bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of ZnO Morhpology by Solution Route
Authors: Sun Lingdong , Zhang Jun , Liao Chunsheng 
Published: April 2011

AbstractIn this paper, ZnO with a rich variety of well-defined morphologies have been achieved by solution route using different kind of precursors, which can prepare particles by only one step without calcination. The influences of solvent, and temperature on the particle size and morphology of ZnO were investigated. It was revealed by the scanning electron microscope (SEM) and transmission electron microscope (TEM) images that the morphological feature of ZnO can be controlled as rod-, polyhedron-, fluffy sphere-, snowflake- and flower-like, etc. XRD measurement showed that all of the ZnO samples with different morphologies has the same hexagonal structure, which is well consistent with electron diffraction (ED) characterization. This communication not only provides promising candidates for materials science due to the importance of shape in relationship with materials, but also presents an effective route to synthesize the well-defined inorganic materials.
Optically Detected Magnetic Resonance Study of Core-Shell and Alloy Nanocrystals of HgTe and CdS
Authors: Fradkin L. , Langof L. , Lifshitz E. 
Published: April 2011

AbstractThe synthesis of HgTe nanocrystals (NCs), coated with a CdS shell, presumably results in the formation of HgTe/CdS, HgTe/CdHgS core-shell structures or separated CdHgS alloys. Photoluminescence (PL), continuous-wave (cw) and time-resolved optically detected magnetic resonance (ODMR) spectroscopy examined the magneto-optical properties of the dominating resonance aforementioned products. The cw ODMR measurements indicated that the NCs exhibit a band, centered at 0.39 Tesla, corresponding to an excited state electron (e) and hole (h) spin manifold, with total angular momentum (F=S+L) Fe=1/2 and Fh=3/2, respectively. Theoretical simulation of the ODMR band revealed an anisotropy of the g-factor, indicating the existence of trapped carriers' at a mixed Cd-Hg tetrahedral site, confirming the formation of an alloy component. The time-resolved ODMR measurements reveal a characteristic radiative decay time and spin-lattice relaxation time of these trapped carriers of hundreds of microseconds.
Current Images of CdSe Colloidal Nanodots Observed by Conductive-tip Atomic Force Microscopy
Authors: Tanaka Ichiro , Kawasaki Eri , Ohtsuki O. , Hara M. , Asami H. , Kamiya I. 
Published: April 2011

AbstractWe have fabricated submonolayer-thick films of CdSe colloidal nanodots in order to investigate electronic properties of individual nanodots by conductive-tip atomic force microscopy (AFM). Topographic and current images of isolated single CdSe colloidal dots on single crystalline Au (111) surface which was covered with dodecanethiol self-assembled monolayer were obtained by AFM operating in contact mode with a conductive tip under appropriate bias voltages. In the current image, it is found that the dot regions have higher electric resistances due to tunneling resistance through the CdSe dots. We also found 10 nm-scale electric inhomogeneity around the dots, which may corresponds to the previously reported etch-pits of Au (111) surfaces formed during the deposition of the dodecanethiol molecules.
Continuous and Time Resolved Optically Detected Magnetic Resonance Studies of InP Nanoparticles
Authors: Langof L. , Ehrenfreund E. , Lifshitz E. , Micic O. I. , Nozik A. J. 
Published: April 2011

AbstractCarriers in small colloidal InP nanoparticles are in strong quantum confinement regime. The low temperature photoluminescence spectrum of InP nanoparticles is composed of an excitonic luminescence at high energies and a non-excitonic defect emission band at lower energies. HF etching of the nanoparticles reduces the defect emission and enhances the exciton process.In this work we apply optically detected magnetic resonance spectroscopy (ODMR) both in continuous wave and time resolved mode (TR-ODMR) to study the defect luminescence in InP nanoparticles. The results show that the defect luminescence originates from weakly coupled electron-hole pair, where the electron is trapped at the surface by phosphorous vacancy, Vp, and the hole is located at the valence band. Additionally, the results suggest that the non-etched samples are dominated by Vp at the surface. Those are mainly eliminated upon HF treatment, leaving behind small percent of Vp in the core of the nanoparticle. We also find the electron-hole exchange interaction from circular polarized ODMR measurements. The TR-ODMR measurement further clarifies the spin dynamics and characteristic of the magnetic sites. Fitting these measurements to the simulated response of the PL intensity to the square wave modulated microwave power revealed that the spin relaxation time and radiative lifetime of electron-hole pair in the nanoparticles are in the microseconds regime.
On the Optical Memory of a Thin-Film pInSb-nCdTe Heterojunction Obtained by Laser Pulsed Deposition
Authors: Alexanian Arik G. , Aramyan Nikolay S. , Grigoryan Romen P. , Khachatrian Ashot M. , Matevossian Lenrik A. , Yeremyan Arsham S. 
Published: April 2011

AbstractThin film pInSb-nCdTe heterojunctions (HJs) were produced using pulsed laser deposition (PLD) technique and their photoelectric properties were studied for various thickness of the CdTe layer at nitrogen temperature and under a background radiation the photo-EMF for which was around 1.5 mV. At radiative excitation of the HJ a photo-EMF is observed, which persists when the excitation is turned off. The optical memory (OM) effect is observed in an idling regime and in a wide spectral range: (0.37–1.37)μm with “recording” (0.37–0.575)μm, (0.75–1.37)μm, and “clearing” (0.575–0.75)μm sub-regions. The maximum OM signal is observed at λ=0.575μm while the minimum is at λ=0.768μm. In the spectral dependence of the OM signal at direct and reverse scanning of monochromatic irradiation an hysteresis is observed which is evident for the OM effect. The time dependence of OM signal is investigated at λ=0.575μm and at various intensities of the radiation source. Here, an effect of saturation is clearly observed, and the time during which the OM signal runs up to saturation, depends strongly on the incident light flow power and decreases drastically as the latter is increased. The external bias applied to the HJ enhances the OM on 2 orders over its value in the idling regime. The OM signal persists for a time period no less than 105 sec, either with or without an external bias. The actually obtained values of “recording” sensitivity and the “recording” time are U=0.66 μJ/mm2 and τ=10−4 sec., respectively. The OM signal reaches its maximal value as the thickness of CdTe layer increases (up to d=0.45 μm). It is shown that the investigated HJ possess the property of integration of the radiation.
Doping profiles of n-type GaAs layers grown on Si by the conformal method
Authors: Ardila Angel M. , Martínez O. , Avella M. , Jiménez J. , Gérard B. , Napierala J. , Gil-Lafon E. 
Published: April 2011

AbstractWe study doping profiles in selectively Si-doped GaAs layers grown by the conformal method. This growth technique allows to obtain GaAs/Si with optoelectronic quality. The samples are laterally grown, and selective doping with Si is carried out in such a way that doped stripes are intercalated with undoped ones. The study of the doping profiles was carried out by cathodoluminescence (CL) and micro-Raman (μR) spectroscopy. Abrupt doping profiles between doped and undoped stripes were demonstrated by monochromatic CL images. Deep level related CL bands can be observed between 1000 and 1400 nm, evidencing the complex mechanism for Si incorporation at the growth temperature (730 °C). Net doping concentrations and mobilities across the layers were determined from the analysis of the phonon-plasmon coupled modes in the μR spectra obtained with a lateral resolution better than 1 μm.
Gallium vacancy in GaSb studied by positron lifetime spectroscopy and photoluminescence
Authors: Mui W. K. , Lui M. K. , Ling C. C. , Beling C. D. , Fung S. , Cheah K. W. , Li K. F. , Zhao Y. W. 
Published: April 2011

AbstractPositron lifetime technique and photoluminescence (PL) were employed to study the vacancy type defects in p-type Zn-doped and undoped GaSb samples. In the positron lifetime study, Ga vacancy related defect was identified in these materials and it was found to anneal out at temperature of about 350°C. For the PL measurement on the as-grown undoped sample performed at 10K, a transition peak having a photon energy of about 777meV was observed. This transition peak was observed to disappear after a 400°C annealing. Our results is consistent with the general belief that the 777meV transition is related to the VGaGaSb defect, which is the proposed residual acceptor of GaSb.
Defects Created by 25 keV Hydrogen Implantation in n-type GaN
Authors: Auret F. D. , Meyer W. E. , Laarhoven H. A. van , Goodman S. A. , Legodi M. J. , Beaumont B. , Gibart P. 
Published: April 2011

AbstractWe have studied defects introduced in n-GaN during 25 keV hydrogen and 40 keV He implantation using deep level transient spectroscopy (DLTS). These measurements revealed that 25 keV hydrogen implantation introduces a complex set of electron traps, of which most are different to the defects observed after high-energy (MeV) electron and proton implantation. At least three of the defects detected after 25 keV proton implantation exhibit a metastable character in that they can be reproducibly removed and re-introduced during reverse and zero bias anneal cycles. Isochronal and isothermal annealing experiments yielded low activation energies of approximately 0.1 – 0.2 eV for both processes. By comparison, 40 keV He ion implantation introduced the same metastable defects, but in different relative concentrations.
Study of Interface Properties of InN and InN-Based Heterostructures by Molecular Beam Epitaxy
Authors: Lu Hai , Schaff William J. , Eastman Lester F. , Wood Colin 
Published: April 2011

AbstractIn this work, we prepared epitaxial InN on (0001) sapphire with an AlN or GaN buffer layer by molecular beam epitaxy (MBE). A series of samples were grown with different thickness under the optimized growth conditions. Films were characterized by x-ray diffraction (XRD), reflective high-energy electron diffraction (RHEED), atomic-force microscopy (AFM), transmission electron microscopy (TEM) and Hall measurements. By extrapolating the fitted curve of sheet carrier density vs. film thickness to zero film thickness, a strong residual sheet charge was derived, which may be located at the interface between the buffer layer and the InN film, or at the near-surface. It was found that for InN film on AlN buffer, the residual sheet charge is about 4.3×1013 cm-2, while for InN films on GaN buffer, the residual sheet charge is about 2.5×1013 cm-2. At present, we tentatively believe that the residual charge is surface charge accumulation similar to what is observed at the InAs surface. InN samples with Hall mobility beyond 1300 cm2/Vs and carrier concentration below 2×1018 cm-3 were routinely achieved in this study.The first study on InN-based FET structures was performed. Amorphous AlN was used as the barrier material, which was prepared by migration enhanced epitaxy (MEE) at low growth temperature. It was found that the surface morphology is improved after an AlN barrier layer is added to InN. Hg was used as a back-to-back Schottky metallization. Very low leakage current and weak rectifying behavior were observed.
Reverse-annealing phenomenon during the high-temperature implantation of Ar+ into GaN
Authors: Usov Igor O. , Parikh Nalin R. , Thomson Darren , Davis Robert F. 
Published: April 2011

AbstractA systematic investigation of the damage accumulation in GaN films induced by 150keV Ar ions as a function of implantation temperature and dose rate has been conducted. The depth distribution of the disorder in the Ga sublattice has been measured by RBS/channeling spectrometry with a glancing angle detector geometry to provide enhanced depth resolution. Two disordered regions were identified in the damage depth distribution: a near-surface peak and a bulk damage peak. These regions exhibit different behavior as a function of implantation temperature. The height of the near-surface peak, as expected, decreased with implantation temperature approaching the magnitude of the unimplanted sample. The displaced atomic density in the bulk damage peak also followed this tendency and decreased in the temperature range from room temperature to 500°C. The implantation at higher temperatures resulted in an increase in the amount of damage, reaching a maximum at about 700°C and displayed a characteristic “reverse annealing” behavior. Further increase of the implantation temperature to 1000oC reduced the disorder. The influence of the dose rate and implantation temperature on the radiation damage accumulation is discussed.
Production Scale Growth of AlGaN/GaN Field Effect Transistors
Authors: Gotthold David , Gibb Shawn , Peres Boris , Ferguson Ian , Palmer Chris , Armour Eric 
Published: April 2011

AbstractThis paper addresses issues with the manufacturability of AlGaN/GaN FET structures. A robust Metalorganic Chemical Vapor Deposition growth process has been developed that will now allow reliability measurements to be obtained on the resulting devices. During a small scale production run mobilities in excess of 1600 cm2/V.s, sheet charge (Ns) between 0.8x1013 and 1.2x1013 cm-2, and Rs<400 Ω/square with less than 2% variation across the wafer and less than 0.5% variation from wafer to wafer were obtained. Issues for producing a manufacturable process on sapphire and semi-insulating SiC substrates using in-situ monitoring will be addressed. The equivalence of growth on sapphire and SiC substrates for process optimization will be shown.
Electric Field Induced Heating and Energy Relaxation in GaN
Authors: Eckhause T. A. , Süzer Ö. , Kurdak Ç. , Yun F. , Morkoç H. 
Published: April 2011

AbstractWe report results of an investigation of electric field induced heating at low temperature in GaN 3-dimensional electron gas films grown on sapphire substrates. The excess noise of the electron gas in a patterned GaN film, while the substrate is held at low temperature, is used to determine the electron temperature. We calculate the rate of power dissipation and compare our results with a calculation of acoustic deformation potential scattering processes in GaN. We discuss the existence of a thermal boundary resistance between the GaN film and the sapphire substrate.
Chemical, Electrical, and Structural Properties of Au/Pd Contacts on Chemical Vapor Cleaned p-type GaN Surfaces
Authors: Hartlieb P. J. , Roskowski A. , Rodriguez B. J. , Nemanich R. J. , Davis R. F. 
Published: April 2011

AbstractThe chemical, electrical, and microstructural properties of Au/Pd contacts on p-type GaN(0001) surfaces previously cleaned either ex situ or ex situ and in situ have been investigated. The in situ process involved a high temperature, NH3-based chemical vapor clean (CVC); it produced ordered, stoichiometric, p-type GaN surfaces with no detectable C and an O constituent which was subsequently reduced from 15 at% on the ex situ treated surface to 2 ± 1 at% following the CVC process. The Pd contacting layer grew epitaxially in a layer-by-layer mode on the CVC surface and formed an abrupt, unreacted metal-semiconductor interface. The Au capping layer also grew epitaxially on the Pd. Au/Pd contacts on both HCl and CVC treated surfaces exhibited identical surface roughness values (RMS) in the as-deposited state and following a 500°C anneal. Contact structures on CVC treated surfaces demonstrated excellent high-temperature microstructural stability as evidenced by the absence of significant change in the surface roughness (RMS) with successive annealing at 600 and 700°C. Identical contact structures on ex situ cleaned surfaces exhibited poor high temperature microstructural stability, as indicated by a significant increase in the surface roughness (RMS) following successive anneals at 600 and 700°C. There was a significant degradation in the morphology of both surfaces following the 800°C anneal as evidenced by the formation of large voids in the contact metallization and the exposure of the underlying p-type GaN substrate. The lowest resistance contact structures with uniform metal coverage were obtained for Au/Pd contacts on a CVC treated surface annealed at 700°C.
Layer by Layer Growth of GaN Films by Low Temperature Cyclic Process
Authors: Sanguino P. , Koynov S. , Niehusl M. , Melo L. V. , Schwarz R. , Alves H. , Meyer B. K. 
Published: April 2011

AbstractRecently we have proposed a new layer-by-layer method for deposition of group-III nitrides from elemental precursors (Ga, N2). This technique is based on a two-step cyclic process, which alternates Pulsed Laser Deposition (PLD) and nitrogen plasma treatment. We have shown that such a process allows to control independently the structure and the N-content of the growing film. The objective of this work is to develop the cyclic process for achieving high quality GaN films. We explore the opportunities to grow stoichiometric epitaxial films on different substrates at relatively low temperatures (400°C to 600°C). This will gives us the possibility to use ZnO epitaxial layers as a buffer without thermal degradation. UV- Visible transmission spectra, X-ray diffraction scans and Atomic Force Microscopy are some of the tools used to characterise and compare the deposited films.
Structural and Optical Characteristics of Laterally Overgrown GaN Pyramids on (111) Si Substrate
Authors: Cho Yong-Hoon , Kim H. M. , Kang T. W. , Song J. J. , Yang W. 
Published: April 2011

AbstractStructural and optical characteristics of laterally overgrown GaN pyramids on a (111) Si substrate were investigated by scanning electron microscopy, transmission electron microscopy (TEM), and cathodoluminescence (CL) microscopy and spectroscopy. Cross-sectional TEM images revealed that the threading dislocation density over the window openings is very high, but gradually decreases with increasing GaN thickness, and that dislocations observed over the mask are parallel to the mask interface. Cross-sectional-view CL images taken at different emission wavelengths clearly showed significant differences between the overgrown areas on top of the mask and the coherently grown regions over the windows. A clear reverse contrast in the cross-sectional CL images of bandedge (identical contrast in case of yellow-band) emission was observed by comparing the defect density observed in cross-sectional TEM images. The CL peak intensity ratio of band-edge-emission to yellow luminescence was also investigated as a function of position in the GaN pyramid cross section. It was demonstrated that there exists a strong correlation between structural defects and optical properties in laterally overgrown GaN pyramids on (111) Si substrate.
Growth of Carbon-Nitrogen Films with a Broad Beam RF Ion Source
Authors: Ingram David C. , Lanter William C. , DeJoseph Charles A. , Kayani Asghar 
Published: April 2011

AbstractWith the lack of suitable native oxides, gallium nitride based semiconductor devices will need other materials for dielectric, insulating and passivating layers in a variety of device applications. A carbon-nitrogen film is a possible candidate for this application. Insulating films can be made of this material with a variety of techniques. Ion beam techniques are a well accepted way to demonstrate the existence of a material with certain properties and a way to establish the range of those properties in the material. Ion beam assisted deposition has been used in this work to fabricate materials with various stoichiometries in order to determine the range of properties available for this material.Thin films containing predominantly carbon and nitrogen have been grown using a mixture of methane and nitrogen from a 20 cm rf ion source. The stoichiometry of the films has been measured with Rutherford Backscattering Spectroscopy (RBS), and Elastic Recoil Spectroscopy (ERS). The effect of nitrogen-to-methane ratio, ion energy, and RF power on the film composition, properties, and growth rate is reported together with an analysis of the anticipated growth mechanics.
Microstructure of ELO-GaN Layers Grown by Hydride Vapor Phase Epitaxy
Authors: Gradecak Silvija , Wagner Volker , Ilegems Marc , Bobard Fabienne , Stadelmann Pierre 
Published: April 2011

AbstractElectron microscopy techniques are applied to investigate structural properties of GaN layers selectively grown by hydride vapor phase epitaxy on crystalline and amorphous GaN seed layers deposited on (0001)Al2O3 substrates. Optimalization of the growth conditions lead to a reduction both of the stacking fault concentration and c-axis tilting in the laterally grown regions. During the lateral growth threading dislocations from the seed layer bend from vertical direction of propagation. Bending behavior depends on the type of the dislocation and on the shape of the GaN film in the initial stage of the growth. Optical properties of laterally grown regions are correlated with the high point-defect incorporation that is revealed by high-resolution electron microscopy.
Effect of High Temperature Single and Multiple AlN Intermediate Layers on N-polar and Ga-polar GaN Grown by Molecular Beam Epitaxy
Authors: Fedler F. , Stemmer J. , Hauenstein R. J. , Rotter T. , Sanchez A. M. , Ponce A. , Molina S. I. , Mistele D. , Klausing H. , Semchinova O. , Aderhold J. , Graul J. 
Published: April 2011

AbstractWurtzite GaN samples containing one, three and five 4nm thick high temperature (HT) AlN Interlayers (IL) have been grown on (0001) sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). N-polar as well as Ga-polar thin films have been characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), and electrical measurements.All samples under consideration show excellent AFM rms surface roughness below 1nm. Previously, we published a reduction of the threading dislocation (TD) density by a factor of seven due to the introduction of one AlN-IL. When introducing multiple AlN-IL a reduction by a factor of 5.2 is achieved.Hall measurements show a rise in electron mobility due to possible 2DEG formation at the interface between GaN and the AlN-ILs. Significant growth mode differences between Ga-polar and N-polar samples result in drastically higher electron mobility values for N-polar material. For N-polar samples the exceptional mobility increase from 68 (no AlN-IL) to 707 cm2/Vs (one AlN-IL) as well as the extremely low intrinsic carrier density of 1 x 1017 cm-3 prove the applicability of AlN barriers in inverted FET devices.
Formation of GaN Self-Organized Nanotips by Nanomasking Effect
Authors: Yoshida Harumasa , Urushido Tatsuhiro , Miyake Hideto , Hiramtsu Kazumasa 
Published: April 2011

AbstractWe have successfully fabricated self-organized GaN nanotips by reactive ion etching using chlorine plasma, and have revealed the formation mechanism. Nanotips with a high density and a high aspect ratio have been formed after the etching. We deduce from X-ray photoelectron spectroscopy (XPS) analysis that the nanotip formation is attributed to nanometer-scale masks of SiO2 on GaN. The structures calculated by Monte Carlo simulation of our formation mechanism are very similar to the experimental nanotip structures.