bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self-assembled quantum dots and nanoholes by molecular beam epitaxial growth and atomically precise in situ etching
Authors: Kiravittaya S. , Songmuang R. , Schmidt O. G. 
Published: January 2017

AbstractEnsembles of homogeneous self-assembled quantum dots (QDs) and nanoholes are fabricated using molecular beam epitaxy in combination with atomically precise in situ etching. Self-assembled InAs QDs with height fluctuations of ±5% were grown using a very low indium growth rate on GaAs (001) substrate. If these dots are capped with GaAs at low temperature, strong room temperature emission at 1.3 νm with a linewidth of 21 meV from the islands is observed. Subsequently, we fabricate homogeneous arrays of nanoholes by in situ etching the GaAs surface of the capped InAs QDs with AsBr3. The depths of the nanoholes can be tuned over a range of 1-6 nm depending on the nominal etching depth and the initial capping layer thickness. We appoint the formation of nanoholes to a pronounced selectivity of the AsBr3 to local strain fields. The holes can be filled with InAs again such that an atomically flat surface is recovered. QDs in the second layer preferentially form at those sites, where the holes were initially created. Growth conditions for the second InAs layer can be chosen in such a way that lateral QD molecules form on a flat surface.
Effect of the internal electric fields in Quantum Dot laser structures grown by Metal Organic Chemical Vapor Deposition
Authors: Passaseo A. , Maruccio G. , Vittorio M. De , Rinaldis S. De , Todaro T. , Cingolani R. 
Published: January 2017

AbstractBy means of a systematic study carried out on In0.5Ga0.5As/GaAs quantum dot electroluminescent devices grown by Metal Organic Chemical Vapor Deposition, we show that the combination of internal electric fields in such structures dramatically blue shifts the emission wavelength with respect the photoluminescence emission that occurs at the expected value of 1.3 νm at room temperature. By comparing photoluminescence (PL), electroluminescence (EL) and photocurrent (PC) measurements in In0.5Ga0.5As QD structures emitting between 1.28 νm and 1.4 νm (at 300 K), we demonstrate that the electric field associated to the built-in dipole in the dots, directed from the base of the dots to their apex, and the device junction field (when parallel to the dipole field) lead to the depletion of the ground state. As a consequence, structures grown on n-type GaAs substrates exhibit electroluminescence only from the excited states. Instead, by growing the same device structure on p-type GaAs substrates, i.e. by reversing the direction of the built-in electric field of the device, the effect of the permanent dipole is strongly reduced, thus allowing us to obtain EL emission at the designed wavelength of 1.3 νm at 300 K, coincident to the PL. The consequence on the achievement of efficient lasing in the spectral region of interest for optical transmission. are illustrate.
Defect free InGaAs-based strain balanced MQW grown on virtual substrate by metallorganic chemical vapor deposition
Authors: Passaseo A. , Cingolani R. , Mazzer M. , Lomascolo M. , Tundo S. , Lazzarini L. , Nasi L. , Salviati G. , Barnham K.W. 
Published: January 2017

AbstractIn this work we describe a novel system for photovoltaic applications which combines InGaAs based strain-balanced multiple quantum wells (MQWs) with a “virtual substrate”, designed to extend the absorption edge of the photovoltaic devices to about 1 eV. The virtual substrate is designed by properly choosing a sequence of InGaAs layers having different In content, in order to obtain the desired lattice parameter at the topmost layer and to confine at the deepest interfaces the misfit dislocations, well away from the QW active region.A series of InGaAs p-i-n junctions, containing a strain balanced MQW in the intrinsic region, were deposited by metallorganic chemical vapor deposition on different virtual substrates. In all the samples the virtual substrates were proved to be successful to grow zero net strain MQW and to confine defects at the buffer/substrate interface. Transmission electron microscopy observation shows that no defects propagate from the strain accommodating layers to the active region. The total density of threading dislocations reaching the surface was found to be less than 1*E5/cm2.The confined misfit dislocation network, however, results in marked cross-hatched morphology that was found to affect the lateral strain distribution in the whole structure. By optimizing the growth condition of the structures, the influence of the surface roughness induced by CH pattern is partially suppressed.
Materials for Solid State Lighting
Authors: Johnson S.G. , Simmons J. A. 
Published: January 2017

AbstractDramatic improvement in the efficiency of inorganic and organic light emitting diodes (LEDs and OLEDs) within the last decade has made these devices viable future energy efficient replacements for current light sources. However, both technologies must overcome major technical barriers, requiring significant advances in material science, before this goal can be achieved. Attention will be given to each technology associated with the following major areas of material research: 1) material synthesis, 2) process development, 3) device and defect physics, and 4) packaging.The discussion on material synthesis will emphasize the need for further development of component materials, including substrates and electrodes, necessary for improving device performance. The process technology associated with the LEDs and OLEDs is very different, but in both cases it is one factor limiting device performance. Improvements in process control and methodology are expected to lead to additional benefits of higher yield, greater reliability and lower costs. Since reliability and performance are critical to these devices, an understanding of the basic physics of the devices and device failure mechanisms is necessary to effectively improve the product. The discussion will highlight some of the more basic material science problems remaining to be solved. In addition, consideration will be given to packaging technology and the need for the development of novel materials and geometries to increase the efficiencies and reliability of the devices. The discussion will emphasize the performance criteria necessary to meet lighting applications, in order to illustrate the gap between current status and market expectations for future product.
Influence of Defects on Current Transport in GaN/InGaN Multiple Quantum Well Light-Emitting Diodes
Authors: Cao X. A. , Stokes E. B. , LeBoeuf S. F. , Sandvik P. M. , Kretchmer J. , Walker D. 
Published: January 2017

AbstractWe have studied the electrical and optical characteristics GaN/InGaN based light-emitting diodes (LEDs) grown on sapphire using metalorganic chemical vapor deposition (MOCVD). Strong correlation has been found between material quality and the mechanism of current transport through the wide-bandgap p-n junction. Tunneling behavior dominates throughout all injection regimes in the devices with high-density defects in the space-charge region, which act as deep-level carrier traps. The approximately current-squared dependence of light output at low currents indicates dominant nonradiative recombination in the active region. However, in a high quality LED diode, tunneling current is only a major contributor at low forward biases. At moderate biases, temperature dependent diffusion-recombination current has been identified as I0 exp(qV/1.6kT). In these devices, nonradiative recombination centers are saturated at current densities as low as 1.4×10-2 A/cm2.
Electrical and Optical Characteristics of Isoelectronic Al-doped GaN Films Grown by Metal Organic Chemical Vapor Deposition
Authors: Lee Jae-Hoon , Kim Jong-Hyun , Ko Hyun-Min , Bae Sung-Bum , Lee Kyu-Suk , Cho Yong-Hoon , Hahm Sung-Ho , Lee Yong-Hyun , Lee Jung-Hee 
Published: January 2017

AbstractThe effects of the isoelectronic Al-doping of GaN grown by metal organic chemical vapor deposition were investigated for the first time using scanning electron microscopy (SEM), Hall measurements, photoluminescence (PL), and time-resolved PL. When a certain amount of Al was incorporated into the GaN films, the room temperature photoluminescence intensity of the films was approximately two orders larger than that of the undoped GaN. More importantly, the electron mobility significantly increased from 130 for the undoped sample to 500 cm2/Vs for the sample grown at a TMAl flow rate of 10 νmol/min, while the unintentional background concentration only increased slightly relative to the TMAl flow. The incorporation of Al as an isoelectronic dopant into GaN was easy during MOCVD growth and significantly improved the optical and electrical properties of the film. This was believed to result from a reduction in the dislocation-related non-radiative recombination centers or certain other defects due to the isoelectronic Al-doping.
GaInNAs: A New Material in the Quest for Communications Lasers
Authors: Harris James S. , Gambin Vincent 
Published: January 2017

AbstractDilute nitride GaInNAs alloys grown on GaAs have quickly become an excellent candidate for lower cost 1.3-1.55νm vertical cavity surface emitting lasers (VCSELs) and high power edge emitting lasers in the past few years. Despite the relative immaturity and challenges of this new materials system the results have been very promising. Some of the material challenges include the limited solubility of nitrogen in GaAs, non-radiative defects that may be caused by nitrogen incorporation, and characterization of the unique set of properties nitrogen adds to this metastable alloy. In addition, a new component has been added in order to improve epitaxial growth and optical properties at wavelengths longer than 1.3νm. By adding Sb to the alloy, luminescence has been greatly enhanced between 1.3-1.6νm where normally poor quality material results. This paper describes some of the material challenges and progress in devices based on the GaInNAs and GaInNAsSb system.
Performance and Reliability of a MEMS-based tunable optical filter operating in the 1565 nm-1525 nm wavelength range
Authors: Sriram T. S. , Strauss B. , Pappas S. , Baliga A. , Jean A. , Parodos T. , Dietz D. , Wang P. , Azimi M. , McCallion K. , Vakhshoori D. 
Published: January 2017

AbstractThis paper describes the results of extensive performance and reliability characterization of a silicon-based surface micro-machined tunable optical filter. The device comprises a high-finesse Fabry-Perot etalon with one flat and one curved dielectric mirror. The curved mirror is mounted on an electrostatically actuated silicon nitride membrane tethered to the substrate using silicon nitride posts. A voltage applied to the membrane allows the device to be tuned by adjusting the length of the cavity. The device is coupled optically to an input and an output single mode fiber inside a hermetic package. Extensive performance characterization (over operating temperature range) was performed on the packaged device. Parameters characterized included tuning characteristics, insertion loss, filter line-width and side mode suppression ratio. Reliability testing was performed by subjecting the MEMS structure to a very large number of actuations at an elevated temperature both inside the package and on a test board. The MEMS structure was found to be extremely robust, running trillions of actuations without failures. Package level reliability testing conforming to Telcordia standards indicated that key device parameters including insertion loss, filter line-width and tuning characteristics did not change measurably over the duration of the test.
Interplay of Defects, Microstructures, and Surface Stoichiometry during Plasma Processing of GaN
Authors: Ramam A. , Tripathy S. , Chua S.J. 
Published: January 2017

AbstractWe have investigated optical properties of dry etched GaN using photoluminescence (PL) and micro-Raman scattering. The stoichiometry of the dry etched surface has been analyzed by x-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) technique has been employed to investigate the microstructures resulting from dry processing. The damage introduced by inductively coupled plasma etching has been assessed and improvement of the luminescence properties is observed during post etch annealing. The observed changes in the Raman spectra of plasma etched Si- and Mg- doped GaN can be associated with electronic and vibronic scattering mechanisms of defects.
Optical and Structural Studies of InGaN Layers and GaN/InGaN MQWs Using TPIS-MOCVD
Authors: Kim Sunwoon , Seo Junho , Lee Kyuhan , Lee Haeseok , Park Keunseop , Kim Chang-Soo 
Published: January 2017

AbstractInGaN device quality films and their related heterostructures play a critical role in the development of nitride devices. InGaN growth needs to be performed at much lower temperatures than GaN growth, due to the lower dissociation temperature of InN. Furthermore, decomposition of ammonia becomes less efficient with decreasing temperature due to high kinetic barrier for breaking N-H bonds and InGaN growth needs high NH3/TMIn ratio. We investigated the optical and structural properties of InGaN bulk layers and GaN/InGaN MQWs using thermally precracked ion supplied metalorganic chemical vapor deposition (TPISMOCVD) system. The temperature range for this study was 670 -770°C. In a low NH3 flow condition, In metal droplet appeared on the surface on InGaN layer in conventional MOCVD system, but it disappeared in TPIS-MOCVD system. An increasement of In mole fraction in InGaN could be achieved even in low NH3 flow. As the NH3 flow rate and the InGaN growth temperature decreased, In metal droplet was more effectively reduced by ammonia precracking. The quality of InGaN/GaN MQWs was evaluated with high resolution XRD and TEM.
The Role of AlN Interlayer in AlxGa1-xN/GaN Heterostructures with high x from 0.35 to 0.50 Grown on Sapphire (0001)
Authors: Seo In-Seok , Lee Seung-Jae , Jang Seong-Hwan , Yeon Jeong-Mo , Leem Jae-Young , Park Yong-Jo , Lee Cheul-Ro 
Published: January 2017

AbstractWe report the role of thin AlN interlayer in the fabrication of AlxGa1-xN/GaN heterostructures with high x from 0.35 to 0.50 on sapphire (0001) by MOVPE. After growing the AlN interlayer of 20 nm thick on GaN/sapphire (0001) epitaxy, the AlxGa1-xN epitaxial layers of 1.0 um thick were grown on it with increasing the flow rate of TMA. The measured Al mole fractions of AlxGa1-xN/GaN heteroepitaxy grown using the thin AlN interlayer from each TCD rocking curve are 0.35, 0.37, 0.45 and 0.50, respectively. As incorporation rate of Al in the AlxGa1-xN increases, the crystallinity is getting well and the RMS values scanned by AFM of their surfaces become lower. And also, the optoelectronic characteristics of those heteroepitaxy evaluated by cathodeluminescence(CL) are improved with the increase of x. To the contrary these trends, it is usually known that crystallinity, surface morphology and optical property of the AlxGa1-xN/GaN heteroepitaxy grown without AlN interlayer between them become worse with the increase of x above 0.2. Meanwhile, electrical resisitivities of Al0.35Ga0.65N, Al0.37Ga0.63N, Al0.45Ga0.55N and Al0.50Ga0.50N epitaxy, which were grown with the thin AlN interlayer, measured by four point probing method are 13.5, 18.1, 31.7 and 36.2 Mohm-cm, respectively. These resisitivities increase by degrees in spite of the advance of characteristics with the raising of x.
Formation of thallium antimony sulfide and thallium bismuth sulfide thin films by heating chemically deposited multi-layer thin films
Authors: Estrella Verónica , Nair M. T. S. , Nair P. K 
Published: January 2017

AbstractAntimony sulfide (Sb2S3) and bismuth sulfide (Bi2S3) thin films of 200 nm thickness each were deposited from aqueous baths on glass substrates. Subsequently, thin films of thallium sulfide (Tl2S) with thickness around 120 nm were deposited on to these films from a bath containing thallium nitrate, sodium citrate, sodium hydroxide and thiourea. The multilayer films of Sb2S3-Tl2S, Bi2S3-Tl2S and Bi2S3-Sb2S3-Tl2S, thus produced, were heated in a nitrogen atmosphere around 300°C. XRD studies confirmed the formation of TlSbS2, TlBiS2, Tl4Bi2S5 and TlSb3S5 compounds. Optical band gaps of these materials are 1.85 eV (TlSbS2), 0.15 eV (TlBiS2), and about 1 eV for the composite film (Tl4Bi2S5 + TlSb3S5). In the visible spectral region, the optical absorption coefficients of these materials are about 105 cm-1. Values of dark conductivity are 10-7 Ωcm-1 (TlSbS2), 10-4 Ωcm-1 for TlBiS2 and 10-6 Ωcm-1 for the composite film. All the films are photoconductive.
Novel organic, polymeric materials for electronics applications
Authors: Sabnis Ram W. , Spencer Mary J. , Guerrero Douglas J. 
Published: January 2017

AbstractNovel organic, polymeric materials and processes of depositing thin films on electronics substrates by chemical vapor deposition (CVD) have been developed and the lithographic behavior of photoresist coated over these CVD films at deep ultraviolet (DUV) wavelength has been evaluated. The specific monomers synthesized for DUV applications include [2.2](1,4)- naphthalenophane, [2.2](9,10)-anthracenophane and their derivatives which showed remarkable film uniformity on flat wafers and conformality over structured topography wafers, upon polymerization by CVD. The chemical, physical and optical properties of the deposited films have been characterized by measuring parameters such as thickness uniformity, solubility, conformality, adhesion to semiconductor substrates, ultraviolet-visible spectra, optical density, optical constants, defectivity, and resist compatibility. Scanning electron microscope (SEM) photos of cross-sectioned patterned wafers showed verticle profiles with no footing, standing waves or undercut. Resist profiles down to 0.10 νm dense lines and 0.09 νm isolated lines were achieved in initial tests. CVD coatings generated 96-100% conformal films, which is a substantial improvement over commercial spin-on polymeric systems. The light absorbing layers have high optical density at 248 nm and are therefore capable materials for DUV lithography applications. CVD is a potentially useful technology to extend lithography for sub-0.15 νm devices. These films have potential applications in microelectronics, optoelectronics and photonics.
Electrical Properties of Beta-Irondisilicide/Germanium Heterojunctions
Authors: Ehara Takashi , Kokubun Yoshihiro 
Published: January 2017

AbstractThe electrical properties of heterojunctions composed of polycrystalline films of beta-irondisilicide and n-type germanium substrate are investigated. The heterojunctions have been prepared by co-sputtering of iron and silicon on germanium substrate followed by thermal annealing. The samples were prepared over various annealing temperature and chemical compositions. Most of the samples showed rectifying characteristics in current-voltage characteristics measurement. However, large backward leakage current was observed. The result is consistent with that in the case of beta-irondisilicide/silicon heterojunctions. In addition, the leak current showed significant dependence on annealing condition and chemical composition. It was suggested that the high density of trap levels existing at the interface caused by diffusion of Fe into substrate induce the inadequate electrical properties of the samples.
Cathodoluminescence and Photoluminescence of Crystaline Silicon-Epilayer Grown on Si+-Implanted (1-102) Sapphire
Authors: Park C. J. , Kwon Y. H. , Kang T. W. , Cho H. Y. , Choi S.-H , Elliman R.G. 
Published: January 2017

AbstractLuminescence on Si-epitaxial layers grown on Si-implated Al2O3 ( 1102) with 30 keV Si+ to a dose of 5×1015/cm2 has been investigated. To active the implanted Si+ ions in Al2O3, the post annealing was performed at 1100°C in Ar ambiant. Also, cathodoluminescence (CL) and photoluminescence (PL) have been used to study struc Al2O3tural and optical properties of nc-Si in the Si+-implanted (1102) Al2O3 substrates. In the PL and CL spectra for Si+-implanted samples, peaks to be responsible for nanocrystalline-Si (nc-Si) appear at 316 nm (3.92 eV) and 574 nm (2.16 eV), respectively. The crystallinity of nc-Si imbeded in Al2O3 has been about 5nm in size and the dislocation aligned parallel to the (0001) planes of (1102) Al2O3, confirmed by transmission electron microscopy (TEM).
Channel-Add Operation of a Device Using Defects in a Two-Dimensional Photonic Crystal Slab
Authors: Asano Takashi , Noda Susumu , Kiyota Kazuaki , Tanaka Yoshinori , Akahane Yoshihiro , Song Bonshik , Mochizuki Masamtsu , Imada Masahiro 
Published: January 2017

AbstractA channel add-filtering function of a device based on defects in a two dimensional photonic crystal slab is investigated in addition to a channel drop-filtering function reported previously. It is considered that photons irradiated to a point defect from free space are trapped by the point defect, are transferred to a line defect waveguide nearby, and are emitted from the waveguide edge. It is shown that the spectrum of the add-filtering function is almost same as that of the drop-filtering function, which demonstrates that photons can be not only dropped-from but also added-to a line-defect waveguide through the resonant trapping by point defects.
Coupled-Cavity Structures in Photonic Crystals
Authors: Bayindir Mehmet , Ozbay E. 
Published: January 2017

AbstractWe investigate the localized coupled-cavity modes in two-dimensional dielectric photonic crystals. The transmission, phase, and delay time characteristics of the various coupled-cavity structures are measured and calculated. We observed waveguiding through the coupled cavities, splitting of electromagnetic waves in waveguide ports, and switching effect in such structures. The corresponding field patterns and the transmission spectra are obtained from the finite-difference-time-domain (FDTD) simulations. We also develop a theory based on the classical wave analog of the tight-binding (TB) approximation in solid state physics. Experimental results are in good agreement with the FDTD simulations and predictions of the TB approximation.
Pore Etching in Compound Semiconductors for the Production of Photonic Crystals
Authors: Foell Helmut , Langa Sergiu , Carstensen Juergen , Christophersen Marc , Tiginyanu Ivan , Dichtel Karin 
Published: January 2017

AbstractOrdered arrays of pores in Si provided the first (two dimensional) photonic crystals with bandgaps in the μm region. The paper explores the potential of pore etching for two- and threedimensional photonic crystals in GaAs, InP, and GaP. A striking feature of pore etching in III-V semiconductors is the strong tendency to self-organization and pattern formation. As an example, self-organized well-defined pore lattices (a = 100 nm – 1 μm) can be made in InP. All materials show self organized diameter oscillations, often synchronized over large distances between pores. Extremely strong diameter oscillations are observed in GaAs. Pores in all materials tend to grow in <111> directions, but can be induced to grow in the direction of current flow, too. These features can be used to produce two- and three dimensional photonic crystals. The latter goal might be achieved by switching periodically between different pore morphologies with depth, or by modulating the diameter with depth - always helped by the tendency to self organization. Self organization, however, will not lead to perfect crystal structures; lithographically defined nucleation is needed and has been tried. First results show that there are pronounced differences to what is known from Si. While the production of externally defined photonic crystals in the sub μm region appears to be feasible, the strong tendency to self organization must be taken into account by matching internal time and length scales to the desired external ones.