bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Growth of Homo-Epitaxial Silicon at Low Temperatures Using Hot Wire Chemical Vapor Deposition
Authors: Thiesen J. , Jones K.M. , Matson R. , Reedy R. , Iwaniczko E. , Mahan H. , Crandall R. 
Published: April 2011

ABSTRACTWe report on the first known growth of high-quality epitaxial Si via the hot wire chemical vapor deposition (HWCVD) method. This method yields epitaxial Si at the comparatively low temperatures of 195° to 450°C, and relatively high growth rates of 3 to 20 Å/sec. Layers up to 4500-Å thick have been grown. These epitaxial layers have been characterized by transmission electron microscopy (TEM), indicating large regions of nearly perfect atomic registration. Electron channeling patterns (ECPs) generated on a scanning electron microscope (SEM) have been used to characterize, as well as optimize the growth process. Electron beam induced current (EBIC) characterization has also been performed, indicating defect densities as low as 8×104/cm2. Secondary ion beam mass spectrometry (SIMS) data shows that these layers have reasonable impurity levels within the constraints of our current deposition system. Both n and p-type layers were grown, and p/n diodes have been fabricated.
Epitaxial Growth of Zinc-Blende Ain by Plasma Source Molecular Beam Epitaxy
Authors: Thompson Margarita P. , Auner Gregory W. , Drews Andrew R. , Zheleva Tsvetanka S. , Jones Kenneth A. 
Published: April 2011

ABSTRACTEpitaxial zinc-blende AIN films as thick as 2000Å were deposited on Si (100) substrates by plasma source molecular beam epitaxy (PSMBE). The metastable zinc-blende form of AIN was observed to occur when pulse d.c. power was supplied to the PSMBE hollow cathode source. Reflection High Energy Electron Diffraction (RHEED) showed that the films possess a four fold symmetry. X-Ray Diffraction (XRD) revealed two strong peaks corresponding to the (200) and (400) reflections from the zinc-blende AIN. The lattice parameter of the films was calculated to be approximately 4.373Å. TEM, performed on one of the films, revealed that the AIN is cubic, single crystalline and epitaxial with respect to the Si (100) substrate.
Mesoscopic Models of Sintering of Metallic Clusters. A Study by Molecular Dynamics Simulations
Authors: Mazzone A.M. 
Published: April 2011

ABSTRACTMotivated by the ulbiquitous role of clusters in film growth, we study coalescence of metallic clusters (Ag.Cu.Pb). of size from 50 to 300, with an isothermal molecular dynamics simulation method using classical forces. A comparison is made between the melting behavior of the isolated clusters, onl one side. and classical theories of sintering, on the other side. An evident failure of the macroscopic models appears from this comparison and this casts considerable doubts on the adequacy of continuum models for low dimensional systems.
Smoothing Surfaces by an AC Field: An Application of the Ratchet Effect
Authors: Lee C.-S. , Derényi I. , Barabási A.-L. 
Published: April 2011

ABSTRACTWe demonstrate that for surfaces that have a nonzero Schwoebel barrier, the application of an ac field parallel to the surface will induce a net electromigration current. Most important, the direction of the net current will be always downhill; i.e. it will point in the step-down direction. The magnitude of this equilibrium current is calculated analytically, and compared with Monte Carlo simulations. A downhill current is known to smooth the surface, thus we suggest that the application of ac fields during annealing might aid the smoothing process and during growth it has the potential to slow or eliminate the Schwoebel barrier induced mound formation
Roughening of Au(111) Surfaces During Ion Beam Erosion: A Scanning Tunneling Microscope and X-Ray Diffraction Study
Authors: Judy A. , Murty M.V. Ramana , Butler E. , Pomeroy J. , Cooper B.H. , Woll A.R. , Brock J.D. , Kycia S. , Headrick R.L. 
Published: April 2011

ABSTRACTUsing Scanning Tunneling Microscopy(STM) and X-ray diffraction(XRD), we have studied the development of surface roughness on Au(111) during 500eV Ar+ ion irradiation at different angles. During normal incidence erosion the surface roughens and pattern formation occurs. The surface morphology is a mixture of mounds and pits superimposed onto a larger structure of channels and valleys. The characteristic spacing between features grows with a power law behavior t27, where t is the amount of time the sample was irradiated, in agreement with previous measurements[l]. At glancing angles, erosion proceeds smoothly, but not in layer-by-layer fashion. Finally, a combination of glancing angle and normal incidence erosion is used to create a rippled morphology
Annealing Effects of Schottky Contacts on the Characteristics of 4H-SiC Schottky Barrier Diodes
Authors: Kang S. C. , Kum B. H. , Do S. J. , Je J. H. , SHIN M. W. 
Published: April 2011

ABSTRACTThis paper reports on the relationship between the microstructure and the device performance of Pt/4H-SiC schottky barrier diodes ( SBDs ). The evolution of microstructure in the metal/SiC interfaces annealed at different temperatures was characterized using X-ray scattering techniques. The reverse characteristics of the devices were degraded with annealing temperatures. The maximum breakdown voltages of as-deposited devices and 850 °C annealed devices are 1300 V and 626 V, respectively. However, the forward characteristics of the devices were found out to improve with annealing temperatures. X-ray scattering analysis showed that Pt-silicides were formed by annealing performed at or higher than 650 °C. The formation of silicides was shown to increase the roughness of the Pt/SiC interface. It is believed that the forward characteristics of the SBDs be strongly dependent on the crystallity of silicides formed in the Pt/SiC interface during the annealing process.
Epitaxial Growth of SiC in a Vertical Multi-Wafer CVD System: Already Suited as Production Process?
Authors: Rupp Roland , Hecht Christian , Wiedenhofer Arno , Stephani Dietrich 
Published: April 2011

ABSTRACTResults about a new CVD system suited for epitaxial growth on six 2 inch SiC-wafers at a time are presented. Excellent gas flow stability is achieved for this new reactor type as shown by in- situ observations of the gas flow dynamics in the reactor chamber. These experimental results agree favorably with numerical process simulation results.The epitaxial layers grown in the multi-wafer system so far show a by an order of magnitude higher background impurity level (≤1015 cm−3) as reported previously for layers grown in single-wafer systems by the authors and other groups (≤ 1014 cm−3). On the other hand, the doping homogeneity achieved until today is very encouraging. The variation on a 2 inch wafer is less than ± 20% at about 1*1016 cm−3. The wafer to wafer variation of the average doping value both within a run and from run to run is within 15 %. The reproducibility and uniformity of the layer thickness is even better (total thickness variation ≤5% on a 2 inch wafer). The surface of the epitaxial layers is very smooth with a typical growth step height of 0.5 nm (4H, 8° off orientation). First measurements on Schottky diodes build on these layers show low leakage current values indicating low point defect density in the epitaxial layers.
Multi-Wafer VPE Growth of Highly Uniform SiC Epitaxial Layers
Authors: O'Loughlin M. J. , Nordby H. D. , Burk A. A. 
Published: April 2011

ABSTRACTA multi-wafer silicon carbide vapor phase epitaxy reactor is employed that features full planetary motion and is capable of high quality epitaxy on seven, two-inch diameter substrates. We are currently performing preproduction growths of static induction transistor (SIT) and metal semiconductor field effect transistor (MESFET) active layers. On a 2-inch diameter substrate, layer uniformity is typically ±5% (standard deviation/mean) for both dopant concentration and layer thickness (for 1 3/8-inch substrates, layer uniformity is around ±3%). For the seven wafers within a run, interwafer uniformity has been dramatically improved to approximately ±8% for dopant concentration and ±3% for layer thickness. Process control charts will be presented which exhibit that interrun (run-to-run) variation in both thickness and doping can be kept within ±10% of the desired values.
3C-SiC Buffer Layers Converted from Si at a Low Temperature
Authors: Liaw H. M. , Hong S. Q. , Fejes P. , Werho D. , Tompkins H. , Zollner S. , Wilson S. R. , Linthicum K. J. , Davis R. F. 
Published: April 2011

ABSTRACTWe have obtained single-crystal 3C-SiC films via conversion of the surface region of Si (111) and (100) wafers at 970 °C by reaction with C2H4 in an MBE reactor. The major defects in the films were clusters, voids, and misfit dislocations. Investigation by high resolution TEM images showed low lattice strains in the epitaxial layer due to the formation of 1 misfit dislocation for every 4 to 5 regular SiC planes that are bonded to Si at the interface. The clusters and voids often occurred in pairs. A model for forming the void-cluster pairs is suggested.
Time Resolved Photoluminescence of Cubic Mg Doped GaN
Authors: Seitz R. , Gaspar C. , Monteiro T. , Pereira E. , Schoettker B. , Frey T. , As D. J. , Schikora D. , Lischka K. 
Published: April 2011

ABSTRACTMg doped cubic GaN layers were studied by steady state and time resolved photoluminescence. The blue emission due to Mg doping can be decomposed in three bands. The decay curves and the spectral shift with time delays indicates donor-acceptor pair behaviour. This can be confirmed by excitation density dependent measurements. Furthermore temperature dependent analysis shows that the three emissions have one impurity in common. We propose that this is an acceptor level related to the Mg incorporation and the three deep donor levels are due to compensation effects.
Dielectric Function of AlN Grown on Si (111) by MBE
Authors: Zollner Stefan , Konkar Atul , Gregory R. B. , Wilson S. R. , Nikishin S. A. , Temkin H. 
Published: April 2011

ABSTRACTWe measured the ellipsometric response from 0.7–5.4 eV of c-axis oriented AlN on Si (111) grown by molecular beam epitaxy. We determine the film thicknesses and find that for our AlN the refractive index is about 5–10% lower than in bulk AlN single crystals. Most likely, this discrepancy is due to a low film density (compared to bulk AlN), based on measurements using Rutherford backscattering. The films were also characterized using atomic force microscopy and x-ray diffraction to study the growth morphology. We find that AlN can be grown on Si (111) without buffer layers resulting in truely two-dimensional growth, low surface roughness, and relatively narrow x-ray peak widths.
Mid Infrared Photoconductivity Spectra of Donor Impurities in Hexagonal Silicon Carbide
Authors: Linville R. J. , Brown G. J. , Mitchel W. C. , Saxler A. , Perrin R. 
Published: April 2011

ABSTRACTMid-infrared photoconductivity (PC) is a useful technique for identifying and investigating donor and acceptor centers in many semiconductors. This is especially true when the PC results are combined with other measurements such as Hall Effect and DLTS. We report on the first Fourier Transform Infrared (FTIR) photoconductivity spectra for n-type 6H and 4H-SiC. The samples studied had temperature dependent Hall activation energies around 45 meV and 85 meV in the 4H samples, and a single activation energy of 106 meV in the 6H. For the 4H samples, the PC spectra showed an increase in photoresponse between 40 and 47 meV, with another sharp increase at 120 meV. In the 6H-SiC, the photoresponse also had a rapid increase at 120 meV, and at 77 meV in one sample. The photoresponse spectra of the n-type 4H and 6H-SiC samples were distinctly different in the mid-infrared.
SiC Power Electronic Devices, MOSFETs and Rectifiers
Authors: Cooper J. A. , Ryu S-H. , LI Y. , Matin M. , Spitz J. , Morisesette D. T. , McGlothlin H. M. , Das M. K. , Melloch M. R. , Capano M. A. , Woodall J. M. 
Published: April 2011

ABSTRACTSiC power switching devices have demonstrated performance figures of merit far beyond the silicon theoretical limits, but much work remains before commercial production will be feasible. A significant fraction of the remaining work centers on materials science issues. This paper reviews the current status of unipolar power switching devices in SiC and identifies the major technological and material science barriers that need to be overcome.
Comparative Study of Emission from Highly Excited (In, Al) GaN Thin Films and Heterostructures
Authors: Little B. D. , Bidnyk S. , Schmidt T. J. , Lam J. B. , Kwon Y. H. , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P. , Yang W. 
Published: April 2011

ABSTRACTThe optical properties of (In, Al) GaN thin films and heterostructures have been compared under the conditions of strong nanosecond excitation. The stimulated emission (SE) threshold from AIGaN epilayers was found to increase with increasing Al content compared to GaN, in contrast to InGaN epilayers, where an order of magnitude decrease is observed. Optically pumped SE has been observed from AIGaN films with aluminum concentrations as high as 26%. Room temperature SE at wavelengths as low as 327 nm has been achieved. In contrast to the increase of SE threshold seen for AlGaN films, we found that AlGaN/GaN heterostructures which utilize carrier confinement and optical waveguiding drastically enhance the lasing characteristics. We demonstrate that AIGaN/GaN heterostructures are suitable for the development of deep ultraviolet laser diodes.
TEM Study of Mg-Doped Bulk GaN Crystals
Authors: Liliental-Weber Z. , Benamara M. , Ruvimov S. , Mazur J. H. , Washburn J. , Grzegory I. , Porowski S. 
Published: April 2011

ABSTRACTTransmission electron microscopy was applied to cross-sectioned samples to study surface morphology, sample polarity and defect distribution in bulk GaN samples doped with Mg. These crystals were grown from a Ga melt under high hydrostatic pressure of Nitrogen. It was shown that the types of defects and their distribution along the c-axis depends strongly on sample polarity. Based on this finding the growth rate along the c-axis for the two polar directions was compared and shown to be approximately ten times larger for Ga polarity than for N-polarity. In the part of the crystals with Ga polarity pyramidal defects with a base consisting of high energy stacking faults were found. The parts of the crystals grown with Npolarity were either defect free or contained regularly spaced stacking faults. Growth of these regularly spaced cubic monolayers is polarity dependent; this structure was formed only for the growth with N polarity and only for the crystals doped with Mg. Formation of this superstructure is similar to the polytypoid structure formed in AlN crystals rich in oxygen. It is also likely that oxygen can decorate the cubic monolayers and compensate Mg. This newly observed structure may shed light on the difficulties of p-doping in GaN:Mg.
Piezoelectric Coefficients of Aluminum Nitride and Gallium Nitride
Authors: Lueng C. M. , Chan H. L. W. , Fong W. K. , Surya C. , Choy C. L. 
Published: April 2011

ABSTRACTAluminum nitride (AlN) and gallium nitride (GaN) thin films have potential uses in high temperature, high frequency (e.g. microwave) acoustic devices. In this work, the piezoelectric coefficients of wurtzite AlN and GaN/AlN composite film grown on silicon substrates by molecular beam epitaxy were measured by a Mach-Zehnder type heterodyne interferometer. The effects of the substrate on the measured coefficients are discussed.
Epitaxial Growth of AlN on Si Substrates with Intermediate 3C-SiC as Buffer Layers
Authors: Hong S. Q. , Liaw H. M. , Linthicum K. , Davis R. F. , Fejes P. , Zollner S. , Kottke M. , Wilson S. R. 
Published: April 2011

ABSTRACTSingle crystalline AlN was successfully grown on a 3C-SiC coated Si (111) substrate by organometallic vapor phase epitaxy. The 3C-SiC film was obtained via the conversion of the Si near-surface region to SiC using gas-source molecular beam epitaxy. The quality of the AlN was mainly controlled by that of the SiC. The effects of Si pits and SiC hillocks formed during the conversion on subsequent AlN growth are discussed. Process optimization is suggested to improve the SiC buffer layer for subsequent AlN deposition.
The Influence of Spontaneous and Piezoelectric Polarization on Novel AlGaN/GaN/InGaN Device Structures
Authors: Foutz B. E. , Murphy M. J. , Ambacher O. , Tilak V. , Smart J. A. , Shealy J. R. , Schaff W. J. , Eastman L. F. 
Published: April 2011

ABSTRACTThe strong spontaneous polarization and piezoelectric effects in the wurtzite IIInitride semiconductors lead to new possibilities for device design. In typical heterojunction field effect transistors these effects are used to create large electron concentrations at the AlGaN/GaN interface. However, we examine several other possible device structures which include heterojunctions of AlGaN, GaN, and InGaN. For example, we find the strong electric fields present in these structures allow us to create quantum wells greater than 1 eV deep. Both Ga-faced and N-faced materials are explored. The two-dimensional electron gas concentrations in these structures are found using a self-consistent 1-D Schrödinger-Poisson solver modified to incorporate the effects of spontaneous and piezoelectric polarization. The boundary conditions at the heterojunction interfaces and at the surface and substrate are discussed in detail. Electron concentrations are compared with those obtained experimentally through capacitance-voltage and Hall effect measurements.
Effect of Varying Oxidation Parameters on the Generation of C-Dangling Bond Centers in Oxidized SiC
Authors: Macfarlane P. J. , Zvanut M. E. 
Published: April 2011

ABSTRACTSiC is perhaps the most appropriate material to replace Si in power-metal-oxidesemiconductor- field-effect-transistors (MOSFETs), because, unlike the other wide band-gap semiconductors, SiC can be thermally oxidized similarly to Si to form a SiO2 insulating layer. In our studies of oxidized SiC, we have used electron paramagnetic resonance (EPR) to identify Cdangling bonds generated by hydrogen release from C-H bonds. While hydrogen's effect on SiCbased MOSFETs is uncertain, studies of Si-based MOSFETs indicate that it is important to minimize hydrogen in MOS structures. To examine the role of hydrogen, we have studied the effects of SiC/SiO2 fabrication on the density of C-related centers, which are made EPR active by a dry heat-treatment. Here we examine the starting and ending procedures of our oxidation routine. The parameter that appears to have the greatest effect on center density is the ending step of our oxidation procedure. For example, samples that were removed from the furnace in flowing O2 produced the smallest concentration of centers after dry heat-treatment. We report on the details of these experiments and use our results to suggest an oxidation procedure that limits center production.
Activation Characteristics of Donor and Acceptor Implants in GaN
Authors: Cao X. A. , Pearton S. J. , Singh R. K. , Wilson R. G. , Sekhar J. A. , Zolper J. C. , Han J. , Rieger D. J. , Shul R. J. , Guo H. J. , Pennycook S. J. , Zavada J. M. 
Published: April 2011

ABSTRACTThe ionization levels of different donor and acceptor species implanted into GaN were measured by temperature-dependent Hall data after high temperature (1400 °C) annealing. The values obtained were 28 meV (Si), 48 meV (S), 50 meV (Te) for the donors, and 170 meV for Mg acceptor. P-type conductivity was not achieved with either Be or C implantation. Basically all of the implanted species show no distribution during activation annealing. For high implant doses (5×1015 cm−2) a high concentration of extended defects remains after 1100 °C anneals, but higher temperatures (1400 °C) produces a significant improvement in crystalline quality in the implanted region.
Transmutation Doping of III-Nitrides
Authors: Popovici Galina 
Published: April 2011

ABSTRACTTransmutation doping of (In, Ga, Al)N compounds by neutron irradiation is a promising and totally unexplored field to date. It is much more effective than that of Si due to large neutron capture cross section and abundance of In, Al and Ga isotopes participating in reaction. This should make the irradiation possible in low-flux reactors and result in smaller radiation damage. Annealing of the radiation damage seems feasible.
Bias-Temperature-Stress Induced Mobility Improvement in 4H-SiC MOSFETs
Authors: Chattyt K. , Chowt T. P. , Gutmannt R. J. , Arnoldi E. , Alok D. 
Published: April 2011

ABSTRACTIn this work, we report on an instability which affects the field effect mobility in 4HSiC MOSFETs. The devices (MOSFETs and capacitors) were subjected to a biastemperature stress (BTS) for 30 minutes at 150°C at stress voltages corresponding to oxide fields upto 1MV/cm. Following a positive BTS(i.e. gate voltage positive), the field effect mobility increased by upto two orders of magnitude from the original value; upon application of a negative BTS to the MOSFET, the device characteristics degraded to the unstressed state. The high mobility state could be recovered by a positive BTS and was reversible with repeated bias stressing. An explanation of this phenomenon is proposed based on the effect of interfacial ions on the dependence of both trapped charge and inversion charge densities on gate bias.
A Materials Investigation of Nickel Based Contacts to n-SiC Subjected to Operational Thermal Stresses Characteristic of High Power Switching
Authors: Cole M. W. , Hubbard C. W. , Fountzoulas C. G. , Demaree D. J. , Ren F. 
Published: April 2011

ABSTRACTThis study developed and performed Laboratory experiments which mimic the acute cyclic thermal loading characteristic of pulsed power device switching operation. Ni contacts to n-SiC were the device components selected for cyclic thermal testing. Modifications of the contact- SIC materials properties in response to cyclic thermal fatigue were quantitatively assessed via Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM), atomic force microscopy (AFM), surface profilometry, transmission electron microscopy (TEM), nanoindentation testing and current-voltage measurements. Decreases in nanohardness and elastic modulus were observed in response to thermal fatigue. No compositional modifications were observed at the metal-semiconductor interface. Our results demonstrated that the majority of the material changes were initiated after the first thermal pulse and that the effects of subsequent thermal cycling (up to 10 pulses) were negligible. The stability of the metalsemiconductor interface after exposure to repeated pulsed thermal cycling lends support for the utilization of Ni as a contact metallization for pulsed power switching applications.
Structure of Single-Crystal Gd2O3Films on GaAs(100)
Authors: Kortan A. R. , Hong M. , Kwo J. , Mannaerts J. P. , Kopylov N. 
Published: April 2011

ABSTRACTWe have studied the single-crystal Gd2O3films grown epitaxially on GaAs(100) substrate with single-crystal x-ray diffraction. The sesquioxide Gd2O3forms two hexagonal phases, one monoclinic and one cubic phase in bulk form. In our studies of different thickness films, we have found that the Gd2O3grows only in the cubic phase with a unique epitaxial orientation. The two-fold (110) planes of the Gd2O3are oriented parallel to the four-fold GaAs(100) surface, while alligning its [001] and [110] axes with the [011] and [011] axes of GaAs within the plane, respectively. The film chooses only one of the two such possible orientations, which can be explained by the local bonding configuration at the interface. We find evidence for an elastic strain in the films less than 50 A thick.