Symposium : D
Multidimensional electrical and chemical characterization at the nanometer-scale of organic and inorganic semiconductors
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| Advanced Scanning Probe Microscopy I : ----- | ||
| 14:00 | Multidimensional Characterization at the Nanometer Scale by Scanning Probe Methods Authors : Roland Wiesendanger Interdisciplinary Nanoscience Center Hamburg, University of Hamburg, D-20355 Hamburg, Germany wiesendanger@physnet.uni-hamburg.de, www.nanoscience.de Resume : The emerging field of spintronics is based on three important pillars: I) metal-based multilayer systems and nanostructures, II) semiconductor-ferromagnet heterostructures and diluted magnetic semiconductors, and III) molecular-based spintronics. Advances in all three areas depend critically on a fundamental understanding of magnetic and spin-dependent properties and interactions at the atomic level, requiring the determination of spin structures and spin excitations down to the atomic scale.
The direct visualization of atomic-scale spin structures [1-3] has first been accomplished for magnetic metals by combining the atomic resolution capability of Scanning Tunnelling Microscopy (STM) with spin sensitivity, based on vacuum tunnelling of spin-polarized electrons [4]. The resulting technique, Spin-Polarized Scanning Tunnelling Microscopy (SP-STM) [5], nowadays provides unprecedented insight into collinear and non-collinear spin structures at surfaces of magnetic nanostructures and has already led to the discovery of new types of magnetic order at the nanoscale [6,7].
[1] R. Wiesendanger et al., Science 255, 583 (1992)
[2] S. Heinze et al., Science 288, 1805 (2000)
[3] A. Kubetzka et al., Phys. Rev. Lett. 94, 087204 (2005)
[4] R. Wiesendanger et al., Phys. Rev. Lett. 65, 247 (1990)
[5] R. Wiesendanger, Rev. Mod. Phys. 81, 1495 (2009)
[6] K. von Bergmann et al., Phys. Rev. Lett. 96, 167203 (2006)
[7] M. Bode et al., Nature 447, 190 (2007) | 1 1 |
| 14:35 | Scanning Capacitance Microscopy Authors : J.Smoliner, W.Brezna, C.Eckhardt, O.Bethge, E.Bertagnolli, Institut fuer Festkoerperelektronik, TU-Wien, Austria Resume : Capacitance spectroscopy on semiconductor samples such as Metal / Oxide / Silicon (MOS) systems, is a standard characterization tool since the early days of silicon technology. By measuring capacitance vs. voltage curves, a multitude of sample parameters such as oxide thickness, dielectric constants, work function differences, oxide charges, traps, and also doping levels were determined. Shrinking device dimensions, however, raised the need for local sample characterization down to the nanoscale.
Atomic Force Microscopes with conducting tip connected to a sensitive capacitance meter, nowadays allow local capacitance measurements with nanometer spatial resolution. This technique is called Scanning Capacitance Microscopy / Spectroscopy (SCM/S) and combines the wide possibilities of capacitance spectroscopy with the outstanding resolution of Atomic force Microscopy. In practice, however, SCM is not straightforward. The signals are extremely small, sample preparation is difficult and parasitic geometry effects can play major a role. Thus, quantitative SCM measurements are still a major challenge.
In this talk the possibilities and limitations of SCM will be presented. Typical qualitative SCM applications will be shown, and several quantitative spectroscopic measurements will be discussed in detail including two-dimensional simulations. First results on the latest and very promising development in SCM, the so-called Scanning Microwave Microscopy, will be shown, too. | 1 2 |
| 15:10 | Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films Authors : Patrick Fiorenza, Raffaella Lo Nigro, Vito Raineri Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche (IMM-CNR); Strada VIII 5, 95121 Catania (Italy) Resume : CaCu3Ti4O12 (CCTO) has attracted considerable attention in recent years due to its impressive apparent permittivity ~ 104 - 105 at 1 MHz, which remains constant in the 100-600 K temperature range. The origin of such “giant” permittivity in CCTO ceramics seems to be due to an internal barrier layer mechanism related to the dielectric inhomogeneous nature of grain and grain boundaries. However, this model has not be demonstrated to be valid in the case of CCTO thin films. In this case, microscopic electrical measurements indicated that surface barrier layer capacitor effect (SBLC) at the top electrode plays an important role.
This paper reports on the combination of scanning impedance microscopy and conductive atomic force microscopy to provide a local characterization of the dielectric heterogeneities in CCTO thin films deposited by MOCVD on IrO2 bottom electrode. In particular, both techniques can be employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films were studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated. | 1 3 |
| 15:30 | Coffee break | |
| Semiconductor Nanowires : ----- | ||
| 15:50 | Atom-by-atom deconstruction of semiconductor nanowires Authors : Lincoln J. Lauhon, Northwestern University, USA Resume : Impurity doping is the basis by which we control the function of many semiconductor devices, so it is of technological importance to advance understanding and control of doping in new semiconductor materials. Semiconductor nanowires are ‘new’ materials by virtue of their small sizes, distinct growth methods, and large surface-area-to-volume ratios. The objective of our work is to understand and control dopant incorporation rates and junction profiles in Si and Ge nanowires grown by the vapor-liquid-solid (VLS) process in a chemical vapor deposition system. We have used atom probe tomography (APT) to map the distribution of dopant atoms in individual VLS grown Si and Ge nanowires. We find that nanowires grown by the VLS process may have non-uniform dopant distributions due to surface doping during synthesis, particularly for hot-wall CVD based growth. Surface doping may produce radially and axially non-uniform carrier concentration profiles, which has important implications for device performance and modeling. In addition, we find that the VLS doping efficiency using hydride precursors with Au catalysts is lower than expected, with the P doping of Ge nanowires being particularly suppressed. We will compare dopant incorporation efficiencies in the Si-Ge-B-P system in the context of a simple doping model to provide insights into the thermodynamic and kinetic factors that influence doping. APT analysis of dopant homojunctions will be presented to extract important thermodynamic parameters, and to show why alterative catalysts are needed to realize abrupt junctions. | 2 1 |
| 16:25 | Characterization of silicon heterojunctions and silicon nanowires for solar cells Authors : J.P. Kleider, J. Alvarez, I. Ngo, O. Maslova Laboratoire de Génie Electrique de Paris, 11 rue Joliot-Curie, Plateau de Moulon, 91192 Gif-sur-Yvette Cedex, France E.V. Gushina, A.V. Ankudinov, E. I Terukov A.F. Ioffe Physico-technical Institute, Polytechnicheskaya str. 26, 194021 St.-Petersburg, Russia A. S. Gudovskikh Saint-Petersburg Physics and Technology Centre for Research and Education of the Russian Academy of Sciences, Hlopina str. 8/3, 194021, St.-Petersburg, Russia M. Labrune, P. Roca i Cabarrocas Laboratoire de Physique des Interfaces et des Couches Minces , Ecole Polytechnique, CNRS, 91128 Palaiseau, France Resume : In the field of silicon solar cells, recent progress has been achieved in two directions : silicon heterojunctions and silicon nanowires. In this presentation, we give a short overview of latest developments in this field and emphasize the use of local characterization, especially from contacting probe atomic force microscopy (CP-AFM).
Silicon heterojunctions are formed between crystalline silicon (c-Si) and hydrogenated amorphous silicon (a-Si:H). Solar cell efficiencies of up to 23% have been demonstrated on high quality n-type c-Si wafers with very thin layers of p-type a-Si:H deposited at the front (as the emitter) and n-type a-Si:H deposited at the back (as the back surface field), respectively. We here show that strongly inverted regions do exist at the c-Si interfaces due to the heterojunction band offsets with a-Si:H. These are revealed by planar conductance measurements, and, for the first time, directly by cross-sectional scanning spreading resistance microscopy.
Silicon nanowires applied to photovoltaics generally exhibit radial pn junctions, where one can take advantage of the decoupling between light trapping in the axial direction and the minority carrier collection in the radial direction. Results on the formation steps of the nanowires and on their electrical properties will be presented. | 2 2 |
| 17:00 | Transmission Electron Microscopy of Si and Ge nanowires Authors : Simona Boninelli, MATIS-IMM-CNR, Via S. Sofia 64, 95123 Catania, ITALY Emanuele Francesco Pecora, MATIS-IMM-CNR and Dipartimento di Fisica e Astronomia, Universitŕ di Catania, Via S. Sofia 64, 95123 Catania, ITALY Pietro Artoni, MATIS-IMM-CNR and Dipartimento di Fisica e Astronomia, Universitŕ di Catania, Via S. Sofia 64, 95123 Catania, ITALY Alessia Irrera, MATIS-IMM-CNR, Via S. Sofia 64, 95123 Catania, ITALY Lucia Romano, MATIS-IMM-CNR and Dipartimento di Fisica e Astronomia, Universitŕ di Catania, Via S. Sofia 64, 95123 Catania, ITALY Corrado Spinella, IMM-CNR, VIII Strada 5, 95121 Catania, Italy Francesco Priolo, MATIS-IMM-CNR and Dipartimento di Fisica e Astronomia, Universitŕ di Catania, Via S. Sofia 64, 95123 Catania, ITALY Resume : Low-dimensional semiconductors, such as nanoclusters, nanotubes and nanowires (NWs), account for a new class of materials with great potential as building blocks for future electronics. In particular, as Ge and Si are the leading materials in microelectronics, Ge and Si NWs are currently receiving a considerable attention from a wide scientific community searching for intriguing modifications of the bulk properties.
We demonstrated through SEM and TEM techniques the epitaxial growth on Si substrates of single-crystal Ge and Si NWs by electron beam evaporation, which is a cheap, non-UHV, widely diffused deposition technique. Crystallographic analysis demonstrated that NWs have specific crystallographic growth directions which depend on the growth parameters.
Moreover, in the perspective of NWs application in electronics, photonics, sensing and photovoltaics, their controlled doping is one of the main challenges. In this work the effects of ion implantation and the damage recovery in Si NWs are elucidated. Ion implantation induced a clear bending of a portion of the NWs and TEM images and diffraction patterns demonstrated that this effect is related to the formation of an amorphous/crystal interface along the NW axial direction. Furthermore, a complete structural recovery and a consequent unbending was obtained by means of thermal annealing processes. The competition between Solid Phase Epitaxy and Random Nucleation and Growth is the key parameter controlling the recovery. The comprehension of the structural effects at the nanoscale is expected to have strong implications for the use of ion implantation for Si NWs doping. | 2 3 |
| Poster Session I : ----- | ||
| 17:30 | Effect of Ag and N Addition on Crystallization of Sb-rich GeSb Binary Phase Change Material Authors : Hyung Keun Kim, Department of Materials Science and Engineering, Yonsei University, Korea Nam Hee Kim, Department of Materials Science and Engineering, Yonsei University, Korea Jae Sung Roh, Memory R&D Division, Hynix Semiconductor Inc., Korea Doo Jin Choi, Department of Materials Science and Engineering, Yonsei University, Korea Resume : As well known, write/erase operation of the phase change memory is accomplished by changing the phase of phase changeable material such as GeSbTe. GeSbTe ternary compound having the atomic ratio 2:2:5 is the most famous phase change material, however, there are various reports about the problem such as large reset current consumption, poor phase, thermal stability and so on. To solve these problems, many research groups are trying to apply different phase change materials or incorporate additional impurity elements in phase change material. In present study, Sb-rich GeSb was applied as a phase change material, and Ag and N were incorporated as additional elements. And we measured the sheet resistance of phase change material annealed at various temperatures to report electrical properties. To report electrical properties, we made a method to define resistivity of the crystalline state and phase change temperature via ex-situ sheet resistance measurement with our originality using spline-function method. To report structural properties, we carried out XRD and TEM analysis. It was clearly observed that impurity elements affect the crystallization properties and phase separation phenomenon of GeSb. Crystalline grain size was varied with the amount of impurity elements and precipitated Sb crystal was observed clearly. We concluded that these electrical and structural properties are thought as important results to apply GeSb as a phase change materials. | P1 1 |
| 17:30 | Impact of near-surface processing on the electrical and structural properties of AlGaN/GaN heterostructures grown on Si: a nanoscale characterization approach Authors : G. Greco (1), F. Roccaforte (1), F. Giannazzo (1), A. Frazzetto (1), C. Tringali (2), G. Abagnale (2), V. Raineri (1) (1) Consiglio Nazionale delle Ricerche – Istituto per la Microelettronica e Microsistemi (CNR-IMM), Strada VIII n. 5, Zona Industriale, 95121 Catania, Italy (2) ST Microelectronics, Stradale Primosole 50, 95121 Catania, Italy Resume : AlGaN/GaN heterostructures are excellent materials for the fabrication of high electron mobility transistors (HEMTs). For some applications, normally-off operation of HEMTs is a challenging goal, for which several solutions involving nanoscale local modifications of the AlGaN layer (recessed gate process, fluorine plasma etch, surface oxidation, etc.) have been proposed in literature. Clearly, the properties of the two dimensional electron gas (2DEG) generated at AlGaN/GaN interfaces are strongly affected by those processes. Hence, using nanoscale characterization methods is the optimal way to monitor these local changes and to fully assess the basic transport phenomena, in order to ultimately achieve reliable processes for devices fabrication.
In this work, the effects of near-surface processing on the properties of AlGaN/GaN heterostructures were studied, combining conventional analysis of round-HEMTs with advanced nanoscale characterization techniques (TEM, AFM, C-AFM, SCM,…).
First, the effects of a fluorine-based plasma process on the threshold voltage and current capability of HEMTs were discussed considering the near-surface damage and the electrical modifications induced by charged fluorine ions, as deduced by TEM and SCM analyses.
Thereafter, it will be shown that a rapid thermal oxidation of AlGaN results in a very thin surface oxide (Al2O3-Ga2O3), whose local formation can be used to tailor the sheet carrier density in the 2DEG and, hence, the device characterists. | P1 2 |
| 17:30 | Nanoscale electro-structural characterization of p-type implanted regions and Ohmic contacts on 4H-SiC Authors : A. Frazzetto (1), F. Roccaforte (1), F. Giannazzo(1) , R. Lo Nigro(1) , C. Bongiorno (1), M. Saggio (2), E. Zanetti (2), V. Raineri (1) (1) Consiglio Nazionale delle Ricerche – Istituto per la Microelettronica e Microsistemi Strada VIII n.5, Zona Industriale, 95121, Catania, Italy (2) ST-Microelectronics, Stradale Primosole 50, 95121, Catania, Italy Resume : This work reports on a nanoscale electro-structural characterization of p-type implanted silicon carbide (4H-SiC).
N-type 4H-SiC epilayers (ND= 11016 cm-3 ) were implanted with Al-ions at different energies and fluencies (30-80 keV, 1.31014-1.31015 cm-2) to achieve selectively p-type doped regions. Thermal annealing at 1700°C was carried out to activate the dopant, with and without a protective carbon capping layer on the surface. Ohmic contacts on the p-type regions were formed by an annealed Al/Ti bilayer after removing the capping layer. The morphology, local electrical properties and microstructure of Ohmic contacts and implanted layers were monitored by AFM, SSRM, TEM and XRD.
AFM analyses showed that the surface roughness (RMS) strongly decreases by using capping layer, i.e. from 18.9 nm (without capping) to 2.4 nm (with capping). Also the morphology of the annealed contacts was strongly affected by the roughness of the underlying implanted regions. It is worth noting that the Al/Ti Ohmic contact formed on the capped samples showed, on average, a lower specific contact resistance (c = 3.3210-4 cm-2), with respect to the un-capped one (c = 3.8110-3 cm-2). Structural analysis (XRD, TEM) showed the formation of a ternary phase (Ti3SiC2) and a strongly inhomogeneous interface. The inhomogeneity of the metal/SiC interface was monitored at a nanoscale level by local current measurements (SSRM) and could explain the macroscopic electrical behaviour of the contacts. | P1 3 |
| 17:30 | Aluminum nitride micro and nanopowder Authors : D. Smoleń1, P. Dominik1, K. Trocewicz1,K. Łyżwa1, A. Giżycka1, A. Ostrowski1, S. Podsiadło1, C. Jastrzębski2, J. Judek2, W. Gębicki2, W. Paszkowicz3 1. Warsaw University of Technology, Faculty of Chemistry, Noakowskiego 3, 00-664 Warsaw, Poland 2. Warsaw University of Technology, Faculty of Physics, Koszykowa 75, 00-662 Warsaw, Poland 3. Polish Academy of Sciences, Institute of Physics, Al. Lotników 32/46, 02-668 Warsaw, Poland Resume : Aluminum nitride was synthesized for the first time over a hundred years ago. It has attracted much interest in recent years, particularly in the electronics industry, due to of its chemical and physical properties. Aluminum nitride has a high intrinsic thermal conductivity (320Wm-1K-1), high electrical insulation (>1014ohm.cm) and thermal expansion coefficient (5,7.10-6K-1) close to that of silicon, high mechanical strength and wide direct band gap (6,2eV), which makes it attractive for potential applications in laser diodes, solar blind photodiodes (PD), blue/UV Light Emitting Diodes (LED) and high- temperature electronic devices. In scientific literature there are many methods to synthesize AlN nanopowder but, the problem is to synthesized nanopowder of aluminum nitride with high purity and low grain size.
The main goal of our research was to develop a method to synthesize nanopowder of aluminum nitride, which will be free of carbon, with almost 100% productivity and size of the grain less than 100nm. The reaction was carried out in horizontal tube furnace. As starting materials we used micro and nanopowders of aluminum oxide (average particle size from 45nm to 10μm). Gaseous ammonia was used as a source of nitrogen. The reaction can be expressed as follow:
Al2O3 + 2NH3 → 2AlN + 3H2O
The process was carried out in the temperature range 1050 -1350oC for time 1- 5h. The samples were investigated by: powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Ramman spectroscopy and infrared spectroscopy with Fourier transform (FT-IR). Our investigation show some “nano effects” in powder diffraction line profile, infrared and Ramman spectroscopy measured for obtained aluminum nitride powders. | P1 4 |
| 17:30 | Giant permittivity ceramics surface at sub-micrometer scale Authors : Patrick Fiorenza, Raffaella Lo Nigro, Vito Raineri Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche (IMM-CNR); Strada VIII 5, 95121 Catania (Italy) Resume : Scanning probe microscopy (SPM) with conductive tips has been used to image the dielectric properties of ceramics with giant permittivity. In particular, measurements in impedance mode of local resistivity provided the imaging of the permittivity maps on CaCu3Ti4O12 ceramics. Such imaging showed the correlation between the dielectric properties and the sample structure, in particular indicating the presence of defects inside the single grains or heterogeneities at the grain boundaries.
Great attention has been devoted to the possible artefacts due to surface imperfections, such as huge roughness and/or contaminations. A reliable surface investigation has been obtained after the definition of both the physical and geometrical criteria to avoid the artefacts due to the superficial contaminations or anomalous tip-sample contact area.
In particular, the power spectral density (PSD) gives the different periodic components of the surface roughness and demonstrated to be a sensitive tool to check the surface conditions after the polishing procedures. Moreover, empirically the imaging resolution has been proved.
The best operating conditions from both geometrical and analytical points of view have been set and could be defined just in term of root mean square (RMS) after a correlations between geometrical and electrical properties. | P1 5 |
| 17:30 | Conductive AFM characterization of nanoscale transport properties at metal/3C-SiC interfaces Authors : Jens Eriksson1, 2), Fabrizio Roccaforte1), Filippo Giannazzo1), Raffaella Lo Nigro1), Sergey Reshanov3), Vito Raineri1) 1) CNR-IMM, Strada VIII n. 5, Zona Industriale, 95121, Catania, Italy 2) Scuola Superiore - Universitŕ di Catania, Via San Nullo 5/i, 95123, Catania, Italy 3) Acreo AB, Electrum 236, SE-16440 Kista, Sweden Resume : Cubic silicon carbide (3C-SiC) has some potential advantages over the hexagonal SiC polytypes for power devices, chiefly in terms of drift velocity and channel mobility [1]. However, 3C-SiC is held back by material defects hindering the formation of ideal rectifying contacts, in turn yielding unacceptable off-state characteristics for power devices.
The roots of the poor electrical behavior of rectifying contacts to 3C-SiC were investigated by studying the influence of specific material defects on the properties of Schottky barriers on this polytype. Defects were studied by transmission electron microscopy (TEM) and Conductive Atomic Force Microscopy (C-AFM). By observing the nanoscale electrical behavior of the 3C-SiC (111) surface, it was found that the most pervasive defect, the stacking fault, can be passivated by an ultraviolet irradiation treatment [2]. However, for the Au/3C-SiC interface, a contact area dependence on the Schottky barrier height was found after this passivation, indicating that there are still some active defects at the interface. Annealing of Pt/3C-SiC contacts was found to remove this area dependence. A structural analysis of the reaction zone by XRD and TEM showed that he improved electrical properties can be attributed to an interface reaction that forms Pt2Si, resulting in an increased homogeneity at the contact interface.
[1] A.A. Lebedev, Semicond. Sci. Technol. 21, R17 (2006)
[2] J. Eriksson et al., Mater. Sci. Forum 645–648, 677 (2010) | P1 6 |
| 17:30 | Impact of AFM-induced nano-pits in a-Si:H films on silicon crystal growth Authors : E. Verveniotis, B. Rezek, E. Šípek, J. Stuchlik, J. Kočka Institute of Physics, ASCR, Cukrovarnická 10, 16253 Prague 6, Czech Republic Resume : Conductive tips in AFM can be used to localize field-enhanced metal-induced solid phase crystallization (FE-MISPC) of amorphous silicon at room temperature down to nanoscale dimensions (<100 nm). The process is driven by the electrical current between the tip and the bottom nickel electrode. As detected by current-sensing AFM (CS-AFM), FE-MISPC results in both conductive and non-conductive pits on amorphous silicon depending on the specific exposition current profile.
In this contribution, we present an idea that such local modifications can be used to selectively induce further growth of crystalline silicon. We prepared a-Si:H films by PE-CVD (50 oC, 170 nm) on nickel/glass substrates. After FE-MISPC experiments yielding both conductive and non-conductive pits in the films, we deposited the second silicon layer at the boundary condition of amorphous and μ-crystalline silicon in similar thickness. Comparing AFM morphology and CS-AFM data on the 1st and 2nd layer we found that the silicon crystals have the tendency to nucleate preferentially around and inside the pre-exposed areas. This makes the previously non-conductive pits conductive and also increases the conductivity of the initially conductive pits by an order of magnitude. Further lateral miniaturization of the crystalline area is also observed for the latter after the 2nd layer deposition. We analyze the results considering crystallization and growth mechanisms including possible contributions of thermal annealing. | P1 7 |
| 17:30 | Scanning tip measurement for identification of point defects Authors : L. Dózsa1, G. Molnár1, V. Raineri2, F. Giannazzo2, J. Ferencz1, and S. Lanyi3 1Research Institute for Technical Physics and Materials Sciences, H-1525 Budapest, P. O. B. 49., HUNGARY 2CNR-IMETEM , Stradale Primosole 50, 95121 Catania, ITALY 3Institue of Physics Dubravska cesta 9, SK-845 11 Bratislava, Slovakia Resume : Self-assembled iron-silicide nanostructures prepared by reactive deposition epitaxy of Fe onto silicon were investigated. Capacitance-voltage, current-voltage, and deep level transient spectroscopy (DLTS) were used to measure the electrical properties of Au/silicon Schottky junctions. Spreading resistance and scanning probe capacitance microscopy were applied to measure local electrical properties. With a special preamplifier the sensitivity of the DLTS was increased 200 times, which is satisfactory to measure transients of the scanning-tip semiconductor wafer junction. In the Fe deposited area about 2x1016/cm3 density of Fe related defects was found in about 0.5 m depth. This defect concentration is large compared to the doping of the substrate (2x1015/cm3) and deteriorated the Schottky junction characteristic, making DLTS measurement difficult and limiting spatial resolution of scanning capacitance microscopy. Outside but near the Fe deposited area Fe related defect concentration was comparable with the dopant concentration in a thin layer near the surface, well suited for DLTS identification of point defects. The defect transients in this area could be measured both in macroscopic Schottky junctions and by scanning tip DLTS using the preamplifier, and exhibited similar characteristics. It is shown that using appropriate preamplifier identification of point defects is possible by scanning tip capacitance DLTS. The apparent local doping measured by SCM in this area varied with the bias modulation frequency, which is attributed to transients of Fe related defects. | P1 8 |
| 17:30 | Microscopic study of electrical properties of CrSi2 nanocrystals in silicon Authors : L. Dózsa1, Š. Lányi2, V. Raineri3, F. Giannazzo3, N. G. Galkin4 1 Research Institute for Technical Physics and Materials Science, H-1525 Budapest , P. O. Box 49, Hungary 2 Institute of Physics, Dubravska Cesta 9, SK-84511 Bratislava, Slovakia 3 CNR-IMETEM Stradale Primosole 50, 95121 Catania, Italy 4 Institute for Automation and Control Processes of FEB RAS, 690041, Radio 5, Vladivostok, Russia Resume : Homogenously distributed semiconducting CrSi2 nanocrystals (NC) were grown by reactive deposition epitaxy of 0.6 nm Cr on (111) n-type silicon and covered by 50 nm silicon cap. In one group of samples the Cr related point defect concentration in the cap was high while in the other it was low. Au Schottky junctions were prepared on the cap for electrical characterization. The structures were investigated by current-voltage and capacitance-voltage measurements, by transmission electron microscopy and scanning probe techniques. Conductive AFM and scanning capacitance microscopy (SCM) has been applied for high resolution local electrical characterization of the structures. The electrically active scanning probe methods (SCM, conductive AFM) have shown better resolution and contrast than tapping or contact mode AFM. The NCs were embedded in the flat silicon cap, so tapping or contact mode AFM detected only the deformation of the surface over NCs, but SCM has revealed also the NCs deeper in the cap. Tapping-mode AFM has shown up to 13-nm-high protrusions of much larger diameter than the size of NCs. These protrusions were not seen in the topography acquired in contact-mode simultaneously with SCM. The conductive AFM prove that the CrSi2 NCs near the surface are responsible for the leakage of the Schottky junctions. It was found that scanning probe current may degrade the sample surface and SCM can detect with high spatial resolution NCs at 50 nm depth in the defect free host material. | P1 9 |
| 17:30 | Atomic Force Microscopy investigation of the kinetic growth mechanisms of sputtered nanostructured Au film on mica: towards a nanoscale morphology control Authors : F. Ruffino1, 2, *, V. Torrisi3, G. Marletta3, M. G. Grimaldi1, 2 1Dipartimento di Fisica e Astronomia, Universitŕ di Catania via S. Sofia 64, I-95123 Catania, Italy 2CNR-IMM MATIS, via S. Sofia 64, I-95123 Catania, Italy 3Laboratory for Molecular Surface and Nanotechnology (LAMSUN), Department of Chemical Sciences- University of Catania and CSGI, Viale A. Doria 6, I-95125, Catania Resume : The study of surface morphology of Au deposited on mica is crucial for the fabrication of flat Au films for applications in biological, electronic, optical devices. The understanding of the growth mechanisms of Au on mica allows to tune the process parameters (substrate temperature, pressure, rate deposition, film thickness) to obtain ultra-flat film as suitable platform for anchoring self-assembling monolayers, molecules, nanotubes, nanoparticles. Furthermore, atomically flat Au substrates are ideal for imaging adsorbate layers using scanning probe microscopy techniques. The control of these mechanisms is a prerequisite for control of the film nano- and micro-structure to obtain materials with desired morphological properties.
We report on an atomic force microscopy (AFM) study of the morphology evolution of Au film deposited on mica by room-temperature sputtering as a function of the film thickness and temperature and time of annealing processes. The AFM technique allowed us to quantify the evolution of size, shape and surface density of the Au nanoclusters forming the growing film and the roughness of the film as a function of these parameters. These quantitative data allowed us, also, to elucidate the kinetic growth mechanisms of the sputtered Au on mica reaching a strong correlation between experiment and theory. As a consequence we acquired a methodology to tune in a controlled way the morphological characteristics of the Au film controlling the process parameters. | P1 10 |
| 17:30 | Local Charge-Transient Spectroscopy characterisation of surfactant/iron-oxides nanoparticle system Authors : V. Nádaždy, Š. Lányi, Institute of Physics, Slovakian Academy of Sciences, Bratislava, Slovakia Resume : Isothermal Charge-Transient Spectroscopy (IQTS), designed to local analysis in scanning probe microscopy, has been used to study surfactant changes in thin films of Fe2O3/Fe3O4 nanoparticles, deposited by drop-casting or Langmuir-Blodgett technique on metal plate. The surfactant consisted of mixture of oleic acid and oleyl amin. On as prepared thin film we have observed a well defined peak with maximum at 5 ms at room temperature. Its shape depends on bias voltage and excitation voltage pulse amplitude, and it reflects a spectrum of relaxation times. The duration of pulses affects the extent up to which the spectrum is excited. Upon exposing the sample to UV radiation the electrical properties of the surfactant are modified due to action of ozone. The modification is reflected in changes of the amplitude and shape of the spectrum. At the same time flow of steady-state current was observed showing that ozone decomposes the oleic acid into products, which in contact with different metal substrates and the tungsten tip create a galvanic cell. The shift of the peak position with temperature allows to estimate the activation energy of the underlying mechanism, and fitting the whole peak also the changes of the energy spectrum. | P1 11 |
| 17:30 | Transmission electron microscopy study of end of range defects in Ge and their role on B diffusion Authors : S. Boninelli 1, E. Napolitani 2, G. Bisognin 2, E. Bruno 1, M. Mastromatteo 2, G. G. Scapellato 1, D. De Salvador 2, S. Mirabella 1, C. Spinella 3, A. Carnera 2, and F. Priolo 1 1 MATIS-IMM-CNR and Dipartimento di Fisica e Astronomia, Universitŕ di Catania, Via S. Sofia 64, 95123 Catania, Italy 2 MATIS-IMM-CNR and Dipartimento di Fisica, Universitŕ di Padova, Via Marzolo 8, 35131 Padova, Italy 3 IMM-CNR, VIII Strada 5, 95121 Catania, Italy Resume : Nowadays, Ge is gaining a renewed interest in microelectronics as a promising material to substitute Si for more performing and smaller devices. As far as this point is concerned, a comprehensive knowledge of the diffusion processes of the most common impurities used to create p- or n-type regions in Ge and how point and extended defects could affect their behavior is still incomplete. For example the role of defects in the diffusion of B, the most used p-type dopant, is still unclear.
It is known that preamorphization followed by low temperature epitaxial regrowth leaves extended defects beyond the original crystal-amorphous interface, called end of range (EOR) defects, whose evolution could affect B diffusion. The visualization of defects in Ge is more difficult that in Si, as they are usually smaller in size and density, and they have significantly weaker image contrast. Nonetheless, though the appropriate use of Transmission Electron Microscopy technique, we realized the imaging of EOR defects and studied their thermal evolution. In addition, by crossing these analyses with High Resolution X-Ray Diffraction measurements of the strain induced by the defects in the Ge lattice, and with the diffusion produced by their dissolution on a B delta layer, we were able to study their dissolution kinetics, finding an activation energy of (2.1 ± 0.3) eV. Moreover, the relationship of the EOR dissolution with the diffusion allowed to evidence the role of self-interstitials in B diffusion mechanism. | P1 12 |
| 17:30 | Electrical and optical characterization of MOS capacitors with GdSiO dielectric layers Authors : W. Rzodkiewicz, T. Małachowski, T. Gutt Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland Resume : In this work electrical and optical characterization results of MIS capacitors with GdSiO as a new dielectric material for nanoelectronic semiconductor devices were presented.
Standard C(V) and R(V) characteristics were measured at 1MHz using Agilent 4294A. The doping concentration was calculated. The surface potential vs. gate voltage characteristic was derived from theoretical and experimental C(V) characteristics. The flat-band voltage was then estimated as gate voltage at surface potential φs = 0.
The I(V) characteristics were measured using Agilent B1500 meter. A local peak was found on the characteristics. The local peaks were reversed at about the same gate voltage during return runs, which presumably resulted from charging and discharging of a set of traps located at the energy position relevant to that gate voltage. The leakage current density characteristics were also examined using transformations relevant to typical leakage mechanisms.
Additionally, Variable Angle Spectroscopic Ellipsometer (VASE) with rotated analyzer was applied for the investigations of optical properties. The ellipsometric measurements have been performed at the angle of incidence 65o in the following spectral range: 250-1000nm with 5nm step. Tauc-Lorentz (T-L) model was used to determine optical coefficients (refractive and extinction indexes as well as dielectric function) of high-k dielectric layer. | P1 13 |
| 17:30 | Photoluminescence studies of AlN nanopowders and GaN nanowires Authors : P. Dominik1, D. Smoleń1, W. Adamkiewicz1,S. Podsiadło1, K. Fronc2, J. Mierczyk3, P. Nyga3 1. Warsaw University of Technology, Faculty of Chemistry, Noakowskiego 3, 00-664 Warsaw, Poland 2. Institute of Physics, Polish Academy of Science, Al. Lotników 32/46, 02-668 Warsaw, Poland 3. Institute of Optoelectronics, Military University of Technology, 2 Kaliskiego Street, 00-908 Warsaw 49, Poland Resume : Herein, we report a results of photoluminescence stuidies of aluminium nitride nanopowder and gallium nitride nanowires.
The experimental setups to obtain both materials were basically similar. The adequate reactor (for AlN it was mullit reactor, for GaN it was quartz reactor) was placed in horizontal tube furnace with resistance heating. Both processes were undertaken in ammonia atmosphere.
As starting material to obtain AlN nanopowder nanopowder of aluminum oxides was used. The process was carried out in the temperature range:1050 -1350oC for 1- 5h in ammonia atmosphere. The reaction can be expressed as follow:
Al2O3 + 2NH3 → 2AlN + 3H2O
Growth of GaN nanowires took place in agreement with vapour-liquid solid mechanism. As a catalyst Au-Ga alloy was applied. A process of its formation was realized in nitrogen atmosphere in temperature 930 oC for 45 min. The nanowires growth was carried out in the temperature range:700 -950oC for 5- 60 min in ammonia atmosphere. The reactions can be expressed as follow:
Ga + Au → GaAu(alloy)
GaAu(alloy )+ NH3 → GaN + 3H2 + Au.
This work was supported in part by the State Committee for Scientific Research (Grant No. N N209 117737) and in part by the European Union in the framework of European Social Fund through the Warsaw University of Technology Development Programme. | P1 14 |
| 17:30 | Difference in interfacial electronic structure between ZnO and Alq3 by the orientation of ZnO substrate Authors : Jung Han Lee a,b, and Yeonjin Yi a,b* a Department of Nano and Bio surface science, University of Science and Technology, 52 Eoeun-Dong, Yuseong-Gu, Daejeon 305-333, Republic of Korea b Center for Nanocharacterization, Korea Research Institute of Standards and Science, 209 Gajeong-Ro, Yuseong-Gu, Daejeon, 305-600, Republic of Korea Resume : ZnO has been introduced as one of the good candidates for next generation opto-electronics. Recently, ZnO is known to be suitable for the transparent electrode in organic solar cells and light emitting devices. The contact with n-type organic material has been studied due to the n-type properties of ZnO. However, the surface of ZnO has shown different electronic property with respect to its surface orientation. Therefore, it is presumed that there are differences in the interfacial electronic structures between organic materials and ZnO with different orientation. Therefore, it is highly required to classify the interfacial electronic structures according to the surface orientation of ZnO. In this study, we measured the interfacial electronic structures between the ZnO substrate having various orientations and a typical n-type organic material, tris-(8-hydroxyquinoline) aluminum (Alq3). In-situ x-ray and ultraviolet photoelectron spectroscopy measurements revealed the interfacial electronic structures. We found the changes in the electronic structures with respect to the orientation of ZnO substrate and it could be used to improve the contact between ZnO and Alq3. | P1 15 |
| 17:30 | Investigation of SiO2/SiC systems for new generation MOS devices Authors : T. Małachowski, W. Rzodkiewicz, , T. Gutt Resume : A range of silicon carbide devices have been produced by leading manufacturers in the world for about ten years. Acceptable structures are very difficult to achieve and the attempts to manufacture such structures in Polish laboratories are still far from being ready for commercialization. There are several problems occurring in the samples available from our laboratories which will be illustrated and discussed in this paper.
The fundamental problem in manufacturing of a SiC MOS transistor is the content of traps in the insulator/semiconductor interface. An interesting and specifically SiC-related issue which is worth discussing but often neglected, is the presence of the slow traps deep in the band-gap which can cause flat-band and threshold voltage instability in semiconductor devices. The other problem, very common in the initial research on the technology of the gate insulator on SiC, is the integrity of the insulating layer, namely high leakage currents.
Additionally, spectroscopic ellipsometry in the near infrared to ultraviolet was used to determine the optical properties of most common polymorhs of silicon carbide. We report both ordinary and extra ordinary dielectric function data of 4-H SiC.
Electrical properties of the SiC MOS capacitors were characterized using Agilent 4294A and Agilent B1500 meter. Whereas, optical characterization of the silicon carbide and oxidized substrates was performed by Variable Angle Spectroscopic Ellipsometer (VASE) with rotated analyzer. | P1 16 |
| 17:30 | (In,Mn)Sb studied by cross-sectionnal STM Authors : S. J. C. Mauger Eindhoven University of Technology J. K. Garleff Eindhoven University of Technology P. M. Koenraad Eindhoven University of Technology C. Feeser Northwestern University N. Parashar Northwestern University B. W. Wessels Northwestern University Resume : Theory predicts that transitions metals in wide gap semiconductors should lead to DMS with the highest Curie temperature. However transition metals in wide gap semiconductors form deep levels in the band gap, increase the formation of defects in the host material such as As antisites and Mn interstitials in (Ga,Mn)As for example, and therefore reduce the carrier concentration and lower the carrier mediated ferromagnetism. Recently, high Curie temperatures have been achieved for narrow gap (III,Mn)V semiconductors with respectively 330K for (In,Mn)As and more than 400K for (In,Mn)Sb, despite the prediction of a low Curie temperature by the mean field theory. The Mn acceptor level in narrow gap III-V semiconductors has been predicted to be shallow or resonant in the valence band. Thus, narrow gap III-V semiconductors that are used as a host material for DMS have the advantage to remain highly conductive even for a high Mn concentration and therefore should allow for interesting magnetic properties.
We present here the first cross-sectional STM microscopy study on (In,Mn)Sb films with a Mn concentration of 9x10^19 cm-3. We performed both topographical and spectroscopy measurements. Our results show that the grown material has excellent structural properties and shows no cluster formation. The Mn atoms appear in topographical images as bright triangular features at low positive tunnel | P1 17 |
| 17:30 | Development and optimization of FIB-based sample preparation for SSRM. Authors : Pierre Eyben(a), Jay Mody(a,b), Aftab Nazir(a,b), Andreas Schulze(a,b), , Thomas Hantschel(a), and Wilfried Vandervorst(a,b) (a) IMEC, Kapeldreef 75, B-3001 Leuven, Belgium (b) Instituut voor Kern- en Stralingsfysika, K.U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium Resume : Scanning spreading resistance microscopy (SSRM) is an electrical characterization technique based on an atomic force microscope equipped with a conductive tip. It is used to measure two-dimensional carrier distributions in semiconductor device structures with a unique combination of resolution (spatial resolution of 0.5–3 nm and dopant gradient resolution of
1-2 nm/dec) and sensitivity (5-20%) over a wide dynamic range (1E15 to 1E21 carriers/cm3).
SSRM is typically performed on cross-sectioned devices. The preparation of such cross-sections is a challenging task since perfectly flat surfaces (RMS below 0.5 nm) with minimal damage (in order to minimize the density of extrinsic surface charges) need to be obtained. Therefore we are currently using polishing and micro-cleavage techniques. However, due to decreasing device dimensions as well as the advent of three-dimensional structures like nanowires, we are reaching the positioning accuracy limits of these techniques.
Within this work we have analyzed the possibility to use a focused ion beam (FIB) in order to prepare the cross-sectioned SSRM surface. FIB offers a surface preparation with accurate positioning (down to 100 nm) and low roughness (RMS below 1nm) but leads at the same time to the incorporation of Ga and the generation of ion beam damage. Optimizing the FIB conditions (energy, beam direction, etch gas,...), we have however demonstrated the possibility to successfully perform SSRM on FIB-prepared surfaces. | P1 18 |
| 17:30 | Defect electrical activity at nanoscale in Silicon Carbide and Gallium Nitride using Atomic Force Microscopy techniques Authors : D. Alquier1, M. Lamhamdi1, X. Song1,2, F. Cayrel1 and J.F. Michaud1 1 Universit?ran?s Rabelais de Tours, Laboratoire de Micro?ctronique de Puissance, 16, rue Pierre et Marie Curie, BP 7155, 37071 Tours Cedex 2, France 2 STMicroelectronics, 16, rue Pierre et Marie Curie, BP 7155, 37071 Tours Cedex 2, France Resume : Both Silicon Carbide (SiC) and Gallium Nitride (GaN) exhibit high interest for power electronic devices. Nevertheless, the wafer high cost limits their developments. Today, SiC and GaN can be heteroepitaxially grown on Si or other substrates that may open the field for new power devices. One of the main challenges is to have high quality epitaxial layer, compatible with process integration. Unfortunately, epitaxial growth is far from being defect free. The defect electrical activity knowledge becomes then crucial for the development of reliable components. Atomic Force Microscopy (AFM) is a unique technique that can provide such information with nanoscale resolution through its electrical modes (SCM, SSRM or C-AFM).
In this work, n-type GaN samples grown on sapphire or Si as well as n-type 3C-SiC grown on Si were used. Both cross-sectional and plan view samples were prepared. A specific preparation, involving deposition, cleaving, polishing and cleaning, was adapted for each technique. Surfaces and interfaces were observed (or prepared) using a FIB-SEM system with a STEM detector. Reference samples with increasing concentrations from 1017 to 1019 cm-3, separated by non-intentionally doped layers, have been used in each case in order to estimate the electrical activity. Our results clearly evidence and evaluate the defect electrical activity in such heteroepitaxial layers. This enlighten that defects need to be reduced or avoided to limit their prejudicial impact on devices | P1 19 |
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