bluuebunny/crossref_metadata_2025_split huggingface dataset:
Excitation Properties of Er-Doped GaP from Photoluminescence and High Pressure Studies
Authors: Culp T. D. , Wang X. Z. , Kuech T. F. , Wessels B. W. , Bray K. L. 
Published: April 2011

AbstractThe photoluminescence properties of MOCVD GaP:Er were investigated as a function of temperature, applied hydrostatic pressure, and excitation wavelength. Four sharp peaks are observed on the high energy side of the 1.54 μm Er3+ emission. These peaks are selectively excited by below-gap energies and have a significantly shorter lifetime than the main Er3+ emission, suggesting that at least two distinct Er3+ centers contribute to the luminescence. The low temperature photoluminescence excitation (PLE) spectrum of the 1.54 μm emission was also measured. Strong broad excitation of the Er3+ centers occurs with energies well below the indirect bandgap energy. In fact, the Er3+ emission intensity is significantly stronger when excited with below-gap wavelengths than with above-gap wavelengths. This result has been explained in terms of competition between Er3+ excitation and nonradiative deep level recombination for free carriers under above-gap excitation. With below-gap excitation, carriers are promoted directly into the Er3+ excitation pathway via absorption at an erbium-related trap. At 42 kbar, below-gap excitation is no longer more efficient than above-gap excitation, suggesting that competitive capture of free carriers by deep levels has been reduced.
1.54 μm Electroluminescence from Erbium Doped Gallium Phosphide Diodes
Authors: Ford G. M. , Wessels B. W. 
Published: April 2011

AbstractEr-doped GaP diodes that exhibit strong room temperature characteristic 4f-shell luminescence under forward bias have been fabricated. The output of the diode increases linearly with current for low current densities but eventually saturates. The radiative decay lifetime is 2.6 msec and is independent of current. It is proposed that the observed intensity dependence on excitation power results from saturation of the optically active Er3+ centers. Some diodes showed a superlinear dependence, with a threshold of about 2 A/cm2.
Erbium Doped GaAs by Mocvd
Authors: Greenwald A. C. , Linden K. J. , Rees W. S. , Just O. , Haegel N. M. , Donder S. 
Published: April 2011

AbstractThe overall objective of this research is to develop temperature stable 1.54 ptm light sources based upon ionic emitters. LEDs and diode lasers were fabricated in MOCVD grown AIGaAs materials but only weak electroluminescence was observed. The III-V compound semiconductors were doped with erbium amide sources of the form: Er{N[Si(CH 3)3]R}3 where R s an organic unit. These amide sources had reduced carbon and oxygen levels in a GaAs film compared to the use of a cyclopentadienyl erbium source, but did dope the semiconductor with silicon. Silicon doping levels were a function of growth temperature. Erbium photoluminescence was enhanced with oxygen codoping, but diode electrical characteristics were degraded. PLE showed that erbium ions were excited by above bandgap light absorbed by GaAs.
Improved Nickel Silicide Ohmic Contacts to N-Type 4H and 6H-SiC Using Nichrome
Authors: Luckowski E. D. , Williams J. R. , Bozack M. J. , Isaacs-Smith T. , Crofton J. 
Published: April 2011

AbstractResults are reported for ohmic contacts formed on n-type 4H and 6H-SiC using nichrome (80/20 weight percent Ni/Cr). In comparison to contacts formed on 6H-SiC using pure Ni, the electrical characteristics of these NiCr contacts are similar (∼ 1E-5 Ω-cm2 for moderately doped material), and composite Au/NiCr contacts exhibit good stability during long-term anneals (∼ 2500 hr) at 300 C without the requirement of a diffusion barrier layer between the ohmic contact layer and the Au cap layer. The use of NiCr also results in success rates near 100% for direct wire bonding to the Au cap layers.
Low Resistance Ohmic Contact on p-type GaN Grown by Plasma-Assisted Molecular Beam Epitaxy
Authors: Yoo Myung C. , Lee J. W. , Myoung J. M. , Shim K. H. , Kim K. 
Published: April 2011

AbstractOhmic contacts on p-type GaN have been investigated. High quality GaN epilayers on cplane sapphire were prepared using plasma-assisted molecular beam epitaxy that utilized an inductively coupled rf nitrogen plasma source and solid source beams. The resulting film thickness and the doping concentration of the grown samples were in the range of 0.7–1.35 μm and 1018 – 1020/cm3, respectively. The metallization consisted of high work function metal bilayers which included a combinations of 25 nm-thick Ni, Ti, Pt and/or Cr and 200 nm-thick Au on the highly p-doped GaN in a transmission line model pattern. Ohmic contacts were formed by alloying the bi-layers using rapid thermal annealing (RTA) at temperatures in the range of 300–700 °C for 1 min under nitrogen ambient. Current-voltage measurements showed that the specific contact resistance was as low as 1.2 × 10 −4 Ω–cm2 for the sample having 1.4 × 1020/cm3p-type doping concentration with a Cr/Au contact annealed at 500 °C for 1 min by RTA. Judging from the scanning Auger microscopy results and the glancing angle x-ray diffraction analysis, this resistance is attributed to Cr diffusion into the GaN layer.
Optical Spectroscopy of Dry-Etched GaN-Nanostructures
Authors: Zull H. , MÜller J. , Koeth J. , Kieseling F. , Forchel A. 
Published: April 2011

AbstractWe have realized GaN wire gratings with periods down to 80 nm and with wire widths down to 26 nm- GaN layers of good structural and optical quality with thicknesses down to 100 nm were grown by electron cyclotron resonance assisted MBE (ECR-MBE). The grating structures were fabricated by high resolution electron beam lithography and electron cyclotron enhanced reactive ion etching (ECR-RIE) using CL2/Ar as etching gas. The optical properties of the GaN structures were investigated by photoluminescence (PL) spectroscopy in the temperature range between 40 K and 110 K. The wire patterns show intense excitonic photoluminescence and only a small dry etched induced degradation of the quantum efficiency even for the narrowest wires.
Si Implantation and Annealing OF GaN FOR n-Type Layer Formation
Authors: Molnar B. , Wickenden A. E. , Rao M. V. 
Published: April 2011

AbstractHigh dose Si has been implanted into MOCVD grown high resistivity and n-type GaN in the 26–500°C temperature range. The implant activation varies widely (30 −>100%) depending on, what energy level is assigned to the Si, the implantation and annealing temperatures, and the quality of the substrate. The usable maximum temperature for activation is limited by the severe decomposition of the GaN. After 1050°C 15s RTA Ga liquid droplet formation has been observed by SEM. This decomposition changes the surface morphology but did not introduce measurable change in the electrical properties up to 1150°C /120s RTA.
P-And N-Type Implantation Doping Of GaN With Ca And O
Authors: Zolper J. C. , Wilson R. G. , Pearton S. J. , Stall R. A. 
Published: April 2011

AbstractIII-N photonic devices have made great advances in recent years following the demonstration of doping of GaN p-type with Mg and n-type with Si. However, the deep ionization energy level of Mg in GaN (∼160 meV) limits the ionized of acceptors at room temperature to less than 1.0% of the substitutional Mg. With this in mind, we used ion implantation to characterize the ionization level of Ca in GaN since Ca had been suggested by Strite [1] to be a shallow acceptor in GaN. Ca-implanted GaN converted from n-to-p type after a 1100°C activation anneal. Variable temperature Hall measurements give an ionization level at 169 meV. Although this level is equivalent to that of Mg, Ca-implantation may have advantages (shallower projected range and less straggle for a given energy) than Mg for electronic devices. In particular, we report the first GaN device using ion implantation doping. This is a GaN junction field effect transistor (JFET) which employed Ca-implantation. A 1.7 µm JFET had a transconductance of 7 mS/mm, a saturation current at 0 V gate bias of 33 mA/mm, a ft of 2.7 GHz, and a fmax of 9.4 GHz. 0-implantation was also studied and shown to create a shallow donor level (∼25 meV) that is similar to Si. SIMS profiles of as-implanted and annealed samples showed no measurable redistribution of either Ca or0inGaNat 1125°C.
Tem Structure Characterization Of Ti/Al and Ti/Al/Ni/Au Ohmic Contacts For n-GaN
Authors: Ruvimov S. , Liliental-Weber Z. , Washburn J. , Duxstad K. J. , Hailer E. E. , Fan Z.-F. , Mohammad S. N. , Kim W. , Botchkarev A. E. , Morkoq H. 
Published: April 2011

AbstractTransmission electron microscopy has been applied to characterize the structure of Ti/Al and Ti/Al/Ni/Au ohmic contacts on n-type GaN (˜1017 cm−3 ) epitaxial layers. A thin polycrystalline cubic TiN layer epitaxially matched to the (0001) GaN surface was detected at the interface with the GaN substrate. This layer was studied in detail by electron diffraction and high resolution electron microscopy. The orientation relationship between the cubic TiN and the GaN was found to be: {111}TiN//{00.1}GaN, [110]TiN//[11.0]GaN, [112 ]TiN//[ 10.0]GaN. The formation of this cubic TiN layer results in an excess of N vacancies in the GaN close to the interface which is considered to be the reason for the low resistance of the contact.
Analysis of the Sublimation Growth Process of Silicon Carbide Bulk Crystals
Authors: Eckstein R. , Hofmann D. , Makarov Y. , Müller St. G. , Pensl G. , Schmitt E. , Winnacker A. 
Published: April 2011

AbstractExperimental and numerical analysis have been performed on the sublimation growth process of SiC bulk crystals. Crystallographic, electrical and optical properties of the grown silicon carbide (SIC) crystals have been evaluated by various characterization techniques. Numerical models for the global simulation of SiC bulk growth including heat and mass transfer and chemical processes are applied and experimentally verified.
Growth of Crystalline Quality Sic on Thin and Thick Silicon-on-Insulator Structures
Authors: Namavar F. , Colter P. , Gagnon E. , Cremins-Costa A. , Perry D. , Pirouz P. , Wu C-H. 
Published: April 2011

AbstractWe have grown silicon carbide (SiC) on ultrathin Si (about 300Å) and on thick Si (about 2000Å) on commercial SIMOX (from IBIS Corp and SOITEC, Inc.), and bulk Si. Electron diffraction and Rutherford backscattering spectroscopy (RBS)/channeling studies indicate epitaxial growth of singlecrystal β-SiC even at growth temperatures as low as 1100°C.We have already demonstrated the fabrication of ultrathin Si, as thin as 140Å on SiO2 by using the low-energy SIMOX (LES) (20 to 30 keV) process to produce films of lower cost and excellent integrity compared to thinned commercial SIMOX. Based on these results, ultrathin Si-on-insulator (SOI) substrates appear to have great potential for device quality SiC films. However, the carbonization and/or growth of SiC on ultrathin Si requires further optimization because the processes for surface cleaning and growth of SiC on bulk Si substrates cannot be applied because of the thinness of the substrate layers. Additional carbonization work at higher temperatures has indicated the possibility of converting the entire Si top layer.
High Temperature Gas Phases Reactions Of Trimethylgallium with Ammonia and Trimethylamine
Authors: Thon A. , Safvi S. A. , Kuech T. F. 
Published: April 2011

AbstractThe use of trimethylgallium-trimethylamine (TMG:TMN) adduct as alternative cation precursor for MOVPE of GaN was studied by means of in-situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure and reaction time were chosen to emulate the gas phase environment typical of the metal-organic vapor phase: epitaxy (MOVPE) of GaN. Dynamic changes in the mass spectra are reported for the gas phase reactions between trimethylgallium (TMG) and TMN in hydrogen (H2/D2) and ammonia (NH3/ND3) ambients. Evidence presented for the high temperature TMG:TMN adduct formation, followed by ethane elimination. The strength of the adduct bonding is comparable to that of TMG:NH3 and thus suppresses TMN displacement by ammonia. The thermal stability of TMG:TMN was found to be higher in ammonia ambient than it is in hydrogen. Kinetic parameters for some of the decomposition processes are given.
Electrical and optical investigation of the position of vanadium related defects in the 4H and 6H SiC bandgaps
Authors: Jenny J. R. , Skowronski M. , Mitchel W. C. , Smith S. R. , Evwaraye A. O. , Hobgood H. M. , Augustine G. , Hopkins R. H. 
Published: April 2011

AbstractHall effect, deep level transient spectroscopy, optical absorption, and optical admittance spectroscopy were employed to determine the position of the vanadium acceptor and vanadiumnitrogen complex in vanadium- and nitrogen-doped 4H and 6H SiC. Hall effect results indicate that the acceptor position in 4H(6H) SiC is 0.80(0.66) eV beneath the conduction band edge. The DLTS signature of the defect in the 4H polytype showed an ionization energy of 806 meV and a capture cross section of 1.8×10−16 cmr−2 The optical absorption measurements proved that the acceptor level investigated is related to isolated vanadium, and therefore the vanadium acceptor level. Based upon DLTS and SIMS measurements, the maximum solubility of vanadium in SiC was determined to the 3×10−17 crn3. An examination of polarized light experiments indicates that vanadium also complexes with another element to form electronic(at 5000 cm−1) and vibrational absorption(at 683 cm−1) bands. While the other constituent cannot be identified, evidence suggests that nitrogen is a likely candidate. This complex introduces a deep level at Ec−0.78 eV as determined using optical admittance spectroscopy.
Structure of the 2H-Ain/6H-SiC Interface
Authors: Vermaut P. , Ruterana P. , Nouet G. , Morkoç H. 
Published: April 2011

AbstractSteps at the AIN/SiC interface have been investigated by HREM. Some of them do not introduce any defects. Others steps present a dislocation character which can contribute to relieve the strain due to the lattice mismatch. A third kind of steps gives rise to a prismatic planar fault for which a model is given. A reaction between prismatic and basal stacking faults is analyzed.
Defect Dominant Junction Characteristics of 4H-SiC p+/n Diodes
Authors: Scofield J. , Dunn M. , Reinhardt K. , Yeo Y. K. , Hengehold R. 
Published: April 2011

AbstractForward and reverse current-voltage (I-V-T) measurements of MOCVD grown 4H-SiC p+/n diodes are compared to classical recombination-generation theory over the temperature range of 100 to 750 K. The forward bias data indicate that the I-V characteristics of the wellbehaved devices follow a classical recombination dominant transport mechanism. Ideality factors were determined to be in the range of 1.85 to 2.09, and the forward activation energy found to be EA = l.56 eV compared to a nearly ideal value of 1.6 eV. A majority of the devices tested under forward bias conditions were, however, found to exhibit significant leakage current components due to tunneling at forward biases of up to 2.2 V for turn-on voltages in the 2.5 to 3.0 range. Deep level transient spectroscopy (DLTS) was also performed on the diode structures over the same wide temperature range, and the results were correlated to those obtained from reverse I-V-T and C-V-T characterization. Deep level defects at energies between 200 and 856 meV were identified from the DLTS data, and these levels are believed to be responsible for the tunneling dominant current conduction. Intrinsic deep levels, common to all devices tested, are emphasized and suggested as possible reverse bias tunneling paths for breakdown to explain the lack of an avalanche mechanism in all of the 4H-SiC diodes tested.
Theory and Realization of a Two-Layer Hall Effect Measurement Concept for Characterization of Epitaxial and Implanted Layers of SiC
Authors: Schöner Adolf , Rottner Kurt , Nordell Nils 
Published: April 2011

AbstractEpitaxial and implanted layers are generally characterized by Hall effect measurements using a pn-junction as electrical insulation of the layer from the substrate. Due to defects, low doping concentrations or thin layers the resistivity of epitaxial or implanted layers is comparable to the resistivity of the pn-junction and the substrate. This results in inefficient electrical insulation between both regions. To be able to determine the properties of epitaxial or implanted layers even in the case of substantial leakage current we developed a two-layer Hall effect measurement concept. This concept is based on the conventional van der Pauw technique applied to the layer and the substrate separately. In addition the current-voltage characteristic of the pn-junction is measured and modeled in the analysis as an ohmic resistor.This two-layer concept is applied to epitaxial grown SiC and the results are compared with conventional van der Pauw technique. In addition both techniques are compared with the results of capacitance-voltage (CV) measurements and secondary ion mass spectroscopy (SIMS).
A Study of Electroluminescent Emission from CVD Diamond
Authors: Manfredotti C. , Fizzotti F. , Vittone E. , Polesello P. , Wang F. , Schwarz R. , Grebnert S. 
Published: April 2011

AbstractCVD diamond could be an electroluminescent material. While its photoluminescent and cathodoluminescent properties are relatively well known, the electroluminescent ones have not been intensively investigated. The electroluminescent emission of CVD diamond is reminescent of the so-called “band A”; it is centered at 2.8 eV and extends from 2.6 to 3 eV. The luminescenceintensity increases linearly with the electric current and corresponds to a superquadratic regime of I-V characteristics in the dark and to a quadratic regime under a λ = 442 nm illumination. The I-V characteristics can be related to space charge limited current (SCLC) phenomena. Besides, the temperature behaviour of electroluminescence and of photoexcited current can be put into relation with the presence of a deep state in the bandgap where injected carriers from both electrodes recombine. The electroluminescent emission, even in a wavelength region far away from the photopic response, is clearly and strongly visible at naked eye. The luminescence efficiency is being discussed in order to consider CVD diamond as a material for optoelectronic devices.
Cathodoluminescence Studies of Bound Excitons and Near Band Gap Emission Lines in Boron- and Phosphorus-Doped CVD-Diamonds
Authors: Sternschulte H. , Albrecht T. , Thonke K. , Sauer R. , Grieβer M. , Grasserbauer M. 
Published: April 2011

AbstractCathodoluminescence measurements at cryogenic temperatures are reported on boron- and phosphorus-doped CVD-diamond films grown on silicon substrates. Boron and phosphorus concentrations were determined by SIMS measurements; for boron, they reached from unintentional background doping levels up to 3500 ppm. At increasing boron concentrations, the radiative recombination of boron bound excitons (BEto) at 5.22 eV photon energy systematically broadens and shifts down to 4.99 eV whereas the free exciton emission (FEto) disappears for 40 ppm and higher. In the phosphorus-doped films we observe new lines at 5.16 eV and 4.99 eV which we ascribe to TO- and (TO+Or)-phonon assisted transitions of an exciton bound to a shallow impurity other than boron, possibly phosphorus or a phosphorus-related shallow complex.
Photoreflectance Study of Gan Film Grown by Metalorganic Chemical Vapor Deposition
Authors: Yang K. , Zhang R. , Zheng Y. D. , Qin L. H. , Shen B. , Shi H. T. , Huang Z. C. , Chen J. C. 
Published: April 2011

AbstractPhotoreflectance was used to study the optical properties of single crystal hexagonal GaN film on (0001) sapphire substrate grown by metalorganic chemical vapor deposition. The energy gap of GaN was determined as 3.400 eV, and the possible origin of the PR signal was attributed to the modulation of the surface field and lineshape broadening of defects. Optical absorption and cathodoluminescence of the GaN sample were measured, and the optical absorption edge of 3.39 eV and the cathodoluminescence emission peak of 3.461 eV at low temperature (15.6K) confirmed the results of Photoreflectance.
Pyroelectric Effect in Wurtzite Gallium Nitride
Authors: Bykhovski A. D. , Kaminski V. V. , Shur M. S. , Chen Q. C. , Khan M. A. 
Published: April 2011

AbstractWe report on the measurements of the pyroeffect in wurtzite n-type GaN films deposited over basal plane sapphire substrates. The voltage drop between the contacts was measured while the sample was subjected to uniform heating. Our results show that the pyroelectric effect in GaN can be partially attributed to the secondary pyroelectricity, caused by the development of strain in the material due to thermal expansion.
Optical and Structural Properties of α-Si1-xCx Films
Authors: Chen Zhizhong , Yang Kai , Zhang Rong , Shi Hongtao , Zheng Youdou 
Published: April 2011

AbstractIn this paper, we reported experimental results about optical and structural properties of amorphous silicon carbide (α-Si1-xCx). The films of a-Si1-xCx) were grown by CVD on substrate of quartz glass. Optical constants (n-refractive index, a-absorption coefficient, Eg-optical energy band gap) of these films were determined by transmission spectra. The radial distribution functions (RDFs) of α- Sil−xCx) films were drawn out from the data of x-ray diffraction spectra. According to the RDFs, we imagined the statistic scene from which we could obtain the information of atomic radial distribution. The bond lengths and bond numbers of Si-Si, Si-C, and C-C could be also determined by RDFs. From the analysis of Raman spectra, we obtained the information of their vibration state density, and discerned the peaks of bond vibration, which agreed well with the results of α-Si1-xCx) RDF.
Investigation of the Field Emission Current from Polycrystalline Diamond Films
Authors: Glesener J. W. , Morrish A. A. 
Published: April 2011

AbstractThe field emission current from boron doped polycrystalline diamond films was characterized as a function of voltage and temperature. The motivation for the current-temperature measurements was to assess the thermal stability of the diamond emitters and gain some insight into a possible emission mechanism.Results from the current-temperature (I-T) measurements found that the field emission current appeared independent of temperature. The best characterization of the results implied a temperature independent electron tunneling mechanism if not electron emission from the valence band of diamond.
Critical Materials, Device Design, Performance and Reliability Issues in 4H-SiC Power Umosfet Structures
Authors: Agarwal A. K. , Siergiej R. R. , Seshadri S. , White M. H. , McMullin P. G. , Burk A. A. , Rowland L. B. , Brandt C. D. , Hopkins R. H. 
Published: April 2011

AbstractThe long-term reliability of gate insulator under high field stress of either polarity presents a constraint on the highest electric field that can be tolerated in a 4H-SiC UMOSFET under on or off condition. A realistic performance projection of 41H-SiC UMOSFET structures based on electric field in the gate insulator (1.5 MV/cm under on-condition and 3 MV/cm under offcondition) consistent with long-term reliability of insulator is provided for the breakdown voltage in the range of 600 to 1500 V. The use of P+ polysilicon gate allows us to use a higher field of 3 MV/cm in the insulator under off-condition and leads to a higher breakdown voltage as the Fowler Nordheim (FN) injection from the gate electrode is reduced. FN injection data is presented for p type 4H-SiC MOS capacitor under inversion at room temperature and at 325°C. It is concluded that the insulator reliability, and not the SiC, is the limiting factor and therefore the high temperature operation of these devices may not be practical.