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Register a new userIII-V/Si Wafer Bonding Using Transparent, Conductive Oxide Interlayers
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We present a method for low temperature plasma-activated direct wafer bonding of III-V materials to Si using a transparent, conductive indium zinc oxide interlayer. The transparent, conductive oxide (TCO) layer provides excellent optical transmission as well as electrical conduction, suggesting suitability for Si/III-V hybrid devices including Si-based tandem solar cells. For bonding temperatures ranging from 100$^{circ}$C to 350$^{circ}$C, Ohmic behavior is observed in the sample stacks, with specific contact resistivity below 1 $Omega$cm$^2$ for samples bonded at 200$^{circ}$C. Optical absorption measurements show minimal parasitic light absorption, which is limited by the III-V interlayers necessary for Ohmic contact formation to TCOs. These results are promising for Ga$_{0.5}$In$_{0.5}$P/Si tandem solar cells operating at one sun or low concentration conditions.
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Magnetoplasmonics is highly promising to devise active optical elements: modulating the plasmon resonance condition with magnetic field can boost the performance of refractometric sensors and nanophotonic optical devices. Nevertheless, real life applications are hampered by the magnetoplasmonic trilemma: 1) a good plasmonic metal has sharp optical resonances but low magneto-optical response; 2) a magnetic metal has strong magneto-optical response but a very broad plasmonic resonance; 3) mixing the two components degrades the quality of both features. To overcome the trilemma, we use a different class of materials, transparent conductive oxide nanocrystals (NCs) with plasmonic response in the near infrared. Although non-magnetic, they combine a large cyclotron frequency (due to small electron effective mass) with sharp plasmonic resonances. We benchmark the concept with F- and In- doped CdO (FICO) and Sn-doped In2O3 (ITO) NCs to boost the magneto-optical Faraday rotation and ellipticity, reaching the highest magneto-optical response for a non-magnetic plasmonic material, and exceeding the performance of state-of-the-art ferromagnetic nanostructures. The magnetoplasmonic response of these NCs was rationalized with analytical model based on the excitation of circular magnetoplasmonic modes. Finally, proof of concept experiments demonstrated the superior performance of FICO NCs with respect to current state of the art in magnetoplasmonic refractometric sensing, approaching the sensitivity of leading localized plasmon refractometric methods with the advantage of not requiring complex curve fitting.
We have developed a classical two- and three-body interaction potential to simulate the hydroxylated, natively oxidised Si surface in contact with water solutions, based on the combination and extension of the Stillinger-Weber potential and of a potential originally developed to simulate SiO2 polymorphs. The potential parameters are chosen to reproduce the structure, charge distribution, tensile surface stress and interactions with single water molecules of a natively oxidised Si surface model previously obtained by means of accurate density functional theory simulations. We have applied the potential to the case of hydrophilic silicon wafer bonding at room temperature, revealing maximum room temperature work of adhesion values for natively oxidised and amorphous silica surfaces of 97 mJ/m2 and 90mJ/m2, respectively, at a water adsorption coverage of approximately 1 monolayer. The difference arises from the stronger interaction of the natively oxidised surface with liquid water, resulting in a higher heat of immersion (203 mJ/m2 vs. 166 mJ/m2), and may be explained in terms of the more pronounced water structuring close to the surface in alternating layers of larger and smaller density with respect to the liquid bulk. The computed force-displacement bonding curves may be a useful input for cohesive zone models where both the topographic details of the surfaces and the dependence of the attractive force on the initial surface separation and wetting can be taken into account.
The development of graphene electronics requires the integration of graphene devices with Si-CMOS technology. Most strategies involve the transfer of graphene sheets onto silicon, with the inherent difficulties of clean transfer and subsequent graphene nano-patterning that degrades considerably the electronic mobility of nanopatterned graphene. Epitaxial graphene (EG) by contrast is grown on an essentially perfect crystalline (semi-insulating) surface, and graphene nanostructures with exceptional properties have been realized by a selective growth process on tailored SiC surface that requires no graphene patterning. However, the temperatures required in this structured growth process are too high for silicon technology. Here we demonstrate a new graphene to Si integration strategy, with a bonded and interconnected compact double-wafer structure. Using silicon-on-insulator technology (SOI) a thin monocrystalline silicon layer ready for CMOS processing is applied on top of epitaxial graphene on SiC. The parallel Si and graphene platforms are interconnected by metal vias. This method inspired by the industrial development of 3d hyper-integration stacking thin-film electronic devices preserves the advantages of epitaxial graphene and enables the full spectrum of CMOS processing.
Here, we experimentally and theoretically clarify III-V/Si crystal growth processes. Atomically-resolved microscopy shows that mono-domain 3D islands are observed at the early stages of AlSb, AlN and GaP epitaxy on Si, independently of misfit. It is also shown that complete III-V/Si wetting cannot be achieved in most III-V/Si systems. Surface/interface contributions to the free energy variations are found to be prominent over strain relief processes. We finally propose a general and unified description of III-V/Si growth processes, including the description of antiphase boundaries formation.
The electronic transport through Au-(Cu$_{2}$O)$_n$-Au junctions is investigated using first-principles calculations and the nonequilibrium Greens function method. The effect of varying the thickness (i.e., $n$) is studied as well as that of point defects and anion substitution. For all Cu$_{2}$O thicknesses the conductance is more enhanced by bulk-like (in contrast to near-interface) defects, with the exception of O vacancies and Cl substitutional defects. A similar transmission behavior results from Cu deficiency and N substitution, as well as from Cl substitution and N interstitials for thick Cu$_{2}$O junctions. In agreement with recent experimental observations, it is found that N and Cl doping enhances the conductance. A Frenkel defect, i.e., a superposition of an O interstitial and O substitutional defect, leads to a remarkably high conductance. From the analysis of the defect formation energies, Cu vacancies are found to be particularly stable, in agreement with earlier experimental and theoretical work.
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