bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoluminescence Characteristics of GaN Layers Grown on Soi Substrates and Relation to Material Properties
Authors: Philippe A. , Bru-Chevallier C. , Guillot G. , Cao J. , Pavlidis D. , Eisenbach A. 
Published: April 2011

AbstractGaN layers were grown by MOCVD on Silicon on Insulator (SOI) substrates in an effort to improve the material quality compared to more traditionally employed sapphire substrates. Their photoluminescence properties are reported and found to exhibit an intense and relatively large PL band around 3.47eV at low temperature (7K). This is about 10meV lower than the PL energy of samples grown on sapphire substrates and suggests the presence of lower strain in the layers which is expected for compliant growth on SOI substrates. The shape of the main PL peak appears to indicate that Silicon diffusion takes place from the substrate during growth. The behavior of the PL spectra is studied as a function of temperature. The GaN films show good overall electrical properties with Hall mobilities at room temperature in the range of 150 to 300cm2/Vs and background carrier concentration from 2.9 to 3.9×1019cm−3.The promising optical and electronic features of these layers could be of great interest for the development of high quality optical and electronic devices.
Energy Dependent Growth Rates of AIN using Pulsed Supersonic Jets
Authors: Ballarotto V. W. , Kordesch M. E. 
Published: April 2011

AbstractAIN films were grown on Si< 100 >, using unskimmed pulsed supersonic jets of ammonia and trimethylaluminum (TMA). By seeding the ammonia gas in hydrogen or helium, several different energies of the N precursor were used to examine the effect of N kinetic energy on the growth rate of AIN. The energy of the Al precursor, TMA, was 130 meV in all cases. The highest growth rate (0.115 μm/hr) was achieved with the high energy ammonia jet. The role of number density on film growth is discussed.
Design and Characterization of a UHV Arcjet Nitrogen Source
Authors: Bicknell-Tassius R. N. , Deelman P. W. , Grunthaner P. J. , Grunthaner F. J. , Bryson C. E. , Snyder E. , Giuliani J. L. , AprUzes J. P. , Kepple P. 
Published: April 2011

AbstractA UHV-compatible nitrogen arcjet suitable for the growth of III-nitrides by molecular beam epitaxy is described and characterized. The arcjet operates at powers between 10W and 300W (the highest power used for these studies); typical nitrogen flows range between 5sccm and 100sccm. Optical emission spectra show the presence of activated atomic (N*) and molecular (N2*) nitrogen. A collisional radiative equilibrium model has been employed to provide insight into the excitation state of the active nitrogen. These results indicate that the arcjet is capable of supplying atomic nitrogen fluxes consistent with growth rates on the order of several monolayers per second. Langmuir probe measurements conducted near the position of the sample holder in the MBE chamber show the charged particle flux density is very low. The arcjet operates over a large powerpressure parameter space, and properties of the arc can be systematically “tuned” to provide a source suitable for selected-energy-epitaxy.
Deposition Sequences for Atomic Layer Growth of AlN Thin Films on Si(100) Using Dimethylethylamine Alane and Ammonia
Authors: Kuo Jason S. , Rogers J. W. 
Published: April 2011

AbstractRecent studies have demonstrated that dimethylethylamine alane (DMEAA) is a viable group III precursor for depositing high quality aluminum nitride thin films during atomic layer growth with ammonia as the group V source. However, a practical consideration that is questioned but seldom investigated is whether one should initiate the growth with the group III or the group V source. Clearly DMEAA interacts differently with silicon than does ammonia; hence, reversing the deposition sequence will lead to different interfacial composition. Earlier studies involving TMAA and ammonia indicate that direct interaction of group III precursor with the surface may lead to higher carbon contamination. In this work, adsorption of DMEAA on Si(100) and on ammonia-covered Si(100) are characterized with Temperature-Programmed Desorption (TPD), Secondary-Ion Mass Spectrometry (SIMS), and Temperature-Programmed Secondary-Ion Mass Spectrometry (TPSIMS). Preliminary results indicate that DMEAA adsorbs molecularly on both Si(100) and ammonia-covered Si(100), but to a much smaller coverage on the latter surface. Results from reversing the adsorption sequence, i.e. ammonia first then DMEAA, will be compared as a possibility for interfacial quality control.
Structure and Properties Of III-N Semiconductor Thin Films Grown at Low Temperatures by N-Radical-Assisted Pulsed Laser Deposition
Authors: Fernandez F. E. , Pumarol M. , Martinez A. , Pantojas V. , Garcia M. 
Published: April 2011

AbstractThin films of nitride semiconductors are usually grown by means requiring high substrate temperatures. Deposition techniques providing higher kinetic energies of incident species offer an alternative route which might allow growth of good quality films at lower temperatures. Pulsed Laser Deposition can provide higher kinetic energies than most thin film growth methods. However, III-nitride thin films grown by PLD are often nitrogen deficient. We have been able to obtain good stoichiometry for aluminum nitride films even at room temperature by providing atomic nitrogen at low (thermal) energies during growth. Very good orientation can be obtained on (001) sapphire substrates at moderate temperatures (∼ 500 C). AIN films were grown from either AIN or Al targets. We also report on preliminary work by the same method with GaN film growth from a liquid Ga target.
Role of Dopants and Impurities on Pinhole Formation; Defects Formed At Ingan/Gan And AlGaN/GaN Quantum Wells
Authors: Liliental-Weber Z. , Ruvimov S. , Swider W. , Kim Y. , Washburn J. , Nakamura S. , Kern R. S. , Chen Y. , Yang J. W. 
Published: April 2011

AbstractTransmission electron microscopy has been applied to study defects in epitaxial doped and undoped GaN layers grown by MOCVD on sapphire and SiC substrates. Samples with InGaN/GaN and AlGaN/InGaN heterostructures have also been investigated. The results of this study show that incorporation of “foreign” atoms increases formation of nano-tubes and pinholes. The highest density of these defects was formed close to the interface with sapphire where oxygen outdiffusion might be expected, or in the subsurface area in the samples where oxygen was added deliberately. Addition of In (or Al) at QW's also leads to pinhole formation. Increased In fraction or a larger number of QW's results in a greater density of pinholes and more surface roughness. Many of the “hollow” nanotube defects are terminated during growth.
The Effect Of Si And Mg Doping In The Microstructure Of Epitaxially Grown Gan
Authors: Katsikini M. , Paloura E. C. , Fieber-Erdmann M. , Holub-Krappe E. , Moustakas T. D. 
Published: April 2011

AbstractThe effect of p- and n-type doping (using Mg and Si, respectively) in the microstructure of GaN, grown epitaxially on (0001)Al2O3 and (111)Si, is studied with X-ray absorption measurements at the N-K-edge. A distortion in the local microstructure around the N atom is detected in the undoped and the Mg doped samples. The N atom is 4-fold coordinated with n Ga atoms in the expected distance and 4-n atoms at a distance longer by 0.28Å, where 2.9 < n < 3.3. Such a distortion, which is attributed to the inward relaxation and the strong interaction between the Ga atoms surrounding the nitrogen vacancies (VN), does not exist in the Si doped sample (carrier concentration=1.57×1018cm−3) where the formation of VN is suppressed due to the n-type doping. However, in GaN:Si the N atom is undercoordinated with 3.3 nearest neighbors instead of 4. This undercoordination indicates the presence of VGa and/or NGa antisite defects. Finally, from the nearest neigbohr distances the lattice parameters were calculated and it is found that although the a and c vary by about 1.5%, the ratio of the lattice constants, c/a, remains constant and equal to 1.63.
Microstructure of InGaN Quantum Wells
Authors: Ponce F. A. , Cherns D. , Goetz W. , Kern R. S. 
Published: April 2011

AbstractThe microstructure of lnxGal-xN quantum wells with intermediate indium concentrations (x = 0.28 and 0.52) has been studied using transmission electron microscopy. High-resolution lattice images and dark-field images taken under high tilt conditions indicate that the quantum wells are inhomogeneous in character. Most of the area of the quantum wells is pseudomorphic with the GaN adjacent layer. However, misfit dislocations are sometimes observed, although with an inhomogeneous distribution. Strained cluster regions are observed in the high-indium concentration quantum wells, with dimensions ranging fi'om 3 to 10 nm in diameter. Evidence is presented suggesting the extent of clustering depends on the exact orientation of the growth surface which is related to the columnar nature of the GaN/sapphire epitaxy.
Localized Donors in Gan: Spectroscopy Using Large Pressures
Authors: Wetzel C. , Amano H. , Akasaki I. , Suski T. , Ager J. W. , Weber E. R. , Haller E. E. , Meyer B. K. 
Published: April 2011

AbstractProperties of GaN and its alloys are strongly controlled by impurities and strain. Using large hydrostatic and biaxial pressure we identify the role of donor dopants and stress induced fields. The doping of Si and 0 as relevant representatives of group-IV and group-VI impurities are studied in Raman spectroscopy. For pressures above 20 GPa we find that oxygen induces a strongly localized gap state while Si continues to behave as a hydrogenic donor. Such a DX-like behavior of 0 indicates and corresponds to doping limitations in AIGaN alloys. The site specific (ON, SiGa) formation of a gap-state is attributed to bond strengths of the respective neighbors. In photoreflection of pseudomorphic GaInN we observe pronounced Franz-Keldysh oscillations corresponding to piezoelectric fields of 0.6 MV/cm. An observed redshift of the luminescence is found to originate in electric field induced tailstates. A reduced but similar effect is expected for GaN possibly explaining observations of persistent photoconductivity in a wide range of materials.
Electron Mobility of N-Type GaN Films
Authors: Ng H. M. , Doppalapudi D. , Singh R. , Moustakas T. D. 
Published: April 2011

AbstractThe lateral transport in GaN films produced by electron cyclotron resonance plasma-assisted molecular beam epitaxy (ECR-MBE) doped n-type with Si to the levels of 1015 − 1020 cm−3 was investigated. The room temperature electron mobility vs carrier concentration was found to follow a family of bell-shaped curves consistent with a recently proposed model in which dislocations with an edge component introduce acceptor centers along the dislocation lines which capture electrons from the conduction band in n-type GaN. The mechanism of scattering was investigated by studying the temperature dependence of the carrier concentration and electron mobility. We found that for the samples with high carrier concentration (> 1018cm−3), the scattering at low temperatures is dominated by impurities while for samples with low carrier concentration (<1017 cm−3), the scattering is dominated by charged dislocations.
Location Of Residual Donors In GaN Epitaxial Layers
Authors: Glaser E. R. , Kennedy T. A. , Wickenden A. E. , Koleske D. D. , Perry W. G. , Davis R. F. 
Published: April 2011

AbstractOptically-detected electron-nuclear double resonance (ODENDOR) studies at 24 GHz on high-resistivity GaN films grown on Al2O3 have been combined with x-ray diffraction measurements to obtain information on the location of the residual shallow donors. Strong ODENDOR assigned to 69,71Ga lattice nuclei was detected on the g=1.951 effective-mass donor resonance found on the 2.2 eV emission bands. The x-ray studies reveal that the layers are under biaxial compression with high values of strain (∼ 2–3 × 10−3). The quadrupole splittings for 69Ga are smaller than those reported for strain-free samples by 15–25 %. The dominant sources of the local electric field gradient (EFG) responsible for the splittings are attributed to the wurtzite crystal structure and the strain fields that arise from the lattice constant mismatch and the difference in thermal expansion coefficients. An EFG/strain relationship of 3 × 1022 Vm−2 per unit strain at the 69,71Ga nuclei is deduced. The ODENDOR can be described with asymmetry parameter η=0. This provides evidence that the donors are in the crystallites rather than near grain boundaries.
Electron-Phonon Scattering in GaN/AlN and GaAs/AlAs Quantum Wells
Authors: Forbang T. F. , McIntyre C. R. 
Published: April 2011

AbstractWe have studied the effects on the phonon spectrum and on the electron-longitudinal optical phonon scattering in GaN/AlN and GaAs/AlAs quantum wells. Phonon modes and potentials have been calculated for both systems. Results for emission due to electroninterface phonons interactions are presented. We will discuss the implications for relaxation times and electron mobility due to modified LO-phonon scattering in both systems.
Photoluminescence Quenching Spectroscopy of Trapmediated Er3+ Excitation Mechanisms in Er-Implanted GaN
Authors: Rhee S. J. , Kim S. , Li X. , Coleman J. J. , Bishop S. G. 
Published: April 2011

AbstractTwo-source optical quenching spectroscopy demonstrates that the four site-selective Er3+ photoluminescence (PL) spectra observed in Er-implanted GaN contribute to the above-gap excited Er3+ PL spectrum, with relative efficiencies determined by the carrier capture cross sections and concentrations of the defects or traps which mediate the excitation of each Er site. The above-gap pumped PL spectrum is dominated by two of the trap-mediated Er3+ PL spectra, while the highest concentration Er site, which is efficiently pumped only by direct 4f absorption, contributes only weakly. These experiments indicate that the same defects and impurities are involved in the trapmediated processes responsible for both the above- and the below-gap excitations of the Er3+ PL.
Probing The Indium Mole Fraction In An Ingan Epilayer By Depth Resolved Cathodoluminescence
Authors: Trager-Cowan C. , Middleton P. G. , Mohammed A. , O'Donnell K. P. , Stricht W. Van der , Moerman I. , Demeester P. 
Published: April 2011

AbstractCathodoluminescence spectroscopy is used to depth profile the indium mole fraction of a 0.4 μm InGaN epilayer grown by metalorganic chemical vapour deposition, and to probe an underlying 1.0 μm GaN epilayer and the sapphire substrate beneath. Spectral information is obtained by using a variable energy electron beam as the excitation source. Calibration of beam penetration is achieved using Monte Carlo simulations of electron beam trajectories. The indium mole fraction is found to decrease from a mean value of 27% at the surface of the InGaN layer to ≈ 24% at its interface with the GaN layer.
The Effect Of The Nucleation Layer On The Low Temperature Growth Of Gan Using A Remote Plasma Enhanced – Ultrahigh Vacuum Chemical Vapor Deposition (RPE-UHVCVD)
Authors: Kim Kyoung-Kook , Kim Dong-Jun , Paek Jong-Sik , Jo Je-Hee , Kim Hyo-Gun , Seong Tae-Yeon , Park Seong-Ju 
Published: April 2011

AbstractThis study investigated the low temperature growth of GaN on a nucleation layer in a remote plasma enhanced-ultrahigh vacuum chemical vapor deposition (RPE-UHVCVD) system which is equipped with an rf plasma cell for a nitrogen source. It was found that the growth temperature and the film thickness of the nucleation layer and the nitrogen flow rate for GaN growth play important roles in the improvement of crystallinity of the GaN layer. The nitridation of sapphire was also found to enhance the formation of facet shaped nuclei on the nucleation layer. As the temperature of the nucleation layer increased, islands with hexagonal and other facet shapes were formed on the grown GaN surface. This facet formation was related with the surface morphology and crystallinity of GaN. The best crystallinity was measured in a GaN layer with hexagonal facets on the surface and such GaN layers could be grown on a nucleation layer grown at 375 °C. Nitridation of sapphire and the growth temperature of the nucleation layer were also found to change the island shapes which enhances the formation of columnar structures in the GaN layer, resulting in the growth of a high crystalline GaN layer at low temperature.
Nitridation Of Sapphire Substrate Using Remote Plasma Enhanced-Ultrahigh Vacuum Chemical Vapor Deposition At Low Temperature
Authors: Paek Jong-Sik , Kim Kyoung-Kook , Lee Ji-Myon , Kim Dong-Jun , Kim Hyo-Gun , Park Seong-Ju 
Published: April 2011

AbstractA remote plasma enhanced-ultrahigh vacuum chemical vapor deposition (RPE-UHVCVD) system equipped with a radio frequency-inductively coupled plasma (RF-ICP) which produces the reactive nitrogen species was employed to study the nitridation process at low temperature. The sapphire surface nitridated under various conditions was investigated with x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The nitridation process seems to be mostly affected by the RF power even at low temperature since the intensity of the N1s, peak was not dependent on the substrate temperature but on the RF power. The AFM images showed that the protrusion density on the sapphire surface decreased rapidly when the nitridation temperature was decreased. This result suggests that the formation of the protrusions is closely related to the process temperature, indicating that the formation of such protrusions is caused by the change of an elastic strain energy due to the thermal stress. It was possible to nitridate the sapphire surface without protrusion at a very low temperature. The crystallinity of GaN grown at 450 °C was found to be much improved when the sapphire substrate was nitridated at low temperature prior to the GaN layer growth.
Constant Pressure First-Principles Molecular Dynamics Study On Bn, Ain, And Gan
Authors: Shimada K. , Sota T. , Suzuki K. 
Published: April 2011

AbstractWe have performed first-principles total energy calculations to obtain various physical parameters for both zinc-blende and wurtzite BN, AIN, and GaN. The calculation has been done within the local density approximation to the density functional theory together with plane wave expansion and norm-conserving pseudopotentials. Constant-pressure first-principles molecular dynamics method has been used to relax the unit cell shape and the atomic geometry. In calculating the elastic constants and the deformation potentials, the internal displacement of atoms in the strained crystal is simulated by moving atoms with first-principles molecular dynamics method. The optical phonon frequencies at the Brillouin zone center except for LO phonons are calculated within harmonic approximation by calculating the forces acting on atoms which are displaced from equilibrium positions according to the symmetry of each mode.
A Tem Study Of The Microstructural Evolution Of Mbe-Grown Gan
Authors: Tricker David M. , Brown Paul D. , Martin Graeme , Lu J. , Westwood D. I. , Hill P. , Haworth L. , Macdonald J. E. , Cheng T. S. , Foxon C. T. , Humphreys Colin J. 
Published: April 2011

AbstractThe evolution of the microstructure of GaN grown by molecular beam epitaxy on {001} and {111} oriented GaAs substrates has been followed using transmission electron microscopy and reflection high energy electron diffraction. A thin layer of GaN has been shown to form during the nitridation of the GaAs surface prior to growth. Growth of GaN then proceeds by an island mechanism. Faulting on the four {111} planes of the cubic zinc-blende phase which grows on the {001 } surface occurs at an early stage as a consequence of misfit strain. The distribution of the {111} microtwins is initially isotropic, but growth of one pair of {111} twins proceeds much faster than that of the other pair, leading to a final microstructure which has an anisotropic distribution of microtwins. Doping of GaN with Si hinders the growth of the zinc-blende phase, leading to a textured, columnar (0001) wurtzite microstructure. Evidence is presented to show that addition of Mg as a dopant may reduce the stacking fault energy of wurtzite GaN.
GaN Device Processing
Authors: Pearton S. J. , Ren F. , Zolper J. C. , Shul R. J. 
Published: April 2011

AbstractRecent progress in the development of dry and wet etching techniques, implant doping and isolation, thermal processing, gate insulator technology and high reliability contacts is reviewed. Etch selectivities up to 10 for InN over AIN are possible in Inductively Coupled Plasmas using a Cl2/Ar chemistry, but in general selectivities for each binary nitride relative to each other are low (≤2)b ecause of the high ion energies needed to initiate etching. Improved ntype ohmic contact resistances are obtained by selective area Si+ implantation followed by very high temperature (>1300°C) anneals in which the thermal budget is minimized and AIN encapsulation prevents GaN surface decomposition. Implant isolation is effective in GaN, AlGaN and AlInN, but marginal in InGaN. Candidate gate insulators for GaN include AIN, A1ON and Ga(Gd)Ox, but interface state densities are still to high to realize state-of-the-art MIS devices.
Covalent Silicon Bonding At Room Temperature In Ultrahigh Vacuum
Authors: Plöbl Andreas , Stenzel Heinz , Tong Qin-Yi , Langenkamp Martin , Schmidthals Cord , Gösele Ulrich 
Published: April 2011

AbstractOne possibility of a low temperature joining techniques relies on the bonding of atomically clean surfaces. Results on the application of this method to silicon direct bonding are being presented. Clean surfaces for bonding were prepared by ex situ chemical cleaning with ensuing hydrogen passivation and their subsequent activation by thermal desorption of the hydrogen in ultrahigh vacuum (UHV). In UHV at room temperature, the wafers were gently brought into contact to initiate the bonding process. Without any subsequent heat treatment, the adhesive strength thus achieved was equivalent to the cohesion of bulk silicon: covalent bonds join the two crystals.
Icp Etching Of SiC
Authors: Wang J. J. , Lambers E. S. , Pearton S. J. , Ostling M. , Zetterling C.-M. , Grow J. M. , Ren F. 
Published: April 2011

AbstractA number of different plasma chemistries, including NF3/O2, SF6/O2 , SF6/Ar, ICI, IBr, Cl2/Ar, BCl3/Ar and CH4/H2/Ar, have been investigated for dry etching of 6H and 3C-SiC in a Inductively Coupled Plasma tool. Rates above 2,000 Å·cm−1 are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl2-based etching does not provide high rates, even though the potential etch products (SiCl4 and CCl4 ) are volatile. Photoresist masks have poor selectivity over SiC in F2 - based plasmas under normal conditions, and ITO or Ni are preferred.
4H-SiC Power Devices: Comparative Overview of UMOS, DMOS, and GTO Device Structures
Authors: Casady J. B. , Agarwal A. K. , Rowland L. B. , Seshadri S. , Siergiej R. R. , Mani S. S. , Sheridan D. C. , Sanger P. A. , Brandt C. D. 
Published: April 2011

AbstractSilicon Carbide (SiC) is an emerging semiconductor material which has been widely predicted to be superior to both Si and GaAs in the area of power electronic switching devices [1]. This paper presents an overview of SiC power devices and concludes that MOS Turn-Off Thyristor (MTOTM) is one of the most promising near term SiC switching device given its high power potential, ease of turn-off, 500°C operation and resulting reduction in cooling requirements. It is further concluded that in order to take advantage of SiC power devices, high temperature packages and components with double sided attachment need to be developed along with the SiC power devices.