bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of InGaN-GaN quantum well chemistry and interfaces by transmission electron microscopy and X-ray scattering
Authors: Smeeton T. M. , Kappers M. J. , Barnard J. S. , Humphreys C. J. 
Published: April 2011

ABSTRACTWe have studied the distribution of indium in InxGa1-xN single quantum wells (SQWs) with compositions of In0.18Ga0.82N and In0.22Ga0.78N. Based on lattice parameter maps extracted from HRTEM lattice fringe images, we do not find evidence for strong nanometre-scale fluctuations in the composition of the wells (indium “clusters”). Z-contrast (high-angle annular dark field) scanning TEM (STEM) and X-ray reflectivity (XRR) results both show that the width of the interface at the top of the quantum well is slightly greater than that at the bottom, which is quite abrupt. The quantum wells exhibit bright photoluminescence so these results suggest that the conventional explanation for the high efficiency of light emission from InGaN LEDs may not apply in these structures.
High Temperature Implantation of Tm in GaN
Authors: Lorenz K. , Wahl U. , Alves E. , Dalmasso S. , Martin R. W. , O'Donnell K. P. 
Published: April 2011

ABSTRACTThulium ions were implanted into MOCVD grown GaN films with a fluence of 2.5×1015 at/cm2 at temperatures between 20 and 500 °C. The lattice damage introduced by the implantation and the effect of post-implant annealing were investigated using the Rutherford backscattering/channeling (RBS/C) technique. Whereas for room temperature implantation the implanted layer becomes amorphous, high temperature implantation inhibits amorphisation. For implantation temperatures higher than 300 °C the RBS/C results clearly show two different damage regions - one at the surface and the second deeper in the crystal coinciding with the Tm depth profile. Annealing causes a decrease of the surface damage as well as initiating regrowth from the unimplanted bulk GaN. For the samples that were not completely amorphous a large part of the Tm atoms were found to be incorporated in Ga-sites. The optical properties of the ion implanted GaN films have been studied by room temperature cathodoluminescence. Directly following the implantation no Tm-related luminescence was observed. Subsequent annealing of the samples achieved optical activation, revealing well-defined emissions due to intra-4f-shell transitions of the Tm3+ ions in the blue spectral range at 477 nm and in the near infra-red at 804 nm.
Reciprocal Space Mapping of X-Ray Diffraction Intensity of GaN-Based Laser Diodes Grown on GaN Substrates
Authors: Tachibana K. , Harada Y. , Saito S. , Nunoue S. , Katsuno H. , Hongo C. , Hatakoshi G. , Onomura M. 
Published: April 2011

ABSTRACTCharacterization by reciprocal space mapping of x-ray diffraction (XRD) intensity was carried out for epitaxial layers of GaN-based laser structures on two GaN substrates: GaN substrate and GaN template on sapphire substrate. The difference between these two substrates was shown clearly. The distribution of XRD intensity of the epitaxial layers on GaN substrate was smaller than that of the epitaxial layers on GaN template on sapphire substrate. In the lasers with the epitaxial structure on GaN substrate, the light output power was as high as 200 mW under continuous-wave operation at room temperature. Excellent noise characteristics with relative intensity noise of -132 dB/Hz were also obtained at a low light output power of 3 mW without any high-frequency modulation. These results support that GaN substrates are promising for realizing GaN-based lasers with high performance.
Spectroscopy of Intraband Electron Confinement in Self-Assembled GaN/AlN Quantum Dots
Authors: Helman Ana , Moumanis Khalid , Tchernycheva Maria , Lusson Alain , Julien Francois , Damilano Benjamin , Grandjean Nicolas , Massies Jean , Adelmann Christophe , Fossard Frederic , Dang Daniel Le Si , Daudin Bruno 
Published: April 2011

ABSTRACTWe present a detailed analysis of inter- and intraband transitions in GaN/AlN self-organized quantum dots grown on sapphire, silicon (111) and 6H-SiC substrates. Quantum dot samples have been characterized by means of transmission electron microscopy, photoluminescence and photo-induced absorption spectroscopy. Interlevel transitions in the conduction band are observed in the 0.52–0.98 eV energy range, thus covering the telecommunication band. The s-pz absorption is peaked at 0.8 eV (0.52 eV) for samples with dot height of 1.5 nm (6 nm). Calculations show that in bigger dots the transition energy is governed by the value of the internal field.
Structure and photoluminescence investigations of Er doped GaN layers grown by MBE
Authors: Wojtowicz T. , Ng H. M. , Ruterana P. 
Published: April 2011

ABSTRACTIn this work, we carry out TEM analysis on GaN layers grown on sapphire and doped in situ by MBE. In parallel, photoluminescence and electroluminescence experiments are used to determine the possible emission of the grown layers. It has been shown previously that the emission peaks at Er concentrations of about 1% and that their intensity dramatically decreases with increasing Er concentration probably due to compositional quenching. We report on the evolution of the microstructure versus composition and try to explain the quenching effects that can be related to the microstructure.
Manifestation of structural defects in photoluminescence from GaN
Authors: Reshchikov M. A. , Jasinski J. , Yun F. , He L. , Liliental-Weber Z. , Morkoç H. 
Published: April 2011

ABSTRACTSharp peaks of unidentified nature are detected in the low-temperature photoluminescence (PL) spectrum of undoped GaN in the photon energy range between 3.0 and 3.46 eV. These PL lines are commonly attributed to excitons bound to yet unidentified structural defects. We analyzed X-ray diffraction data in a large set of GaN samples grown by molecular beam epitaxy in order to find any correlation between these unusual PL peaks and the GaN crystal structure. Moreover, in selected samples exhibiting such peaks, cross-sectional transmission electron microscopy was taken in an effort to detect the presence and density of various structural defects. The preliminarily results indicate that most of unusual PL lines in GaN (Y lines) are not directly related to the observed structural defects, such as edge, screw, mixed dislocations, or stacking faults. However, there exists the possibility that point defects trapped at dislocations or other structural defects are responsible for these PL lines.
Strong dependence of the fundamental band gap on the alloy composition in cubic InxGa1-xN and InxAl1-xN alloys
Authors: Dridi Z. , Bouhafs B. , Ruterana P. 
Published: April 2011

ABSTRACTAb initio total energy calculations, based on the full-potential augmented plane wave method within the local density approximation, are used to study the influence of alloying on the structural and electronic properties of cubic InxGa1-xN and InxAl1-xN ordered alloys in the chalcopyrite and luzonite structures.We have investigated the lattice parameters and band gap energies. The lattice parameters, exhibit an upward bowing of -0.05 Å and -0.15 Å, respectively for the InxGa1-xN and InxAl1-xN alloys. The composition dependence of the band gap shows a bowing parameter of 1.36 eV for InxGa1-xN. The band gap InxAl1-xN alloys exhibits a bowing parameter of 3.19 eV, and a direct to indirect band gap transition at x (Al) = 0.83. The large bowing effect in InxAl1-xN alloys has been discussed in terms of a composition dependent bowing parameter.
Luminescent Holmium Doped Amorphous AlN Thin Films for use as Waveguides and Laser Cavities.
Authors: Maqbool Muhammad , Richardson H. H. , Van Patten P. G. , Kordesch M. E. 
Published: April 2011

ABSTRACTHolmium doped AlN thin films have been deposited on flat silicon substrates and optical fibers of different diameters, in order to fabricate resonant cavities for lasers. In particular, the films on fiber substrates are expected to perform as cylindrical waveguides or “whispering gallery” mode cavities. The AlN films are deposited by reactive sputtering at liquid nitrogen temperature, using 100–200 Watts RF power, 5–8 mTorr nitrogen, using a metal target of Al and Ho. One micron thick films of AlN:Ho have been deposited on flat silicon substrates and 10 micron thick films on 80μm and smaller optical fibers. X-ray Diffraction and SEM studies show that films deposited on flat silicon are amorphous while those deposited on the fibers show columnar growth and some gain structure, most probably due to a temperature rise at the substrate during deposition. Cathodoluminescence (CL) emission is observed in thermally activated AlN:Ho in both crystalline and amorphous forms. An intense, narrow emission peak is observed at 549 nm. Less intense peaks are also observed at 362nm, 394 nm, 461 nm, and 659 nm. The most promising wavelength for our design is emission from the 5S2 → 5I8 transition at 549 nm.
Time-Resolved Reflectivity Studies of Electric Field Effects in III-Nitride Semiconductors
Authors: Wraback M. , Shen H. , Sampath A. V. , Collins C. J. , Garrett G. A. , Sarney W. L. , Fedyunin Y. , Cabalu J. , Moustakas T. D. 
Published: April 2011

ABSTRACTComparison of room temperature, frequency degenerate and nondegenerate femtosecond pump-probe reflectivity measurements reveal an additional component in the transient reflectivity (ΔR) decays for near bandgap probe in GaN that is attributed to a reduction of bandedge broadening due to screening of internal electric fields by photogenerated carriers. Pump-probe measurements with pulses spectrally centered at 363 nm show a ΔR component with a nanosecond decay time that is essentially absent from data obtained from nondegenerate experiments performed under identical pumping conditions, but with a probe at 385 nm far enough from the bandedges to minimize the electric field contribution and monitor primarily the carrier lifetime in the band states. The observation of significantly shorter decay times for 385 nm probe suggests that the carriers leave the band states on a picosecond time scale, but the slow decay of the field screening observed with 363 nm probe implies that they recombine from trap states at longer times. In addition, this field screening provides a mechanism for generation and detection of strain pulses in strained GaN and AlGaN epilayers that is used to measure the longitudinal sound velocity in bulk GaN and AlGaN with up to 0.4 Al content.
High Temperature Operation of A New Normally-Off AlGaN/GaN HFET on Si Substrate
Authors: Yoshida Seikoh , Li Jiang , Wada Takahiro , Takehara Hironari 
Published: April 2011

ABSTRACTWe report on the novel normally-off AlGaN/p-type GaN heterojunction field effect transistors (HFETs). We grew the AlGaN/p-GaN heterostructure on p-type Si (111) substrate using a metalorganic chemical vapor deposition (MOCVD). A homogeneous buffer layer was first formed on a Si (111) substrate at 1123 K. After that, AlGaN (30 nm)/high resistive p-type GaN (500 nm) heterostructure was also grown at 1303 K without cracking. We fabricated an HFET using AlGaN/p-type GaN on Si substrate. The ohmic electrode material was Al/Ti/Au and the gate electrode was Pt/Au. The distance between the source and the drain was 0.01 mm. The gate length and width were 2000 nm and 0.15 mm, respectively. As a result, the HFET was operated at the condition of the positive gate bias. The pinch-off voltage was 0 V. A normally-off operation was thus confirmed for the first time. The breakdown voltage of FET was over 250 V. We also confirmed that the normally-off HFET was operated at 573 K for over 150 h.
High-Power Characteristics of GaN/InGaN Double Heterojunction Bipolar Transistors with a Regrown p-InGaN Base Layer
Authors: Makimoto Toshiki , Yamauchi Yoshiharu , Kumakura Kazuhide 
Published: April 2011

ABSTRACTWe have investigated high-power characteristics of GaN/InGaN double heterojunction bipolar transistors on SiC substrates grown by metalorganic vapor phase epitaxy. The p-InGaN extrinsic base layers were regrown to improve ohmic characteristics of the base. Base-collector diodes showed low leakage current at their reverse bias voltages due to a wide bandgap of a GaN collector, resulting in a high-voltage transistor operation. A 90 μm × 50 μm device operated up to a collector-emitter voltage of 28 V and a collector current of 0.37 A in its common-emitter current-voltage characteristics at room temperature, which corresponds to a DC power of 10.4 W. A collector current density and a power density are as high as 8.2 kA/cm2 and 230 kW/cm2, respectively. These results show that nitride HBTs are promising for high-power electronic devices.
Electrical and Optical Properties of Carbon Doped Cubic GaN Epilayers Grown Under Extreme Ga Excess
Authors: As D. J. , Pacheco-Salazar D. G. , Potthast S. , Lischka K. 
Published: April 2011

ABSTRACTP-type doping of cubic GaN by carbon is reported with maximum hole concentration of 2 6.1×1018cm-3and hole mobility of 23.5 cm /Vs at room temperature, respectively. The cubic GaN:C was grown by rf-plasma assisted molecular beam epitaxy (MBE) under Ga-rich growth conditions on a semiinsulating GaAs (001) substrate (3 inches wafer). E-beam evaporation of a graphite rode with an C-flux of 1×1012cm-2s-1was used for C-doping of the c-GaN. Optical microscopy, Hall-effect measurements and photoluminescence were performed to investigate the morphological, electrical and optical properties of cubic GaN:C. Under Ga-rich growth conditions most part of the carbon atoms were incorporated substitutially on N-site giving p-type conductivity. Our results verify that effective p-type doping of c-GaN can be achieved under extrem Ga excess.
Optical Properties of Mn-doped GaN
Authors: Gelhausen O. , Malguth E. , Phillips M. R. , Goldys E. M. , Strassburg M. , Hoffmann A. , Graf T. , Gjukic M. , Stutzmann M. 
Published: April 2011

ABSTRACTMolecular beam epitaxy-grown GaN with different Mn concentrations (5–23 × 10 cm-3) and codoped with Si were investigated by cathodoluminescence (CL) spectroscopy and optical transmission measurements. In the GaN:Mn, an intense absorption peak at 1.414 +/- 0.002 eV was observed. This peak was attributed to an internal T2∼> E transition of the deep neutral Mn3+ state since its intensity scaled with the Mn3+ concentration. The CL measurements showed that Mn-doping concentrations around 1020 cm-3 had three effects on the emission spectrum: (i) the donor bound exciton at 3.460 eV was reduced by more than one order of magnitude, (ii) the donor-acceptor-pair band at 3.27 eV was completely quenched and (iii) the yellow luminescence centered at 2.2 eV was the strongly decreased. The latter two effects were attributed to a reduced concentration of VGa. In the infrared spectral range, three broad, Mn-doping related CL emission bands centered at 1.01 ± 0.02 eV, 1.09 ± 0.02 eV and 1.25 ± 0.03 eV were observed. These bands might be related to deep donor complexes, which are generated as a result of the heavy Mn-doping, rather than internal transitions at the Mn atom.
MBE Growth Study of GaAsSbN/GaAs Single Quantum Wells
Authors: Wu Liangjin , Iyer Shanthi , Nunna Kalyan , Li Jia , Bharatan Sudhakar , Collis Ward , Matney Kevin 
Published: April 2011

ABSTRACTIn this work, the growth and properties of GaAsSbN single quantum wells are investigated. The heterostructures were grown on GaAs substrates in an elemental solid source molecular beam epitaxy system with a RF plasma nitrogen source. A systematic study has been carried out to determine the influence of growth temperature on the optical properties of the layers. For reference low temperature photoluminescence (PL) characteristics of the GaAsSb/GaAs QWs as a function of Sb is also presented. A significant increase in PL intensity with a corresponding blue shift in emission energy and a decrease in full width at half maximum (FWHM) has been observed on annealing the GaAsSbN/GaAs sample in a nitrogen ambient at 700°C. PL emission wavelength as long as 1.52 μm at room temperature has been obtained on annealed samples.
Modeling of recombination lifetimes in charge-separation device structures
Authors: Dashdorj Jamiyanaa , Ahrenkiel Richard , Metzger Wyatt 
Published: April 2011

ABSTRACTRecombination processes in semiconductors are inhibited by charge-separation mechanisms that are produced in structures such as pn junctions. In this work, we calculated the recombination rates in Si and GaAs n+p junction structures by both analytical and numerical techniques. Transport effects can be divided into three physical phenomena. The first is the flow of carriers that results in the build up of a junction voltage or charge-separation. The time constant of this effect is determined by the junction dopant concentrations and the mobilities. The second is the flow of carriers due to diffusion. The time constant of this event is a function of the carrier diffusion coefficient and physical width of the absorbing medium. In most semiconductor structures, this time constant is relatively short relative to the recombination lifetime. The third effect is the discharge of the open-circuit voltage of the junction by minority carrier charge injection. A heuristic analysis of the long-term decay in this regime indicates that the decay time varies as CkT /qJ0, where C is the junction capacitance and J0 is the dark current. In this regime, the decay time is a function of recombination lifetime through the dependence of J0, but the measured excess carrier decay time is often not the true recombination lifetime of the underlying materials.
Defects and Surfactant Action of Antimony on GaAs and GaAs1-xNx on GaAs [100] by Molecular Beam Epitaxy
Authors: Cheah W. K. , Fan W. J. , Yoon S. F. , Wicaksono S. , Liu R. , Wee A. T. S. 
Published: April 2011

ABSTRACTLow temperature (4.5K) photoluminescence (PL) measurements of GaAs(N):Sb on GaAs grown by solid source molecular beam epitaxy (MBE) show a Sb-related defect peak at ∼1017nm (1.22eV). The magnitude of the Sb-related impurity PL peak corresponds in intensity with the prominence of the additional two-dimensional [115] high-resolution x-ray diffraction (HRXRD) defect peaks. The elimination of these defects can be a measure of the improvement in crystal quality of GaAsN:Sb and a Sb flux ≥ 1.3×10−8 Torr is needed to invoke the surfactant behavior in III-V dilute nitride MBE growth for a growth rate of 1μm/hr.
Fabrication of side-illuminated p-i-n Photodiode with waveguide layers
Authors: Jeon Byungok , Yang Seungkee , Kang Hwayoung , Rhee Doyoung 
Published: April 2011

ABSTRACTWe present the fabrication of side-illuminated p-i-n photodiode. This is suitable for passive integration on the planar lightwave circuit (PLC), which is able to make the low-cost packages. Epitaxial structures have two main layers, diode layer and waveguide layer. It was determined by beam propagation method (BPM) simulation. To get a high responsivity and reliability, each layer must be etched. The alignment tolerances were tested. We carried out some experiments on various methods and several devices were satisfactory for the optical communication system at 1.3- and 1.55 micrometer wavelengths.
Determination of the Nitrogen Acceptor Ionization Energy in Zinc Oxide by Photoluminescence Spectroscopy
Authors: Wang Lijun , Garces N. Y. , Halliburton L. E. , Giles N. C. 
Published: April 2011

ABSTRACTPhotoluminescence (PL) experiments performed on bulk ZnO crystals are used to establish the ionization energy of the substitutional nitrogen acceptor. The temperature dependence of the nitrogen-related electron-acceptor (e,A°) emission band has been monitored in as-grown single crystals. A lineshape analysis of this band is used to determine the acceptor ionization energy. The temperature variation of the ZnO band gap was included in our analysis and the low-temperature acceptor ionization energy for substitutional nitrogen at an oxygen site in ZnO was found to be EA = 209 ± 3 meV. Electron paramagnetic resonance and Hall-effect measurements were also used to characterize these bulk ZnO samples.
Near-Field Magneto-Photoluminescence of Singe Self-Organized Quantum Dots.
Authors: Mintairov A. M. , Vlasov A. S. , Merz J. L. 
Published: April 2011

ABSTRACTWe present results obtained using low temperature near-field scanning optical microscopy for the measurements of Zeeman splitting and the diamagnetic shift of single self-organized InAs/AlAs, InAs/GaAs and InP/GaInP quantum dots. The measurements allow us to relate the bimodal size distribution of InAs dots with variations in In content. For single InP QDs we observed a strong circular polarization at zero magnetic field accompanied with a negative energy shift, suggesting that strong internal magnetic fields exist in these QDs.
Quantum Dot Lasers and Amplifiers
Authors: Pohl Udo W. , Bimberg Dieter 
Published: April 2011

ABSTRACTProgress in self-organized epitaxy of quantum dots lead to fabrication of edge- and surface-emitting lasers featuring excellent device characteristics. Exceedingly low lasing threshold, an internal quantum efficiency near unity, high characteristic temperature was proved, and high power operation was demonstrated. We present recent achievements on lasers and optical amplifiers based on InGaAs quantum dots in GaAs matrix.
Nanoengineered Quantum Dot Active Medium for Thermally-Stable Laser Diodes
Authors: Tokranov V. , Yakimov M. , Katsnelson A. , Lamberti M. , Agnello G. , Oktyabrsky S. 
Published: April 2011

ABSTRACTThe influence of a nanoengineering procedure on the properties of single- and multi-layer self-assembled InAs quantum dot (QDs) has been studied using photoluminescence, transmission electron microscopy (TEM), and electroluminescence. Optical properties of QDs were optimized by shape engineering via adjustment of a GaAs overlayer thickness prior to a heating (truncation) step. TEM micrographs have confirmed that the employed growth procedure results in truncated pyramidal QDs covered entirely by AlAs with smooth top interfaces. Truncated QDs with two-monolayer-thick AlAs capping have demonstrated a strong blue shift of ground state (GS) energies and up to 10 meV larger separation between GS and first excited state energy levels as compared to non-capped QDs. We believe that AlAs capping, in combination with truncation procedure, results in significant suppression of carrier transport between QDs within the same layer as well as between QD layers. A record high characteristic temperature for GS lasing threshold, T0 = 380 K up to 55 °C, as well as a maximum saturated gain of 16 (5.3 per layer) cm-1, were measured for a 1.22 μm edge-emitting lasers with this truncated triple layer QD gain medium. A maximum saturated gain, 27 (3.9 per layer) cm-1, and T0 = 110 K have been demonstrated in a 1.19 μm lasers with truncated seven layer QD medium.
First electrically injected QD-MCLED emitting at 1.3 μm, grown by metal organic chemical vapour deposition
Authors: Tasco V. , Todaro M. T. , De Giorgi M. , De Vittorio M. , Cingolani R. , Passaseo A. 
Published: April 2011

ABSTRACTWe present the fabrication of a Quantum Dot Microcavity Light Emitting Diode (QD-MCLED) emitting at 1.3 μm at room temperature. The long wavelength emission is achieved by using for the first time InGaAs QDs directly grown on GaAs, by metal organic chemical vapour deposition. Electroluminescence bright emission, peaked at 1298 nm with a FWHM of 6.5 meV and a line shape independent on the applied bias is found.