bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isotropic interface roughness of pseudomorphic In0.74Ga0.26As/In0.52Al0.48As quantum wells grown on (411)A InP substrates by molecular beam epitaxy
Authors: Kitada T. , Kusuonki S. , Kinouchi M. , Morita K. , Isu T. , Shimomura S. 
Published: May 2008

AbstractAnisotropy of the interface roughness has been investigated for pseudomorphic In0.74Ga0.26As/In0.52Al0.48As modulation doped quantum wells (MD‐QWs) grown on (411)A and (100) InP substrates by molecular beam epitaxy. Significant difference of low‐temperature electron mobility between two different in‐plane current directions ([0$ \bar 1 $1] and [011]) was observed for the (100) MDQW with a well width of 4 nm, while it was not observed for the (411)A MD‐QW.The observed electron mobility was analyzed by the theory of interface roughness scattering. Lateral size of the roughness along the [0$ \bar 1 $1] direction (Λ = 5.8 nm) is 29% larger than that of the [011] direction (Λ = 4.5 nm) for the (100) interface. On the other hand, the (411)A interface shows isotropic roughness (Λ ∼ 4.5 nm) with much smaller amplitude (Δ = 0.24 nm) comparing to the (100) interface (Δ = 0.33 nm). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
n‐Channel GaAs MESFETs for cryogenic application
Authors: Chen Y. G. , Itatani T. , Ohkubo M. 
Published: May 2008

AbstractSome normally‐on n‐channel GaAs MESFETs with large size gates are designed and fabricated for low‐noise, low power consumption application at cryogenic temperatures. Low‐doping n‐type GaAs (Si‐doped) epitaxial wafers are used to fabricate n‐channel MESFETs. The comparison of DC characteristics of the MESFETs at room temperature and at 4.2 K is reported. The maximum consumption power of the fabricated MESFETs is calculated to be 0.8mW. With the increasing of gate length, the power consumption and transconductance of MESFETs reduce consequently. The specific contact resistance of the metal/GaAs ohmic contacts determined from circular transfer line model and four‐point probe method at 4.2K is at the order of 10–7 Ωcm2, which is available for low noise application at cryogenic temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman scattering study of BxGa1–xN growth on AlN template substrate
Authors: Ould Saad Hamady S. , Baghdadli T. , Gautier S. , Bouchaour M. , Martin J. , Ougazzaden A. 
Published: May 2008

AbstractIn this study, Raman scattering measurements are reported on the BxGa1–xN layers grown on AlN‐on‐sapphire templates by MOVPE. The boron content covered the composition range from 0% (pure GaN) to 1.75%. The Raman spectra were recorded at 300 K with a confocal micro‐Raman spectrometer in the backscattering geometries. Raman cartography at a lateral resolution of 1 µm was performed to study the spatial variation of the phonon peaks characteristics. The homogeneity of BGaN layers was studied and the phonon modes characteristics are determined as a function of composition, with respect to the laser polarisation. The E2 and A1(LO) modes frequencies are shifted with respect to the pure GaN. The A1(LO) mode behaviour correlates well with the free carriers concentration measured by Hall Effect method, indicating a phonon‐plasmon coupling decreasing with increasing boron content in alloy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InGaN growth on ZnO (0001) substrate by metalorganic vapor phase epitaxy
Authors: Kawai Y. , Ohsuka S. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I. 
Published: May 2008

AbstractInGaN growth has been performed on nearly lattice‐matched ZnO (0001) substrates by metalorganic vapor phase epitaxy at relatively low temperatures below 600 °C. The grown layers were confirmed to be single crystalline by X‐ray diffraction and reflection high energy electron diffraction analyses. By annealing the ZnO substrate under oxygen atmosphere prior to the growth, scratches due to polishing were completely removed, as observed by atomic force microscopy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sub‐100 nm gate‐length SiGe/Si MIS‐HFET using Cat‐CVD SiN
Authors: Onojima N. , Kasamatsu A. , Hirose N. , Mimura T. , Matsui T. 
Published: May 2008

AbstractWe fabricated sub‐100 nm gate‐length SiGe/Si n‐channel metal‐insulator‐semiconductor (MIS) heterostructure field‐effect transistors (HFETs) using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat‐CVD). The Cat‐CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. Due to the MIS structure, large gate bias swing was achieved from ‐3 to 3 V, and the maximum drain current density exceeded 450 mA/mm. The maximum transconductance (gm) was 220 mS/mm at VGS = 3 V, which was larger than that for a Schottky‐gate device. RF measurements of the MIS‐gate device, however, showed a relatively lower current gain cutoff frequency (fT) compared with the Schottky‐gate device, suggesting that two electron transport channels existed for the MIS‐gate structure, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shallow Li‐acceptor levels in ZnO films codoped with Li and F atoms
Authors: Kobayashi K. , Tomita Y. , Maeda Y. , Haneda H. 
Published: May 2008

AbstractLi,F‐codoped ZnO films have been prepared by simultaneous evaporation of LiF at 780 °C during the ZnO growth. The codoped ZnO film has the resistivity of 79 Ωcm and the electron density of 6.8 ×1016 cm–3. Photoluminescence spectra of the codoped ZnO film in the range of 14 to 120 K show new emissions at 3.3136 and 3.3270 eV, besides bound excitonic emissions. The emission at 3.3136 eV disappears at a temperature higher than 40 K, and is assigned to donor‐acceptor pair emission. The emission at 3.3270 eV is ascribed to free‐electron to acceptor transition. The Li‐acceptor levels are estimated to be 0.11 eV from free‐electron to acceptor transition. As excitation intensity increases, the photon energy of the donor‐acceptor pair emission remains unchanged. These results lead to the interpretation that Li and F atoms are located at nearest neighbour sites in the ZnO lattice and that the presence of Li‐F complexes suppresses the formation of interstitial Li. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular‐beam epitaxy fabrication and analysis of GaN nanorods on patterned silicon‐on‐insulator substrate
Authors: Seo J. U. , Hasegawa S. , Asahi H. 
Published: May 2008

AbstractGaN nanorods field emission arrays (FEAs) were fabricated on patterned silicon‐on‐insulator substrates with 10×10 μm2 and 1×1 μm2 periodic‐windows by molecular beam epitaxy. Their morphologies and field emission characteristics were investigated. FEAs fabricated on the 1×1 μm2 periodic‐window substrates exhibited lower threshold electric field of 2.6 V/μm, higher field emission current density of 10–3 A/cm2 and higher field enhancement factor of 1685 than those for the FEAs fabricated on the 10×10 μm2 periodic‐window substrates in spite of the reduced active areas. The improved field emission characteristics for the FEAs with smaller area periodic‐window are considered to be due to the edge effect at the patterned area. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical conductivity of carbon nanotubes and polystyrene composites
Authors: Kažukauskas V. , Kalendra V. , Bumby C. W. , Ludbrook B. M. , Kaiser A. B. 
Published: May 2008

AbstractWe report investigation of electrical conductivity of high resistivity polystyrene/carbon nanotube composites. The films consisted of a thiol‐bonded network of wrapped MWNTs within a polystyrene matrix with mass ratios ranging from 0% to 1%. The electrical conductivity and its thermal activation energy were systematically depending on the CNT doping level. A number of phenomena could be explained by the presence of CNT ‘islands’ in the polystyrene matrix at doping levels below the percolation threshold. At higher levels of CNTs an interconnected conducting network is formed. The results appear consistent with fluctuation‐assisted tunnelling through barriers between conducting carbon nanotubes for medium and large voltages. However, at low voltages there is a sharper decrease in conductance as voltage decreases that could arise from Coulomb blockade effects or other small barriers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and optical properties of Er doped GaN with various Er concentrations
Authors: Chen Shaoqiang , Seo Jongwon , Sawahata Junji , Akimoto Katsuhiro 
Published: May 2008

AbstractLuminescence properties of Er in GaN combined with the structural properties were studied by photoluminescence measurements and X‐ray diffraction measurements. It was found that Er atoms occupy two kinds of incorporation sites in GaN and only one kind of site is suggested to be active for the light emission. The maximum luminescence intensity was obtained with the Er concentration at around 4 at%. The concentration quenching was observed and the cause of the quenching is related to the degradation of crystal quality rather than the formation of the segregation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Metalorganic chemical vapor deposition of ZnO(0001) thin films on GaN(0001) templates and ZnO(0001) substrates
Authors: Ive T. , Ben‐Yaacov T. , Murai A. , Asamizu H. , Van de Walle C. G. , Mishra U. , DenBaars S. P. , Speck J. S. 
Published: May 2008

AbstractWe investigated the properties of ZnO layers grown by metalorganic chemical vapor deposition on GaN(0001) templates and ZnO(0001) bulk substrates. Steps and hexagonal pits were observed on the surfaces of the ZnO/GaN films as revealed by atomic force microscopy. The root‐mean‐square roughness was 2.6 nm over 20×20 mm2. The surfaces of the homoepitaxially grown ZnO films were smooth and featureless with a rootmean‐square roughnesses of 0.12 nm over 6×6 mm2. Full width at half maximums of ω‐scans for the on‐axis (0002) and the off‐axis (20$ \bar 2 $1) reflections were 0.091° and 0.159°, respectively. The corresponding values for the ZnO/ZnO films were 0.025° and 0.035°, respectively. Reciprocal space maps for the (10$ \bar 1 $5) reflection revealed that the ZnO films grown on GaN were fully relaxed and that the peaks of the homoepitaxially grown ZnO layers were indistinguishable from the ZnO substrate peaks. Ga‐doped ZnO layers were grown at 300 °C on (In,Ga)N light emitting diodes as transparent electrodes and for wafer bonding to ZnO substrates in order to enhance the light extraction. The forward voltage was 4.5 V at 20 mA. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Light propagation in a coupled waveguide‐triple quantum well structure
Authors: Yamaguchi M. , Yokoi M. , Sawaki N. 
Published: May 2008

AbstractThe light propagation in a waveguide which was weakly coupled to a quantum well (QW) structure was studied to demonstrate the detectability of the electronic states in the small area of QW. The small area of QW was made with a GaAs/AlGaAs asymmetric triple QW. Since the electronic states in the triple QW were easily controlled by an electric field which was induced by an optical injection, we observed the optical spectra obtained from the waveguide under the various intensities of optical injection. The spectral change was observed around the characteristic wavelengths of the QW. In order to verify the observed spectral change, we measured the optical spectra of the traveling wave in a sample whose QW surface has been etched off. By comparing the results, we interpreted that the spectral change is due to the reconstruction of the electronic states in the small area of QW due to the optically excited carriers. This proves the detection of small electronic state changes in the small area of QW with the traveling light in the waveguide. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vertically scaled 80‐nm‐gate InP‐based HEMTs with a cutoff frequency of 450 GHz
Authors: Hara Naoki , Takahashi Tsuyoshi , Ohki Toshihiro , Makiyama Kozo 
Published: May 2008

AbstractWe have successfully fabricated vertically scaled 80‐nm‐gate InP‐based HEMTs with fully SiN passivated gate‐recess regions and achieved high cutoff frequency of 450 GHz. By reducing gate‐recess length to 50 nm, high performance was realized even with a rather long gate length of 80 nm. We also employed a fully passivated gate‐recess structure, which is essential for obtaining thermally stable devices. Au interconnections with benzocyclobutene as an interlayer dielectric film were formed on this device and no change in DC characteristics was observed. These results indicate that the device reported in this paper is promising for integrated circuits used in millimeter‐wave applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First principles study of the decomposition processes of AlN in a hydrogen atmosphere
Authors: Panyukova U. , Suzuki H. , Togashi R. , Murakami H. , Kumagai Y. , Koukitu A. 
Published: May 2008

AbstractThe growth of AlN films by the hydrogen vapor phase epitaxy method is generally carried out at a high temperature over a hydrogen atmosphere. The difficulties concerned with the decomposition processes on the surface during the film growth result in necessity of computer modelling of that processes. First principles calculations of the decomposition processes of AlN in a hydrogen atmosphere are reported. The mechanism of desorption of atoms from the surface was determined. Al atoms desorb as AlH from (0001) surface and as Al from (000‐1) surface of AlN. And N atoms desorb as NH3 from (0001) surface and as NH from (000‐1) surface of AlN. The desorption of Al atoms is a rate limiting reaction. The calculation results correspond well with the experimental date published earlier. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Refractive index of TlGaAs
Authors: Ohnishi K. , Shiba M. , Yamakage M. , Kajikawa Y. 
Published: May 2008

AbstractRefractive index has been determined from reflectance measurements at 77‐300 K for Tlx Ga1–x As samples with x ≤ 0.077 prepared by low‐temperature molecular‐beam epitaxy. A very high refractive index of around 4.5 at room temperature in the transparent wavelength region has been revealed for Tlx Ga1–x As with x = 0.077. The temperature coefficient of the refractive index was found to increase with Tl content. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN‐ and AlGaN‐based UV‐LEDs on sapphire by metal‐organic chemical vapor deposition
Authors: Okimoto T. , Tsukihara M. , Kataoka K. , Kato A. , Nishino K. , Naoi Y. , Sakai S. 
Published: May 2008

AbstractWe investigated the relationship between the dislocation densities and the electro‐luminescence (EL) peak intensities in AlGaN, which was grown on GaN‐ or AlGaN‐on sapphire, by low‐pressure metalorganic chemical vapor deposition. Crystallographic properties of the AlGaN epilayer has been investigated by a high‐resolution X‐ray diffraction method. We showed that EL intensity was strongly dependent on the full‐width at half maximum (FWHM) from (10$ \bar 1 $2) AlGaN diffraction peaks for GaN‐ or AlGaN‐ based LEDs at omega mode. This result indicated the reduction of edge and mixed dislocation densities led to improvement of the EL characteristics. Although the GaN‐based LEDs absorb UV‐light, the EL intensity was higher than that AlGaN‐based LEDs. Comparing at the same FWHM value of AlGaN (10$ \bar 1 $2) peaks, EL intensity of AlGaN‐based LEDs were several times higher than that of GaN‐based LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarized laser oscillation from polygon crystals of thiophene/phenylene co‐oligomers grown by liquid‐phase growth
Authors: Yamao Takeshi , Yamamoto Kazunori , Miki Tomoharu , Akagami Hiroshi , Nishimoto Yoshihiro , Hotta Shu 
Published: May 2008

AbstractWe have investigated the laser oscillation and its polarization feature of a thin polygon crystal of a thiophene/phenylene co‐oligomer grown by the novel liquid‐phase method. The emission spectrum from the crystal ca ‐plane (along the b‐axis) narrows with increasing energy of the pulsed laser excitation, which is incident perpendicularly to the crystal plane (the ab ‐plane). The multi‐mode laser oscillation was observed around 515 nm with the excitation over 5 mJ/cm2 per pulse. A mode separation and a full width at half maximum of the peak were estimated to be ∼0.2 nm and ∼65–85 pm, respectively. The laser emission was confirmed to be strongly polarized along the c‐axis. Its polarization ratio of the c‐axis to the a‐axis was estimated to be ∼550. This large ratio is due to the upright configuration of the molecular long axis that is almost perpendicular to the ab‐plane. These results indicate that the present polygon thin crystal is suitable for laser device application. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaAs high‐k dielectric metal‐insulator‐semiconductor structure having silicon interface control layer
Authors: Akazawa M. , Hasegawa H. 
Published: May 2008

AbstractA pinning‐free high‐k dielectric metal‐insulator‐semiconductor (MIS) gate stack was realized on GaAs surfaces by using a Si interface control layer (Si ICL). The MIS structure has a SiNx/Si ICL ultrathin double layer inserted between GaAs and HfO2. Si ICL was grown epitaxially on a Ga‐stabilized GaAs surface by molecular beam epitaxy (MBE). The ultrathin SiNxbuffer film was formed byin situpartial nitridation of Si ICL in the MBE chamber. An X‐ray photoelectron spectroscopy (XPS) analysis indicated that the ultrathin SiNx/Si ICL structure is chemically stable against air‐exposure, preventing the Si ICL/GaAs hetero‐interface from oxidation, although the ultrathin SiNxfilm itself partially turns into SiOxNy. Using this feature, a high‐k MIS capacitor was formed by ex situ deposition of HfO2on the SiOxNy/Si ICL/GaAs structure. The capacitance‐voltage (C‐V) analysis of the high‐k MIS sample after rapid thermal annealing at 500 °C for 30 sec indicated that the MIS interface is completely free from Fermi level pinning with a minimum interface state density below 1011 cm–2eV–1. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantitative imaging of residual strain profile in large diameter GaAs substrates
Authors: Fukuzawa M. , Yamada M. 
Published: May 2008

AbstractA near‐infrared imaging polariscope (NIRIP) has been developed quantitatively to measure residual strain profiles in large‐diameter GaAs substrates, in which a near‐infrared camera connected to an image‐processing system is used as a 2D multi‐channel sensor and also a collimated light beam is used to illuminate the whole area of substrate, in addition to a pair of computer‐controlled rotating polarizer and analyser. The measurement time is less than 5 minutes for the GaAs substrate with the diameter of 6‐inch, which is drastically reduced in comparison to that of the scanning infrared polariscope (SIRP) using a single channel sensor and a focused light beam. By comparing the residual strain profiles measured in the same substrates with NIRIP and SIRP, it is confirmed that the NIRIP developed here has the sensitivity equivalent to the SIRP. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The substrate orientation dependence of Be doping in molecular layer epitaxy of GaAs
Authors: Ohno Takeo , Oyama Yutaka , Nishizawa Jun‐ichi 
Published: May 2008

AbstractBe‐doped GaAs epitaxial layers were grown on (100), (111)A, (111)B and (110) GaAs substrates by MLE. In the growth on (111)A GaAs, the incorporation of Be was enhanced significantly when Be(MeCp)2 was introduced after exposure to AsH3 (AA mode) at 277 °C, and consequently Be concentrations up to 8x1019 cm–3 were achieved. It was shown that the concentration of Be on (111)B GaAs substrate was high when exposed to Be(MeCp)2 after exposure to TEG. The relationship between the surface stoichiometry and Be incorporation is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of GaAs1–xBix/GaAs multi‐quantum wells by molecular beam epitaxy
Authors: Tominaga Yoriko , Kinoshita Yusuke , Feng Gan , Oe Kunishige , Yoshimoto Masahiro 
Published: May 2008

AbstractGaAs1–xBix/GaAs multi‐quantum well (MQW) structures were grown for the first time by molecular beam epitaxy (MBE). Successful growth of MQWs was demonstrated by observing clear satellite peaks in high‐resolution X‐ray diffraction (HR‐XRD) measurements. Photoluminescence (PL) emission at room temperature (RT) was observed from the MQWs. The peak energy of RT PL emitted from GaAs0.948Bi0.052/GaAs MQWs increased with decreasing thickness of the well layer, which implies quantum size effect. The MQW structures were thermally stable even after annealing up to 800 °C, and the PL emission was observed even after annealing up to 600 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evaluation of surface roughness and nanostructure of indium tin oxide (ITO) films by atomic force microscopy
Authors: Kavei G. , Zare Y. , Mohammadi Gheidari A. 
Published: May 2008

AbstractIndium tin oxide was deposited on a glass (soda lime glass) by radiofrequency sputtering system at different sputtering gas (argon/oxygen 90/10%) pressures (20–34 mTorr) at room temperature. The sputtering rate was affected by the sputtering gas pressure. The optimum sputtering gas pressure was found to be 27 mTorr. The samples at different thicknesses (168, 300, 400, 425, 475, 500 and 630 nm) were deposited on the substrate. Transparency, electrical conductivity and surface roughness of the films were characterized. The samples were annealed at 350, 400 and 450°C to evaluate annealing process effects on the concerned parameters and, therefore, the above‐mentioned measurements were repeated again. The films exhibited reasonable optical transmittance and electrical conductivity and greatly improved after annealing. The characterization was focused on the scanning of the film surfaces before and after annealing, which has a prominent effect on the optical properties of the films. Film surfaces were scanned by scanning probe microscopy in contact atomic force mode. The most consideration was devoted to image analysis. SCANNING 30: 232–239, 2008. © 2008 Wiley Periodicals, Inc.
Cathodoluminescence study of semiconductor oxide micro‐ and nanostructures grown by vapor deposition
Authors: Piqueras J. , Maestre D. , Ortega Y. , Cremades A. , Fernández P. 
Published: May 2008

AbstractNano‐ and microstructures of SnO2, In2O3 and ZnO have been grown during thermal treatment of compacted powders under argon flow. Indium‐doped SnO2 tube‐shaped structures with rectangular cross‐section are obtained by adding a fraction of In2O3 to the starting SnO2 powder. In‐rich nanoislands were found to grow on some edges of the tubes. ZnO nanostructures doped with Sn or Eu were grown by adding SnO2 and Eu2O3 powder, respectively, to the ZnO precursor powder. All the samples have been characterized by the emissive and cathodoluminescence (CL) modes of scanning electron microscopy. CL images from SnO2:In and In2O3:Sn tubes and islands show a higher emission from the Sn‐rich structures related to oxygen deficiency. CL of doped ZnO enables to detect the presence of dopant in specific regions or structures. CL appears to be a useful technique to study optical and electronic properties of semiconductor oxide nanostructures. SCANNING 30: 354–357, 2008. © 2008 Wiley Periodicals, Inc.