Wide Bandgap Semiconductors

We propose simple, analytic approximations that describe properties of semiconductors with nonparabolic energy bands. The approach is based on the two-level k . p model of the semiconductor statistics which includes effects of band nonparabolicity and carrier degeneracy. The new expressions are in the form of a correction to the classical, Boltzmann's approximation of the semiconductor statistics and do not introduce any new adjustable parameters. These relations can be applied to both narrow-and wide-bandgap nonparabolic semiconductors. First, we derive expressions for semiconductor intrinsic properties, n . p product, and the Einstein relation. Then, we solve a one-dimensional Poisson's equation and obtain an analytical model of the total semiconductor charge. Finally, we calculate the low-frequency capacitance of a nonparabolic MIS structure and compare the results with an accurate numerical model and experimental measurements of a HgCdTe capacitor. The solution includes the contribution of both types of carriers and the effect of impurity freezeout. The new approximations should be useful for characterization and modeling of semiconductor devices with nonparabolic energy bands. Eliezer Finkman received the B.S., M.S., and

Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor seems the most promising. This paper attempts to present the status of the technology and the market with a view of highlighting both the progress and the remaining problems.

Silicon-based power semiconductor devices, ranging from diodes, thyristors, gate turn-off thyristors, metal-oxide-semiconductor field-effect transistors, and, more recently, insulated-gate bipolar transistors, integrated gate-commutated thyristors, and metal-oxide-semiconductor turn-off thyristors, are the workhorse of power electronic systems and circuits. Silicon offers multiple advantages to power circuit designers, but at the same time suffers from limitations that are inherent to silicon material properties, such as low bandgap energy, low thermal conductivity, and switching frequency limitations. Wide bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), provide larger bandgaps, higher breakdown electric field, and higher thermal conductivity. Power semiconductor devices made with SiC and GaN are capable of higher blocking voltages, higher switching frequencies, and higher junction temperatures than silicon devices. SiC is by far the most advanced material and, hence, is the subject of attention from power electronics and systems designers. This paper looks at the benefits of using SiC in power electronics applications, reviews the current state of the art, and shows how SiC can be a strong and viable candidate for future power electronics and systems applications.

In this paper, the static and switching
characterizations of a SiC MOSFET’s body diode are presented.
The static characterization of SiC MOSFET’s body diode is
carried out using a curve tracer and a double pulse test bench is
built to characterize the inductive switching behavior of SiC
MOSFET’s body diode. The reverse recovery of SiC MOSFET’s
body diode is shown at different forward conduction currents,
junction temperatures and current commutation slopes. In order
to evaluate the performance of SiC MOSFET’s body diode in
different applications, an accurate physics-based diode model is
introduced to perform simulations of SiC MOSFET’s body
diode. The parameter extraction procedure for this body diode
model is given. The validation of the body diode model shows
good agreement between simulation and experimental results,
which proves the accuracy of the model.

—This paper presents a control scheme to operate boost converter in Boundary Conduction Mode (BCM). In the proposed method, it is assumed that the zero-current information is not available for controlling the converter operation mode. Therefore, a cursor is identified to detect the converter operation mode, i.e. Continuous Conduction Mode (CCM)/BCM. Details of the cursor and associated control method will be discussed in this paper. We demonstrate experimentally the effectiveness of the proposed method on a GaN boost converter whose active switch current is monitored through current-mirroring technique.

Wide bandgap power devices have emerged as an
often superior alternative power switch technology for many
power electronic applications. These devices theoretically have
excellent material properties enabling power device operation at
higher switching frequencies and higher temperatures compared
with conventional silicon devices. However, material defects
can dominate device behavior, particularly over time, and this
should be strongly considered when trying to model actual
characteristics of currently available devices. Compact models
of wide bandgap power devices are necessary to analyze and
evaluate their impact on circuit and system performance.
Available compact models, i.e., models compatible with circuit level
simulators, are reviewed. In particular, this paper presents
a review of compact models for silicon carbide power diodes and
MOSFETs.

Wide bandgap (WBG) device-based power electronics converters are more efficient and lightweight than Silicon-based converters. WBG devices are an enabling technology for many motor drive applications and new classes of compact and efficient motors. This paper reviews the potential applications and advances enabled by WBG devices in ac motor drives. Industrial motor drive products using WBG devices are reviewed and the benefits are highlighted. This paper also discusses the technical challenges, converter design considerations and design trade-offs in realizing the full potential of WBG devices in motor drives. There is a trade-off between high switching frequency and other issues such as high dv/dt and electromagnetic interference. The problems of high common mode currents and bearing and insulation damage, which are caused by high dv/dt, and the reliability of WBG devices are discussed.

In this paper, a simple and accurate analytical loss
model for Silicon Carbide (SiC) power devices is proposed. A
novel feature of this loss model is that it considers the package
and PCB parasitic elements in the circuits, nonlinearity of device
junction capacitance and ringing loss. The proposed model
identifies the switching waveform subintervals, and develops the
analytical equations in each switching subinterval to calculate the
switching loss. Inductive turn-on and turn-off are thoroughly
analyzed. A double pulse test-bench is built to characterize
inductive switching behavior of the SiC devices. The analytical
results are compared with experimental results. The results show
that the proposed loss model can predict switching loss more
accurately than the conventional loss model.

"WET NANO-BONDING OF SILICA-TO-SI AND SILICA-TO-SILICA BELOW 200°C  BY H2O CATALYSIS AND A 2-D PRECURSOR PHASE:
TMAFM, HYDROAFFINITY AND SURFACE FREE ENERGY ANALYSIS

R. Bennett-Kennett*, S. D. Whaley, N. Herbots*, C. F. Watson*, R.J. Culbertson, A. Murphy,* S. Farmer,** P. Rez, D.A. Sell,** B. Hughes, A. Acharya,
ARIZONA STATE UNIVERSITY,
Department of Physics, of Chemistry & Bio-Chemistry Tempe, AZ 85287-1504,
* SiO2 NanoTech LLC,Tempe, AZ 85282
** Marquette University, Marquette, WI
*** Caltech, Pasadena, CA

R.L. Rhoades, Scott N.  Drews 
Entrepix, Inc. Tempe AZ 85282.

Hydroxylated silica about 2.1 ± 0.1 nm thick are nucleated on OH(1x1)Si(100) as precursor phase to cross-bond directly silica to Si, and silica to silica using planarization via extended atomic terraces,  T≤ 200°C, an H2O/O2 ambient, and p ≥ 1 atm. This method, "Wet Nano-Bonding™”, relies on the Herbots-Atluri process [1] to nucleate precursor phases to bond via direct hydroxylated silica molecular cross-bridges two surfaces brought into contact at the nano-scale. 
Ordered Si2(OH)4 β-cristobalite precursor phases exhibit atomic terraces that extend to > 20 nm, in contrast to the 2 nm width in "as received" Si(100) wafers. β-cristobalite nano-phases can desorb at low temperatures (T </~ 200 °C) [3]. These ordered oxides can promote the growth of flatter, smoother, better controlled oxides at low temperatures in ambient air. When put into close contact at T≥ 200°C with oxygen-deficient phases of SiOx used in microelectronics, they can consistently nucleate a cross-bridging between the two substrates, or “nano-bonding” inter-phase [4] between various combinations Si and silica provided an H2O/O2 ambient catalyzes low temperature oxidation and nano-contacting is achieved via pressurization in the nano-bonding chamber.

[1] V. Atluri et al MRS Symp. Proc. Vol 477 (1997)
[2] N. Herbots et al. Mater. Sc. & Eng, B87 (2001), 303
[3] N. Herbots et al., US patent 6,613,617 (2003) & 7,851,365 (2011)
[4]  K.T. Queeney et al. Appl. Phys. Lett., Vol. 84, No. 4, 26 (2004)"

With its remarkable electro-thermal properties such as the highest known thermal conductivity (~22 W cm−1bold dotK−1 at RT of any material, high hole mobility (>2000 cm2 V−1 s−1), high critical electric field (>10 MV cm−1), and large band gap (5.47 eV), diamond has overwhelming advantages over silicon and other wide bandgap semiconductors (WBGs) for ultra-high-voltage and high-temperature (HT) applications (>3 kV and  >450 K, respectively). However, despite their tremendous potential, fabricated devices based on this material have not yet delivered the expected high performance. The main reason behind this is the absence of shallow donor and acceptor species. The second reason is the lack of consistent physical models and design approaches specific to diamond-based devices that could significantly accelerate their development. The third reason is that the best performances of diamond devices are expected only when the highest electric field in reverse bias can be achieved, something that has not been widely obtained yet. In this context, HT operation and unique device structures based on the two-dimensional hole gas (2DHG) formation represent two alternatives that could alleviate the issue of the incomplete ionization of dopant species. Nevertheless, ultra-HT operations and device parallelization could result in severe thermal management issues and affect the overall stability and long-term reliability. In addition, problems connected to the reproducibility and long-term stability of 2DHG-based devices still need to be resolved.

This review paper aims at addressing these issues by providing the power device research community with a detailed set of physical models, device designs and challenges associated with all the aspects of the diamond power device value chain, from the definition of figures of merit, the material growth and processing conditions, to packaging solutions and targeted applications. Finally, the paper will conclude with suggestions on how to design power converters with diamond devices and will provide the roadmap of diamond device development for power electronics.

The fast switching times of Wide Bandgap (WBG) devices pose a challenge for the insulation design of voltage source inverter (VSI)-fed motors, interturn insulation in particular. This paper discusses interturn insulation breakdown problem due to steep fronted voltage at motor terminals and calculates the electrical stress for different insulations in a motor based on the standards IEC 60034-18-42 and IEC 60034-18-41. IEC TS 61800-8 is used to estimate voltage appearing at the terminals of motor in an electric drive installation so that the insulation can be designed accurately. With Silicon Carbide (SiC) devices enabling Medium-Voltage (MV) Pulse Width Modulation (PWM) VSI drives for high speed, MW class motors, accurate insulation design is critical for reliability of these motors. This paper uses FEM model to calculate non-uniform voltage distribution in the winding and coil. The contribution of this paper is a comprehensive overview of insulation design for WBG device based converter-fed motors and accurate estimation of increase in insulation volume for random wound and MV form wound motors.

We achieved robust bonding of a large area power chip (> 100 mm 2) with sintered Ag joint produced by the electrical current assisted sintering (ECAS) technique operating at low current (1.1 kA) and short sintering time (10 s). Our ECAS-ed Ag joint possessed low thermal resistance (∼0.18 °C/W), high density (89.6%), as well as good static and dynamic electrical properties during switching on and off of the power chip. Our TEM analysis explained that the good electrical and thermal performances of the power chip were attributed to the high density of twins formed in the ECAS-ed nano-Ag joint.

This paper presents an implementation of the
SenseGaN current sensing technique using Gallium Nitride
(GaN) transistors as representative of Wide Bandgap (WBG)
semiconductors. For effective feedback control, fast over-current
protection, and diagnostics-prognostics developments, precise
current measurement becomes more crucial. While the integration
and miniaturization of power semiconductors are getting
more feasible to operate at higher current as well as switching
frequency, most of the available current measurement techniques
have some technical challenges such as bandwidth limitations,
higher power dissipation, and sensitivity variations. SenseGaN
technique is along with the integration of semiconductors to
monitor the power module current without significant effects
on power stage performance and opens a new era for smart
devices in future power electronics; however, implementation of
this method in practice, has some difficulties that needs to be
addressed for careful design consideration. This paper verifies the
concept in WBG-based power converters with Spice simulations
and mathematical analysis. Finally, a prototype using power
650V-GaN is successfully tested at 150kHz.

Silicon Carbide (SiC) power semiconductor devices
are expected to achieve better performance than silicon power
devices in high-switching-frequency, high-power and hightemperature
applications. Several commercial SiC MOSFETs
and SiC Schottky diodes are available on the market, and SiC
power devices with higher power ratings are expected in the
future. This paper presents a performance projection method
and a scalable loss model for both SiC MOSFETs and SiC
Schottky diodes. The performance projection method provides
estimated parameters also for upcoming devices with higher
power ratings than currently commercially available. These
parameters are used in the scalable loss models to estimate power
losses. The performance projection and scalable loss model are
established based on data from Cree抯 product datasheets. The
loss breakdown analysis of a SiC DC-DC boost converter is
presented to demonstrate the proposed performance projection
method and scalable loss model.

Compact models of wide-bandgap power devices are
necessary to analyze and evaluate their impact on circuit and
system performance. Part I reviewed compact models for silicon
carbide (SiC) power diodes and MOSFETs. Part II completes
the review of SiC devices and covers gallium nitride devices as
well.

Wide bandgap (WBG) devices made from materials such as SiC, GaN, Ga2O3 and diamond, which can tolerate higher voltages and currents compared to silicon-based devices, are the most promising approach for reducing the size and weight of power management and conversion systems. Silicone gel, which is the existing commercial option for encapsulation of power modules, is susceptible to partial discharges (PDs). PDs often occur in air-filled cavities located in high electric field regions around the sharp edges of metallization in the gel. This study focuses on the modeling of PD phenomenon in an air filled-cavity in silicone gel for the combination of (1) a fast, high-frequency square wave voltage and (2) low-pressure conditions. The low-pressure condition is common in the aviation industry where pressure can go as low as 4 psi. To integrate the pressure impact into PD model, in the first place, the model parameters are adjusted with the experimental results reported in the literature an...

Wide bandgap (WBG) devices made from materials such as SiC, GaN, Ga2O3 and diamond, which can tolerate higher voltages and currents compared to silicon-based devices, are the most promising approach for reducing the size and weight of power management and conversion systems. Silicone gel, which is the existing commercial option for encapsulation of power modules, is susceptible to partial discharges (PDs). PDs often occur in air-filled cavities located in high electric field regions around the sharp edges of metallization in the gel. This study focuses on the modeling of PD phenomenon in an air filled-cavity in silicone gel for the combination of (1) a fast, high-frequency square wave voltage and (2) low-pressure conditions. The low-pressure condition is common in the aviation industry where pressure can go as low as 4 psi. To integrate the pressure impact into PD model, in the first place, the model parameters are adjusted with the experimental results reported in the literature an...

Silicon offers multiple advantages to power circuit designers, but at the same time suffers from limitations that are inherent to silicon material properties, such as low bandgap energy, low thermal conductivity, and switching frequency limitations. Wide bandgap ...

Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor seems the most promising. This paper attempts to present the status of the technology and the market with a view of highlighting both the progress and the remaining problems.

In this study, praseodymium barium cobalt oxide nanofiber interfacial layer was sandwiched between Au and n-Si. Frequency and voltage dependence of e 0 , e 0 , tand, electric modulus (M 0 and M 00) and r ac of PrBaCoO nanofiber capacitor have been investigated by using impedance spectroscopy method. The obtained experimental results show that the values of e 0 , e 0 , tand, M 0 , M 00 and r ac of the PrBaCoO nanofiber capacitor are strongly dependent on frequency of applied bias voltage. The values of e 0 , e 00 and tand show a steep decrease with increasing frequency for each forward bias voltage, whereas the values of r ac and the electric modulus increase with increasing frequency. The high dispersion in e 0 and e 00 values at low frequencies may be attributed to the Maxwell–Wagner and space charge polarization. The high values of e 0 may be due to the interfacial effects within the material, PrBaCoO nanofibers interfacial layer and electron effect. The values of M 0 and M 00 reach a maximum constant value corresponding to M 1 % 1/e 1 due to the relaxation process at high frequencies, but both the values of M 0 and M 00 approach almost to zero at low frequencies. The changes in the dielectric and electrical properties with frequency can be also attributed to the existence of N ss and R s of the capacitors. As a result, the change in the e 0 , e 00 , tand, M 0 , M 00 and ac electric conductivity (r ac) is a result of restructuring and reordering of charges at the PrBaCoO/n-Si interface under an external electric field or voltage and interface polarization.

Nanophase of Ga2O3has potentially important
applications in photocatalysis. We report the synthesis of
nanophase of the metastablec- and stable b-Ga2O3 and
demonstrate that it is possible to prepare a continuously
varying mixture starting from the pure metastablec- to the
pureb-phase. This is achieved by employing a facile and
reliable combustion route, using urea as a fuel. Typical
grain sizes, as estimated from XRD studies, are about
3 nm. Given the importance of surface chemistry for
potential applications, thermogravimetric coupled with
mass spectrometry is used in conjunction with FTIR to
elucidate the chemistry of the adsorbed surface layer.
Studies on thec-Ga2O3 phase indicate the occurrence of
weight loss of 8.1% in multiple steps. Evolved gas analysis
and FTIR studies show presence of physisorbed H2O
molecules and chemisorbed –(OH) ions bonded to active
surface states and accounts predominantly for the observed
weight loss.

As the smart-grid realization is becoming more pragmatic, the analysis on transactive energy systems (TESs) is also getting more substantial. Bidirectional DC-DC converter (BDDC) is the energy flow driver for a TES connected electric vehicles (EVs) and energy storage systems (ESSs). In this work, we have performed a detailed thermal and efficiency analysis of Silicon (Si), Silicon Carbide (SiC), and Si-SiC hybrid half-bridge commercial power modules for BDDC. Considering the power modules&#39; operating junction temperature as 85% of the rated maximum value, the optimum switching frequency (OSF) for Si, hybrid, and SiC modules is evaluated as 4, 10.5, and 27.5 kHz, respectively. For the full load OSF operation, the required heatsink maximum thermal resistance is estimated as 0.037, 0.040, and 0.080 0 C/W, respectively and the SiC MOSFET module shows the highest efficiency of 99%. The BDDC simulation is performed in PLECS, which comprises a control block for bi-directional power oper...

Defects in BN thin films, produced by reactive sputtering, were investigated by Electron Paramagnetic Resonance (EPR) measurements. The EPR signals of films produced with up to 10% N2 in the argon discharge are consistent with films having a cubic structure, and becoming more ordered with nitrogen incorporation in the films. The concentration of spins is in the order of 10'9 spins/g and they are attributed to nitrogen vacancies with an electron trapped in. Carbon incorporation changes the EPR signal and increases the concentration of spins significantly. This result is consistent with the notion that carbon doping stabilizes the electron in a nitrogen vacancy.

In this paper we report an experimental study of photocurrent mobility = lifetime products and free carrier lifetimes in CVD grown polycrystalline diamond of various qualities. The investigated samples are low impurity samples, nitrogen content ; 10 15 cm y3 , with an average grain size ranging from 25 m up to 110 m. This large difference in average grain size makes it possible to distinguish effects due to lifetime limiting trapping and recombination defect centers inside the grains from effects caused by defect centers at grain boundaries. At low carrier densities, -10 13 cm y3 , the effective free carrier lifetime is in the sub-nanosecond to nanosecond range in all samples due to intra-grain trapping and recombination centers. At high carrier densities, ) 10 13 cm y3 , the intra-grain centers becomes saturated and the effective lifetime becomes predominately given by carrier diffusion to and recombination at the defects related to the grain boundaries. Hence, the effective lifetime at high carrier densities is strongly related to the average grain size and increases up to several tens of nanoseconds, in samples with a large average grain size, whereas it remains in the nanosecond range for samples with small average grain size. In addition, we observe a lower mobility = lifetime product and decay constant with increasing nitrogen content, clearly showing the negative influence of nitrogen and nitrogen-related defects on these important material parameters. ᮊ

A method for probing the temporal evolution of ultra-fast
carrier generation and recombination processes in widebandgap
semiconductors, e.g. diamond, is described. Two
extreme ultraviolet (pump) pulses produced by high-order
harmonic generation in Argon gas (with a photon energy of
32 eV) are superimposed on a sample with a small angle between
them, inducing periodic changes in the refractive index
of the material causing it to act as a transient diffraction
grating. A delayed synchronized infrared (probe) pulse
gets diffracted on the induced phase grating and is detected
in the first diffraction order. By varying the time-delay between
pump and probe, the full temporal evolution of the
free carrier generation and recombination processes can be
resolved. Feasibility calculations and the first steps towards
experimental implementation are presented.

The magnetic properties, electronic band structure and Fermi surfaces of the hexagonal Cr2GeC system have been studied by means of both generalized gradient approximation (GGA) and the +U corrected method (GGA+U). The effective U value has been computed within the augmented plane-wave theoretical scheme by following the constrained density functional theory formalism of Anisimov et al. [1991 Phys. Rev. B 45, 7570]. On the basis of our GGA+U calculations, a compensated anti-ferromagnetic spin ordering of Cr atoms has been found to be the ground state solution for this material, where a Ge-mediated super-exchange coupling is responsible for an opposite spin distribution between the ABA stacked in-plane Cr-C networks. Structural properties have also been tested and found to be in good agreement with the available experimental data. Topological analysis of Fermi surfaces have been used to qualitatively address the electronic transport properties of Cr2GeC and found an important asymmetrical carrier-type distribution within the hexagonal crystal lattice. We conclude that an appropriate description of the strongly correlated Cr-d electrons is an essential issue for interpreting the material properties of this unusual Cr-based MAX-phase.

A novel design of metamaterial (MTM) based absorber with reduced cell size is proposed in this paper.The absorber is designed to operate in the mid infrared (IR) regime using gold nano-pillar inclusions embedded ina dielectric spacer. The absorption band can be controlled by adjusting the nano- pillar’s properties. Numerical simulations have been conducted to investigate the effect of these inclusions on the absorber performance.Moreover, a wideband absorber is designed by combining four different sized resonant elements within the unitcell. The absorber shows enhanced characteristics such as large bandwidth, small cell size to wavelength ratio and high absorption level for wide range of incident angles for different wave polarizations. The achieved bandwidth isaround 60% with normalized absorption percentage of 80% over the band 5.2-9.8µm, and cell size ratio of 0.34λ.

A high-voltage transmission line pulse transformer has been constructed based on modem cable technology. The transformer has been successfully tested for secondary voltages up to 85 kV. The high-voltage cable is equipped with a resistive layer (semicon) on the inner conductor and on the inside of the outer conductor. Semicon cables are commonly used in high-voltage transmission of electrical power.

We have demonstrated the fabrication of highly continuous and smooth CdSe semiconductor films containing self-assembled nanocrystals (NCs) using a simple, low cost solution-processed deposition technique. The impact of thermal annealing and ethanedithiol (EDT) treatment on oleate capped CdSe NCs films is illustrated. Post deposition EDT treatment enhances strong electron coupling between NCs by reducing the inter-particle distance, which enhances four orders of magnitude of photocurrent in the pn-device. Mild thermal annealing of NC films cause large redshift and significant broadening. Our findings suggest that NCs with short-range organic ligands are suitable for high-performance Thin-Film-Transistors and next generation high-efficiency photovoltaics.

Silicon offers multiple advantages to power circuit designers, but at the same time suffers from limitations that are inherent to silicon material properties, such as low bandgap energy, low thermal conductivity, and switching frequency limitations. Wide bandgap ...

Wide bandgap (WBG) devices made from materials such as SiC, GaN, Ga2O3 and diamond, which can tolerate higher voltages and currents compared to silicon-based devices, are the most promising approach for reducing the size and weight of power management and conversion systems. Silicone gel, which is the existing commercial option for encapsulation of power modules, is susceptible to partial discharges (PDs). PDs often occur in air-filled cavities located in high electric field regions around the sharp edges of metallization in the gel. This study focuses on the modeling of PD phenomenon in an air filled-cavity in silicone gel for the combination of (1) a fast, high-frequency square wave voltage and (2) low-pressure conditions. The low-pressure condition is common in the aviation industry where pressure can go as low as 4 psi. To integrate the pressure impact into PD model, in the first place, the model parameters are adjusted with the experimental results reported in the literature and in the second place, the dependencies of various PD characteristics such as dielectric constant and inception electric field on pressure are examined. Finally, the reflections of these changes in PD intensity, duration and inception time are investigated. The results imply that the low pressure at high altitudes can considerably affect the PD inception and extinction criterion, also the transient state conditions during PD events. These changes result in the prolongation of PD events and more intense ones. As the PD model is strongly dependent upon the accurate estimation electric field estimation of the system, a finite-element analysis (FEA) model developed in COMSOL Multiphysics linked with MATLAB is employed that numerically calculates the electric field distribution.

The electronic structure and the anisotropy of the Al - N π and σ chemical bonding of wurtzite AlN has been investigated by bulk-sensitive total fluorescence yield absorption and soft x-ray emission spectroscopies. The measured N K, Al L1, and Al L2,3 x-ray emission and N 1s x-ray absorption spectra are compared with calculated spectra using first principles density-functional theory including dipole transition matrix elements. The main N 2p - Al 3p hybridization regions are identified at -1.0 to -1.8 eV and -5.0 to -5.5 eV below the top of the valence band. In addition, N 2s - Al 3p and N 2s - Al 3s hybridization regions are found at the bottom of the valence band around -13.5 eV and -15 eV, respectively. A strongly modified spectral shape of Al 3s states in the Al L2,3 emission from AlN in comparison to Al metal is found, which is also reflected in the N 2p - Al 3p hybridization observed in the Al L1 emission. The differences between the electronic structure and chemical bonding of AlN and Al metal are discussed in relation to the position of the hybridization regions and the valence band edge influencing the magnitude of the large band gap.

In this work, room temperature oxidation of GaAs was investigated using ion beam oxidation (mO). In lBO, an ion beam is used to introduce oxygen athermally into the substrate, in this case GaAs. GaAs bonds are broken upon collision with the ions, making gallium and arsenic atoms readily available to react with the oxygen species. Ion beam oxidation of GaAs at room temperature was studied as a function ofoxygen ion energy between 500 and is keY. The ion beam oxidized GaAs was characterized in situ by Auger electron spectroscopy (AES) and ex situ with x-ray photoelectron spectroscopy (XPS) for accurate determination of the film chemical composition. Below 1 keY, a thin oxide film is formed: it is composed of Ga20 3 and AS20 3 with almost no metallic arsenic, and presents insulating properties.
As the ion energy increases, preferential sputtering of As and decomposition of AS203 increase and prevent formation of an
insulating film. No damage was detected by Rutherford backscattering spectrometry (RES) combined with ion channeling, in the substrate subjected to IBO below 1 keV.""

The article presents investigations of CdZnSSe crystals synthesized in silicate glass melt. Zn-rich glass manufactured in the 19th century has been found to contain CdZnSSe crystals of hexagonal crystal system exhibiting intense band-edge cathodoluminescence. The exciton luminescence peak of these crystals ranges 2.00 to 2.03 eV at 300 K and 2.02 to 2.06 eV at 80 K. Its shifts in individual crystals are attributed to minor variations of their composition. The value of the band gap derivative dE g /dT lies in the range from −2.5 × 10 −4 to 0 eV/K in the interval from 80 to 300 K. CdZnSSe crystals in glass demonstrate high temperature and temporal stability. The glass-crystal composite on their basis is resistant to the electron-beam irradiation and long-term weath

A novel design of metamaterial (MTM) based absorber with reduced cell size is proposed in this paper. The absorber is designed to operate in the mid infrared (IR) regime using gold nano-pillar inclusions embedded in a dielectric spacer. The absorption band can be controlled by adjusting the nano-pillar&#39;s properties. Numerical simulations have been conducted to investigate the effect of these inclusions on the absorber performance. Moreover, a wideband absorber is designed by combining four different sized resonant elements within the unit cell. The absorber shows enhanced characteristics such as large bandwidth, small cell size to wavelength ratio and high absorption level for wide range of incident angles for different wave polarizations. The achieved bandwidth is around 60% with normalized absorption percentage of 80% over the band 5.2-9.8µm, and cell size ratio of 0.34λ.

Silicon offers multiple advantages to power circuit designers, but at the same time suffers from limitations that are inherent to silicon material properties, such as low bandgap energy, low thermal conductivity, and switching frequency limitations. Wide bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), provide larger bandgaps, higher breakdown electric field, and higher thermal conductivity. Power semiconductor devices made with SiC and GaN are capable of higher blocking voltages, higher switching frequencies, and higher junction temperatures than silicon devices. SiC is by far the most advanced material and, hence, is the subject of attention from power electronics and systems designers. This paper looks at the benefits of using SiC in power electronics applications, reviews the current state of the art, and shows how SiC can be a strong and viable candidate for future power electronics and systems applications.

Physics-based breakdown voltage optimization in Schottky-barrier power RF and microwave field-effect transistors as well as in high-speed power-switching diodes is today an important topic in technology computer-aided design (TCAD). OFF-state breakdown threshold criteria based on the magnitude of the Schottky-barrier leakage current can be directly applied to TCAD; however, the results obtained are not accurate due to the large uncertainty in the Schottky-barrier parameters and models arising above all in advanced wide-gap semiconductors and to the need of performing high-temperature simulations to improve the numerical convergence of the model. In this paper, we suggest a novel OFF-state breakdown criterion, based on monitoring the magnitude (at the drain edge of the gate) of the electric field component parallel to the current density. The new condition is shown to be consistent with more conventional definitions and to exhibit a significantly reduced sensitivity with respect to physical parameter variations.

This paper proposes an adaptive control architecture for maximum power point tracking (MPPT) in photovoltaic systems. MPPT technologies have been used in photovoltaic systems to deliver the maximum available power to the load under changes of the solar insolation and ambient temperature. To improve the performance of MPPT, this paper develops a two-level adaptive control architecture that can reduce complexity in system control and effectively handle the uncertainties and perturbations in the photovoltaic systems and the environment. The first level of control is ripple correlation control (RCC), and the second level is model reference adaptive control (MRAC). By decoupling these two control algorithms, the system achieves MPPT with overall system stability. This paper focuses mostly on the design of the MRAC algorithm, which compensates the underdamped characteristics of the power conversion system. The original transfer function of the power conversion system has time-varying parameters, and its step response contains oscillatory transients that vanish slowly. Using the Lyapunov approach, an adaption law of the controller is derived for the MRAC system to eliminate the underdamped modes in power conversion. It is shown that the proposed control algorithm enables the system to converge to the maximum power point in milliseconds. Index Terms-Maximum power point tracking (MPPT), model reference adaptive control (MRAC), photovoltaic system, ripple correlation control (RCC).

This paper investigates on the reaction of 10 and 15MGy, 3MeV electron irradiation upon off-the-shelves (commercial) Silicon Carbide Schottky diodes from Infineon Technologies (model: IDH08SG60C) and STMicroelectronics (model: STPSC806). Such irradiation reduces the forward-bias current. The reduction is mainly due to the significant increase of the series resistance (i.e. Infineon: 1.45Ω at before irradiation → 121×10 3 Ω at 15MGy); STMicroelectronics: 1.44Ω at before irradiation → 2.1×10 9 Ω at 15MGy). This increase in series resistance gives 4.6 and 8.2 orders of magnitude reduction for the forward-bias current density of Infineon and STMicroelectronics respectively. It is also observed that the ideality factor and the saturation current of the diodes increases with increasing dose (i.e. ideality factor-Infineon: 1.01 at before irradiation → 1.05 at 15MGy; STMicroelectronics: 1.02 at before irradiation → 1.3 at 15MGy | saturation current-Infineon: 1.6×10-17 A at before irradiation → 2.5×10-17 A at 15MGy; STMicroelectronics: 2.4×10-15 A at before irradiation → 8×10-15 A at 15MGy). Reverse-bias leakage current density in model by Infineon increases by one order of magnitude after 15MGy irradiation, however, in model by STMicroelectronics decreases by one order of magnitude. Overall, for these particular samples studied, Infineon devices have shown to be better in quality and more radiation resistance toward electron irradiation in forward-bias operation while STMicroelectronics exhibit better characteristics in reverse-bias operation.

A review is given about the influence of strain fields on the optical properties of GaN epilayers. We find the basic constant of the material: crystal field splitting, spin-orbit interaction parameter, deformation potentials. We discuss the evolution of the exciton binding energy with strain. © 2000 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS