Electromagnetic Field Enhancement on Axially Heterostructured NWs: The Role of the Heterojunctions

Semiconductor nanowires are the building blocks of future nanoelectronic devices. The study of the interaction between nanowires and visible light reveals resonances that promise light absorption/scattering engineering for photonic applications. We carried out experimental measurements through the micro-Raman spectroscopy of different group IV nanowires, both homogeneous Si nanowires and axially heterostructured SiGe/Si nanowires. These experimental measurements show an enhancement of the Raman signal in the vicinity of the heterojunction of SiGe/Si nanowires. The results are analysed in terms of the electromagnetic modelling of the light/nanowire interaction using finite element methods. The presence of axial heterostructures is shown to produce electromagnetic resonances, and the results are understood as a consequence of a finite change in the relative permittivity of the material at the SiGe/Si heterojunction. This effect opens a path to controlling interactions between light and matter at the nanoscale with direct applications in photonic nanodevices.Junta de Castilla y Leo´n (Projects VA293U13, and VA081U16), and Spanish Government (CICYT MAT2010-20441-C02 (01 and 02)). J. L. Pura was granted by the FPU programme (Spanish Government FPU14/00916)

Stability of Schottky and Ohmic Au Nanocatalysts to ZnO Nanowires

Manufacturable nanodevices must now be the predominant goal of nanotechnological research to ensure the enhanced properties of nanomaterials can be fully exploited and fulfill the promise that fundamental science has exposed. Here, we test the electrical stability of Au nanocatalyst-ZnO nanowire contacts to determine the limits of the electrical transport properties and the metal-semiconductor interfaces. While the transport properties of as-grown Au nanocatalyst contacts to ZnO nanowires have been well-defined, the stability of the interfaces over lengthy time periods and the electrical limits of the ohmic or Schottky function have not been studied. In this work, we use a recently developed iterative analytical process that directly correlates multiprobe transport measurements with subsequent aberration-corrected scanning transmission electron microscopy to study the electrical, structural, and chemical properties when the nanowires are pushed to their electrical limits and show structural changes occur at the metal-nanowire interface or at the nanowire midshaft. The ohmic contacts exhibit enhanced quantum-mechanical edge-tunneling transport behavior because of additional native semiconductor material at the contact edge due to a strong metal-support interaction. The low-resistance nature of the ohmic contacts leads to catastrophic breakdown at the middle of the nanowire span where the maximum heating effect occurs. Schottky-type Au-nanowire contacts are observed when the nanowires are in the as-grown pristine state and display entirely different breakdown characteristics. The higher-resistance rectifying I-V behavior degrades as the current is increased which leads to a permanent weakening of the rectifying effect and atomic-scale structural changes at the edge of the Au interface where the tunneling current is concentrated. Furthermore, to study modified nanowires such as might be used in devices the nanoscale tunneling path at the interface edge of the ohmic nanowire contacts is removed with a simple etch treatment and the nanowires show similar I-V characteristics during breakdown as the Schottky pristine contacts. Breakdown is shown to occur either at the nanowire midshaft or at the Au contact depending on the initial conductivity of the Au contact interface. These results demonstrate the Au-nanowire structures are capable of withstanding long periods of electrical stress and are stable at high current densities ensuring they are ideal components for nanowire-device designs while providing the flexibility of choosing the electrical transport properties which other Au-nanowire systems cannot presently deliver

Electromagnetic field enhancement effects in group IV semiconductor nanowires. A Raman spectroscopy approach

Semiconductor nanowires (NWs) are the building blocks of future nanoelectronic devices. Furthermore, their large refractive index and reduced dimension make them suitable for nanophotonics. The study of the interaction between nanowires and visible light reveals resonances that promise light absorption/scattering engineering for photonic applications. Micro-Raman spectroscopy has been used as a characterization tool for semiconductor nanowires. The light/nanowire interaction can be experimentally assessed through the micro-Raman spectra of individual nanowires. As compared to both metallic and dielectric nanowires, semiconductor nanowires add additional tools for photon engineering. In particular, one can grow heterostructured nanowires, both axial and radial, and also one could modulate the doping level and the surface condition among other factors than can affect the light/NW interaction. We present herein a study of the optical response of group IV semiconductor nanowires to visible photons. The study is experimentally carried out through micro-Raman spectroscopy of different group IV nanowires, both homogeneous and axially heterostructured (SiGe/Si). The results are analyzed in terms of the electromagnetic modelling of the light/nanowire interaction using finite element methods. The presence of axial heterostructures is shown to produce electromagnetic resonances promising new photon engineering capabilities of semiconductor nanowires.Junta de Castilla y Le on (Projects VA293U13 and VA081U16) and Spanish Government (CICYT MAT2010-20441-C02 (01 and 02) and ENE 2014-56069-C4-4-R). J. L. Pura was granted by the FPU programme (Spanish Government) (FPU14/00916)

VLS croissance et caractérisation de axiale Si/SiGe heterostructured nanofils pour la réalisation de tunnel FET

L'augmentation des performances des circuits intégrés s'est effectué durant les trentes dernières années par la miniaturisation du composant clé à savoir le transistor MOSFET. Cette augmentation de la densité d'intégration se heurte aujourd'hui à plusieurs verrous, notamment celui de la puissance consommée qui devient colossale. Il devient alors nécessaire de travailler sur de nouveaux composants, les transistors à effet tunnel, où les porteurs sont injectés par effet tunnel bande à bande permettant de limiter considérablement la puissance consommée en statique. Les nanofils semiconducteurs sont de bons candidats pour être intégrés comme canaux de ces nouveaux composants de part la possibilité de moduler leur gap et leur conductivité au cours de la croissance. Dans ce contexte, cette thèse traite de la croissance d'hétérostructures axiales Si/Si1-xGex élaborés par croissance VLS par RP-CVD. Tout d'abord, nous identifions les conditions de croissance pour réaliser des interface Si/Si1-xGex et Si1-xGex/Si abruptes. Les deux heterointerfaces sont toujours asymétrique quelle que soit la concentration en Ge ou le diamètre des nanofils ou des conditions de croissance. Deuxièmement, nous étudions les problématiques impliquées par l'ajout d'atomes dopants. Nous discutons de l'influence des paramètres de croissance (le rapport flux de gaz (Si / Ge), et la pression partielle de dopants) sur la morphologie des nanofils et la concentration de porteurs. Grâce à cette étude, nous avons été capable de faire croitre des hétérojonctions P-I-N. Troisièmement, nous présentons une technique basée sur la microscopie à sonde locale pour caractériser les hétérojonctions.After more than 30 years of successful scaling of MOSFET for increasing the performance and packing density, several limitations to further performance enhancements are now arising, power dissipation is one of the most important one. As scaling continues, there is a need to develop alternative devices with subthreshold slope below 60 mV/decade. In particular, tunnel field effect transistors, where the carriers are injected by quantum band to band tunneling mechanism can be promising candidate for low-power design. But, such devices require the implementation of peculiar architectures like axial heterostructured nanowires with abrupt interface. Using Au catalyzed vapor-liquid-solid synthesis of nanowires, reservoir effect restrains the formation of sharp junctions. In this context, this thesis addresses the growth of axial Si and Si1-xGex heterostructured nanowire with controlled interfacial abruptness and controlled doping using Au catalyzed VLS growth by RP-CVD. Firstly, we identify the growth conditions to realize sharp Si/Si1-xGex and Si1-xGex/Si interfacial abruptness. The two heterointerfaces are always asymmetric irrespective of the Ge concentration or nanowire diameter or growth conditions. Secondly, we study the problematics involved by the addition of dopant atoms and focus on the different approaches to realize taper free NWs. We discuss the influence of growth parameters (gas fluxes (Si or Ge), dopant ratio and pressure) on NW morphology and carrier concentration. With our growth process, we could successfully grow p-I, n-I, p-n, p-i-n type junctions in NWs. Thirdly, we present scanning probe microscopy to be a potential tool to delineate doped and hetero junctions in these as-grown nanowires. Finally, we will integrate the p-i-n junction in the NW in omega gate configuration

MRS Fall Meeting & Exhibit 2017

Axially heterostructuredsemiconductor NWs under visible light illumination present a strong confinementof the electromagnetic field at the heterojunction. This optical behaviourpromises the use of axial.PósterMinisterio de Economía, Industria y Competitividad (Project ENE2014-56069-C4-4-R

Fabrication and Electrical Characterization of tunnel FET Devices Based on Si/SiGe Heterojunction PIN nanowires

session B.6.3International audienc

Composition-dependent interfacial abruptness in Au-catalyzed Si1- xGex/Si/Si1- xGex nanowire heterostructures

International audienc

Fabrication and electrical characterisations of Si/Si1-xGex nanowires Tunnel FET device : impact of Germanium concentration

session S6.09International audienc

Fabrication and Electrical Characterization of tunnel FET Devices Based on Si/SiGe Heterojunction PIN nanowires

session B.6.3International audienc