bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crucible Selection in AlN Bulk Crystal Growth
Authors: Dalmau Rafael , Raghothamachar Balaji , Dudley Michael , Schlesser Raoul , Sitar Zlatko 
Published: April 2011

ABSTRACTGrowth of AlN bulk single crystals by sublimation of AlN powder was carried out in a resistively heated reactor at temperatures up to 2300°C. A variety of crucible materials, such as BN, W, Ta, Re, ZrO2, TaN, and TaC, were evaluated. Our studies have shown that the morphology of crystals grown by spontaneous nucleation strongly depends on the growth temperature and contamination in the reactor. Crucible selection had a profound effect on contamination in the crystal growth environment, thus influencing nucleation, coalescence, and crystal morphology. Spontaneously grown single crystals up to 15 mm in size were characterized by x-ray diffraction (XRD), x-ray topography (XRT), glow discharge mass spectrometry (GDMS), and secondary ion mass spectrometry (SIMS). Average dislocation densities were on the order of 103 cm−3, with extended areas virtually dislocation-free, while high-resolution XRD showed rocking curves as narrow as 7 arcsec.
Electrical and Optical Characteristics of Delta Doped AlGaN Cladding Layer Materials for Highly Efficient 340nm Ultra Violet LEDs
Authors: Xin H. P. , Flynn J. S. , Dion J. A. , Hutchins E. L. , Antunes H. , Fieschi-Corso L. , Van Egas R. , Brandes G. R. , LeBoeuf S. F. , Cao X. A. , Garrett J. L. , Rowland L. B. 
Published: April 2011

ABSTRACTIn this paper, we report the electrical and optical characteristics of Si delta-doped AlGaN cladding layers, p-cladding structure optimization and the impact on the efficiency of 340nm AlGaN UV LEDs. Compared to the uniformly doped n-AlGaN layer, adding Si Δ-doping layers reduced the sheet resistance by improving both the Hall mobility and carrier concentration. Increasing the number of Si Δ-doped layers further lowered the sheet resistance without cracking the material. The Δ-doped layers in n-Al0.3Ga0.7N improved the optical properties by enhancing near band edge emission as much as 2-fold relative to deep level emission. Additionally, Δ-doping in n-AlGaN layers had no detrimental effect on the optical transparency of the LEDs. The p-cladding layer was found to have a strong absorption at 340nm. Reducing the p-GaN cap layer from 35nm to 10nm tripled the light emission intensity. By optimizing the n- and p-AlGaN cladding layers, a highly efficient UV LED at 340nm was achieved with 1mW output under 800mA/mm2 DC drive current.
Growth Evolution of Gallium Nitride Films on Stepped and Step-Free SiC Surfaces
Authors: Eddy Charles R. , Culbertson James C. , Bassim Nabil D. , Twigg Mark E. , Holm Ronald T. , Stahlbush Robert E. , Henry Richard L. , Neudeck Philip G. , Trunek Andrew J. , Anthony Powell J. 
Published: April 2011

ABSTRACTSilicon carbide (SiC) is rapidly becoming the substrate of choice for the development of high frequency and high power electronic devices employing the III-V nitride family of materials. This heteroepitaxial growth system continues to receive considerable attention, as materials issues remain the fundamental limiters to device performance. The heteroepitaxial growth of gallium nitride (GaN) thin films on stepped and step-free 4H SiC surfaces is reported. Step-free SiC surfaces are created by mesa patterning of a SiC wafer and subsequent epitaxial growth in a process described previously. This process results in a collection of both step-free and stepped surfaces on a given sample. We have employed an established metalorganic chemical vapor deposition process to grow first a thin (1200Å) aluminum nitride (AlN) nucleation layer and then a 2 μm thick GaN thin film. We have interrupted growth at various stages of AlN and GaN growth to evaluate the growth evolution using atomic force microscopy (AFM). The results show marked differences in the manner in which the initial AlN layer deposits. Nucleation is random with elongated grains on step-free SiC surfaces, while stepped surfaces have round nuclei of uniform dimensions and a high degree of spatial correlation with the nuclei arranged in rows. These differences diminish as the AlN layer approaches the desired thickness. Growth of the GaN epilayer is also markedly different on the two types of surfaces with step-free surfaces leading to random and low density nucleation of crystallites that remain as single grains for long growth times, whereas the stepped surfaces have large numbers nuclei that rapidly grow laterally. Cross-sectional transmission electron microscopy (TEM) reveals that grain sizes are 2–3X larger on step-free surfaces.
Structural and Optical Properties of GaN Quantum Dots
Authors: Daudin B. , Gogneau N. , Adelmann C. , Sarigiannidou E. , Andreev T. , Enjalbert F. , Monroy E. , Fossard F. , Rouvière J. L. , Hori Y. , Biquard X. , Jalabert D. , Si Dang Le , Tanaka M. , Oda O. 
Published: April 2011

ABSTRACTGrowth conditions, structural and optical properties of GaN quantum dots (QDs) grown by plasma-assisted molecular beam epitaxy will be examined. It will be shown that, depending on the Ga/N ratio value and on growth temperature, the growth mode of GaN deposited on AlN can be either of the Stranski-Krastanow or of the Frank-Van der Merwe type. It will be shown that vertical correlation results in a red shift and in a narrowing of the photoluminescence spectra.Growth of Eu-doped GaN quantum dots embedded in AlN will be described. Intense photoluminescence associated with Eu has been measured, with no GaN band-edge emission, as an evidence that carrier recombination mostly occurs through rare earth ion excitation. Persistent photoluminescence of Eu-doped GaN quantum dots as a function of temperature has been put in evidence, as a further confirmation of the recombination of confined carriers through Eu ion excitation.
InN Nanostructures: Strain and Morphology
Authors: Demangeot Francois , Frandon Jean , Pinquier Claire , Caumont Michel , Briot Olivier , Maleyre Benedicte , Clur-Ruffenach Sandra , Gil Bernard 
Published: April 2011

ABSTRACTWe presented an experimental work on InN nanostructures grown on a GaN buffer layer deposited on sapphire (0001) by Metal Organic Vapor Phase Epitaxy. InN islands of controlled sizes were fabricated by using specific growth conditions and taking advantage of self-organization that results from Stranski-Krastanov growth mode. Then nanometric islands as small as 25 nm were characterized by using atomic force microscopy (AFM) and micro-Raman spectroscopy. AFM measurements revealed that the current shape of islands correspond to truncated hexagons. In-plane residual strain field was deduced from the E2 phonon frequency shift in micro-Raman spectra recorded on islands of various sizes. Careful analysis of these data made clear that the key parameter in determining the strain magnitude was the height of the islands: this was not surprising, keeping in mind that the shape was roughly independent of the size. Nevertheless, the dislocation density was believed to increase as function of the island thickness, leading to various degrees of strained relaxation, as probed by the present micro-Raman study. This conclusion was reinforced by the strain variation on the facets of single islands with respect to its value at the centre.
Extended X-ray Absorption Fine Structure Studies of GaN Epilayers Dopedin situwith Er and Eu During Molecular Beam Epitaxy
Authors: Katchkanov V. , Mosselmans J. F. W. , Dalmasso S. , O'Donnell K. P. , Martin R. W. , Briot O. , Rousseau N. , Halambalakis G. 
Published: April 2011

ABSTRACTThe local structure around Er and Eu atoms introduced into GaN epilayers was studied by means of Extended X-ray Absorption Fine Structure above the appropriate rare-earth X-ray absorption edge. The samples were dopedin situduring growth by Molecular Beam Epitaxy. The formation of ErN clusters was found in samples with high average Er concentrations of 32±6% and 12.4±0.8%, estimated by Wavelength Dispersive X-ray analysis. When the average Er concentration is decreased to 6.0±0.2%, 1.6±0.2% and 0.17±0.02%, Er is found in localised clusters of ErGaN phase with high local Er content. Similar behaviour is observed for Eu-doped samples. For an average Eu concentration of 30.5±0.5% clusters of pure EuN occur. Decreasing the Eu concentration to 10.4±0.5% leads to EuGaN clusters with high local Eu content. However, for a sample with an Eu concentration of 14.2±0.5% clustering of Eu was not observed.
Effect of Impurities on Raman and Photoluminescence Spectra of AlN Bulk Crystals
Authors: Sarua A. , Rajasingam S. , Kuball M. , Garro N. , Sancho O. , Cros A. , Cantarero A. , Olguin D. , Liu B. , Zhuang D. , Edgar J. H. 
Published: April 2011

ABSTRACTRaman scattering and photoluminescence (PL) spectroscopy with sub-bandgap excitation has been applied to explore tracing of common impurities (in particular of oxygen) in AlN. Bulk AlN crystals grown by the high temperature sublimation method were studied. PL bands have been observed at around 375 nm and at 560–660 nm and have been attributed to oxygen and to nitrogen vacancy/aluminium excess defects, respectively. The 375 nm UV PL band was found to shift with oxygen concentration. Micro-Raman spectra of the bulk AlN samples were measured in different polarisations. Besides normal Raman modes of AlN the presence of additional vibrational modes was detected. The modes were discussed and tentatively attributed to oxygen and silicon local vibrational modes (LVMs) in AlN.
Platelet Inversion Domains Induced by Mg-doping in ELOG AlGaN Films
Authors: Liu R. , Ponce F. A. , Cherns D. , Wills H. H. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTWe have studied the microstructure of heavily Mg-doped Al0.03Ga0.97N films grown by metal-organic vapor phase epitaxy in the lateral overgrowth mode (ELOG). A new type of defects with a platelet shape has been observed. According to TEM analysis, these defects are embedded in the overgrowth regions. The platelet is normal to the ELOG stripe direction [1100]AIGaN, forming trapezoidal trenches on the film surface. The thickness of the platelet is about 100nm. We have identified these defects as inversion domains using convergent beam electron diffraction and HR-TEM. Mg segregation at the coalescence boundaries between ELOG islands is believed to result in the formation of the defects.
Structural Study of V-like Columnar Inversion Domains in AlN Grown on Sapphire
Authors: Jasinski J. , Tomaszewicz T. , Liliental-Weber Z. , Paduano Q. S. , Weyburne D. W. 
Published: April 2011

ABSTRACTV-like columnar inversion domains with a divergence angle of about 4.5° ± 1° grown in AlN films with N-polarity were studied using transmission electron microscopy (TEM) and atomic force microscopy. Such domains emerge at the surface forming a small islands in form of hexagonal, truncated pyramids. A model of such pyramid was proposed. TEM studies indicate a displacement of c/2 along the [0001] direction at the inversion domain boundary. A boundary itself is composed of long segments located on the {1100} planes, which are alternated by short segments on some inclined planes.
The microstructure of GaN nucleation layers grown by MOCVD on (1120) sapphire versus pressure and temperature
Authors: Wojtowicz T. , Ruterana P. , Twigg M. E. , Henry R. L. , Koleske D. D. , Wickenden A. E. 
Published: April 2011

ABSTRACTIn this work, the evolution of morphology and defect structure in GaN nucleation layers on the a-plane of sapphire are investigated using TEM. The growth temperature and pressure were varied from 560 to 1100°C and from 20 to 600 torr, respectively. Whereas the highest growth temperature leads to a continuous layer, a 2D growth mode is not attained when the chamber pressure is varied from 20 to 600 torr at 1028°C. At the highest pressures (>300 t orr), a large distribution is obtained for the island sizes.
Anomalous Composition Dependence of Optical Energies of MBE-grown InGaN
Authors: Fernandez-Torrente I. , Amabile D. , Martin R. W. , O'Donnell K. P. , Mosselmans J.F.W. , Calleja E. , Naranjo F. B. 
Published: April 2011

ABSTRACTA direct comparison of the optical energies of MBE- and MOVPE-grown InxGa1-xN epilayers of similar InN content is performed for the first time. The InN fraction in the 7 MBE samples examined ranged from x ∼ 0.11 to x ∼ 0.35 while the range in available MOVPE epilayers is [0, 0.4]. Wavelength Dispersive X-ray (WDX) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopies were used to measure composition and local structure (alloy character) of the samples. Cathodoluminescence (CL) spectroscopy in situ, ex situ photoluminescence (PL) mapping and large-area optical absorption spectroscopy were used to measure various optical energies. The composition dependence of the optical energies is determined by the growth method. The absorption bandgap and luminescence peak energies vary linearly with x for both growth methods, suggesting a near-zero value of the bowing parameter. But the energy intercept at zero InN content in MOVPE samples is close to the wurtzite-GaN bandgap of 3.4 eV at room temperature, as expected, while the equivalent for MBE samples falls near 3.2 eV.
Optical and Microstructural Properties of N- and Ga-Polarity GaN
Authors: Bell A. , Smit J. L. , Liu R. , Mei J. , Ponce F. A. , Ng H. M. , Chowdhury A. , Weimann N. G. 
Published: April 2011

ABSTRACTThe effect of polarity on the optical and microstructural properties of GaN is presented. A sample with adjacent domains of Ga- and N-polarity material was grown by varying the nucleation layer. This allows a unique opportunity to study the two different polarities under controlled conditions. We found that the N-polarity material has a much lower dislocation density than the Ga-polarity material. The N-polarity material contains voids that are not present in the Ga-polarity region. The surface roughness of the N-polarity material appears to be caused by Ga-polarity inversion domains which lead the growth. A cathodoluminescence study showed that the N-polarity material is much brighter than the Ga-polarity material, suggesting a higher donor concentration, probably due to increased impurity incorporation in the [0001] growth direction or possibly due to an increase in intrinsic point defects. There is also evidence that the N-polarity region contains two types of material, one is flat and can be etched, the other has an inclined facet and does not etch.
Advances in the Realisation of GaN-Based Microcavities: Towards Strong Coupling at Room Temperature
Authors: Semond F. , Byrne D. , Natali F. , Leroux M. , Massies J. , Antoine-Vincent N. , Vasson A. , Disseix P. , Leymarie J. 
Published: April 2011

ABSTRACTIn a recent paper [Phys. Rev. B 68, 153313 (2003)], we reported the first experimental observation of the strong coupling regime in a GaN-based microcavity. The λ/2 GaN optical cavity was grown by molecular beam epitaxy on a Si(111) substrate. The upper mirror is a SiO2/Si3N4 dielectric mirror and the silicon substrate acts as the bottom mirror. With such a relatively simple and low-finesse microcavity, a Rabi splitting of 31 meV was measured at 5K. On the basis of this very encouraging result, approaches to fabricate high-finesse GaN-based cavities exhibiting strong coupling with stable polaritons at room temperature are discussed.
Characterization of III-nitride Based Schottky UV Detectors with Wide Detectable Wavelength Range (360–10 nm) using Synchrotron Radiation
Authors: Motogaito Atsushi , Hiramatsu Kazumasa , Shibata Yasuhiro , Watanabe Hironobu , Miyake Hideto , Fukui Kazutoshi , Ohuchi Youichiro , Tadatomo Kazuyuki , Hamamura Yutaka 
Published: April 2011

ABSTRACTCharacterizations of transparent Schottky barrier GaN and AlGaN UV detectors in the vacuum UV (VUV) and soft X-ray (SX) region using synchrotron radiation are described. In the GaN UV detectors, the responsivity achieved about 0.05 A/W at 95 eV (13 nm). Thus, their device performance is shown between 3.4 and 100 eV (10 and 360 nm). Furthermore, the high responsivity spectra were realized by using AlGaN Schottky UV detectors consisting of Al0.5Ga0.5N on AlN epitaxial layer.
Mg Doped GaN Using a Valved, Thermally Energetic Source: Enhanced Incorporation, Control and Quantitative Optimization
Authors: Burnham Shawn D. , Alan Doolittle W. , Namkoong Gon , Henderson Walter 
Published: April 2011

ABSTRACTIn this study, a thermally-energetic Mg source with an independent, valved-flux control was used to study the behavior of Mg incorporation into GaN. To observe effects of the thermal energy of the Mg flux on Mg incorporation, two Mg flux temperatures were investigated: one (900°C) well above the melting point of Mg and one (625°C) slightly below the melting point of Mg. Alternating Mg-doped and undoped GaN layers were grown at steps of increasing Mg flux, retaining a constant thermal energy, from below the saturation limit, to above the saturation limit. Results were analyzed and compared using secondary ion mass spectroscopy (SIMS). For a constant measured Mg flux, the incorporated Mg increased by more than an order of magnitude when the Mg thermal source temperature was raised from 625°C to 900°C. During SIMS analysis, the energy spectra of sputtered Ga atoms were fairly constant for a Mg flux above the saturation limit, and shifts for a Mg flux slightly below the critical flux for saturation, indicating a conductivity change, and possibly providing a quantitative means of optimizing p-type conduction. Furthermore, Mg incorporation into GaN strongly depends on the III-V flux ratio. During this study it was also observed that Mg incorporation into GaN was enhanced on a rough growth-layer surface under N-rich conditions, while a smoother growth-layer surface resulted in lower Mg incorporation, even under N-rich conditions1.
Epitaxy of highly optical efficient GaN on O and Zn face ZnO
Authors: Gu Xing , Reshchikov Michael A. , He Lei , Teke Ali , Yun Feng , Johnstone Daniel K. , Nemeth Bill , Nause Jeff , Morkoç Hadis 
Published: April 2011

ABSTRACTZnO is a highly efficient photon emitter, has optical and piezoelectric properties that are attractive for a variety of applications. Due to its stacking order and close lattice to GaN, it is also considered as a substrate material for GaN epitaxy. In the past the poor preparation of ZnO surface has been a major handicap to GaN epitaxy. However, proper treatment we developed recently can make both faces of ZnO smooth with atomic level terraces. Epitaxy of GaN on O-face and Zn-face ZnO by reactive molecular beam epitaxy was performed. We used low-temperature RF growth of GaN buffer layer on ZnO surface to protect it from both ammonia and Ga. No Ga2ZnO4, an oxide with the spinel structure formed due to reaction of ZnO with Ga, was found, in contrast to earlier reports. The low-temperature photoluminescence (PL) indicates that both faces of ZnO can provide a high quality GaN with high radiative efficiency. In previous research it has been reported that O-face ZnO is slightly better for GaN epitaxy. Our new finding demonstrates that high-quality GaN epilayers can be grown on Zn face of ZnO.
Deep Levels in Multilayer Structures of Si/Si0.8Ge0.2 Grown by Low-Pressure Chemical Vapor Deposition
Authors: Tokuda Yutaka , Shirai Kenichi 
Published: April 2011

ABSTRACTDeep levels in multilayer structures of ten periods Si/Si0.8Ge0.2 (16/5 nm) grown by low-pressure chemical vapor deposition have been characterized by deep level transient spectroscopy (DLTS). DLTS measurements reveal one dominant peak (E1) at around 130 K with a minor peak (E2) at around 240 K. The dominant trap E1 (Ec – 0.19 eV) is ascribed to the dislocation-related defect. The increase of the E1 concentration by a factor of 2 to 3 and the change of its energy level to Ec – 0.22 eV are observed with annealing up to 120°C. It is speculated that hydrogen incorporated during growth associates with E1 and the behavior of E1 upon annealing is caused by the release of hydrogen from E1.
Pulsed Laser Deposition of Bi- And Sb-based Solid Solutions and Multilayer Structures
Authors: Alexanian Arik G. , Avetisyan Hovsep N. , Avjyan Karapet E. , Aramyan Nikolay S. , Aleksanyan Garegin A. , Grigoryan Romen P. , Khachatryan Ashot M. , Yeremyan Arsham S. 
Published: April 2011

ABSTRACTThin films of Bi, Sb, solid solutions Bi1-xSbx, as well as multilayer structures Bi-Sb-Bi-Sb--from elementary sources were produced by pulsed laser deposition for optoelectronic applications. KBr crystals were used as substrates. The solid solutions Bi1-xSbx were obtained by co-evaporation of single targets of Bi and Sb. Structural investigations show that the performance of produced films depends on both the amount of material deposited per pulse of laser energy and the ratio of this amount for bismuth and antimony. Based on this the technological regimes of growth temperature and laser intensity ranges were determined in which single-crystalline growth of films with certain x is possible. Single-crystalline films of Bi1-xSbx were obtained in the range of x (0.12—0.48), which corresponds to semiconductor state of this solution. The method of sequential deposition is used for fabrication of multilayer structures Bi/Sb with quantum-confined layers of bismuth. The growth regime with practically excluded interdiffusion of materials is found. Results of spectral investigations are shown to be in agreement with the theoretically predicted semimetal-to-semiconductor transition of bismuth as a result of quantum confinement.
Observation of Retarded Recombination in ChargeSeparation Structures
Authors: Ahrenkiel R. K. , Friedman D. , Metzger W. K. , Page M. , Dashdorj J. 
Published: April 2011

ABSTRACTMeasurement of recombination and minority-carrier lifetimes has become a very common activity in current semiconductor technology. The two primary measurement techniques are based on photoconductive decay (PCD) and time-resolved photoluminescence (TRPL). The measurement of the “true” lifetime depends on the carriers being confined to a given spatial region of a diagnostic device. When internal electric fields exist that separate the charges, the measured value does not represent the real minority-carrier lifetime. In these cases, the measured quantity is a function of the true lifetime and the measurement technique.