bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intersubband transitions in InGaAsN/AlGaAs quantum wells with a high confinement energy
Authors: Duboz Jean‐Yves 
Published: June 2007

AbstractWhen N is introduced in bulk InGaAs, the N level pushes the conduction band towards lower energies. In InGaAsN quantum wells however this repulsion leads to more complicated situations, in particular when confined levels are close to the N level. We calculate the energy of quantified levels in InGaAsN/AlGaAs quantum wells by using an analytical model based on the band anticrossing model and the repulsion by the nitrogen level. When the confinement becomes large enough to support subbands above the localized nitrogen level, subbands are split and have a dispersion strongly affected by the repulsion by the N level. In this case, intersubband transitions are deeply modified, with a splitting of the transitions and important spectral shifts of the lines, allowing to reach the 3‐4 µm spectral range. Due to the admixing of nitrogen wavefunction in the electron wavefunction, the amplitude of the intersubband transitions decreases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of highly resistive Ga‐polar GaN by LP‐MOVPE
Authors: Mita Seiji , Collazo Ramón , Dalmau Rafael , Sitar Zlatko 
Published: June 2007

AbstractElectrical characteristics of 1.3 µm thick GaN films were investigated with respect to the polar type. Unintentionally doped N‐polar GaN grown on nitrided sapphire substrates had a hexagonal facetted morphology and consistently exhibited a high n‐type conductivity with a sheet resistance of ∼10 Ω/sq, corresponding to a carrier concentration on the order of 1019 cm–3. In contrast, Ga‐polar GaN films grown on low temperature AlN buffer layers showed a high sheet resistance of ∼109 Ω/sq. GaN films of mixed polarity exhibited sheet resistance in‐between the two extreme values obtained for polarity pure films. The results of this work show that the existence of N‐polar domains (even on the nano‐scale) in an otherwise Ga‐polar matrix significantly decreases the insulating properties of unintentionally doped GaN films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Origin and elimination method of parasitic gate leakage current for AlGaN/GaN heterostructure field effect transistor
Authors: Baksht Tamara , Knafo Yaron , Kaplun Joseph , Bunin Gregory 
Published: June 2007

AbstractThe Schottky gate leakage current of AlGaN/GaN HFET was systematically investigated. Experimental results were acquired from gates of HFET and from round diodes on the same wafer. The performed analysis clearly shows that HFET gate current behaves according to additional physical mechanism. Hypothesis, that the source of parasitic leakage is the contact point between gate metal and two dimensional electron gas on the mesa edges, was theoretically and experimentally proved. Cost effective technological solution with SiO2 “patch” layer is presented. Transistors, manufactured with “patch” layer, have higher breakdown, two orders of magnitude lower gate leakage current, excellent performance and should be more reliable. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical and optical characterization of M‐plane GaN films grown on LiAlO2 substrates
Authors: Rivera C. , Misra P. , Pau J. L. , Muñoz E. , Brandt O. , Grahn H. T. , Ploog K. H. 
Published: June 2007

AbstractWe report on a study of the electrical and optical properties of strained M‐plane GaN films grown on LiAlO2 substrates. We have electrically characterized Schottky barrier devices fabricated on strained M‐plane GaN films. The current leakage found in these devices is probably related to a surface effect. The influence of the current direction for in‐plane transport in M‐plane GaN was also studied. Polarized photoluminescence spectroscopy shows the effect of residual biaxial strain on the optical selection rules, allowing to identify intrinsic transitions involving holes from the two uppermost valence bands. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inductively coupled plasma etching of GaN using SiCl4/Cl2/Ar for submicron‐sized features fabrication
Authors: Dylewicz R. , Hogg R. A. , Fry P. W. , Parbrook P. J. , Airey R. , Tahraoui A. , Patela S. 
Published: June 2007

AbstractIn this paper we report the optimization of the fabrication process of a grating coupler, which is fully integrated with a GaN planar waveguide. To our knowledge, this is the first report of a grating‐assisted optical coupler in gallium nitride. ICP dry etching of n‐doped GaN layers was investigated, where SiCl4/Cl2/Ar gas mixture was used under different etching conditions. We report n‐GaN ICP etching ratio of 520‐2680 Å min–1 as well as etching selectivity of GaN over SiO2 from 3 to 8, in the most cases. Grating ridge and grating groove width as well as the sidewalls slope were evaluated by SEM microscope. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and optical properties of Si‐doped AlGaN/AlN multiple quantum wells grown by MOVPE
Authors: Li Da‐Bing , Katsuno Takuya , Aoki Masakazu , Miyake Hideto , Hiramatsu Kazumasa , Shibata Tomohiko 
Published: June 2007

AbstractUndoped and Si‐doped AlxGa1–xN/AlN (x > 0.5) multiple quantum wells (MQWs) were grown on AlN/sapphire templates by metalorganic phase vapor epitaxy. The influence of Si doping on the structural and optical properties was investigated by means of high resolution X‐ray diffraction (HRXRD) and cathodoluminescence (CL) measurement. Comparing with unintentionally doped MQWs, the interface quality of the MQWs wasn't reduced by Si doping, even a little improved. CL measurement demonstrated that the MQWs behaved a deep ultraviolet emission. For MQWs with Si doped barrier layer, the deep UV emission peak characterizes blueshift with increasing the Si dopant concentration and the Si doping has no obvious effect on the CL intensity in the case of the dopant content lower than 1×1019 cm–3, however, with increasing the dopant content to 1020 cm–3, the efficiency of deep UV emission was drastically enhanced. The mechanism of enhancement was discussed in detail. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Free standing GaN layers with GaN nanorod buffer layer
Authors: Lee H. J. , Lee S. W. , Goto H. , Lee Hyo‐Jong , Ha J. S. , Cho M. W. , Yao T. 
Published: June 2007

AbstractThick GaN films were grown by HVPE (Hydride Vapor Phase Epitaxy) on c‐sapphire substrates with GaN nano‐rod buffer layers. Lateral epitaxial growth mode was adapted to grow GaN thick films on nano‐structure buffer. Thick GaN films were self‐separated during cooling down by thermal stress caused by the difference of thermal expansion coefficient (TEC) between GaN and sapphire. Since the nano‐rod buffer consists of nano‐rods and voids, it is mechanically weaker than planar GaN layers and contributes to the self‐separation of GaN thick films. 200 μm‐thick free‐standing GaN substrates show smooth surface morphology without any microcracks. The full width at half maximum (FWHM) of (0002) X‐ray rocking curve is 619 [arcsec]. Donor‐bound exciton emission is observed at 3.4718 eV in low‐temperature photoluminescence spectra, which is nearly the same peak position as bulk GaN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Near‐UV to violet LEDs – Wavelength dependence of efficiency limiting processes
Authors: Kunzer M. , Kaufmann U. , Köhler K. , Leancu C. C. , Liu S. , Wagner J. 
Published: June 2007

AbstractTwo wavelength series (373‐435 nm) of GaInN/GaN triple quantum well LED‐structures, one on sapphire and one on GaN‐templates, as well as a quantum well thickness series were grown by MOVPE. In order to study luminescence efficiency limiting effects the LED‐structures were characterized by electroluminescence‐ and by temperature and excitation power dependent photoluminescence spectroscopy. The electroluminescence output and the internal quantum efficiency are peaked near 400 nm in both wavelength series, but output and efficiency are significantly enhanced for growth on templates. The photoluminescence data indicate that below 400 nm the efficiency, apart from insufficient vertical carrier confinement, is limited by poor localization within the quantum film plane while above 400 nm piezo‐electric fields appear to be an important efficiency limiting effect. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear piezoelectric properties of GaN quantum dots nucleated at the edge of threading dislocations
Authors: Dłużewski Paweł , Young Toby D. , Jurczak Gregorz , Majewski Jacek A. 
Published: June 2007

AbstractIt was observed experimentally by Rouviere et al. that GaN/AlN Quantum Dots (QDs) nucleate at the edge of threading dislocations (Appl. Phys. Lett. 75, 2632 (1999) [1]). The preferred nucleation of QDs in this way is generally assumed to be due to the influence of the stress/strain field around the dislocation core, which in turn, gives the chemical and geometric conditions for nucleation of the QDs. We solve the finite element problem for QDs situated at the edge of threading dislocations where different lattice parameters, piezoelectric and spontaneous polarisation coefficients are assumed for the QD and its matrix. By solving the elastic and electric equilibrium problems we obtain both the residual stress and electric fields. The computational scheme employed here was obtained by linking two previous finite element algorithms described inreferences (P. Dłużewski et al., Comput. Mater. Sci. 29, 379 (2004) [2]) and (G. Jurczak et al., phys. stat. sol. (c) 2, 972 (2005) and S.P. Łepkowski et al., Phys. Rev. B 73, 245201 (2005) [3, 4], respectively). This approach allows us to get a deeper physical insight into the mechanics and electrical properties of QDs and ultimately determine the efficiency of light emission from these objects.
Continuous order‐disorder phase transition (2×2)→(1×1) on the (0001)AlN surface
Authors: Mansurov V. G. , Galitsyn Yu. G. , Nikitin A. Yu. , Kolosovsky E. A. , Zhuravlev K. S. , Osvath Z. , Dobos L. , Horvath Z. E. , Pecz B. 
Published: June 2007

AbstractSmooth (0001)AlN surface on a (0001) sapphire substrate was prepared by ammonia Molecular Beam Epitaxy. A continuous (2×2)→(1×1) reconstruction phase transition on the (0001)AlN surface under ammonia flux was experimentally investigated by RHEED. The intensity of a fractional (0 1/2) streak was studied as a function of the sample temperature under different ammonia fluxes. The temperature of the transition increases with increasing of the ammonia flux (an effective activation energy is about 1.3 eV). The phase transition is described in the frame of the Bethe‐Peierls approximation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Localized plasmons at pores and clusters within inhomogeneous indium nitride films
Authors: Shubina T. V. , Vasson A. , Leymarie J. , Gippius N. A. , Jmerik V. N. , Monemar B. , Ivanov S. V. 
Published: June 2007

AbstractWe report on reproducibly observed enhancement of luminescence within inhomogeneous InN films near both In clusters and pores. Low‐temperature absorption in these films deviates from that expected for a conventional semiconductor. The enhancement of emission is discussed in terms of coupling of excited radiative states with localized particle plasmons. It implies concentration of an electric field near the pores and clusters, which are considered, respectively, as metallic and dielectric ellipsoids within a semiconductor matrix. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FE simulation of InGaN QD formation at the edge of threading dislocation in GaN
Authors: Dłużewski Paweł , Belkadi Amina , Chen Jun , Ruterana Pierre , Nouet Gerard 
Published: June 2007

AbstractThe stress induced diffusion process of In‐Ga segregation in InxGa1–xN layer deposited on GaN is simulated step by step by using a 3D nonlinear FE method. From the thermodynamical point of view this process is governed by the driving force induced by the gradient of residual stresses operating in an anisotropic nonlinear elastic structure. The source of stresses we consider is the set of threading dislocations examined in the plane view HRTEM investigation of GaN layer deposited on sapphire.
Impact of polarity control and related defects on the electrical properties of GaN grown by MOVPE
Authors: Collazo R. , Mita S. , Dalmau R. , Sitar Z. 
Published: June 2007

AbstractBy controlling the LT‐AlN nucleation layer, we have demonstrated growth of Ga‐ and N‐polar GaN thin films with identical growth rates on c‐plane sapphire via MOVPE. The Ga‐polar films were highly resistive, while N‐polar films exhibited n‐type conductivity. Under certain nucleation layer processing conditions, the GaN films were mixed‐polar. Using specular X‐ray reflectivity to calculate the density depth profile of the nucleation layers, we identified one mechanism during the processing evolution of the nucleation layer that could give rise to inversion domains within the film, giving raise to mixed‐polar GaN films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanisms of metalorganic vapor phase epitaxy of InGaN quantum wells on GaN microfacet structures
Authors: Ueda M. , Hayashi K. , Kondou T. , Funato M. , Kawakami Y. , Narukawa Y. , Mukai T. 
Published: June 2007

AbstractThe growth mechanisms during metalorganic vapor phase epitaxy of InGaN quantum wells (QWs) on three‐dimensional GaN microfacet structures composed of (0001) and {11‐22} planes were investigated. The cross section of the microfacet structures formed by regrowth was changed from triangle to trapezoid, depending on the mask geometries for the regrowth. The emission peak wavelength of the (0001) microfacet QWs was always longer than that of the {11‐22} microfacet QWs, and the difference is smaller than in planar (0001) and {11‐22} QWs. To clarify this observation, the local thicknesses of constituent InN and GaN on the GaN microfacets were estimated. Using a formula derived from the diffusion equation, the distribution of the local thickness is fitted to estimate the apparent diffusion lengths, λ. For Ga, λ was fitted to be 5.2 μm on (0001) and 3.1 μm on {11‐22}, while for In, λ was 2.7 μm on (0001) and 1.6 μm on {11‐22}. This suggests that the degree of migration of adatoms depends on both facets and atoms, which may cause the facet‐dependent In compositions and lead to multiwavelength emission from microfacet InGaN QWs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mg‐doped high‐quality AlxGa1–xN (x=0‐1) grown by high‐temperature metal‐organic vapor phase epitaxy
Authors: Imura M. , Kato N. , Okada N. , Balakrishnan K. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I. , Noro T. , Takagi T. , Bandoh A. 
Published: June 2007

AbstractWe report on the growth of Mg‐doped AlxGa1–xN alloys and characterization of their optical properties. Under the low Mg concentration in the range 2×1017 to 1×1018 cm–3 of AlxGa1–xN, the activation energy of Mg acceptor became higher and higher with increase in the Al content of AlxGa1–xN. The experimental results for activation energies of Mg acceptor fitted quite well with the hydrogen atom like model. By the Haynes' rule, relationship between bound‐excition energy and activation energy of Mg acceptor was investigated, which coincided with our experimental results. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of junction temperature and its variations on the performance of GaN‐based high power flip‐chip LEDs
Authors: Lin L. , Chen Z. Z. , Pan H. P. , Qi S. L. , Liu P. , Qin Z. X. , Yu T. J. , Zhang B. , Tong Y. Z. , Zhang G. Y. 
Published: June 2007

AbstractIn this paper, high power flip‐chip GaN‐based LEDs were fabricated, and then the effects of junction temperature and its variations were investigated. It was found that the optical output decreases seriously with rising temperature. The variations of junction temperature can be achieved to 9 °C at 350 mA in most regions of flip‐chip LED except for some hot regions around some electrodes. The combination of screening of quantum confined Stark effect (QCSE) and thermal effect surprisingly makes the peak wavelength constant from 300 mA to 800 mA in electroluminescence spectra. The full‐width at half‐maximum (FWHM) of emission peak was narrowed by thermal effect in constant current (CC) injection. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystallographic deterioration of MOVPE InN during the growth
Authors: Sugita K. , Nagai Y. , Houchin Y. , Hashimoto A. , Yamamoto A. 
Published: June 2007

AbstractThis paper reports the crystallographic degradation of MOVPE InN during the growth. Using FWHMs of X‐ray rocking curve, tilt ((0002)) and twist ((10‐10)) angle distributions are evaluated and effects of the major growth parameters, such as growth temperature, growth time and with/without GaN buffer in the degradation, are revealed. With increasing either thickness of grown InN or growth temperature up to 600 °C, the tilt angle distribution is markedly increased, indicating the crystallographic degradation of grown films. The use of a GaN buffer reduces such degradation. Since the twist angle distribution is scarcely changed by such growth parameters, the destruction of InN crystals during growth and annealing is concluded to be anisotropic. The trends of the crystallographic degradation revealed here are in good agreement with those for the electrical and optical degradation previously reported. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Metal catalyst enhanced growth of high quality and density GaN dots on Si(111) by implant source growth
Authors: Buckmaster Ryan , Goto Takenari , Hanada Takashi , Fujii Katsushi , Kato Takashi , Yao Takafumi 
Published: June 2007

AbstractUsing ion implantated material as a growth source, implant source growth, is an alternative growth method where ion implanted atoms diffuse to the surface and can be used to form nanostructures. By introducing a small amount of a steel based contaminate we were able to grow high quality and high density GaN nanodots on Si(111) which showed strong excitonic UV luminescence. Furthermore by varying the implanted Ga dose and annealing conditions, the size of the nanodots can be controlled. This method for producing GaN nanostructures may be useful for optical or electronic device applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time‐resolved photoluminescence spectroscopy in a GaN/AlGaN SQW structure grown on a (111) Si substrate
Authors: Kim Eunhee , Narita Tetsuo , Honda Yoshio , Yamaguchi Masahito , Sawaki Nobuhiko 
Published: June 2007

AbstractTime‐resolved photoluminescence (PL) spectroscopy was performed at 77 K for the near band edge emission band in a GaN/AlGaN single quantum well structure grown on a (111) Si substrate. The near band edge emission band was decomposed into several peaks characteristic to structural defects/dislocations in the sample. By using PL intensity correlation method, the decay time constant of the peak intensity was investigated. The radiative recombination time for the neutral‐donor‐bound exciton (DoX) peak was on the order of 800 ps, while the time constants for the defect/dislocation related peaks depended on the wavelength or the associated energy level ranging between 550 ps and 1,000 ps. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Unusual photoluminescence properties of vertically aligned InN nanorods grown by plasma‐assisted molecular‐beam epitaxy
Authors: Shen C.‐H. , Chen H.‐Y. , Lin H.‐W. , Wu C.‐Y. , Gwo S. , Klochikhin A. A. , Davydov V. Yu. 
Published: June 2007

AbstractWe report the unusual photoluminescence (PL) properties of vertically aligned InN nanorod arrays grown on Si(111) with a Si3N4 buffer layer. The optimum growth conditions of InN nanorods are obtained by controlling the III/V ratio and the growth temperature. Structural characterization by X‐ray diffraction and scanning electron microscopy indicates that individual nanorods are wurtzite InN single crystals with the growth direction along the c‐axis. Near‐infrared PL from InN nanorods is clearly observed at room temperature. However, in comparison to the PL from InN epitaxial films, the PL from InN nanorods is significantly lower in efficiency and exhibit anomalous temperature dependence. We propose that these unusual PL properties are results of considerable structural disorder (especially for the low‐temperature grown InN nanorods) and strong surface electron accumulation effect. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐electron transition spectroscopy of shallow donors in bulk GaN
Authors: Paskov P. P. , Monemar B. , Toropov A. , Bergman J. P. , Usui A. 
Published: June 2007

AbstractWe report a detailed study of the recombination processes of the excitons bound to O and Si shallow donors in bulk GaN. Photoluminescence (PL) and time‐resolved PL measurement at different polarization and temperatures were carried out on a high quality 1‐mm thick sample grown by Hydride Vapor Phase Epitaxy. Together with the principal donor‐bound exciton (DBE) emission lines a large number of two‐electron transitions (TETs) related to the ground and excited states of both DBE were observed allowing an accurate determination of the donor binding energies. Polarization properties and optical selection rules as well as the recombination dynamics of different PL lines were also studied and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Series resistance in a GaN/AlGaN/n‐Si structure grown by MOVPE
Authors: Honda Yoshio , Kato Satoshi , Yamaguchi Masahito , Sawaki Nobuhiko 
Published: June 2007

AbstractGaN film was grown on a (111)Si substrate using AlGaN intermediate layer by selective metalorganic vapor phase epitaxy. The series resistance of the GaN/AlGaN/Si diode was evaluated as a function of the thickness and the alloy composition of the AlGaN intermediate layer. The resistance was decreased by reducing the thickness of the intermediate layer but showed a minimum value. The minimum resistance was evaluated as a function of the alloy composition. Assuming an exponential increase of the minimum resistance as a function of the conduction band offset in the AlGaN/Si interface, the resistance for a GaN/Si hetero interface was estimated to be 0.0018 Ω cm2. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructure of A‐plane InN grown on R‐plane sapphire by ECR‐MBE
Authors: Watanabe S. , Kumagai Y. , Tsuyuguchi A. , Na H. , Naoi H. , Araki T. , Nanishi Y. 
Published: June 2007

AbstractWe used electron cyclotron resonance plasma‐excited molecular beam epitaxy (ECR‐MBE) to grow A‐plane (11$ \bar 2 $0) InN on nitridated R‐plane (1$ \bar 1 $02) sapphire and then measured the structural properties using transmission electron microscopy (TEM). We determined the epitaxial relationship between A‐plane InN and R‐plane sapphire to be (11$ \bar 2 $0)InN // (1$ \bar 1 $02)sapphire and [1$ \bar 1 $00]InN // [11$ \bar 2 $0]sapphire. Moreover, the results indicated that the nitridation of the sapphire produced a (001) cubic AlN layer, and this layer caused the subsequent InN to have its a‐axis normal to the interface. Also, by using two diffraction vector orientations in the TEM measurement, we found that dislocations with a screw component had a density of about 5 × 1010 cm–2, which is about ten times higher than that with an edge component. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)