bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Surface Treatments on Optical Properties of GaN
Authors: Fujimoto Gakuyo , Fujii Katsushi , Minegishi Tsutomu , Goto Hiroki , Goto Takenari , Yao Takafumi 
Published: April 2011

ABSTRACTRemoving artificial oxide layer is important for fabrication process of semiconductor devices. We employed photoluminescence for optical, reflection high energy electron diffraction, atomic force microscope, and Nomarski microscope for surface analysis. We found that it is more difficult to remove the oxide layer made by O-plasma such as in O-plasma asher than that of native one. Our result reached that HF etching is effective for removal of the artificial oxide layer without changing surface morphology. In addition, (NH4)2Sx treatment after HF etching reduces donor bound exciton drastically which is dominant luminescence near the band edge at low temperature.
Development of Aluminum Nitride/Platinum Stack Structures for an Enhanced Piezoelectric Response
Authors: Kabulski Adam , Harman John , Famouri Parviz , Korakakis Dimitris 
Published: April 2011

ABSTRACTAluminum nitride (AlN) films are being investigated for piezoelectric and high temperature applications, but the piezoelectric response is still much lower than that of more common piezoelectric materials such as lead zirconate titanate or zinc oxide. A method of maximizing the piezoelectric response of aluminum nitride has been explored by depositing stack structures composed of aluminum nitride and platinum. These stack structures were created by depositing a thin, ∼50nm, metal layer in between thicker, ∼150-350nm, layers of the piezoelectric film. Platinum was chosen as the metal interlayer due to the tendency of AlN to become highly c-oriented when deposited on Pt. An electric field was applied across the structure and displacements were measured using a Laser Doppler Vibrometer. A maximum piezoelectric coefficient d33 was found to be over two times larger than the theoretical value for AlN (3.9pm/V). However, some of the stack structures were found to be conductive when measuring the displacement. I-V measurements as well as Fowler-Nordheim theory and plots were applied to investigate tunneling due to high electric fields in the structures.
Electroreflectance Spectra of InGaN/AlGaN/GaN p-n-Heterostructures
Authors: Yunovich Alexander E. , Avakyants Lev , Badgutdinov Mansur , Bokov Pavel , Chervyakov Anatoly , Shirokov Stanislav , Vasileva Elena , Feopentov Anatoly , Snegov Fedor , Bauman Dmitry , Yavich Boris 
Published: April 2011

ABSTRACTElectroreflectance (ER) spectra of InGaN/AlGaN/GaN p-n- heterostructures with multiple quantum wells (MQW) are studied. Structures with MQW InGaN/GaN were grown for blue LEDs by MOCVD technology and “flip-chip” mounted. The ER spectral maxima correspond to the high energy side of electroluminescence spectral line. The ER spectra caused by Franz-Keldysh effect are approximated by Aspnes theory. The ER spectra in a range 400 ÷ 800 nm have interference bands caused by the change of refraction index in the structure.
Vertically Increasing Well Thickness and In Content in GaInN MQW's due to V-shaped Pits
Authors: Bremers Heiko , Hoffmann L. , Fuhrmann D. , Rossow U. , Hangleiter A. 
Published: April 2011

ABSTRACTIn this work we investigate the influence of V-shaped pits on the growth of GaInN-GaN MQW's by TEM and x-ray diffraction measurements. We have grown different MQW's using low-pressure MOVPE and studied the influence of the number of QW's as well as of the depth of V-shaped pits. During the growth of the samples a material transport takes place from the pits to the c-plane. We show that the thickness of the GaInN QW's and of the GaN barriers is increased due to material transport. With increasing number of quantum wells the diameter of the pits increases, which leads to a super linear increase of these thicknesses. We present a model which describes the change in thickness due to material transport. Another consequence of material transport is a lateral fluctuation in thickness with a characteristic length on the order of the distances between the dislocations.
Investigation of Optical Properties of Nitrogen Incorporated Sb based Quantum Well and Quantum Dots for Infrared Sensors Application
Authors: Kim Seongsin M , Yuen Homan B , Hatami Fariba , Moto Akihiro , Chin Alan , Harris James S 
Published: April 2011

ABSTRACTWe report the growth and characterization of a new dilute nitride, InNAsSb/InAs, by solid source molecular beam epitaxy. Optimizing growth conditions for nitrogen incorporation has resulted in high-quality InNAsSb epilayers without any structural degradation, as confirmed by high-resolution x-ray diffraction. Optical properties were investigated by temperature dependent and excitation power dependent photoluminescence. We obtained mid-infrared luminescence around 4 mm at low temperature, which reveals strong carrier localization behavior at low temperature induced by nitrogen interacted with antimony. The band alignment of InNAsSb/InAs can be type-I and instead of conventional type-II, InAsSb/InAs, and a conduction band offset, Ec,of ∼102meV was obtained.
Investigation of The Electrical and Chemical Properties of Plasma-Treated AlGaN
Authors: Cao Xian-An , Piao H. , LeBoeuf S. F. , Lin J. Y. , Jiang H. X. 
Published: April 2011

ABSTRACTThe surface properties of n-type AlxGa1−xN (x=0-0.5) exposed to inductively couple plasma were studied systematically using metal contact measurements and X-ray photoelectron spectroscopy (XPS). Cl2/BCl3 and Ar plasma treatment considerably increased the surface conductivity of AlxGa1−xN (x<0.3) and thus improved the characteristics of Ti/Al-based ohmic contacts, but degraded the surface and contact properties of AlxGa1−xN (x≥0.3). XPS measurements revealed a significant increase in oxygen incorporation and energy shifts of the core-level spectra in plasma-treated samples. In contrast to an upward shift of the surface Fermi level in plasma-treated GaN, the surface Fermi level moved away from the conduction band in Al0.5Ga0.5N upon plasma treatment. These findings suggest that the nature of plasma damage in AlGaN appears to be a function of the Al mole fraction. Plasma-induced defects in high-Al AlGaN may act as deep-level compensation centers, degrading the surface electrical properties and contact characteristics.
Synthesis of sub-micron diamond films on Si(100) for thermal applications by BEN-MPCVD
Authors: Saada Samuel , Arnault Jean-Charles , Rocha Licinio , Bergonzo Philippe 
Published: April 2011

ABSTRACTDiamond is the ultimate candidate for heat-spreading applications because of its extreme thermal management properties. The synthesis of sub-micron diamond films is of great interest for SOD (Silicon On Diamond) wafer technology as well as for specific thermal device applications. The challenge here is the necessity to fabricate ultra-thin layers (down to 100 nm) that are continuous and homogeneous. We studied the Bias Enhanced Nucleation (BEN) pretreatment on microwave plasma reactors in order to have very high nucleation densities (> to 1011 cm−2) and optimised the following growth step of the process to obtain sub-micron covering diamond films. In this study, we focus on the bias step parameters to increase the nucleation rate and to limit the growth rate during the bias step. Then, we performed a growth step to control the morphology of the films. We obtained diamond films with thickness lower than 80 nm and with a 6 nm Root-Mean-Square roughness.
Effects of High D.C. Hias Voltage on the Properties of Diamond-Like Carbon Films
Authors: Yang Boqian , Zhang Hongxin , Wang Xinpeng , Feng Xianping 
Published: April 2011

ABSTRACTDiamond-like carbon (DLC) films were synthesized using pulsed plasma sputtering deposition techniques. Microscope and Raman scattering techniques were used to study the effects of bias voltages on the properties of diamond-like carbon films. With d.c. bias voltage up to 1000V, the smooth and thick DLC films together with a few nanoparticles were obtained. An increase of the d.c. bias voltage up to 2000V yielded thicker DLC films but its surface became slightly rough and size of particles became large. The crystalline properties of these particles were studied. A tiny diamond peak from Raman spectrum was also observed.
Electron Emission Mechanism of Doped CVD Diamond Characterized Using Combined XPS/UPS/FES System
Authors: Yamaguchi Hisato , Saito Ichitaro , Kudo Yuki , Masuzawa Tomoaki , Yamada Takatoshi , Kudo Masato , Takakuwa Yuji , Okano Ken 
Published: April 2011

ABSTRACTElectric field of less than 5 V/μm is enough to extract electrons from diamond, whereas field of one to two orders of magnitude higher is needed to extract electrons from metal emitter tips. Despite such low-threshold field, the difficulty in clarification of electron emission mechanism is the factor preventing diamond from being used in a practical use. Quite a few numbers of possible mechanisms were proposed to better understand the origin and properties of the observed emission. Most of these mechanisms were, however, based on the conventional I (Emission current)-V (Anode voltage) characteristics. Energy distribution of the field-emitted electrons is essential in direct clarification of the mechanism. In this study, combined XPS/UPS/FES system was used to characterize the electron emission mechanism of doped chemical vapor deposited (CVD) diamond. The results indicated successful observation of the origin of field-emitted electrons from doped CVD diamond comparison with natural diamond, used as a reference.
Nanofabrication of Diamond-like Carbon Templates for Nanoimprint Lithography
Authors: Tao L. , Ramachandran S. , Nelson C. T. , Overzet L. J. , Goeckner M. J. , Lee G. S. , Hu W. 
Published: April 2011

ABSTRACTDiamond like carbon (DLC) films were deposited on Si and then patterned to form 40 nm features as nanoimprint templates. A plasma enhanced chemical vapor deposition (PECVD) system with CH4 precursor was used to deposit DLC films on Si and quartz substrates. Then these films were characterized using Raman spectroscopy, atomic force microscopy (AFM), nanoindentation, and contact angle measurement. By varying the RF power and pressure of the PECVD, DLC films with good uniformity, smooth surfaces (<0.2 nm RMS), low surface energy (∼40 mJ/m2), and high hardness (∼22 GPa) were achieved. Nanoimprint lithography and liftoff process were used to pattern Cr mask on DLC films. An inductively coupled plasma (ICP) etching process was performed with CF4 to transfer the patterns into the DLC films to form nanostructured template for nanoimprint. Water contact angles on the patterned DLC templates were measured and it was stable at about 70° under thermal annealing at 180 °C for more than 12 hours. With these DLC templates, UV and reversal UV nanoimprint lithography were carried out on SU-8 at typical imprint conditions and then the fidelity of pattern-transfer was investigated. These experimental results indicate that DLC is an excellent material for nanoimprint templates because of its high wear resistance, robust low surface energy, UV transparency, and ease of patterning.
Surface and Electrochemical Studies of Thin Film Diamond
Authors: Foord John , Opperman David 
Published: April 2011

ABSTRACTThe behavior of diamond electrodes for electrochemical applications in aqueous media containing the protein bovine serum albumin has been explored, to examine the degree of electrode poisoning which occurs. Although the diamond electrode retains good activity in such solutions, electrode fouling is found at long contact times due to protein adsorption. Two adsorption processes are observed. The first is a simple physical adsorption mechanism, and can be simply reversed by washing the electrode in water. The second mechanism is only observed when negative potentials are applied to the diamond electrode and is attributed to the attraction and reaction of the positively charged protein at the electrode interface. Electrode poisoning is also observed in the presence of power ultrasound, although the electrochemical signals are usefully enhanced under these conditions due to enhanced mass transport to the electrode surface.
Spatially Resolved Study of Magnesium Incorporation in Zn1-xMgxO Nanostructures
Authors: Schirra Martin , Reiser Anton , Prinz Günther Michael , Schneider Raoul , Sauer Rolf , Thonke Klaus 
Published: April 2011

ABSTRACTWe report on the growth of Zn1-xMgxO nanopillars on a-plane sapphire by the vapor liquid solid (VLS) process. The as-grown nano structures are characterized by scanning electron microscopy (SEM), spatially resolved cathodoluminescence (SEM-CL), and integral photoluminescence (PL). The investigation with SEM applying different secondary electron detectors confirms that the pillars are grown by the VLS process. Integral PL experiments reveal an average value of 7% Mg incorporated in the Zn1-xMgxO nano structures. Both ZnO- and Zn1-xMgxO– related luminescence features are observed. The direct incorpoaration of Mg into single pillars is demonstrated with SEM-CL, and different Mg concentrations are found. First annealing experiments on the sample at 850°C lead to an almost complete breakdown of the ZnO- and Zn1-xMgxO– related near band-edge luminescence, whereas the structural properties of the sample morpholgy remain nearly unchanged.
Ferromagnetic Mn-Mn Interactions in Low Doped Zn1-xMnxO Thin Films
Authors: BenMahmoud Aroussi , von Bardeleben H.Jurgen , Mauger Alain , Cantin Jean Louis , Chikoidze Ekaterina , Dumont Yves 
Published: April 2011

ABSTRACTWe have studied by electron paramagentic resonance spectroscopy the Mn2+ EPR spectra in low doped (x=0.03) Zn1-xMnxO films of n-type conductivity prepared by metalorganic chemical vapour deposition. Contrary to higher doped films with x=0.07, the x=0.03 film shows a weak ferromagnetic Mn-Mn interaction which we attribute to the presence of moderate deep donors leading to magnetic polaron formation.
Study of the Temperature Dependence of E2 and A1(LO) Modes in ZnO
Authors: Alarcon-Llado Esther , Cusco Ramon , Ibanez Jordi , Artus Luis , Jimenez Juan , Wang Buguo , Callahan Michael 
Published: April 2011

ABSTRACTRaman scattering measurements were carried out on a bulk, single crystal of wurtzite ZnO over a temperature range from 80 to 760 K and the temperature-dependent shift and broadening of the E2high and A1(LO) modes was analyzed. The E2high mode exhibits a visibly asymmetric line shape that can be related to the interaction with the continuum of acoustic two-phonon density of states. A Fermi resonance model was used to describe the E2high temperature dependence. On the other hand, the anharmonic shift and broadening of the A1(LO) mode are adequately accounted for by a decay model with a dominating Ridley channel involving TO and LA modes. Phonon lifetimes of ∼0.9 and 0.5 ps are found for the E2high and A1(LO) modes, respectively, which corroborates that anharmonic decay involves in both cases a three-phonon process. The A1(LO)lifetime is one order of magnitude lower than that of GaN, which suggests that hot phonon effects should be expected to play a less relevant role in carrier relaxation in ZnO as compared with GaN.
A Solution Method for Large-scale Selective Growth of Aligned ZnO Nanorods
Authors: Hahn Yoon-Bong , Umar Ahmad , Kim Sang Hoon , Im Yeon Ho , Hahn Yoon Bong 
Published: April 2011

ABSTRACTA facile and convenient aqueous route has been employed to synthesize well -aligned ZnO nanorods. Field emission scanning electron microscopy studies of ZnO nanorod arrays grown at 70°C on ZnO/Si substrates show fine homogeneous surface. The average diameter of ZnO nanorod is in between 50-60 nm .The length of each nanorod is about 400-500 nm. Structural analysis showed that the ZnO nanorods are single crystalline with wurtzite hexagonal phase. Room temperature photoluminescence spectra of the ZnO nanorod arrays exhibit ultra violet emission and green emission. In addition, selective growth of ZnO nanorods on patterned ITO glass substrate is obtained. Each nanorod has diameter of 50 - 70 nm and their length upto 500 nm. XRD pattern shows that ZnO nanorods on patterned ITO substrate are single crystalline in nature with wurtzite hexagonal phase. The room temperature photoluminescence from the aligned ZnO nanorods showed a strong ultra violet emission at 378 nm and broad deep level visible emission at 580 nm.
Surface Preparation of Single Crystals for ZnO Homoepitaxy
Authors: Neumann Christian , Lautenschläger Stefan , Graubner Swen , Volbers Niklas , Meyer Bruno K , Bläsing Jürgen , Krost Alois 
Published: April 2011

ABSTRACTFor the homoepitaxial growth of ZnO it is inevitable to obtain a regular crystalline single crystal surface prior to growth. Commercially available, hydrothermally grown ZnO single crystals show amorphous surfaces due to mechanical cutting and polishing.
Here we present the results of a thermal treatment on these ZnO single crystals. After annealing, a regular crystalline oxygen terminated surface can be obtained. Changes in surface roughness, residual defect concentration and electrical properties can be shown. The bulk crystallinity though was not affected.
Growth and Characterization of Mg0.15Zn0.85O Thin Films by Pulsed Laser Deposition
Authors: Wei Wei , Jin Chunming , Doraiswamy Anand , Narayan Roger J , Narayan Jagdish 
Published: April 2011

ABSTRACTMg0.15Zn0.85O thin films were grown on fused silica substrates at different substrate temperatures using pulsed laser deposition. X-ray diffraction and transmission electron microscopy were used to investigate the structure of the films. High resolution transmission electron microscopy showed that the film contained small grains with low angle boundaries. The optical properties of the films were investigated using absorption spectra. The bandgap energy values of the films was determined by fitting the absorption data.
Electrical Characterization of Defect States in Local Conductivity Domains in ZnO:N,As Layers
Authors: Krtschil Andre , Dadgar Armin , Diez Annette , Krost Alois 
Published: April 2011

ABSTRACTP- and n-type conductivity domains in dual-doped ZnO:As+N layers grown by metal organic vapor phase epitaxy on GaN/sapphire templates were electrically microcharacterized by scanning capacitance (SCM) and scanning surface potential microscopy (SSPM) techniques with respect to their defect states. The p-type domains were found to be dominated by two acceptors with thermal activation energies of about 80 and 270 meV as observed by transient SCM scans at different temperatures. Optically excited SSPM scans revealed defect-to-band-transitions at 400, 459, and 505 nm omnipresent in both domain types as well as a shallower transition at 377 nm exclusively in the p-type regions. According to the similar energy levels the optical transitions at 377 and 400 nm are assigned to acceptor states, whereby the 80meV-acceptor is probably responsible for the conversion from n- to p-type in the domains.
Formation of Nanovoids and Nanocolumns in High Dose Hydrogen Implanted ZnO Bulk Crystals
Authors: Singh Rajendra , Scholz R. , Gösele U. , Christiansen S. H. 
Published: April 2011

ABSTRACTZnO(0001) bulk crystals were implanted with 100 keV H2+ ions with various doses in the range of 5×1016 to 3×1017 cm-2. The ZnO crystals implanted up to a dose of 2.2×1017 cm-2 did not show any surface exfoliation, even after post-implantation annealing at temperatures up to 800°C for 1 h while those crystals implanted with a dose of 2.8×1017 cm-2 or higher exhibited exfoliated surfaces already in the as-implanted state. In a narrow dose window in between, controlled exfoliation could be obtained upon post-implantation annealing only. Cross-sectional transmission electron microscopy (XTEM) of the implanted ZnO samples showed that a large number of nanovoids were formed within the implantation-induced damage band. These nanovoids served as precursors for the formation of microcracks leading to the exfoliation of ZnO wafer surfaces. In addition to the nanovoids, elongated nanocolumns perpendicular to the ZnO wafer surfaces were also observed. These nanocolumns showed diameters of up to 10 nm and lengths of up to 500 nm. The nanocolumns were found in the ZnO wafer even well beyond the projected range of hydrogen ions.
Structure-Property Relationships in the xZnO-(1-x)alpha-Fe2O3 Nanoparticle System
Authors: Sorescu Monica , Diamandescu Lucian , Wood Jason 
Published: April 2011

ABSTRACTThe xZnO-(1-x)α-Fe2O3 nanoparticles system has been obtained by mechanochemical activation for x=0.1, 0.3 and 0.5 and for ball milling times ranging from 2 to 24 hours. Structural and morphological characteristics of the zinc-doped hematite system were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy. As ZnO is not soluble in hematite in the bulk form, the present study clearly demonstrates that the solubility limits of an immiscible system can be extended beyond the limits in the solid state by mechanochemical activation. Moreover, this synthesis route allowed us to reach nanometric particle dimensions, which would make the materials very important for gas sensing applications.
Preparation of Shape and Size-Controlled Zinc Oxide Nanostructures by Chemical Spray Pyrolysis Technique
Authors: Dedova Tatjana , Krunks Malle , Mere Arvo , Klauson Jelena , Volobujeva Olga 
Published: April 2011

ABSTRACTHighly structured layers comprising of vertically aligned zinc oxide rods, tripods or platelets were fabricated by spray pyrolysis method at temperatures of 510-550 °C. The zinc chloride solution was pulverized onto the preheated substrates of glass and ITO, SnO2, ZnO covered glass substrates with the help of compressed air as a carrier gas. ZnO layers were characterized by scanning electron microscopy and Raman spectroscopy. C-axis orientated ZnO nanorod arrays of well-developed hexagonal rods with length from some hundreds of nanometers up to some microns and with diameter from 70 nm up to 900 nm . The rise of both the growth temperature and solution concentration increases rod dimensions. Deposition of the solutions with the concentration of 0.05 up to 0.2 mol/l results in structured layers composed of rods on glass substrates. Using ITO, SnO2 and ZnO thin film covered glasses diluted solutions should be used to obtain ZnO nanorods. Alcoholic solutions allow deposit thinner rods and reduce the deposition temperature. Very strong and relatively narrow E2 Raman bands indicate that ZnO rods prepared by spray pyrolysis technique are of high crystal quality.
Soft-chemistry Route to P-I-N Heterostructured Quantum Dot Electroluminescence Device: All Solution-processed Polymer-Inorganic Hybrid QD-EL Device
Authors: Kwon Soon-Jae , Cho Kyung-Sang , Choi Byoung-Lyong , Kim Byung-Ki 
Published: April 2011

ABSTRACTp-i-n heterostructured quantum-dot electroluminescence (QD-EL) device was fabricated by soft-chemical process, which shows a low turn-on voltage comparable to OLEDs. To construct the multilayered device structure, p-type polymer semiconductor was deposited on the ITO glass by sequential process of coating and thermal curing, thereupon a few monolayers of QD was spin-coated. n-type metal-oxide film was deposited on top of the QD luminescence layer by sol-gel method, providing a facile and low-cost route for the ETL fabrication. Prior to solution-processed ETL construction, a post-treatment is performed using cross-linking agent, in order to chemically-immobilize the QDs. As a cathodic electrode, relatively air-stable aluminum was deposited. The constituent material as well as the electronic band structure of the integrated device guarantees operating stability in air and low turn-on voltage.