bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fabrication of GaN‐based striped structures along the <11$ \bar 2 $0> direction by the combination of RIE dry‐etching and KOH wet‐etching techniques to recover dry‐etching damage
Authors: Itoh Morimichi , Kinoshita Toru , Kawasaki Koji , Takeuchi Misaichi , Koike Choshiro , Aoyagi Yoshinobu 
Published: May 2006

AbstractGaN‐based striped structures were fabricated using Al0.2Ga0.8N/GaN single heterostructure by combination of dry/wet etching with taking into account GaN crystal structure. After following wet‐etching, the sidewalls of striped structures along the <11$ \bar 2 $0> direction became very smooth and straight compared with that of as dry‐etched. We estimated mobility of electron in field effect transistors (FETs) consists striped structures along the <11$ \bar 2 $0> direction from I‐V characteristics. The mobility of the as dry‐etched striped structures was drastically reduced from the not‐patterned Al0.2Ga0.8N/GaN single heterostructure. In contrast, the mobility of the smooth striped structure FETs were effectively recovered to that of the not‐patterned one. These results suggest that following KOH wet‐etching can remove the damaged/rough layer indued by the RIE dry‐etching. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the local structure of AlN:Mn using X‐ray absorption fine structure measurements
Authors: Miyajima Takao , Kudo Yoshihiro , Uruga Tomoya , Hara Kazuhiko 
Published: May 2006

AbstractThe local structure around the Mn atoms in MOCVD‐grown AlN:Mn films which show Mn‐related red‐orange photoluminescence with a 600nm‐peak at room temperature was investigated using the X‐ray absorption fine structure (XAFS) measurements. We found that Mn atoms occupy Al lattice sites in the AlN film and that the Mn ions have a charge between +2 and +3. From these results, we think that the red‐orange luminescence is caused by the transition of d‐electrons in the Mn ions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct correlation between nonradiative recombination centers and threading dislocations in InGaN quantum wells by near‐field photoluminescence spectroscopy
Authors: Kaneta Akio , Funato Mitsuru , Narukawa Yukio , Mukai Takashi , Kawakami Yoichi 
Published: May 2006

AbstractWe performed near‐field photoluminescence (PL) mapping and atomic force microscopy at the same scanning area to clarify relationship between luminescence dynamics and threading dislocations in violet and blue light emitting InGaN single‐quantum‐well structures on epitaxially laterally overgrown GaN templates at room temperature. Clear correlation has been found between the distribution of dark area in PL mapping data and threading dislocations with screw and mixed types in the violet sample. On the other hand, such correlation has not been found in the blue sample. These results indicated that the carriers/excitons are captured easily in nonradiative recombination centers (NRCs) originating from the threading dislocations in the violet sample, because the lateral diffusion length of carriers/excitons is large due to a small potential fluctuation induced by compositional fluctuation of In comparing to those in the blue sample. However, the capture to such NRCs is hindered effectively in the blue one because of the localization to potential minima. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bending in HVPE GaN free‐standing films: effects of laser lift‐off, polishing and high‐pressure annealing
Authors: Paskova T. , Darakchieva V. , Paskov P. P. , Monemar B. , Bukowski M. , Suski T. , Ashkenov N. , Schubert M. , Hommel D. 
Published: May 2006

AbstractWe have studied the effects of laser lift‐off and polishing processes on the bending of free‐standing HVPE grown GaN thick films. Their structural characteristics were accessed by reciprocal space mapping and lattice parameters measurements as well as by Raman scattering and photoluminescence. The in‐plane strain difference between the two faces was found to have determining effect on the bending of the free‐standing films. Removing the high‐defect‐density near‐interface region either by melting caused by laser lift‐off, or by polishing, or by point defects dissociation caused by high‐pressure annealing was found to lead to flattening of the strain distribution along the film thickness and a significant reduction of the bending of the free‐standing films. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence of a ‐plane GaN: comparison between MOCVD and HVPE grown layers
Authors: Paskov P. P. , Schifano R. , Malinauskas T. , Paskova T. , Bergman J. P. , Monemar B. , Figge S. , Hommel D. , Haskell B. A. , Fini P. T. , Speck J. S. , Nakamura S. 
Published: May 2006

AbstractWe report on the emission properties of nonpolar a ‐plane GaN layers grown by metalorganic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE). Together with the typical band edge exciton emission, the low‐temperature photoluminescence spectra reveal several emission bands in the spectral range 3.29‐3.42 eV. These emissions appear with different intensities in layers grown by different techniques and show different thermal quenching and recombination dynamics. The 3.42 eV and 3.35 eV emissions are found to be of an intrinsic origin and are associated with carriers localized at stacking faults. The emission at 3.29 eV, which is present only in MOCVD layers, shows a donor‐acceptor pair behavior suggesting that impurities attached to structural defects are involved. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current crowding effects on blue LED operation
Authors: Evstratov I. Yu. , Mymrin V. F. , Karpov S. Yu. , Makarov Yu. N. 
Published: May 2006

AbstractA hybrid 1D/3D approach to modeling of the electric current spreading in a light emitting diode (LED) die is suggested and validated by comparing the theoretical predictions with available observations. Large‐area LEDs with different contact electrode configurations suitable for high‐power operation are analyzed in terms of simulations with the focus on the current non‐uniformity and its impact on the device electrical and optical characteristics. The factors controlling the LED series resistance are identified by modeling, and ways for the resistance improvement are examined. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A surface trap model and its application to analysis of III‐nitride HEMT performance
Authors: Bulashevich Kirill A. , Karpov Sergey Yu. 
Published: May 2006

AbstractA polarity‐dependent model of electron/hole traps on a free GaN:Si surface is suggested, accounting for both intrinsic and impurity‐induced surface states. The model parameters are fitted to provide the best agreement with available observations. The suggested approach is invoked to explain a recently observed non‐monotonic dependence of the surface barrier due to band bending upon the donor concentration in the GaN bulk. The model is used for analysis of DC performance of high‐electron mobility transistors (HEMTs) with different cap layer design. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Radio‐frequency MBE growth of cubic GaN on 3C‐SiC(001)/Si(001) template
Authors: Ohachi T. , Kikuchi T. , Somintac A. , Yamaguchi S. , Yasuda T. , Wada M. 
Published: May 2006

AbstractA 3C‐SiC(001) was formed by coincidence site lattice matching on Si(001) through carbonization using acetylene (C2H2) supplied by a jet nozzle. The 3C‐SiC serves as a cubic template for the MBE growth of c‐GaN on Si substrates. The Si substrate with lattice constant of a Si = 0.544 nm was covered with strained 3C‐SiC whose lattice constant a 3C‐SiC/Si = 0.445 nm expanded from that of the bulk 3C‐SiC crystal (0.438 nm). Better quality cubic phase GaN film was grown on the strained 3C‐SiC template layer when the Ga/N flux ratio approached unity of Ga rich side. The proportion of the cubic phase in the GaN layer was calculated to be 94.7% from the integrated intensity ratio of the X‐ray diffraction peaks of c‐GaN(002) and h‐GaN(10‐11). The FWHM of the (002) diffraction peak for the 544 nm‐thick c‐GaN was 13.2 arcmin. A precise RHEED analysis also indicated that the c‐GaN had (2x2) surface reconstruction structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of InGaN/GaN quantum wells on sapphire and bulk GaN substrate
Authors: Dworzak M. , Stempel T. , Hoffmann A. , Franssen G. , Grzanka S. , Suski T. , Czernecki R. , Leszczynski M. , Grzegory I. 
Published: May 2006

AbstractWe investigated the recombination dynamics in InGaN quantum well (QW) structures, grown by metal organic chemical vapour deposition on sapphire and bulk GaN crystals. We present the results of time‐integrated and time‐resolved photoluminescence (PL) spectroscopy performed on single QWs with widths of 4.5 nm and 9.5 nm. The recombination mechanisms were studied at 5 K and elevated temperatures up to room temperature. Radiative and nonradiative life‐times were determined. The luminescence properties are strongly influenced by the localization of excitons in a complex potential landscape with localization sites of varying depth. Redistribution of charges from shallow to deeper localization sites were observed. The band profile fluctuations influence the thermal stability of the luminescence. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large enhancement of GaN‐UV light emission using silver mirror resonator
Authors: Ahmed N. M. , Hashim M. R. , Hassan Z. 
Published: May 2006

AbstractIn this paper we used new microcavity resonator design of extracting light with high efficiency from a high index material (GaN), n > 2 for use in light emitting diode (LED) and laser diode (LD). A GaN/sapphire structure as an active layer was sandwiched between two silver mirrors. For the study two types of microcavity were fabricated: (air/GaN/sapphire/silver) and (silver/GaN/sapphire/silver). Via photo‐luminescence measurements we observed 2‐fold intensity enhancement in the UV region (364 nm) at room temperature by using 400 nm silver back mirror compared with uncoated sample. The amplitude of the photoluminescence is enhanced 10‐times when we used 400 nm back coated together with 50 nm silver as front mirror. Further, a tremendous enhancement was obtained when a small hole was made in the front mirror with 50 nm thickness. The large increment of GaN/sapphire light emission in this microcavity could be caused by few important factors: increasing absorption in the cavity, optical field enhancement due to the resonator and coupling of plasmon in the metallic layer with the UV light. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diffraction anomalous fine structure investigation of InGaN quantum dots
Authors: Piskorska E. , Holý V. , Siebert M. , Krause B. , Metzger T. H. , Schmidt Th. , Falta J. , Yamaguchi T. , Hommel D. 
Published: May 2006

AbstractDiffraction anomalous‐fine structure technique was used for the investigation of the chemical composition of self‐assembled non‐capped InGaN quantum dots grown on GaN. In a grazing‐incidence geometry, a dependence of the energy of the GaK absorption edge on the radial scattering vector was found. This dependence is explained by a chemical shift of the GaK absorption edge due to the In content and due to the local elastic strains in quantum dots. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exciton dynamics in nonpolar (11$ \bar 2 $0) InGaN/GaN multiple quantum wells grown on GaN templates prepared by lateral epitaxial overgrowth
Authors: Onuma T. , Chakraborty A. , Haskell B. A. , Keller S. , Sota T. , Mishra U. K. , DenBaars S. P. , Speck J. S. , Nakamura S. , Chichibu S. F. 
Published: May 2006

AbstractExciton dynamics in nonpolar (11‐20) InxGa1–xN/GaN multiple quantum wells (QWs) grown on GaN templates prepared by lateral epitaxial overgrowth were studied. Due to the absence of the polarization fields normal to the QW plane, the photoluminescence (PL) peak energy moderately shifted to the higher energy and the radiative lifetime did not change remarkably with the decrease in the well thickness. Similar to the case for polar InGaN QWs, time‐resolved PL signals exhibited the nonexponential decay shape, which can be explained by thermalization and subsequent localization of excitons. Although the growth conditions were not fully optimized, values of the PL intensity at 300 K divided by that at 8 K were 25 and 17% for the peaks at 2.92 and 2.60 eV, respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MOCVD of InGaN‐based light emitting structures on silicon substrates with strain optimized buffer layers using long Al pre‐deposition
Authors: Clames J.‐Y. , Giesen Ch. , Meyer T. , Heuken M. 
Published: May 2006

AbstractGaN/InGaN multi quantum wells (MQWs) were grown on silicon (Si) substrates by Metalorganic Vapor Phase Epitaxy (MOVPE). A structure of layers consisting of AlN, AlGaN and GaN was used for subsequent deposition of the MQW structures on Si substrates. The Al pre‐deposition time before growing the buffer structure and its effect on the formation of cracks was investigated. The emitted wavelength of the structure was changed by varying the thickness of the Mg‐doped AlGaN electron blocking layer, by reducing the growth temperature of the MQW structure and by increasing the QW width of the structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
AlGaN epitaxial layers grown by HVPE on sapphire substrates
Authors: Soukhoveev V. , Kovalenkov O. , Shapovalova L. , Ivantsov V. , Usikov A. , Dmitriev V. , Davydov V. , Smirnov A. 
Published: May 2006

AbstractGrowth of AlxGa1–xN (x ∼ 0.0‐1.0) alloy layers by hydride vapor pahse epitaxy (HVPE) is reported. Crack‐free undoped AlGaN layers from 0.1 to 2 μm thick were grown on 2″ SiC and 2″and 4″ sapphire substrates. For AlxGa1–xN (x ∼ 0.7‐0.8) layers grown on sapphire, high‐resolution symmetric/asymmetric X‐ray diffraction (XRD) measurements resulted in ω‐scan rocking curve widths ranging from 250 to 650 arcsec and from 1400 to 1900 arcsec, for the (00.2) and (10.2) reflections, respectively. Minimum XRD‐estimated screw and edge dislocation densities in AlGaN layers grown on sapphire were <6 x 108 cm–2 and <2 x 109 cm–2, respectively. Raman studies revealed that the composition dependences of the phonon modes of HVPE‐grown AlxGa1–xN layers are in a good agreement with the one, which have been observed for MOCVD‐grown AlxGa1–xN alloys earlier. Grown layers had n‐type electrical conductivity for the composition range up to x = 0.4. The layer became highly resistive for higher AlN contents. First results on 40 µm thick crack free AlGaN growth on SiC substrates are reported. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carrier confinement effect enhanced by AlGaN/GaN multi‐quantum barrier in AlInGaN based high power blue‐violet laser diodes
Authors: Lee Sung‐Nam , Cho S. Y. , Ha K. H. , Choi K. K. , Jang T. , Chae S. H. , Kim H. K. , Paek H. S. , Sung Y. J. , Sakong T. , Son J. K. , Ryu H. Y. , Kim Y. H. , Yoon E. , Nam O. H. , Park Y. 
Published: May 2006

AbstractAlGaN/GaN multi‐quantum barriers (MQBs) were firstly introduced into violet AlInGaN laser diodes with InGaN multi‐quantum wells structure, resulting in drastic improvements in lasing performance. Comparing with conventional AlGaN single electron blocking layer (EBL), lower threshold current and higher slope efficiency at room temperature could be achieved by AlGaN/GaN multiquantum barrier. It can be explained that p‐type AlGaN/GaN MQBs is more effective to suppress the overflow of electron than single p‐type AlGaN EBL by the increase of effective barrier heights due to the quantum effect of MQB and the enhancement of p‐type doping efficiency. Additionally, the strain effect in InGaN multi‐quantum wells (MQWs) from single p‐type AlGaN EBL can be reduced by forming the AlGaN/GaN super lattice structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of optical phonons and electronic properties of group III‐V nitride multi quantum wells by using far infrared magnetoplasmon spectroscopy
Authors: Farjami Shayesteh S. , Rahmani A. , Parker T. J. 
Published: May 2006

AbstractIn this work, the behavior of optical phonons and magnetoplasmon‐ modes in the doped group III‐V Nitride semiconductor multi quantum wells are investigated in the presence of high magnetic fields parallel to the surface of the layers and perpendicular to the propagation direction by using p‐ and s‐polarized infrared magnetoplasmon reflectivity and employing an effective medium approach. Also, the modified random‐element isodisplacement model is employed to obtain the vibrational modes of GaNAs and AlGaN ternary alloy with zinc‐blend and wurzite structure. The effective carrier mass, the free carrier concentration and the mobility parameters can be quantified upon model analysis of the infrared p‐polarized magnetoplasma reflectivity and the infrared Voigt dielectric function. Theoretical results are compared and discussed with the existing far infrared and Raman scattering data. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of optical loss on blue‐violet laser diodes
Authors: Son J. K. , Hwang J. S. , Lee S. N. , Sakong T. , Paek H. , Chae S. , Kim H. K. , Nam O. , Kim J. Y. , Cho Y. H. , Park Y. 
Published: May 2006

AbstractWe measured optical loss of laser diodes by taking the intensity decay of edge emitting photoluminescence with respect to the distance from cleaved edges of wafers to the position where an excitation laser was focused. Measurements were performed on wafers with different thickness of InGaN p‐waveguide. We found that optical loss of wafers was determined by absorption of Mg doped GaN for narrow InGaN waveguide and by absorption of InGaN for thick InGaN waveguide. From experimental data and fittings, we obtained 40 cm–1 for InGaN absorption at 405 nm. Therefore, we conclude that the optical losses still remain even though the Mg‐doped GaN regions are far enough from QWs and that absorption loss of InGaN layers is relatively high comparing with undoped GaN. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
n‐type conductivity control of AlGaN with high Al mole fraction
Authors: Katsuno Takuya , Liu Yuhuai , Li Dabing , Miyake Hideto , Hiramatsu Kazumasa , Shibata Tomohiko , Tanaka Mitsuhiro 
Published: May 2006

AbstractSilicon doped AlxGa1–xN with high Al mole fraction was grown using epitaxial AlN as a underlying layer by low‐pressure metalorganic vapor phase epitaxy. n‐type conductivity control of high quality Si‐doped AlxGa1–xN was achieved successfully. Structural, electrical and optical properties were investigated for various Al mole fractions, flow rates of silicon, and AlxGa1–xN thickness, respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermalization and recombination in exponential band tail states
Authors: Niehus M. , Schwarz R. 
Published: May 2006

AbstractWe present an analytical model that combines the complementary experimental evidence of spatial dispersion (DAP recombination) and energetic dispersion (band tails). The model describes the competition between thermalization and recombination of excess carriers trapped in exponentially distributed (in energy), discrete localized (in space) states. We use the energy dependence of the relaxation rates to derive the energy and time dependence of sub gap photoluminescence. The model predicts that the yellow luminescence band (YLB) and blue luminescence band (BLB) commonly observed in GaN are not separate entities, but reflect the competition of thermalization and recombination. A distinct kink is observed in transient PL in the microsecond range, in the limiting cases of strong tailing and/or low temperatures, indicating the transition from thermalization‐limited to (radiative) recombination‐limited excess carrier relaxation. Both prediction are in line with experiment, and able to resolve interpretational difficulties. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anisotropy of the Γ‐point effective mass and mobility in hexagonal InN
Authors: Hofmann T. , Chavdarov T. , Darakchieva V. , Lu H. , Schaff W. J. , Schubert M. 
Published: May 2006

AbstractWe determine the anisotropic electron effective mass and mobility parameters in wurtzite InN thin films with free electron concentration N from 1.8 × 1017 cm–3 to 9.5 × 1018 cm–3 using Infrared Magneto‐optic Generalized Ellipsometry. The room‐temperature measurements were carried out with magnetic fields up to 4.5 T. For the Γ‐point we estimate m *⊥ = 0.047m 0 and m *‖ = 0.039m 0 for polarization perpendicular and parallel to the c ‐axis, respectively. Scattering by impurities or ionized donors may explain the decrease of mobility for polarization parallel to the c ‐axis from 1600 cm2/(Vs) to 800 cm2/(Vs) with increase in N , where the perpendicular mobility is further decreased, likely caused by additional grain boundary scattering. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparing proportional hazards and accelerated failure time models: an application in influenza
Authors: Patel Katie , Kay Richard , Rowell Lucy 
Published: May 2006

AbstractThe proportional hazards (PH) model is routinely employed for the analysis of time‐to‐event data in medical research when it is required to assess the effect of an intervention in the presence of covariates. The assumption of PH required for the PH approach may not hold, especially in circumstances where the effect of the intervention is to delay or accelerate the onset of an event rather than to reduce or increase the overall proportion of subjects who observe the event through time. If the assumption of PH is violated, the results from a PH model will be difficult to generalize to situations where the length of follow‐up is different to that used in the analysis. It is also difficult to translate the results into the effect upon the expected median duration of illness for a patient in a clinical setting. The accelerated failure time (AFT) approach is an alternative strategy for the analysis of time‐to‐event data and can be suitable even when hazards are not proportional and this family of models contains a certain form of PH as a special case. The framework can allow for different forms of the hazard function and may provide a closer description of the data in certain circumstances. In addition, the results of the AFT model may be easier to interpret and more relevant to clinicians, as they can be directly translated into expected reduction or prolongation of the median time to event, unlike the hazard ratio. We recommend that consideration is given to an AFT modelling approach in the analysis of time‐to‐event data in medical research. Copyright © 2006 John Wiley & Sons, Ltd.
The contextual meaning of sustainable development: the case of the Dutch drinking water sector
Authors: Klostermann Judith E. M. , Cramer Jacqueline 
Published: May 2006

AbstractThe concept of sustainable development means different things to different people in different contexts, leading to ‘strong’ and ‘weak’ versions of sustainability. This article addresses the question of which meaning of sustainability is given by the Dutch drinking water sector and its main stakeholders. The ‘weak’, or human‐oriented, school was found at three of the four water companies studied. This is understandable, because water companies have a human‐oriented task: to provide the public with drinking water. The ‘strong’ version of sustainability was found within several governmental bodies. Their view of ‘staying within the natural water system’ was unacceptable for most other societal actors. A third form of sustainability was developed by the fourth drinking water company studied. It bridges the human and nature interests in a step by step dialogue. This way of looking at sustainable development may be an interesting perspective in which humans start seeing themselves as an integral part of nature again, instead of as being outside and above nature. Copyright © 2006 John Wiley & Sons, Ltd and ERP Environment.