bluuebunny/crossref_metadata_2025_split huggingface dataset:
A monolithic Cockcroft‐Walton voltage multiplier based on AlGaN/GaN HFET structure
Authors: Ao Jin‐Ping , Matsuda Yoshikazu , Yamaoka Yuya , Ohno Yasuo 
Published: June 2007

AbstractA five‐stage monolithic Cockcroft‐Walton voltage multiplier is reported which uses metal‐insulator‐metal capacitor and Schottky diode based on AlGaN/GaN heterostructure field‐effect transistor (HFET) structure. The voltage multiplier includes 5 capacitors and 5 Schottky diodes. AlGaN/GaN HFET with L/W = 1 μm/10 μm is used as the Schottky diode, where the gate made of Ni/Au/Ti is used for the anode and the ohmic contact is used for the cathode. The size of the chip is 0.567 mm×0.445 mm. The breakdown voltage of the capacitor is around 40 V and the diode breakdown voltage in reverse direction is more than 100 V. At input AC peak to peak voltage of 20 V under frequency of 10 MHz, the measured output voltage is about 40 V with the output impedance less than 1 MΩ. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Band offset measurements of the pulsed‐laser‐deposition‐grown Sc2O3 (111)/GaN (0001) heterostructure by X‐ray photoelectron spectroscopy
Authors: Liu Chang , Chor Eng Fong , Tan Leng Seow , Dong Yufeng 
Published: June 2007

AbstractThe energy band alignment of the Sc2O3/GaN heterointerface has been studied by means of X‐ray photoelectron spectroscopy. The single‐crystalline Sc2O3 was grown epitaxially on GaN template using pulsed laser deposition. A valence band offset of 0.84 ± 0.05 eV has been obtained across the heterointerface by using Ga 3d and Sc 3p energy core levels as the references. Given the bandgaps of 3.42 and 6.3 eV for GaN and Sc2O3, respectively, the conduction band offset has been estimated to be 2.04 eV in this system. These large band offsets are desirable, especially for GaN‐based electronic devices, which are most suited for high‐temperature operations, where the carrier thermionic emission must be maintained at a sufficient low level. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time‐resolved four‐wave mixing studies of excitons in GaN
Authors: Yamaguchi K. , Toda Y. , Ishiguro T. , Adachi S. , Hoshino K. , Tadatomo K. 
Published: June 2007

AbstractQuantum beats in the time‐resolved four‐wave mixing (FWM) signals arising from GaN excitons are observed. Two different types of beats are investigated: beats between the A‐exciton (XA) and B‐exciton (XB) states; beats between the XA and A‐biexciton ((XXA)) states. The former exhibits oscillations along all directions in the delay‐ (τ ) and real‐time (t) plane while the latter exhibits no beat in the direction parallel to the diagonal axis (τ = t). The results are well reproduced by a model calculation, showing good homogeneity of the sample.
Buffer breakdown voltage of AlGaN/GaN HFET on a 4 inch Si(111) substrate grown by MOCVD
Authors: Iwami Masayuki , Kato Sadahiro , Satoh Yoshihiro , Sasaki Hitoshi , Yoshida Seikoh 
Published: June 2007

AbstractThe buffer breakdown voltage and the electron mobility in a two dimensional gas (2DEG) of AlGaN/GaN HFETs on 4 inch Si(111) substrates grown by metalorganic chemical vapor deposition was investigated. The relationship between the electrical properties of HFETs and the crystalline quality of the GaN layer are studied by X‐ray diffraction and photoluminescence measurements. The buffer breakdown voltage decreases with an increase in the FWHM of the X‐ray (0002) diffraction peak. The electron mobility in a 2DEG decreases with an increase in FWHM of the X‐ray (10$ \bar 1 $2) diffraction peak. These results indicate that a screw component of the threading dislocations in the GaN layer is a primary source for buffer leakage, and that edge dislocations in the GaN layer have a scattering effect on the 2DEG transport. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low on‐resistance of GaN p‐i‐n vertical conducting diodes grown on 4H‐SiC substrates
Authors: Nishikawa Atsushi , Kumakura Kazuhide , Makimoto Toshiki 
Published: June 2007

AbstractWe investigated the resistance of conductive AlGaN buffer layers and the current‐voltage characteristics of GaN p‐i‐n vertical conducting diodes on n‐type 4H‐SiC substrates grown by low‐pressure metalorganic vapor‐phase epitaxy. High Si doping of the AlGaN buffer layer at the AlGaN/SiC interface produces ohmic current‐voltage characteristics in spite of the large band offset between AlGaN and 4H‐SiC. Owing to the optimization of the AlGaN buffer layer, a low on‐resistance (Ron) of 1.12 mΩ cm2 with high breakdown voltage (VB) of 300 V is obtained for a GaN p‐i‐n vertical conducting diode on a 4H‐SiC substrate, leading to the figure of merit (VB2/Ron) of 80 MW/cm2, which is larger than that for the diode with the same structure on a 6H‐SiC substrate (62 MW/cm2). This result indicates that 4H‐SiC is preferable for fabricating GaN‐based electronic devices with a low on‐resistance and high breakdown voltage. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution growth of AlN single crystal using Cu solvent under atmospheric pressure nitrogen
Authors: Kamei K. , Shirai Y. , Tanaka T. , Okada N. , Yauchi A. , Amano H. 
Published: June 2007

AbstractWe have grown thick AlN epilayers on SiC substrates by a new solution growth technique using Cu solvents under atmospheric pressure nitrogen. By using growth apparatus based on CZ growth system with inductive heating, we have grown AlN single crystalline layers of which thickness were more than 200 μm on (4H,6H)‐SiC substrates at relatively low growth temperatures such as 1600 °C‐1800 °C. Inch‐size self standing AlN crystals were also prepared by removing the SiC substrate. TEM observation, ω‐scan XRD measurement and cathode luminescence spectroscopy were conducted to characterize the crystallinity of the obtained AlN layers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence study of isoelectronic traps in dilute GaAsN alloys
Authors: Yaguchi H. , Aoki T. , Morioke T. , Hijikata Y. , Yoshida S. , Yoshita M. , Akiyama H. , Aoki D. , Onabe K. 
Published: June 2007

AbstractWe have studied photoluminescence spectra in detail to clarify the character of the isoelectronic traps in dilute GaAsN alloys. Several sharp lines have been observed at the lower energy side of the GaAs bandgap and are in good agreement with the nitrogen pair‐related emission lines previously reported. In addition to the nitrogen pair‐related lines, some other emission lines have been also observed. Compared with the energies of these emission lines and the nitrogen pair‐related emission lines, it was found that the energy differences agree with the longitudinal optical phonon energy at the Γ point of GaAs, showing that the character of isoelectronic traps due to nitrogen pairs in dilute GaAsN alloys is significantly contributed from the conduction band state at the Γ point. The temperature dependence of the peak energy of luminescence due to nitrogen pairs also indicates that the character of isoelectronic traps in dilute GaAsN alloys is due to the conduction band edge state at the Γ point of GaAs. For a dilute GaAsN alloy with lower nitrogen concentration, we have observed that the intensity of an emission line increased superlinearly with excitation power . (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Initial growth stage in PVT growth of AlN on SiC substrates: Influence of Al2O3
Authors: Heimann Paul , Pfeiffer C. , Bickermann M. , Epelbaum B. M. , Nagata S. , Winnacker A. 
Published: June 2007

AbstractAfter the first 2 minutes of growth, the substrate surface demonstrates two areas with very different morphologies: (I) regular arrays of hexagonal hillocks with 3D crystallites of AlN growing well oriented on hillock tops and (II) flat areas with very smooth surface where AlN grows in 2D layered mode. The addition of Al2O3 enhances the second growth mode (II), presumably because of surface melting in a very initial stage of growth. Surface morphologies in these single crystalline layers were studied using scanning electron microscopy (SEM). Chemical composition of selected areas was identified by Auger electron spectroscopy (AES). A chemical model is proposed to explain the obtained layer morphology. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Defect‐selective etching of aluminum nitride single crystals
Authors: Bickermann M. , Schmidt S. , Epelbaum B. M. , Heimann P. , Nagata S. , Winnacker A. 
Published: June 2007

AbstractWe have investigated defect‐selective wet chemical etching of freestanding AlN single crystals in a molten NaOH‐KOH eutectic at temperatures ranging from 240 °C to 400 °C. On nitrogen polar basal planes, hexagonal pyramids/hillocks exceeding 100 µm in diameter may form within seconds of etching at 240 °C. They sometimes are arranged in lines and clusters, thus we attribute them to defects on the surface, presumably originating in the bulk material. On aluminum polar basal planes, the etch pit density after approx. 2…3 min of total etching time at 350 °C corresponds to the screw dislocation density. Additionally, significantly smaller etch pits were found around annealed indentations, in the vicinity of some bigger etch pits after repeated etching, and sometimes also isolated on the surface area. We attribute these etch pits to threading mixed and edge dislocations. On as‐grown rhombohedral and prismatic facets no defect‐related etching features were observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Aluminum nitride/indium nitride bilayer and multilayer thin film systems as coatings for solar cells and longwave‐pass filters
Authors: Khoshman Jebreel M. , Kordesch Martin E. 
Published: June 2007

AbstractThe optical properties of sputtered AlN/InN/bilayer and multilayer thin film systems onto quartz substrates have been investigated in the visible and near infrared (NIF) regions. The designed multilayer was optimized at 500 nm and 50°–70° incidence for bilayers of alternate high and low index configuration. Analysis of these designs revealed that by increasing number of layers the reflectivity decreased to very low values (0% ‐ 8%) over a broad range of wavelengths (300–1400 nm). The transmissivity tended to increase smoothly from about zero at 750 nm to 88% in the NIR region while the absorptivity showed a tendency to decrease with increasing wavelength in the same region. Also, we found that the absorptivity increases with the total physical thickness of the multilayer system over the visible spectra (20% ‐ 99%). Therefore, the nitride bilayer and multilayer systems could be used as a longwave‐pass filter. However, since these systems provided extremely high absorptivity anywhere within the visible spectra they could be used as coatings for solar cells. X‐ray diffraction (XRD) spectra of AlN/InN/quartz multilayer systems were measured. The XRD patterns of the systems revealed a polycrystalline structure with a strong InN (002) diffraction peak at 31.2°. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
LPE growth of AlN single crystal using cold crucible under atmospheric nitrogen gas pressure
Authors: Tanaka T. , Yashiro N. , Shirai Y. , Kamei K. , Yauchi A. 
Published: June 2007

AbstractWe have grown AlN single crystal on 6H‐SiC substrate using Al‐Cu solution of 1500‐1600 °C. Nitrogen is supplied from gas phase under atmospheric pressure and the cold crucible technique is applied. Thickness of AlN reached 40 μm with the growth rate of 10 μm/h. Rather high growth rate in solution method is due to the increase in the melt surface area, dynamic convection of the melt and high temperature gradient along the seeded axis, which are easily realized in cold crucible technique. TEM observation reveals that the dislocation density beyond 10μm from the interface decreases by a factor of 10 to the power of ‐1 or ‐2. The melt included in between the substrate and AlN epi‐layer eases stress in epi‐layer and reduces cracks. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nitride film growth morphology using remote plasma enhanced chemical vapor deposition
Authors: Wintrebert‐Fouquet M. , Butcher K. S. A. , Chen P. P.‐T. , Wuhrer R. 
Published: June 2007

AbstractGallium nitride and indium nitride films have been grown by remote plasma enhanced chemical vapor deposition (RPECVD) at temperatures between 570 and 650 °C for GaN and between 350 and 570 °C for InN on different substrates. For GaN vast improvements in film morphology and quality have resulted from reductions in background impurities when compared to previous reports. Epitaxial material can now be grown at 650 °C under optimized growth conditions. Columnar growth still occurs for growth on some substrates, however film coalescence is observed when using appropriate buffer layers and epitaxial growth can also be observed. High resolution SEM images show examples of this. The root‐mean‐square surface roughness of epitaxial samples, as measured using atomic force microscopy, shows values of as little as 10 Angstroms. While X‐ray diffraction shows that these surfaces are not amorphous but have a strong (0001) preferred axis with FWHM limited by instrumental effects to (2θ) 0.085 degrees. The improvement in film quality has allowed heavily doped n‐type films to be grown with an electron mobility of 160 cm2/V·s for a carrier concentration of ∼ 1x1019 cm–3 at 650 °C. Moss‐Burstein shifted absorption data confirms the high doping level. For InN film growth by RPECVD, columnar growth is commonly observed in the temperature region of interest for films grown directly on sapphire, however film coalescence and epitaxial films are also observed for this material. X‐ray diffraction indicates very sharp (0002) peaks with FWHM of (2θ) 0.07 degrees. High resolution SEM images show examples of film morphology at different growth temperatures. Electron backscattered diffraction images indicate a wurtzite structure even for InN films with strong deviations from the accepted lattice parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InGaN/GaN quantum‐well nanocolumn crystals on pillared Si substrate with InN as interlayer
Authors: Hu F. R. , Ochi K. , Zhao Y. , Hane K. 
Published: June 2007

AbstractNanocolumn InGaN/GaN crystals were deposited on micropillared Si substrate by molecular beam epitaxy. Low‐temperature InN was used as interlayer. With enough free space, the column crystals grew around all the surface plane of the Si pillars and formed InGaN/GaN quantum‐well flower structure. The QW crystals are about 100 nm in diameter and 1.1‐1.4 μm in length. Raman spectra measurement of the fower structure shows that E2 mode peak line observed at 567.28 cm–1. Photoluminescence measurement indicates a room temperature PL peak position of 620 nm and two peak positions of 404 nm and 519 nm at temperature 15 K. Hg lamp excited photoluminescence demonstrated a clear fluorescence distribution in the flower structure and much stronger emission compared with the quantum‐well crystals on the flat Si substrate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Significance of vertical carrier capture for electroluminescence efficiency in InGaN multiple‐quantum well diodes
Authors: Inada T. , Satake A. , Fujiwara K. 
Published: June 2007

AbstractThe electroluminescence (EL) spectral intensity has been investigated in the high‐brightness green InGaN multiple‐quantum‐well light emitting diode (LED) in comparison with the single‐quantum‐well LED over a wide temperature range and as a function of injection current. It is found that the EL variation pattern with temperature and current is dramatically improved when the number of active wells increases as a result of enhanced carrier capture. The importance of vertical carrier capture processes is pointed out to explain the anomalous EL intensity variations at low temperatures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and theoretical study of substrate modes in (Al,In)GaN laser diodes
Authors: Braun H. , Lauterbach C. , Schwarz U. T. , Laino V. , Witzigmann B. , Rumbolz C. , Schillgalies M. O. , Lell A. , Härle V. , Strauß U. 
Published: June 2007

AbstractIn semiconductor laser diodes, high refractive index epitaxial layers can act as parasitic waveguides and cause severe losses to the mode propagating in the laser waveguide. For (Al,In)GaN laser diodes the parasitic modes are typically caused by the SiC or GaN substrate or buffer layers. Substrate modes have an impact on near‐field and far‐field of the waveguide mode, on laser threshold, and on gain spectra. We present scanning near‐field measurements of the substrate mode and demonstrate that the period of the standing wave in the GaN substrate varies over a wide range and critically depends on the effective refractive index of the waveguide mode.
Suppression of gate leakage current in i‐AlGaN/GaN heterostructures by insertion of anodic Al2O3 layer and influence of thermal annealing on channel electrons
Authors: Sawada T. , Takahashi K. , Ise K. , Suzuki K. , Kitamori K. , Kimura N. , Imai K. , Kim S.‐W. , Suzuki T. 
Published: June 2007

AbstractWe have investigated electrical properties of Ni/anodoc‐Al2O3/i‐AlGaN/GaN gate structures formed by insertion of a thin anodic Al2O3 layer, and the influence of surface preparation or thermal stressing of bare i‐AlGaN/GaN heterostructures on channel electrons. The gate structure effectively suppressed the reverse leakage current down to 10–6‐10–7A/cm2 range depending on the wafer, after optimum annealing in N2. Measured C‐V curves indicated a small density of states at anodic‐Al2O3/AlGaN interface. Hall effect measurements revealed that 2DEG density of bare i‐AlGaN/GaN samples is considerably affected by the surface preparation condition, and that a high temperature thermal stressing in O2 ambient rather degrades the electron mobility of 2DEG, suggesting enhanced incorporation of oxygen in AlGaN layer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibrational modes and strain in GaN/AlN quantum dot stacks: dependence on spacer thickness
Authors: Fresneda J. , Cros A. , Llorens J. M. , García‐Cristóbal A. , Cantarero A. , Amstatt B. , Bellet‐Amalric E. , Daudin B. 
Published: June 2007

AbstractWe have investigated the influence of spacer thickness on the vibrational and strain characteristics of GaN/AlN quantum dot multilayers (QD). The Raman shift corresponding to the E2h vibrational mode related to the QDs has been analyzed for AlN thicknesses ranging from 4.4 nm to 13 nm, while the amount of GaN deposited in each layer remained constant from sample to sample. It is shown that there is a rapid blue shift of the GaN vibrational mode with spacer thickness when its value is smaller than 7 nm while it remains almost constant for thicker spacers. A rapid increase of the Raman line‐width in the thicker samples is also observed. The experimental behavior is discussed in comparison with the results of a theoretical model for the strain in the QDs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Radiative and non‐radiative transitions in blue quantum wells embedded in AlInGaN‐based laser diodes
Authors: Son J. K. , Lee S. N. , Paek H. S. , Sakong T. , Ha K. H. , Nam O. H. , Park Y. 
Published: June 2007

AbstractWe performed temperature‐dependent time‐resolved optical studies (TRPL) on AlInGaN‐based blue‐light‐emitting quantum well (QW) with different well widths. Radiative and non‐radiative components of PL lifetime were analyzed by measuring intensity and lifetime of PL. We experimentally confirmed that a non‐radiative lifetime was affected by internal field in InGaN QWs. Therefore, non‐radiative lifetimes were reduced as a well width decreasing in the same way that radiative lifetimes do. In addition, the more efficient optical properties of QWs, such as internal quantum efficiency, were achieved in the narrow QWs rather than the wider one. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synthesis of III‐nitride microcrystals using metal‐EDTA complexes
Authors: Liu Y. H. , Koide S. , Miyake H. , Hiramatsu K. , Nakamura A. , Nambu N. 
Published: June 2007

AbstractA novel method, using metal ethylenediamine tetraacetic acid (EDTA) complexes as starting materials, is proposed to synthesize III‐nitride microcrystals. Ga (Zn, Ga)‐EDTA·NH4 and In‐EDTA·NH4 complexes were reacted with NH3 in the temperature range of 1020–1150 °C and 300–620 °C, respectively. SEM observation and X‐ray diffraction patterns show that pure phase hexagonal GaN and InN are obtained. The CL peak intensity of GaN increases as the synthesis temperature increases up to 1100 °C. The dependence of CL peak intensity on Zn doping content indicates good doping control. For InN synthesis, the temperature window is very narrow and the reaction evolves from In2O3 to InN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
XPS study of surface potential in AlGaN/GaN heterostructure with Cat‐CVD SiN passivation
Authors: Onojima N. , Higashiwaki M. , Matsui T. , Mimura T. , Suda J. , Kimoto T. 
Published: June 2007

AbstractAlGaN surface potentials in AlGaN/GaN heterostructures with and without SiN passivation were investigated using x‐ray photoelectron spectroscopy (XPS). SiN films were formed on AlGaN surfaces by catalytic chemical vapor deposition (Cat‐CVD), which has already been found to increase two‐dimensional electron gas (2DEG) density. Based on a simple electrostatic analysis, the 2DEG density is expected to increase as the AlGaN surface potential decreases. This study experimentally demonstrates that a reduction in the AlGaN surface potential is actually induced by Cat‐CVD SiN passivation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stimulated emission from free‐standing GaN/Si micro‐disk structures
Authors: Choi H. W. , Hui K. N. , Lai P. T. , Chen P. , Zhang X. H. , Teng J. H. , Tripathy S. , Chua S. J. 
Published: June 2007

AbstractArrays of pivoted GaN microdisks have been fabricated on GaN/Si material by a combination of dry and wet etching. The Si material beneath the GaN microdisks is removed by wet etching, leaving behind a fine pillar to support the disks. The top and botton faces of the microdisks are optically smooth, suitable for forming optical cavities. Resonant modes, corresponding to whispering gallery modes, are observed in the photoluminescence spectra. Stimulated emission is achieved at higher optical pumping intensities. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gate leakage currents of AlGaN/GaN HEMT structures grown by metalorganic vapour phase epitaxy
Authors: Yamada T. , Tsuchiya T. , Imada K. , Iwami M. , Kikawa J. , Araki T. , Suzuki A. , Nanishi Y. 
Published: June 2007

AbstractThe gate leakage current of AlGaN/GaN HEMTs increased with increasing Al mole fraction x from 0.25 to 0.36. Donor density Nd of AlGaN layer increased to ∼ 1×1018 (cm‐3) with increasing x to 0.36. It is estimated that rather low Nd may not influence the gate leakage. AlGaN surface morphology became worse with increasing x. Reverse‐bias characteristics were well‐fitted by calculation taking into account localized regions with high conductivity. The results suggest that deteriorating imperfections with x of AlGaN layer produce large gate leakage currents. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
AlGaN/GaN MIS‐HEMTs with HfO2 gate insulator
Authors: Kawano A. , Kishimoto S. , Ohno Y. , Maezawa K. , Mizutani Takashi , Ueno H. , Ueda T. , Tanaka T. 
Published: June 2007

AbstractAlGaN/GaN MIS‐HEMTs using HfO2 gate insulator with a large dielectric constant have been fabricated. HfO2 gate insulator was deposited by pulsed laser deposition at room temperature. It has been demonstrated that the HfO2 gate insulator is effective in suppressing the gate leakage current keeping a large transconductance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)