also developed compact models for the nanomagnet dynamic, electronic and spintronic transport through magnet to non-magnet interfaces, electric currents and spin diffusion.
These models are all based on familiar electrical elements such as resistors and capacitors and can therefore be analyzed using standard circuit simulation tools such as SPICE. New cost-effective nanoimprint lithography methodology improves ordering in periodic arrays from block copolymers. Block copolymers BCPs are the most attractive alternative to date for the fabrication of well-defined complex periodic structures with length scales below nm.
Such small structures might be used in a wide range of technological applications but current available methods are very expensive, especially when those structures present length scales under 20nm. The methodology consists on in situ solvent-assisted nanoimprint lithography of block copolymers, a technique which combines a top-down approach — nanoimprint lithography — with a bottom-up one — self-assembled block copolymers bottom-up.
The process is assisted with solvent vapors to facilitate the imprint and simultaneous self-assembly of high Flory-Huggins parameter BCPs, the ones that yield subnm size features, in what has been called solvent vapors assisted nanoimprint lithography SAIL. SAIL is a scalable technique which has shown its efficiency over a large area of up to four square inches wafers.
The Engineering Materials and Processes series focuses on all forms of materials and the processes used to synthesise and formulate them as they relate to the various engineering disciplines. The series deals with a diverse range of materials: Each monograph in the series is written by a specialist and demonstrates how enhancements in materials and the processes associated with them can improve performance in the field of engineering in which they are used. Stephen J Pearton and Cammy R. They are both leaders of research groups working in the processing and characterisation of semiconductor materials for high-speed device applications.
Fan Ren is a full professor in the university's Department of Chemical Engineering, specialising in research into devices based on GaN wide-bandgap semiconductor materials. Enter your mobile number or email address below and we'll send you a link to download the free Kindle App. Then you can start reading Kindle books on your smartphone, tablet, or computer - no Kindle device required.
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Useful spintronic devices will need materials with practical magnetic ordering temperatures and current research points to gallium and aluminium nitride magnetic superconductors as having great potential. A resonant enhancement from the Yb4f states was found in the valence band region at binding energy of 7.
A weak Fano resonance is consistent with a large 4fd occupancy. It was also found that ytterbium 4d level shows an extended multiple structure instead of a simple spin-orbit doublet characteristic of metallic ytterbium, which indicates that majority of ytterbium atoms are bonded to oxygen and that one of the 4f14 electrons has been promoted to the valence level.
The obtained results enhance understanding of RE ions fundamental properties and are of great importance for the development of optical devices as well as devices operating in the IR region. As a member of the III-nitride wide bandgap semiconductor family, BN has received much less attention in comparison with other nitride semiconductors. The stable phase of BN synthesized at any temperature under ambient pressure is hexagonal. In this talk, a brief overview of the synthesis of wafer-scale h-BN epilayers and optical properties will be presented []. It was shown that the unique 2D structure of h-BN induces exceptionally high density of states, large exciton binding energy and high optical absorption and emission intensity.
Photocurrent excitation spectroscopy results directly provided a room temperature bandgap value for h-BN in between 6. The attainment of p-type h-BN could potentially overcome the intrinsic problem of low p-type conductivity in Al-rich AlGaN for deep UV photonic devices. These solid-state neutron detectors have become increasingly desirable for a wide range of applications from fissile materials sensing to well logging, because 3He gas neutron detectors are inherently bulky, require high pressurization and high voltage application, slow response time, and expensive.
It is our belief that h-BN will lead to many potential applications from deep UV optoelectronics, radiation detectors, to novel layered-structured photonic and electronic devices. Realization of highly efficient hexagonal boron nitride neutron detectors,? Optical properties of boron vacancy-related defects in bulk hexagonal boron nitride h-BN are studied from first-principles theory using hybrid density functionals.
The set of defects include the bare boron vacancy, as well as complexes with oxygen and hydrogen. We have considered all internal and free-to-bound transitions in these defects. Excitation energies of internal transitions have been obtained via the SCF method. By calculating configuration coordinate diagrams and by performing group theory analysis for all processes we have classified them into i predominantly non-radiative transitions, ii dipole-allowed optical transitions, and iii weak dipole-forbidden optical transitions. For dipole-allowed transitions we have calculated Huang-Rhys factors and luminescence lineshapes.
We have compared our calculation results with available experimental data. In particular, these results indicate that recently found single-photon emitters in h-BN are not related to boron vacancies and most likely do not involve defect states derived from nitrogen dangling bonds. Pulsed ON-state IV characterization revealed three unexpected independent effects. First, drain current increases with temperature, although electron mobility decreases with T. Second, drain current decreases with pulse length, which cannot be explained by heating.
The drain current temperature dependence is most likely dominated by the low electron mobility in the inversion layer beneath the gate. The field effect channel mobility is estimated as. Wide bandgap semiconductors have become one of the most investigated materials for applications in high power, high voltage and high frequency electronic devices operated in elevated temperatures. Gallium nitride GaN is one of the most promising candidate in this field thanks to high critical electric field, wide energy bandgap and high value of electron saturation velocity.
However, most of the previously fabricated GaN-based electronic devices such as diodes or FET transistors suffered from lateral geometry of current flow in the active region what limited the maximum current in the device. The reason of that was a lack of native and highly conductive GaN substrates. Since few years, high quality and low dislocation density GaN substrates are commercially available and thus this limitation has been overcame [1,2] In this paper, we report on electrical parameters of n-GaN high voltage Schottky diodes with vertical current flow in the structure.
We present the results of Schottky barrier height SBH , ideality factor n , breakdown voltage Vbr and on-resistance Ron extracted from commonly used thermionic emission approach. Finally, we observed large difference in measured breakdown voltage which is almost three times larger for HVPE sample. The electrical properties of GaN have made it one of the most promising materials for power devices such as Schottky diodes.
Still, major challenges, remain such as the local GaN p-type doping, must be overcome to achieve reliable devices. Ion implantation has proven to be the most efficient technique to achieve such a local doping in most of the semiconductors, even if it is still a complicated process for GaN, due to induced defects and difficulties to anneal.
After removing the double cap-layer, PN diodes were processed on various annealed samples. The electrical characterizations of these diodes illustrated, for the first time, a rectifying behavior forward and low leakage currents reverse confirming the presence of a PN junction and thus, indicating the p-type activation of the Mg-implanted GaN layer. Integration of GaN on Silicon can have different meanings.
While few people understand it as monolithic co-integration of GaN or other III-Nitrides with Silicon electron devices and famous CMOS transistors ahead, the great majority deals with III-Nitrides on a substrate that is seen as a material platform which could be tolerated by a lot of Silicon foundry tools. It comes out from the former that a combination of both kinds of material semiconductors on a same chip may be an advantage for sophisticated circuits as already demonstrated for high frequency applications and it may be worth to be examined for smart power switching systems or for more integrated sensors for instance.
On the other hand, growth on Silicon is considered as a way to produce at lower cost on large wafers. But both have to face common complexity in the crystal growth of materials having nothing in common. Nevertheless, in spite of such difficulties, a lot of issues have been at least partially solved and processes are already under development for production in foundries for RF and power switching applications with HEMTs, and lighting or displays with LEDs based on films or wires. More, the processing of Silicon substrate offers other possibilities, whether to facilitate the management of strain and simplify growth schemes, to enhance GaN device performance as demonstrated for kV range power switching transistors, or to fabricate new objects like MEMS presenting the advantage of possible monolithic co-integration with GaN or Silicon electronics.
To finish, AlN on Silicon films not only constitute robust templates for the growth of III-Nitride structures but also for other materials like graphene in view of developing new electron devices or sensors. Gallium nitride GaN has been attracting a lot of interest for the last few decades due to its successful integration in optoelectronic devices, such as light emitting diodes LEDs , and in power electronics. However, the large lattice and thermal coefficients of expansion mismatch between the GaN epilayer and the heteroepitaxial substrate is still a major setback for GaN devices, since it affects directly the efficiency of such devices.
Several techniques were developed to improve the crystalline quality of the material and reduce the threading dislocation density TDD based on different substrate patterning methods, such as epitaxial lateral overgrowth or pendeo-epitaxy. However, the inherent limitation of these methods rises from the fact that the crystallites originating from the different nucleation sites coalesce at some point during growth, and because of the relative misorientation between the crystallites, coalescence leads to the formation of dislocations to compensate for the misorientations. To deal with this issue, we propose a novel method based on pendeo-epitaxy of GaN on nanopatterned SOI substrates.
First, nanopillars are etched down to the buried oxide with classical e-beam lithography. Second, a pyramidal growth of GaN is achieved on top of the nanopillars, leading to coalescence between adjacent GaN pyramids at a certain point. The advantage of this method lies in the deformation of the underlying nanopillars, when coalescence occurs, which will compensate for the misorientation between the grown pyramids. This entails the crystallographic alignment of the pyramids without forming coalescence defects at their boundaries.
The SOI presents a top Si layer about 50 nm-thick, oriented in the direction. The SiO2 thickness is about nm. We have tested different sizes of nanopillars with different periodicity, ranging between and nm in pillar diameter and to nm as pitch.
GaN and ZnO-based Materials and Devices
Growth is carried out in two phases: Structural investigations TEM and X-ray diffraction together with optical characterizations by cathodoluminescence carried out at different stages of the growth - i. GaN layers were also obtained on arrays of nanopillars, with easy delamination, showing the potential of exfoliating the GaN layer. The tool used for the growth is equipped with chlorine cleaning, allowing a fully clean chamber.
Several GaN templates were grown on Si wafers. The chamber was then cleaned, and the growth restarted on the templates with an extra GaN layer of thickness varying from 0 to nm, followed by the ternary layers.
A quantitative model is proposed here, suggesting that the TMIn precursor reacts with Ga on the showerhead surface to release TMGa or MMGa, which is then incorporated into the ternary layers. In InGaN layers however, the composition did not change despite the change in thickness.
This effect will be examined through different models that will be discussed in the presentation. Gallium nitride GaN is one of the most important semiconductors materials for the new generation of optoelectronic devices. To study its reaction to ion implantation doping films grown on sapphire substrates with a-plane non-polar and c-plane polar orientations [1] were implanted with keV Argon Ar ions at room temperature RT. The results support not only the existing hypothesis that perpendicular strain caused by ion implantation may be the driving mechanism behind defect transformation processes inside the lattice but the believed higher radiation damage resistance for a-GaN in comparison to c-GaN will also be discussed.
Although accepted in the scientific community that polarization effects can be avoided in non-polar nitrides in LEDs and lasers, strain fields created by ion implantation play an important role on the crystal quality and cannot be neglected. Depending on the semiconductor material and origin of impurity atoms, the optical transitions demonstrate a rich fingerprints spectrum falling in the frequency range of 2. On the other hand, solid state electrically pumped terahertz THz sources are of great demand due to several practical applications including spectroscopic THz imaging, non-harmful screening, art conservation etc.
The emission spectra were measured with a Fourier Transform Far-Infrared spectrometer using a conventional lock-in amplifier technique. It was found that the temperature increase of the conductive channel suppressed the electroluminescence signal, and a proper cooling of the sample should be provided in advance. Resonant 1s-2p electronic transitions in energy levels of shallow oxygen, silicon, and carbon impurities were observed in THz electroluminescence spectra at temperatures below K.
Silicon Carbide, especially the polytype 4H-SiC, is an ideal semiconductor material for power electronic devices and visible-blind UV photodiodes due to its intrinsic material properties such as, e. Although defect densities in 4H-SiC substrates and homoepitaxial layers have been reduced to fair levels in the last years, there is still room for further improvement: We will present the current status of structural defects in epilayers like stacking faults, dislocations and point defects, and compare these defect densities to those of other important semiconductor materials.
These kinds of material defects can reduce lifetime and diffusion lengths of electrical carriers and hence, the device performance. We will focus on the correlation between point defects and minority carrier lifetime by Shockley-Read-Hall-recombination at deep levels and present different ways for lifetime engineering by epitaxial growth and post-epi processing in SiC technology. Conclusively, we will show the impact of device processing on the spectral responsivity of SiC photodiodes by lifetime-optimized device processing. Controlling generation and annihilation of point e.
Nowadays the material synthesis processes are commonly optimized by means of expensive design of experiments trials also due to a lack suitable computational supports. We have developed Kinetic Monte Carlo models on super and parallel lattices aiming to assist the experimental studies on group IV material growth with complementary theoretical analyses. Our model are characterize by atomic level accuracy i. Si and C, involved in the kinetic and by the specific character of sp2 and sp3 bonds in the cubic and the hexagonal symmetries.
The model can be also coupled to the continuum simulation of the gas phase status generated in the equipments to estimate the deposition rate and simulate a variety of growth techniques e. Chemical and Physical Vapour deposition, sublimation. Evolution is characterized by nucleation and growth of ideal or defective structures and their balance depends critically on the process related parameters. Quantitative predictions of the process evolution can be obtained and readily compared with structural characterization of processed samples. We discuss simulation aided process development considering similarities and differences between different synthesis procedures.
Silicon carbide 4H-SiC is an excellent wide band gap material for power electronics devices. In 4H-SiC devices technology, ion implantation is the method of choice for n-type and p-type selective doping. This work reports on the effect of high temperature annealing on the electrical properties of n-type and p-type implanted 4H-SiC. Ion implantations of Phosphorous P and Aluminium Al at different energies 30? Scanning microscopy analysis SCM allowed to quantify the activation of the n-type implanted Phosphorous. Room temperature Hall measurements on p-type implanted layers resulted in a hole concentration in the order of 1.
Temperature dependent electrical measurements allowed to estimate an activation energy of the Al-implanted specie of about meV. In this paper, we will investigate the electrical and physical origin of the improvement by seeking to prove the mechanism by which leakage is reduced. Thermal oxidation in oxygen ambient. Thermal oxidation in Nitrous oxide ambient. PSG passivation using a Phosphorous source wafer.
We will report the density of interface traps DIT. Finally, we will discuss the possible mechanisms for leakage current reduction in the passivated Schottky diodes using all these results, and comment on the role of phosphorous in the process. The results of a study into a SiC Schottky rectifier structure based on the superjunction SJ principle are presented, which is designed to improve the trade-off between breakdown voltage and specific on-resistance, compared with traditional SiC power devices.
It is the purpose of this study to investigate, initially via simulation, the sensitivity and controllability of the fabrication processes for SiC full trench SJS devices. A feasibility study must first be performed to optimise mesa geometry, implantation angle, doping and depth of the p-pillar and the effects of partial and full SJ structures.
In order to attain the optimal breakdown, exact doping must be achieved. The SJ device is sensitive to exact dose balancing, and the tight processing tolerance is a challenge for fabrication. In the final submission, the results of on-going computation trials, which investigate the effects of fabrication control and sensitivity on SiC SJS rectifier devices, will be presented. The simulation data will be presented at the conference and the results of the initial fabrication trials.
Differently than for Gr on common insulating substrates, Gr residing onto AlGaN exhibits high n-type doping 1. Finally, a GBHET was obtained by the integration of a base-collector barrier, consisting of 10 nm Al2O3 grown on Gr by a two-steps atomic layer deposition [3]. Status Solidi A , The hot electron transistor HET is a unipolar majority carrier vertical device with great potential for high frequency THz applications.
Various structures have been explored so far to implement this device concept. Recently, graphene Gr has been considered as an ideal base material for HETs, due to its atomic thickness enabling ballistic transport in the vertical direction combined to its excellent conductivity allowing a reduced base resistance. In this work, we have fabricated the emitter using very low dislocation density. The direct growth of graphene on semi-insulating substrates has been a widespread objective since the initial stages of controlled graphene synthesis, especially for applications in micro- and nano-electronics.
The first wide bandgap material used for this type of graphene synthesis has been silicon carbide, due to the well-known graphitization of its surfaces upon temperature annealing. A natural evolution of this concept is the growth of graphene on other wide bandgap materials that are particularly interesting for microelectronics. The growth of graphene on these substrates could further enhance or even expand their features, allowing for a high frequency modulation of the electrical current in vertical heterostructure design concepts.
However, although the first experimental steps have been made towards such direction, theoretical studies that explore the structural and electronic properties of these systems are largely missing. Here we use the Density Functional Theory DFT to study the properties of single-layer graphene on AlN and surfaces, considering both ideal and reconstructed surface terminations. We particularly focus on the aspects of the integrity of the Dirac-cone as well as on carrier doping, which can have important implications when using graphene for microelectronic applications. High temperature annealing of nitride films has been recently explored as a way to improve the crystalline quality, but also as a preliminary step before graphene growth on nitrides.
This contribution will focus on both aspects. Surprisingly, this last configuration does not always give the best results: Finally, graphene growth by CVD requires a classical configuration to expose AlN surface to the carbon flow. Thin layers of the group III nitrides AlN, GaN, and InN with the characteristic tetrahedral sp3 coordination of their constituent atoms have been intensively developed via metal organic chemical vapor deposition MOCVD for implementation in widely spread bright and energy-saving white light-emitting diodes Nobel Prize in Physics Group III nitrides can also adopt layered structures in which the atoms in each layer exhibit planar trigonal sp2 coordination.
Here, we present our most recent results on the development of 2D group III nitrides by MOCVD, which is the primarily employed deposition method for epitaxial growth of materials and device heterostructures in established and emerging technologies. Insights into the growth mechanism will be discussed. However, there are model simulations, which predict the existence of them and determine the properties. There is the case of GaN successfully prepared as 2D material and published a lot of physical data, including the bandgap, which is much higher than the bandgap of the GaN in the form of a thick layer.
The very thin, embedded layers gave challenging tasks as well for the characterization both for AFM and for transmission electron microscopy. The highest quality equipment aberration corrected electron microscopy was used to show the 2D layers at atomic resolution by application of atomic mass contrast. Our results are confirmed by analytical techniques like EDS as well.
We report on cases, when two layers of In2O3 semiconductor was formed instead of the expected InN. Also the successfully grown GaN layers will be shown and discussed. Gallium nitride GaN is promising candidate for high-power and high-frequency devices. For many years the lack of large area free standing bulk GaN materials has limited the technology almost completely to lateral devices. Recently, the progresses in bulk GaN materials have increased the interest towards power electronics applications based on vertical GaN. In fact, the vertical topology enables to obtain higher current density and reduced device size, and avoid the surface-effects e.
In this work, the electrical behaviour of Ni Schottky contacts on commercial bulk GaN material was studied using both macroscopic and microscopic analyses. Vertical Schottky diodes have been fabricated on a n-type GaN epitaxial layer grown onto heavily doped GaN substrates.
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The Ni contacts exhibited an epitaxial orientation with respect to GaN, with some mosaicity. The forward current-voltage I-V characteristics of the diodes showed a temperature dependence of both the ideality factor and of the Schottky barrier height. The correlation between ideality factor and Schottky barrier height indicated the formation of an inhomogeneous barrier. Nanoscale local electrical analysis performed by conductive atomic force microscopy C-AFM allowed to visualize the presence of different conductivity regions, which have been correlated with the surface morphology to explain the barrier inhomogeneity.
In these devices, the formation of Ohmic contacts requires thermal annealing processes, which can lead to electrical and structural modification of the layer under the contact. The common method to determine the specific contact resistance in Ohmic contacts, i. In this work, we employed an additional measurement of? These analyses allowed to ascribe the lower RSK to the interface reactions occurred upon thermal annealing. Plausibly, the lower sheet resistance under the contact RSK, can be associated to a high concentration of N-vacancies i.
A comparison of different metallization schemes allowed to find a correlation between the sheet resistance under the contact RSK and the specific contact resistance rho-C. A new MOS-HEMT concept is proposed with the target to develop a normally-off switching transistor by effectively controlling the interface charge density. The final goal is to decrease the conversion losses in high power switching devices which make a significant part of the total electric energy consumption.
Due to its many favourable properties these devices are manufactured more and more from GaN and related semiconductors.
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In this paper some structural results of this research will be presented using transmission electron microscopic methods. After a cross sectional Ar-ion milling preparation these samples were investigated with a high resolution electron microscope. All films were found to show a crystalline microstructure. Electron diffraction study and high resolution techniques revealed a face centred cubic phase of alumina in the thin dielectric film with lattice parameter of 0. A common feature of the films is the presence of a strongly defected band within Al2O3 close to the interface with AlGaN.
Beyond the structural study the charge density at the dielectric-semiconductor interface was also determined for a comparison with other samples where the dielectric film was deposited by a high temperature MOCVD process. Crystal growth is a complex process governed by the intricate interplay of surface thermodynamics and kinetics. We use density-functional ab initio molecular dynamics AIMD with Van der Waals corrections to identify atomistic pathways and associated electronic mechanisms driving gas and surface reactions during metalorganic vapor phase epitaxy.
Synthesis of aluminum nitride on defect-free graphene is considered here as model case study. The results presented demonstrate that AIMD can be used to efficiently determine reaction pathways with corresponding rates, overcoming the inherent predictive-capability limitations of static computational first-principles methods.
Based on the results of the present work, we suggest plausible atomistic pathways with detailed understanding of underlying electronic mechanisms that lead to AlN nucleation on pristine graphene. Considering that prototype heterostructures of group III nitrides with graphene have been attempted by metalorganic chemical vapor deposition MOCVD, our results further demonstrate the potential and predictive capabilities of AIMD simulations in providing insight into revealing atomic scale surface reactions.
In addition, our AIMD simulations reveal C adatom permeation across the graphene sheet as well as exchange of C monomers with graphene carbon atoms at typical experimental temperatures K. This work is addressed for investigation of the modifications of luminescence spectra of AlGaN-GaN scintillators by radiation defects to increase the threshold of radiation hardness of sensors needed for future experiments at CERN. The impact of radiation defects in AlGaN-GaN scintillator structures is important for transformations of luminescence spectra and electrical characteristics, those employed for registering of high energy radiation.
The modifications of luminescence spectra by varying the hadron fluence in AlGaN-GaN structures of various thickness and of different technology, grown on sapphire and Si substrates were investigated. The impact of irradiations for device parameters has been revealed. The effect or radiation defects for luminescence, recombination and electrical characteristics will be discussed.
Structures of thin InN and AlN films were grown on c-plane sapphire substrate by reactive DC magnetron sputtering in pure nitrogen sputtering gas and annealed above the decomposition temperature of InN directly after growth. The as grown not annealed reference structures and annealed structures were characterized by transmission electron microscopy and X-ray diffraction to study the structural evolution and epitaxial relations during the annealing.
TEM investigations show substantial improvement in the morphology during annealing, while revealing epitaxial orientation for both as grown and annealed structures. XRD pole figures recorded for classification of the misoriented grains in the epitaxial structure reveal relatively large deviation from the epitaxial orientation of a few degrees.
This fact allows the intercalation of different atoms and molecules between packings. From the XRD diagrams and Raman spectra it was determined that as a result of 0. From the photoluminescence PL spectra analysis and PL intensity dependence on temperature, the energy diagram of the levels participating in the radiative recombination of non-equilibrium charge carriers is determined.
Due to superior physical properties, such as wide energy bandgap Eg , high electron saturation velocity ve , high critical electric field Ec and thus high breakdown voltage VBr , gallium nitride GaN is a great candidate for use in high power, high temperature and RF electronic devices [1]. Most of GaN Schottky diodes exhibit much lower reverse breakdown voltage than it is expected from theoretical calculations.
One of the major reason of premature breakdown is extremely high electric field strength near the edges of the Schottky. In the case of Si or SiC based devices several methods of edge termination like mesas, high resistivity regions created by ion implantation, field plates or guard rings have been involved []. These methods reduce electric field crowding near metal-semiconductor interface leading to substantial increase of breakdown voltage VBr. In this paper, we report on our initial studies on field plate contact termination for vertical Schottky diodes structures.
In this approach, we deposit a film of SiN on the surface of the SBD and using lithography techniques the specific pattern with some openings on the surface is created. Finally, we demonstrate a successful fabrication of such field plates and engineering aspects of SiN field plates fabrication are presented. However their positive threshold voltages as well as channel resistivity in on-state are not perfectly uniform.
One of the possible approach to obtain normally-off operation consist in using p-type layer behind the gate to locally fully deplete 2DEG. Regrowth of p-GaN layer have been indicated as a smart solution to obtain uniform and repeatable p-n junction. In this context, pre-growth treatment like cleaning and annealing, as well as epitaxial growth process are exteremly important. Also activation of Mg acceptor should be well controlled for obtaining gate Schottky barrier repeatable.
In addition Merged pn-Schottky diodes MPS with reduced drift region resistance require similar approaches of high purity therefore high quality regrowth interface of p-type GaN on n- drift region material. Introducing p-doped islands in MPS structure additionally shields the electric field from the Schottky contact thus reducing the leakage currents. Hence, using MPS structure enables lower overall resistance by thinning and increasing drift layer doping without significant increase of the leakage current.
Thermal activation process has been optimized for complete acceptor conversion with minimal surface degradation. Regrown layers were characterized with AFM microscopy and their electrical properties were determined using I-V test structures. Finally, using Hg-probe CV profiling we measured rechargeable net acceptor concentration of 1.
Gallium Nitride GaN is a very attractive wide band-gap semiconductor for both power and radio frequency RF devices. The intrinsic properties of the epitaxial layers should be very different if applied to power or RF applications. In the case of RF applications, growth of moderately thin multilayers 5 k?. This is challenging due to difference stress relief on floating zone Si substrates if compared to standard low resistivity substrates. A strong influence on the resulting GaN epitaxial properties is due to the reaction chamber and to the configuration of the metalorganic chemical vapour deposition MOCVD reactors.
In this work, we report about the morphological and electrical performances of a set of samples generated in two different reactors, a turbo disc and a planetary reactors respectively. If on one side turbo disc reactors results in a much higher uniformity on wafer in terms of thickness, specie compositions and sheet resistance, on the other side the industrial appeal of such reactors is limited by the lower throughput achievable. Generated samples were in all cases limited to 2 mm of total epitaxial thickness and atomic force microscopy, x-ray diffraction and SIMS analysis were applied to determine the initial crystal quality and overall morphological as well as the stacking composition of the epitaxial template.
Electrical analysis are in progress to determine sensible parameter affected by the epitaxial process. Wide band-gap gallium oxide Ga2O3 is a promising material for optoelectronics and photonics. Present investigation is devoted to obtaining Ga2O3 crystals using chemical vapor transport CVT in sealed chambers. The TA compositions favorable for the growth of Ga2O3 films, for narrow prismatic crystals and for bulk crystals are found.
Promising perspectives for obtaining Ga2O3 crystals homogeneously doped during the growth process are analyzed. Spatially resolved microwave detected photoconductivity MDP measurements are a powerful and widely employed technique for characterizing minority carrier lifetimes and their spatial distribution on indirect bandgap semiconductor wafers, e. For direct wide bandgap semiconductors, however, their applicability has been limited due to short carrier lifetimes. We report on wafer-scale mappings of MDP and MDP decay transients on GaN wafers, both bulk substrates and thin films, and their correlation to further spatially resolved characterization techniques, such as photoluminescence mappings.
Despite a time resolution in the range of few tens of ns, relevant material inhomogeneities can be detected and characterized. Additionaly, it has a very high laser-induced damage treshold and high efficiency of second-harmonic generation. The last interest of Ga2S3 material is focused on surface pasivation of different semiconductors to enhance their electrical and optical properties [1].
Thin layers of Ga2S3 were obtained by reaction of sulfur vapor with thin plates of the semiconductors. AFM studies showed the topography of the obtained Ga2S3 layers. Their thickness ranged from several dozen nanometers to about micrometers. The obtained layers were structuraly characterized SEM and Raman spectroscopy. The obtained results will be presented. It is well known that Silicon Carbide SiC represents the forthcoming alternative to Silicon Si , to get a higher efficiency and a higher power density in electronic devices.
In particular, SiC devices have the capability to withstand high currents and high breakdown voltages, and to operate at high temperatures. However, while SiC Schottky diodes and MOSFETs are already available in the market, device processing issues and reliability concerns are still limiting the future development of SiC technology in many applications. The ultimate outcome of the project is the design and the demonstration of enhanced SiC components for automotive, railway and aerospace qualification driven by several applications: The achievement of the objectives is supported by a wide range of competences and capabilities within the Consortium, e.
The poster will give an overview of the project goals and running activities. Based on first-principles calculations, the materials properties structural, electronic, vibrational, and optical properties of out-of-plane heterostructures formed from the transition metal dichalcogenides MoS2, WS2, MoSe2, WSe2 , were investigated. Direct band gaps can be achieved by moderate tensile strain in specific cases.
The excitonic peaks show blueshifts as compared to the parent monolayer systems, whereas redshifts occur when the chalcogen atoms are exchanged along the series S-Se-Te. Strong absorption from infrared to visible light can be achieved. However, a direct band gap in the WS2-MoSe2 heterostructure can be achieved by applying compressive strain. Furthermore, the excitonic peaks in both monolayer and bilayer heterostructures are calculated to understand the optical behavior of these systems. The suppression of the optical spectrum with respect to the corresponding monolayers is due to interlayer charge transfer.
The stability of the systems under study is confirmed by performing phonon spectrum calculations. Typical figures of merit for power devices suggest that SiC is approximately ten times better than Si in terms of device on resistance for a given operating voltage.
This limitation is extremely important especially in the region below a breakdown voltage of V where DC-DC converters and DC-AC inverters are needed for electric vehicles or hybrid cars. The best alternative for these applications is 3C-SiC. Today their scientific collaboration is strengthened by a bilateral exchange project funded in the frame of the Collaboration Agreement between CNR and PAS.
In particular, one of the scientific objectives of the project is to develop and characterize new GaN-based materials for normally-OFF HEMTs and vertical diodes, using selectively doping techniques of p-GaN regions. The running experimental activities already resulted in the publication of some joint papers in international journals.
Moreover, mutual visits are regularly organized, which include seminars, small workshops, and training activities for young researchers. Epitaxial graphene EG grown by high temperature decomposition of silicon carbide is a material of choice for high frequency transistors, metrology and high performance sensors. Due to the specifica growth mechanism, EG interface with SiC exhibits a peculiar structure, i.
Intercalation with H2 or other species has been employed to decouple the C buffer layer from the substrate, resulting into a quasi-free-standing epitaxial graphene QFSEG. This peculiar electrical property suggests the possibility of probing the uniformity of H2 intercalation at nanoscale by vertical current mapping using conductive atomic force microscopy CAFM.
The morphology and uniformity of monolayer EG coverage before intercalation were monitored by tapping mode AFM height and phase mode and reflectivity mapping. CAFM current maps showed uniform current injection across the interface, whereas local I-V analyses showed a rectifying contact with relatively low SBH approx 0. After intercalation, micro-Raman spectra were acquired to detect the changes in the characteristic vibrational features associated to the buffer layer. CAFM current mapping and local I-V spectroscopy were employed to evaluate the lateral uniformity of the SBH, which can be related to the uniformity of the H2 intercalation.
The average value of the Schottky barrier was increased up to 1 - 1. By comparing morphology and current maps, a reduced current injection i. Development of GaN single crystals growth technology necessary to produce high quality substrates for GaN homoepitaxy is very important task. However, low solubility of N in Ga limits its practical applications.
One of the ways to increase the solubility of N is using of metals solvents, such as Fe, which leads to higher solubility of nitrogen. Today their scientific collaboration is strengthened by a bilateral exchange project funded in the frame of the Collaboration Agreement between CNR and HAS. The main scientific scope of the collaboration has been to investigate ultra-thin films of wide bandgap semiconductors AlN, GaN on silicon carbide SiC with epitaxial Gr on the top of SiC. To these aim, the advanced characterization expertise present within the two partners institutions i. Furthermore, some key process steps for the fabrication of novel devices based on two-dimensional materials have been investigate, including Ohmic and Schottky contacts and the atomic layer deposition of ultra-thin insulating films.