bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling the crystal growth of cubic silicon carbide by molecular dynamics simulations
Authors: Resta Nicoletta , Kohler Christopher , Trebin Hans-Rainer 
Published: April 2011

ABSTRACTThe crystal growth of a seed of cubic SiC into the amorphous material has been investigated by means of classical molecular dynamics simulations. The crystallization process was studied with a set of supercells containing up to 2000 atoms, initially consisting of a 12 Å thick layer of crystalline SiC and a 18 Å thick layer of amorphous SiC at high pressure. The dynamic evolution of crystallization was then followed for several nanoseconds with the simulated annealing technique performed at constant pressure and temperature. The atomic interactions were described by the Tersoff potential. We studied the dependence of the growth process on the crystallographic orientation of the crystalline/amorphous interface by considering three different crystal planes, namely the {100}, {110}, and {111} planes. Within the pressure-temperature range considered in our simulations, we observed the crystal growth only for the {110} and the {111} orientations, but not for the {100} ones. The atomistic details of the growth mechanism are described and discussed.
Porous SiC – Prospective Applications (Invited)
Authors: Mynbaeva Marina 
Published: April 2011

ABSTRACTPossible applications for porous SiC (PSC) are addressed and related innovative aspects discussed. The formation and properties of PSC itself are considered first, since they define the area where PSC can be used. Then epitaxial growth on PSC substrates is reviewed in detail, with the emphasis on the chemical vapor deposition (CVD) technique. Next, new applications featuring the in-diffusion of V and Si into PSC for obtaining semi-insulating material and autodoping of GaN epitaxial layers from PSC substrates are presented.
A New Process for the Fabrication of SiC Power Devices and Systems on SiCOI (Silicon Carbide On Insulator) Substrates
Authors: Templier François , Daval Nicolas , Cioccio Léa Di , Bourgeat Daniel , Letertre Fabrice , Planson Dominique , Chante Jean-Pierre , Billon Thierry 
Published: April 2011

ABSTRACTFeasibility of 4H-SiC epitaxy on SiCOI substrates has been demonstrated, with high quality of obtained layers. Power Schottky diodes were designed and fabricated on these new structures, and exhibited very interesting electrical performance, particularly in reverse mode, with Vbr ∼ 1000 V. This technology is very promising for the realization of monolithic SiC power systems.
Large-Area, Device Quality GaN on Si Using a Novel Transition Layer Scheme
Authors: Rajagopal Pradeep , Gehrke Thomas , Roberts John C. , Brown J. D. , Weeks T. Warren , Piner Edwin L. , Linthicum Kevin J. 
Published: April 2011

ABSTRACTThe emergence of III-nitride technology and fabrication of high quality GaN based devices is possible due to the advances in the heteroepitaxial growth of III-N thin-films on lattice-mismatched substrates. Typically, the substrate of choice is either SiC or sapphire. We have adopted 100mm Si as our substrate of choice; uniform substrates of high quality are inexpensive and plentiful due to decades of use in the microelectronics industry. Growth of device quality GaN on Si is challenged by the ∼17% lattice mismatch and an additional thermal expansion coefficient (TEC) mismatch of ∼56%. In order to accommodate this strain and TEC mismatch between Si and GaN, a novel transition layer was designed, grown and successfully optimized, ® obviating the need for either a PENDEO based overgrowth process or a SiC interlayer-based process. This growth technique (SIGANTIC®) does not require any wafer conditioning prior to growth and thus reduces the process complexity and maintains the cost effectiveness of the GaN on Si strategy. We will report on this manufacturable 100mm MOCVD heteroepitaxial process that consistently produces device quality AlGaN/GaN heterostructures with two dimensional electron gas (2DEG) mobilities typically around 1400 cm2/Vs at room temperature. Structural and electrical properties as determined by optical reflectance, atomic force microscopy, capacitance-voltage and van der Pauw Hall measurements, which are measured across the 100mm wafer, will be presented. Device results will be mentioned to show continuous wave (CW) RF operation at 2 GHz with competitive power output, gain and power added efficiency (PAE).
III-Nitride Growth on Lithium Niobate: A New Substrate Material for Polarity Engineering in III-Nitride Heteroepitaxy
Authors: Doolittle W. Alan , Namkoong Gon , Carver Alexander , Henderson Walter , Jundt Dieter , Brown April S. 
Published: April 2011

ABSTRACTHerein, we discuss the use of a novel new substrate for III-Nitride epitaxy, Lithium Niobate. It is shown that Lithium Niobate (LN) has a smaller lattice mismatch to III-Nitrides than sapphire and can be used to control the polarity of III-Nitride films grown by plasma assisted molecular beam epitaxy. Results from initial growth studies are reported including using various nitridation/buffer conditions along with structural and optical characterization. Comparisons of data obtained from GaN and AlN buffer layers are offered and details of the film adhesion dependence on buffer layer conditions is presented. Lateral polarization heterostructures grown on periodically poled LN are also demonstrated. While work is still required to establish the limits of the methods proposed herein, these initial studies offer the promise for mixing III-Nitride semiconductor materials with lithium niobate allowing wide bandgap semiconductors to utilize the acoustic, pyroelectric/ferroelectric, electro-optic, and nonlinear optical properties of this new substrate material as well as the ability to engineer various polarization structures for future devices.
Determination of AlGaN/GaN HFET Electric Fields using Electroreflectance
Authors: Kurtz S. R. , Allerman A. A. , Koleske D. D. , Baca A. G. , Briggs R. D. 
Published: April 2011

AbstractA contacted electroreflectance technique was used to characterize the electronic properties of AlGaN/GaN heterostructure field-effect transistors (HFETs). By studying variations in the electroreflectance with applied electric field, spectral features associated with the AlGaN barrier, the 2-dimensional electron gas at the interface, and bulk GaN were observed. Barrier-layer composition and electric field were determined from the AlGaN Franz-Keldysh oscillations. Comparing HFETs grown on SiC and sapphire substrates, the measured AlGaN polarization electric field (0.25±0.05 MV/cm) approached that predicted by a standard model (0.33 MV/cm) for the higher mobility HFET grown on SiC.
Optical and electrical properties of semi-insulating GaN:C grown by MBE
Authors: Armitage R. , Yang Qing , Feick H. , Tzeng S. Y. , Lim J. , Weber E. R. 
Published: April 2011

ABSTRACTSemi-insulating wurtzite GaN:C of high optical quality is obtained with CCl4or CS2 doping sources in plasma-assisted molecular-beam epitaxy in Ga-rich growth conditions. The highest resistivity (107Ω-cm) is found for [C] in the low 1018cm−3range. An increasing fraction of carbon appears to form electrically inactive pair defects for higher doping levels causing the concentration of uncompensated residual donors to be higher in films with [C] in the 1019cm−3range compared with [C] in the 1018cm−3range. Blue (2.9 eV) and yellow (2.2 eV) luminescence bands are associated with carbon-related defects, and additional support is provided for the association of the blue luminescence with the carbon-acceptor deactivating pair defect. Finally, the temperature dependence of the resistivity is described within the grain-boundary controlled transport model of Salzmanet al., Appl. Phys. Lett.76, 1431 (2000).
Excitons of the Structure in Zinc-Blende InxGa1-xN and their Properties
Authors: Alexandrov Dimiter 
Published: April 2011

ABSTRACTThe existence of excitons of the structure in zinc-blende InxGa1-xN is reported in this paper. The LCAO electron band structure of zinc-blende InxGa1-xN is calculated as function of both the electron wave vector and the electron radius-vector. The observed optical absorption edge in In-rich regions in InxGa1-xN is explained on the basis of this electron band structure. The excitons of the structure are found on the basis of the electron band structure of zinc-blende InxGa1-xN. The binding energy and the hydrogen like energy levels of these excitons are determined. It is found that these excitons are localized. The observed photoluminescence spectrum in In-rich regions of InxGa1-xN is explained by the excitons of the structure. It is found that destroying of these excitons occurs in their interactions with hetero-junction and that the electrons and the holes of exciton origin penetrate in the semiconductor of wider energy band gap. This phenomenon is used for explanation of the observed spectral blue shift of the electroluminescence in the quantum well structures on InxGa1-xN.
Optical Band Gap Measurements of InN Films in the Strong Degeneracy Limit
Authors: Haddad D. B. , Thakur J. S. , Naik V. M. , Auner G. W. , Naik R. , Wenger L. E. 
Published: April 2011

ABSTRACTThe optical properties of InN thin films (0.5 μm thick) grown on sapphire substrates by plasma source molecular beam epitaxy deposition have been measured in order to study the effect of electron degeneracy on the band gap measurement. X-ray diffraction measurements show that the films are wurtzite polycrystalline at a growth temperature of 325 °C, whereas a completely c-axis textured growth at a temperature of 475°C. The Raman bands A1 (LO) and E2 are rather broad indicating the presence of a large number of structural defects. Hall effect measurements show that both the films are n-type with carrier concentrations of (8.0 ± 1.6) × 1020 cm−3 and (3 ± 0.6) × 1020cm−3, respectively. The optical absorption data on these samples show n dependent band gap edge and a peak corresponding to plasmon due to strong electron degeneracy. The band gap absorption data were analyzed assuming a direct band gap and incorporating the Moss-Burstein shift effect. By taking into account the non-parabolic dispersion and the band-renormalization effects for the conduction band of InN, the calculated true band gap (0.7 eV) agrees with other recent measurements on high quality InN films.
Electricaland Optical Properties of InN/Si Heterostructure
Authors: Mizuo K. , Yamaguchi T. , Saito Y. , Araki T. , Nanishi Y. 
Published: April 2011

ABSTRACTSingle crystalline InN films were grown on Si substrates by radio-frequency plasma-excited molecular beam epitaxy. Electrical property of InN/Si heterojunction was investigated. We obtained rectifying characteristics in n-InN/p-Si heterostructure for the first time. Forward I-V characteristics were affected by both the buffer layer deposition and the nitridation process. Strong photoluminescence peaks for both single crystalline and polycrystalline InN films grown on the Si substrates were observed at around 0.8 eV, which were smaller than the previous reported PL emission peak of around 1.9 eV.
A Study of the Decomposition of GaN during Annealing over a Wide Range of Temperatures
Authors: Rana M. A. , Choi H. W. , Breese M. B. H. , Osipowicz T. , Chua S. J. , Watt F. 
Published: April 2011

ABSTRACTAnnealing experiments were carried out on gallium nitride layers, which were grown on sapphire through Metal Organic Chemical Vapor Deposition (MOCVD). Rutherford Backscattering Spectrometry (RBS) was performed on as-grown and annealed GaN samples using a 2 MeV proton beam to study the stoichiometric changes in the near-surface region (750 nm) with depth resolution better than 50 nm. No decomposition was measured for temperatures o up to 800 °C. Decomposition in the near-surface region increased rapidly with a further increase o of temperature, resulting in a near-amorphous surface-region for annealing at 1100 °C. The depth profiles of nitrogen and incorporated oxygen in the decomposed GaN are extracted from the nanoscale RBS data for different annealing temperatures. The surface roughness of the GaN layers observed by atomic force microscopy (AFM) is consistent with RBS decomposition measurements. We describe the range of annealing conditions under which negligible decomposition of GaN is observed, which is important in assessing optimal thermal processing conditions of GaN for both conventional and nanoscale optoelectronic devices.
Spectroscopic Characterization of Ion-Implanted GaN
Authors: Chen L. , Skromme B. J. 
Published: April 2011

ABSTRACTWe investigate implantation of high purity HVPE GaN with Mg, Be, C, Zn, Cd, Ca, N, O, P, As, Ne, and Ar. After annealing at 1300 °C, the material is characterized using low temperature photoluminescence (PL). The Mg acceptors exhibit much better optical activation than Be, C, Zn, Cd, or Ca acceptors implanted and annealed under the same conditions. Acceptor-bound exciton peaks and well-resolved donor-acceptor pair bands are observed for both Mg and Zn. A broad peak centered near 2.78 eV is obtained for Cd, confirming that it is deeper than Zn. Isoelectronic As or P exhibit sharp no-phonon bound exciton lines at 2.952 and 3.200 eV, respectively. Defect-related bands centered at 2.2 and 2.35 eV are studied. Both Be and C strongly enhance the yellow (2.2 eV) PL band, but no other impurities do so, including O.
Tunnel radiation in the luminescence spectra of GaN-based heterostructures
Authors: Yunovich A. E. , Kudryashov V. E. , Turkin A. N. , Leroux M. , Dalmasso S. 
Published: April 2011

ABSTRACTTunnel effects in luminescence spectra and electrical properties of LEDs based on InGaN/GaN-heterostructures made by different technological groups were studied. The tunnel radiation in a spectral region of 1.9 - 2.7 eV predominates at low currents (J<0.2 mA). The position of the tunnel luminescence maximum orħħωmaxis approximately equal to the voltage U, orħħωmax= eU. The low energy spectral band is described by the theory of tunnel radiative recombination. Tunnel recombination mechanisms in GaN-based heterostructures are caused by high electric fields in the active InGaN/GaN - MQW layers. The energy diagram of the structures is analyzed. The probability of tunnel radiation is higher due to piezoelectric fields in InGaN quantum wells. The tunnel radiation spectral band was not observed in the more effective LEDs with modulated doped MQWs. The spectra of GaN-based LEDs are compared with tunnel radiation spectra of GaAs-, InP- and GaSb- based LEDs. The equation: orħħωmax= eU describes experimental data in various semiconductors in the range 0.5–2.7 eV.
Properties of Delta Doped Al0.25Ga0.75N and GaN Epitaxial Layers
Authors: Flynn Jeffrey S. , Wallace Leah G. , Dion Joe A. , Hutchins Edward L. , Antunes Helder , Brandes George R. 
Published: April 2011

ABSTRACTDelta doping (paused growth doping) was investigated as an alternative to uniformly distributing the dopant in the nitride semiconductor layer. In this work, delta doped layers were produced in MOVPE-grown AlGaN and GaN layers at a susceptor temperature of 1220°C by turning off the group III precursors (TMG and TMA) and introducing into the reactor a silicon precursor Si2H6 (disilane) for a fixed period (pause time) before growth was restarted. The compositional and electrical properties as a function of aluminum content and dopant flux were investigated for nitride layers on 2 inch c-plane sapphire substrates. Secondary ion mass spectroscopy (SIMS) measurements revealed a sharp silicon peak with a FWHM of 5.7 ± 0.6 nm for an Al0.25Ga0.75N sample and 10.0 ± 0.6 nm for a GaN sample with sheet charges of 7.9×1012 cm−2 and 9.9×1012 cm−2,respectively. Room temperature Hall mobility as high as 265 cm2 V−1s−1 for a sheet charge 7.9×1012 cm−2 was demonstrated for delta doped Al0.25Ga0.75N layers, but the mobility enhancement saturated and then decreased with increasing sheet charge. Room temperature sheet charge increased with increasing dopant flux for delta-doped AlGaN and GaN layers. Sheet charge density as high as 2.2×1013 cm−2 and 1.3×1013 cm−2 was measured at room temperature for Al0.25Ga0.75N and GaN delta doped layers, respectively. Under identical doping conditions, the Hall sheet charge of the delta doped Al0.25Ga0.75N layer was approximately half as large as GaN layers. The impurity and electrical characteristics of the delta doped layers are further discussed.
Comparative morphology of AuTiAlTi, AuPdAlTi and AuAlTi ohmic contacts to AlGaN/GaN
Authors: Fay M W , Moldovan G , Harrison I , Balmer R. S. , Hilton K P , Hughes B T , Uren M J , Martin T , Brown P D 
Published: April 2011

ABSTRACTAuTiAlTi, AuPdAlTi and AuAlTi ohmic contacts to AlGaN/GaN layers rapid thermal annealed at temperatures up to 950°C have been characterised using conventional and chemical transmission electron microscopy techniques. The relationship between the as-deposited metallic structure, annealing temperature, post-anneal interfacial microstructure and contact resistance is examined.The presence of a TiN interfacial layer is found to correlate with the onset of ohmic behaviour. Ti and Pd barrier layers are found to be ineffective at stopping the diffusion of Au to the interface. Au is implicated in the development of the inclusions, which are associated with threading dislocations. Once activated, the presence of the inclusions has little influence on the ohmic behaviour of the sample.
Activation of Mg acceptors in GaN:Mg monitored by electron paramagnetic resonance spectroscopy.
Authors: Matlock D. , Zvanut M. E. , DiMaio Jeffrey R. , Davis R. F. , Henry R. L. , Koleske Daniel , Wickenden Alma 
Published: April 2011

ABSTRACTHydrogen removal from Mg-doped GaN is necessary to activate p-type conductivity, but the exact chemical process is not yet clear. We have investigated this issue by monitoring the intensity of an electron paramagnetic resonance (EPR) signal attributed to Mg through a series of isochronal and isothermal anneals between 600 and 1000 °C. Measurements made on GaN:Mg epitaxial layers deposited on SiC and annealed between 700 and 850 °C indicate that the Mg-related EPR signal increases with temperature as expected for depassivation of a Mg complex by removal of hydrogen. However, data obtained outside this temperature range suggest that additional processes may occur. For example, as-deposited films contain a signal resembling the Mg acceptor that is quenched by a 650 °C N2 anneal. Also, for all samples, N2 annealing at T>850 °C irreversibly decreases the signal thought to be due to Mg. Although the presence of the signal in the as-grown films is not fully understood, the effects observed at T>850 °C may be attributed to preferential N-desorption from Mg-N-H complexes.
Microstructural Defects in Mg-doped AlGaN Layers Grown by Metalorganic Chemical Vapor Deposition
Authors: Cho Hyung Koun , Yang Gye Mo 
Published: April 2011

ABSTRACTWe have investigated the formation of inversion domain boundaries in Al0.13Ga0.87N layers grown on sapphire substrates by metalorganic chemical vapor deposition using transmission electron microscopy. By increasing the Mg source flow rate, the reduction of dislocation density occurred up to the Mg source flow rate of 0.103 μmol/min. While the vertical type inversion domain boundaries (IDBs) were observed in the Al0.13Ga0.87N layers grown with the low Mg source flow rate, the IDBs in the Al0.13Ga0.87N layers grown with the high Mg source flow rate have horizontally multifaceted shapes. The change of polarity by the IDBs of horizontal type also resulted in the 180°rotation of pyramidal defects within the same AlGaN layer. Therefore, We found that the Mg source flow rate affects significantly the dislocation density, the type of IDBs, and the shape of pyramidal defects in AlGaN layers.
The First Wafer-fused AlGaAs-GaAs-GaN Heterojunction Bipolar Transistor
Authors: Estrada Sarah , Stonas Andreas , Huntington Andrew , Xing Huili , Coldren Larry , DenBaars Steven , Mishra Umesh , Hu Evelyn 
Published: April 2011

ABSTRACTWe describe the use of wafer fusion to form a heterojunction bipolar transistor (HBT), with an AlGaAs-GaAs emitter-base fused to a GaN collector. In this way, we hope to make use of both the high breakdown voltage of the GaN and the high mobility of the technologically more mature GaAs-based materials. This paper reports the first dc device characteristics of a wafer-fused transistor, and demonstrates the potential of wafer fusion for forming electronically active, lattice-mismatched heterojunctions. Devices utilized a thick base (0.15um) and exhibited limited common-emitter current gain (0.2–0.5) at an output current density of ∼100A/cm2. Devices were operated to VCE greater than 20V, with a low VCE offset (1V). Improvements in both device structure and wafer fusion conditions should provide further improvements in HBT performance. The HBT was wafer-fused at 750°C for one hour. Current-voltage characteristics of wafer-fused p-GaAs/n-GaN diodes suggest that the fusion temperature could be reduced to 500°C. Such a reduction in process temperature should mitigate detrimental diffusion effects in future HBTs.
The Effect of Growth Stoichiometry on the GaN Dislocation Core Structure
Authors: Baines Marcus Q. , Cherns David , Hsu Julia W. P. , Manfra Michael J. 
Published: April 2011

ABSTRACTPlan-view transmission electron microscopy was used to study the core structures of different dislocations in (0001) GaN layers grown under Ga-rich and Ga-lean conditions by molecular beam epitaxy. In Ga-rich samples at least one third of mixed type dislocations were open-core, and edge dislocations were observed to be closed-core. In contrast, under Ga-lean conditions, all dislocations were observed to be closed-core, and many were associated with pits at the sample surface. High resolution studies of the open core dislocations revealed that many were decorated with a disordered deposit, the origin of which is discussed.
Study on Cubic GaN Growth on (001) Rutile TiO2 Substrates by ECR-MBE
Authors: Araki T. , Mamiya H. , Kitamura K. , Nanishi Y. 
Published: April 2011

ABSTRACTGaN layers were grown on a (001) rutile TiO2 substrate by electron cyclotron resonance plasma-excited molecular beam epitaxy. For the first time, c-GaN with a preferential growth orientation was obtained. Based on the results from electron diffraction and X-ray diffraction analysis, we found that c-GaN with the growth direction of [110] was grown on the TiO2 substrate. The formation of c-GaN was also confirmed by cathodoluminescence, in which a luminescence peak was observed at 3.24eV.
Aluminum Nitride Crystal Growth by Halide Vapor Transport Epitaxy
Authors: Tassev V. L. , Bliss D. F. , Weyburne D. , Bailey J. S. , Wang S.-Q. 
Published: April 2011

AbstractHalide vapor transport epitaxy (HVTE) is demonstrated for growth of AlN layers with thickness up to 50 μm at deposition rates up to 60 μm/h. The HVTE process uses an aluminum chloride amine adduct as the aluminum source of both aluminum and nitrogen. This new technique eliminates the main difficulties of the conventional hydride VPE growth, where aluminum oxidation and the strong reactivity of aluminum chloride with fused silica create the potential for oxygen contamination. This study shows the effect of temperature, gas flow velocities, and reactor pressure on the growth rate and layer quality. It is found that the growth rate and the layer quality strongly depend on the gas ratio. The species of carrier gas, the flow rates and partial pressures can be used as tools to optimize growth rate and to avoid any etching effects resulting from reverse chemical reactions. The crystalline layer quality as determined by x-ray rocking curve measurement shows FWHM of 300–900 and 500–1300 arc-sec for (002) and (102) planes, respectively.PACS: 81.05.Ea; 81.15.Kk; 68.55.Jk.