bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactive Ion Etching of Boron Nitride and Gallium Nitride Materials in C12/Ar and BCl3/Cl2/Ar Chemistries
Authors: Medelci N. , Tempez A. , Kim E. , Badi N. , Starikov D. , Berichev I. , Bensaoula A. 
Published: April 2011

ABSTRACTBoron nitride (BN) and gallium nitride (GaN) are known as superior semiconductor materials for high power and high temperature applications. Undoped BN layers grown using ion beam and electron cyclotron resonance (ECR) assisted physical deposition on conductive GaN films have demonstrated good insulating properties. These films are thus good candidates as thin insulating layers in high temperature GaN-based device structures such as MIS diodes and MISFETs due to their close thermal expansion coefficient. In order to address the device processing issue, reactive ion etching (RIE) tests were performed on these films. Using Cl2/Ar chemistry, etch rates up to 600 Å/min were measured. These rates were found to increase linearly with increasing rf power and Cl2 flow rate. GaN layers grown by gas source MBE were also dry etched, resulting in smooth sidewalls. Etch rates up to 1,400 Å/min were achieved at 200 W rf power (-280 V d.c. bias) in a BCl3/Cl2/Ar chemistry; this is the highest RIE rate reported up to now for GaN. Using Cl2/Ar and BCl3/Cl2/Ar for BN and GaN respectively, etch selectivities in excess of 5:1 can be obtained. Finally, preliminary Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) results on residue deposition and surface composition changes as a function of the different etch conditions are presented.
GaN Materials for High Power Microwave Amplifiers
Authors: Eastman Lester F. , chu Kenneth , smart Joseph , Shealy J. Richard 
Published: April 2011

ABSTRACTThe key parameters of GaN for use in microwave power amplifiers are presented. The electron-scattering effect of dislocations are presented for 2 DEG in HEMT devices. The use of the piezoelectric effect in designing Aly Ga1-yN/GaN HEMT structures is reviewed for a range of y.Short-gate device fabrication methods, and the device characterization, are presented. Maximum frequency of oscillation for .15 μm gates reached 140 GHz, while .3 μm gate power amplifiers reached 74% power-added efficiency at 3 GHz.
Bulk Breakdown in AlGaN/GaN HFETs
Authors: Gradinaru G. , Kao N. C. , Gaska R. , Yang J. , Chen Q. , Khan M. A. , Sudarshan T. S. 
Published: April 2011

ABSTRACTA significant source current generated by a carrier multiplication process is observed at large drain voltages in the subthreshold regime, along with simultaneous increase of the gate current and light emission signal. Provided no on-surface premature breakdown takes place, a bulk channel avalanche breakdown process is proposed as the dominant breakdown mechanism for a large range of gate-to-source dc voltages. This process in the GaN channel is responsible for the excess source and drain currents, light emission, and excess gate current beyond its normal value measured in a gate-to-drain diode configuration. The role of the gate bias in controlling the channel vs. the gate breakdown mechanisms is described.
Interfacial Diffusion/Reaction and Electrical Properties of Pd Ultra-Thin Film on Sic at Different Annealing Temperatures
Authors: Lu W. , Shi D. T. , Collins W. E. , Chen H. , Burger A. 
Published: April 2011

ABSTRACTPd/SiC has been used as a high temperature hydrocarbon and hydrogen gas sensor in environmental and aeronautical applications. In this work, the relationships between diffusion, reaction, and interfacial chemical composition with electrical properties for Pd ultra-thin films on 6H-SiC (∼< 30Å) are studied at different annealing temperatures.Ultra-thin film Pd on 6H-SiC has been prepared by the RF sputtering method. The Schottky barrier heights are measured by XPS for an unannealed sample and samples annealed from 100°C to 400°C for 30 minutes, respectively. No significant change in the Schottky barrier height of the Pd/SiC contact was found in the temperature range. The morphology from UHV-STM and AFM show that the unannealed Pd thin film had good uniformity across the SiC substrate, and the Pd has dispersed, and then partially aggregated into rounded shaped precipitates with increasing annealing temperatures. At 400°C, all Pd metal has reacted and formed to silicides. From XPS, Pd2Si was found on the surface after annealing, and almost all Pd has reacted to become Pd2Si after annealing at 400°C. No other silicide was found. The intensity of Pd on XPS decreases enormously at 400°C. This is explained if Pd has diffused into SiC. The Pd diffusion and the formation of Pd silicides do not significantly affect the Schottky barrier height. The SiO2 was found at the top of surface after annealing, and increased in amount with increasing annealing temperature. The SiO2 formation was accelerated by the presence of Pd. Pd may play a role in absorbing oxygen, and activating Si from SiC to form SiO2.Key Words: Pd thin film, SiC, X-ray photoelectron spectroscopy, scanning tunneling microscopy, and atomic force microscopy.
Growth of AlN Single Crystals
Authors: Slack Glen A. 
Published: April 2011

ABSTRACTAluminum nitride is a wurtzite structure III–V compound, although epitaxial layers of zincblende structure AIN have been made. AlN melts congruently at 2750°C with dissociation pressure of 9 atmospheres. Boules of AIN have been successfully grown by a sublimation-recondensation technique at 2300°C employing tungsten crucibles. Growth rates of 0.3 mm per hour were attained at 1 bar pressure of N2, and crystals up to 22 mm long have been grown. An analysis of the growth process shows that the 9.75eV dissociation energy of N2is the limiting factor in the growth rate. The growth rate is predicted to depend on the N2pressure, but no experiments in this area have yet been concluded. The most satisfactory crucible material found so far for growing AIN is single crystal tungsten.
Polarity of GaN
Authors: Liliental-Weber Z. , Benamara M. , Richter O. , Swider W. , Washburn J. , Grzegory I. , Porowski S. , Yang J. W. , Nakamura S. 
Published: April 2011

ABSTRACTConvergent beam electron diffraction (CBED) was applied to study polarity of GaN heterolayers grown by MOCVD on sapphire and SiC substrates and also mechano-chemically polished bulk GaN platelet crystals grown from Ga melt under hydrostatic pressure of N. Heterolayers of GaN grown on both types of substrates showed (0001) Ga polarity, e.g. Ga to N along c-axis. Mechano-chemical etching of bulk GaN platelet crystals leaves one surface smooth and the opposite surface rough with visible damage caused by mechanical polishing. CBED studies showed that the smooth surface has (0001) N polarity, confirming our earlier studies.
Growth of Iii-Nitrides by Rf-Assisted Molecular Beam Epitaxy
Authors: Piquette E. C. , Bridger P. M. , Bandić Z. Z. , Mcgill T. C. 
Published: April 2011

ABSTRACTGaN, AlGaN, AIN were grown on (0001) A1203 substrates by MBE using a RF plasma source and employing an AIN buffer layer. The films were characterized by RHEED, AFM, and x-ray diffraction, and electrical properties were measured by Hall technique. RHEED observations indicate that the polarity of the films is likely predominantly N-face, although Ga-face inversion domains can be observed in some films by AFM. Symmetric x-ray rocking curve widths as low as 39 arcseconds are achieved for some layers, while asymmetric peaks show widths of 240–300 arcsec. Control of Si doping over a wide range is demonstrated, which is important for design of high power device structures. Gold Schottky barrier m-v-n+diodes were fabricated which achieve high reverse electric fields before edge breakdown.
Epitaxial Films of Faas and Fan on Fianit Substrates
Authors: Buzynin A. N. , Osiko V. V. , Lomonova E. E. , Buzynin Yu. N. , Usikov A. S. 
Published: April 2011

ABSTRACTSubrmicron heteroepitaxial GaAs and GaN films were grown by both conventional MOCVD and «capillary epitaxy» technique on (001) and (111) fianit (YSZ)substrates. A preliminary annealing of the substrates under vakuum was made in order to stabilize the surface by removing of some amount of oxygen. Conditions of single crystalline growth of GaAs submicron films (50–500nm) have been determined. The films had mirror-like surface morphology and high structural perfection. The distribution of Zr, O, Y across the film-substrate interface was sharp and doping impurities contents were uniform over the film. PL spectra of undoped GaN films on YSZ were studied.
Search for New Semiconductors for High Temperature Applications:The BaPb1-x BixO3 System
Authors: Ponnambalam V. , Varadaraju U. V. 
Published: April 2011

ABSTRACTBaPbl-xBixO3 phases with 0.6⋚ x⋚ 1.0 were synthesized by high temperature solid state reaction. Powder X-ray diffraction measurements show that all compositions are in single phase. Linear variation of lattice parameter is observed in BaPb1-xBixO3 with change in x indicating the random distribution of Pb in Bi sites. The activation energies for conduction of phases with x=0.8−0.6 obtained from ρ −T plots are same suggesting that the band gap does not change for compositions with x-0.8−0.6. The low activation energy obtained for BaBiO3 can be attributed to the structure of the compound. S versus (1000/T) data of x=1.0−0.8 exhibit a two-slope behavior. The orthorhombic to cubic phase transition could be the possible reason for the high power factor values of BaBiO3.
Properties of GaN Homoepitaxial Layers Grown on GaN Epitaxial Wafers
Authors: Dmitriev V. , Nikolaev A. , Cherenkov A. , Tsvetkov D. , Stepanov S. , Kuznetsov N. , Nikitina I. , Kovarsky A. , Yagovkina M. , Davidov V. 
Published: April 2011

ABSTRACTThe lack of GaN substrates is a limiting factor for the development of III-V nitride devices.Recently we proposed to use GaN/SiC epitaxial wafers, consisting of thin GaN layer depositedby hydride vapor phase epitaxy (HVPE) on SiC wafer, as substrates for subsequent growth of IIIVnitrides and devices development. These wafers are attractive to be used as substrates for GaNdevice fabrication because the GaN-based device structures can be grown on these wafers byhomoepitaxy without any buffer layer. Due to high SiC thermoconductivity and cleavagepossibility, these wafers are especially attractive for high-power electronic and optoelectronicapplications. In this paper, we focus on crystal structure, optical and electrical properties of GaNhomoepitaxial layers and p-n structures grown by HVPE on GaN/SiC epitaxial wafers. Newtypes of III-V nitride epitaxial wafers are described, insulating GaN/SiC epitaxial wafers andAIN/SiC epitaxial wafers.
Tem and Hrem Study Of mGH-Temperature Aluminum Ion Implantation to 6H-SiC
Authors: Suvorova A. A. , Usov I. O. , Lebedev O. I. , Tendeloo G. Van , Suvorov A. V. 
Published: April 2011

ABSTRACT6H silicon carbide wafers were implanted with 40–50 keV aluminum ions to a dose of 1.5 × 1014 – 1.5 × 1016 cm−2 at high temperatures (1100°C–1700°C). The substrate temperature and the implantation dose were varied to investigate the influence of the implantation parameters on the formation of structural defects. Conventional transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) techniques were applied to study the defects. We found that for low dose implants {0001} interstitial dislocation loops are formed but for high dose implants aluminum precipitates associated with {0001} half-loops are formed.
Electrochemical Etching in the GaN-Based Technology
Authors: Sidorov V. G. , Drizhuk A. G. , Sidorov D. V. , Lundin W. V. , Pushnyi B. V. , Usikov A. S. 
Published: April 2011

ABSTRACTIn this study, both single undoped GaN epilayers and GaN-based device structures was treated by electrochemical etching in the dilute water solution of KOH or NaOH. Our investigations showed that in the undoped GaN epilayers grown by MOCVD the electrical and optical properties were nonuniform in depth. In this case, high defective and high conductive sublayer adjacent to the substrate was revealed by the electrochemical etching. This high conductive region was proved to condition the results of Hall effect measurements. Electrolyte etching of i-n GaN-based device structures grown by HVPE gave rise to significant increasing of the electroluminescence intensity. Influence of electrochemical etching on luminescence properties of the device structure is discussed.
Exafs Studies of Group III-Nitrides
Authors: Jeffs N J , Blant A V , Cheng T S , Foxon C T , Bailey C , Harrison P G , Mosselmans J F W , Dent A J 
Published: April 2011

ABSTRACTThe group III nitrides have important applications for blue/green LEDs, blue/UV laser diodes and for high-power high frequency FETs. In all such devices the alloys play an important role either in the active part of the structure or in the cladding regions. The properties of the group III-nitride alloys are not at present well understood and in particular there are indications that phase separation can occur. We have undertaken a comprehensive study of (InGa)N alloys using EXAFS in order to study such problems.We have demonstrated recently that REFLEXAFS technique can be used to give interatomic distances for (InGa)N alloys using the In edge to measure the bond lengths as a function of In content over the complete range from InN to GaN. We have now extended this study by using the Total Electron Yield (TEY) EXAFS technique to study the bond lengths by using both the Ga and In edges for (InGa)N alloys. The TEY data for the (InGa)N alloy samples gives more reliable data for the In-In and In-Ga separations than the earlier REFLEXAFS studies. Data obtained for the In-Ga separation from the Ga and In edges agree well within experimental error.The data obtained from this study suggest that the (InGa)N samples grown at low temperature do not exhibit evidence for phase separation.
Evidence for Oxygen DX Centers in AlGaN
Authors: Mccluskey M. D. , Johnson N. M. , Van De Walle C. G. , Bour D. P. , Kneissl M. , Walukiewicz W. 
Published: April 2011

ABSTRACTExperimental and theoretical evidence is presented for oxygen DX centers in AlxGa1−xN. As the aluminum content increases, Hall effect measurements reveal an increase in the electron activation energy, consistent with the emergence of a deep DX level from the conduction band. Persistent photoconductivity is observed in Al0 39Ga0. 61N:O at temperatures below 150 K after exposure to light, with an optical threshold energy of 1.3 eV, in excellent agreement with first-principles calculations. Unlike oxygen, silicon does not exhibit DX-like behavior, in agreement with previous theoretical predictions.
Flow Modulation Epitaxial Lateral Overgrowth Of Gallium Nitride On Masked 6H-Silicon Carbide And Sapphire Surfaces
Authors: Smart J. A. , Chumbes E. M. , Srivatsa L. N. , Lo Y. H. , Shealy J. R. 
Published: April 2011

ABSTRACTSelective Area Flow Modulation Epitaxial growth of GaN is carried out in a low pressure Organometallic Vapor Phase Epitaxy reactor. This process is known to enhance reactant surface migration lengths on patterned group III-arsenide and phosphide growth surfaces. With this process, high quality laterally overgrown GaN epitaxial materials result. Under the ammonia rich growth conditions used, enhanced migration (by flux modulation) across masked regions of the substrate has not been observed. The mask materials were silicon dioxide and silicon nitride, both deposited on GaN/AlGaN buffer structures on sapphire and SiC substrates. Window stripes were patterned parallel and perpendicular to the (1100) crystal directions to observe the orientation dependence of the lateral growth rate. Structures exhibited heights above the mask surface as large as 30 microns and atomically smooth surfaces. With a periodic array of stripe window openings in the mask, planarized laterally overgrown surfaces are achieved after roughly 4 microns of overgrowth. Chemical assisted ion beam etching with chlorine gas was used to delineate defects in the selectively grown layers. Additional evidence on the defect reduction is given by Atomic Force and Scanning Transmission Electron Microscopies.
Two-Step Growth of Gan Quantum Dots with Metalorganic Chemical Vapor Deposition
Authors: Chen P. , Shen B. , Zhang R. , Wang M. , Zhou Y. G. , Chen Z. Z. , Zhang L. , Zheng Y. D. 
Published: April 2011

ABSTRACTNanometer-scale GaN dots were successfully fabricated on sapphire using metalorganic chemical vapor deposition(MOCVD) by two-step method, including depositing around 500 IC and annealing at 1050 °C. The density of GaN dots is from 5×108cm−2 to 6×109 cm−2, and the size is around 40nm in diameter. The density and size of GaN dots are determined by an atomic force microscope(AFM), and they are controllable by changing temperature and duration of the growing. GaN dots only formed after annealing at high temperature, which is explained that the initial layer deposited around 500 °C is a high energy intermediate phase in which the large strain energy can not be relaxed because of the low temperature growing.
MOCVD Growth of Gan on Silicon and Related Surfaces
Authors: Han J. , Fleming J. G. , Follstaedt D. M. 
Published: April 2011

ABSTRACTThe growth of GaN on silicon (Si) substrates by MOCVD is reported in this paper. The use of a high-temperature AIN buffer layer appears to be necessary to establish an initial template morphology for the subsequent growth of GaN. Nucleation modes of GaN on SiO2, (100) Si, and (111) Si are compared; it is shown that the spatial coherency among the nuclei is most preserved when the growth occurred on the hexagonal Si (111) surface. To circumvent the problem associated with cracking due to a thermal expansion mismatch, we also investigate the possibility of using a silicon-on-insulator (SOI) scheme.
A Theoretical and Empirical Perspective of SiC Bulk Growth
Authors: Tsvetkov V. F. , Henshall D. N. , Brady M. F. , Glass R. C. , Carter C. H. 
Published: April 2011

ABSTRACTThe production of large diameter, high quality boules of SiC is essential to realize the full potential of this important semiconductor material. The objective of this paper is to provide a state-of-the-art analysis of the key directions for SiC bulk growth research, as well as presenting our most recent empirical results. Based on an analytical review of current knowledge, the following topics concerning growth of large 6H and 4H-SiC bulk crystals are discussed: 1) thermodynamics of the vapor phase including the efficiency of crystal growth, 2) kinetics of growth including mass transport in the boundary layer and 3) defect formation processes including thermoelastic stress. In addition, results of growth modeling are summarized and direction for further work suggested. Results on growth of semi-insulating and 50–75 mm diameter 4H-SiC wafers are presented. A discussion on micropipes, which are currently the most harmful defect in SiC wafers is presented. Although several mechanisms, or combinations of mechanisms, cause micropipes in SiC boules grown by the seeded sublimation method, we have reduced micropipe densities by orders of magnitude over the last few years. This continual reduction and the production of wafers with micropipe densities of less than 1 cm-2 (with >1 cm2 areas void of micropipes), indicate that micropipes will be reduced to a level that makes high current devices viable and that they may soon be totally eliminated.
Quantum Diffusion of H(D) In Semiconductors and Metals, and The Role of the Interaction with Impurities
Authors: Cannelli G. , Cantelli R. , Cordero F. , Giovine E. , Trequattrini F. 
Published: April 2011

ABSTRACTThe mobility of hydrogen and its isotopes in metals has been the object of investigation for several years, whereas the diffusion studies of H in doped semiconductors started more recently. Although the H diffusion coefficient in metals may be several orders of magnitudes higher than in semiconductors, the dynamics of H in metals and semiconductors presents many common features, like precipitation, trapping by heavier impurities and, as indicated by recent results, quantum tunneling at low temperature.In boron doped silicon, the relaxation rates τ−1(T) of H around B obtained from anelastic relaxation were joined with those from infrared absorption: the remarkably wide range obtained (11 decades) clearly shows a deviation of τ−1(T) from the classical dependence at low temperature. However, the results obtained and their analysis do not allow yet to draw conclusions on the mechanism governing the H(D) dynamics.Recently, the investigation of the dynamics of H(D) in GaAs doped with Zn revealed a dissipation peak at 20 K in the kHz range. This relaxation has the highest rate found for H in a semiconductor: more than 15 orders of magnitude higher than in all the other semiconductors measured so far. The analysis of the dissipation curves clearly indicates that the nature of the H reorientation is quantistic.In metals two regimes of the H mobility are observed: hopping with deviations from a classical Arrhenius motion, and a much faster tunneling within few close sites. In the latter regime the H dynamics does not consist of jumps but of transitions between the quantized energy levels of the tunnel systems. The types of interactions assisting the H transitions and the geometry of the tunnel systems are an open problem: although the two-level tunnel system (TLS) has been widely used to explain neutron diffusion, specific heat, and acoustic spectroscopy results in interstitial solutions (NbOxHy), recently this model has appeared not to be valid in substitutional solutions (NbZrxHy, NbTixHy) where the tunnel systems have a higher symmetry. The four-level systems seem to be more appropriate, although the corresponding model has not been developed as much as the TLS yet.
Diffusion Of Hydrogen In Zirconium Foil
Authors: Schur D. V. , Zaginaichenko S.Yu. , Pishuk V. K. , Adejev V. M. 
Published: April 2011

ABSTRACTThe authors of present research have used in experiments the atomic hydrogen and metallic
foil 25–30 jim thick.It have been supposed that these technical operations will permit to exclude the influence of
surface and diffusional processes on the rate of Me-H interaction.The series of experiments have been carried out and they confirm this assumption. It have been shown that hydrogenation reaction of zirconium foil in atomic hydrogen conform to the topochemical model of volume segregation of interaction product and the rate of its flow is independent of the surface processes and hydrogen diffusion in volume.
Hydrogen Diffusion in Chalcopyrite Solar Cell Materials
Authors: Weidinger A. , Krauser J. , Riedle Th. , Klenk R. , Lux-Steiner M. Ch. , Yakushev M. V. 
Published: April 2011

ABSTRACTHydrogen diffusion in CuInSe 2 single crystals and CuInS2 thin films was studied by measuring the spreading of implantation profiles upon annealing. Deep implantation with an ion energy of 10 keV and sub-surface implantation with 300 eV were applied. The diffusion coefficients in both materials were found to be in the order of 10-14 to 10-13 cm2/s in the temperature range between 400 and 520 K.These fairly low diffusivities are typical for a trap and release transport process rather than intrinsic diffusion of interstitial hydrogen. In the polycrystalline CuInS2 films, hydrogen leaves the sample through the grain boundaries.