Waveguide-Integrated MoTe -- Homojunction Photodetector.

Two-dimensional (2D) materials, featuring distinctive electronic and optical properties and dangling-bond-free surfaces, are promising for developing high-performance on-chip photodetectors in photonic integrated circuits. However, most of the previously reported devices operating in the photoconductive mode suffer from a high dark current or a low responsivity. Here, we demonstrate a MoTe -- homojunction fabricated directly on a silicon photonic crystal (PC) waveguide, which enables on-chip photodetection with ultralow dark current, high responsivity, and fast response speed.

CMOS-Compatible Electronic-Plasmonic Transducers Based on Plasmonic Tunnel Junctions and Schottky Diodes.

To develop methods to generate, manipulate, and detect plasmonic signals by electrical means with complementary metal-oxide-semiconductor (CMOS)-compatible materials is essential to realize on-chip electronic-plasmonic transduction. Here, electrically driven, CMOS-compatible electronic-plasmonic transducers with Al-AlO -Cu tunnel junctions as the excitation source of surface plasmon polaritons (SPPs) and Si-Cu Schottky diodes as the detector of SPPs, connected via plasmonic strip waveguides of Cu, are demonstrated. Remarkably, the electronic-plasmonic transducers exhibit overall transduction efficiency of 1.

A Barium Titanate-on-Oxide Insulator Optoelectronics Platform.

Electro-optic modulators are among the most important building blocks in optical communication networks. Lithium niobate, for example, has traditionally been widely used to fabricate high-speed optical modulators due to its large Pockels effect. Another material, barium titanate, nominally has a 50 times stronger r-parameter and would ordinarily be a more attractive material choice for such modulators or other applications.

Effects of Chemical Composition, Film Thickness, and Morphology on the Electrochromic Properties of Donor-Acceptor Conjugated Copolymers Based on Diketopyrrolopyrrole.

A series of diketopyrrolopyrrole (DPP) and propylenedioxythiophene (ProDOT)-containing random copolymers with different donor-to-acceptor ratios is synthesized through Stille coupling polymerizations. The low-bandgap polymers display dark tones with colors ranging from magenta to blue, and reveal reversible colored-to-transmissive electrochromism in absorption/transmission-type devices with high optical contrasts (up to 48 and 77 % in the visible and near-infrared regions, respectively), modest switching speeds (a few to tens of seconds) and coloration efficiencies (267-574 cm  C ), as well as good long-term ambient redox stabilities. The structure-performance relationship of the polymers, in particular, the role of donor-to-acceptor ratio, is investigated, and it is shown that an increase in the amount of acceptor in the polymers leads to slower oxidative but faster reductive switching, accompanied with enhancement of the redox stability.

Towards large area and continuous MoS2 atomic layers via vapor-phase growth: thermal vapor sulfurization.

We report on the effects of substrate, starting material, and temperature on the growth of MoS(2) atomic layers by thermal vapor sulfurization in a tube-furnace system. With Mo as the starting material, atomic layers of MoS(2) flakes are obtained on sapphire substrates while a bell-shaped MoS(2) layer, sandwiched by amorphous SiO(2), is obtained on native-SiO(2)/Si substrates under the same sulfurization conditions. An anomalous thickness-dependent Raman shift (A(1g)) of the MoS(2) atomic layers is observed in Mo-sulfurizations on sapphire substrates, which can be attributed to the competition between the effects of thickness and the surface/interface.

Versatile pattern generation of periodic, high aspect ratio Si nanostructure arrays with sub-50-nm resolution on a wafer scale.

We report on a method of fabricating variable patterns of periodic, high aspect ratio silicon nanostructures with sub-50-nm resolution on a wafer scale. The approach marries step-and-repeat nanoimprint lithography (NIL) and metal-catalyzed electroless etching (MCEE), enabling near perfectly ordered Si nanostructure arrays of user-defined patterns to be controllably and rapidly generated on a wafer scale. Periodic features possessing circular, hexagonal, and rectangular cross-sections with lateral dimensions down to sub-50 nm, in hexagonal or square array configurations and high array packing densities up to 5.

Vapor-phase growth and characterization of Mo(1-x)W(x)S2 (0 ≤ x ≤ 1) atomic layers on 2-inch sapphire substrates.

Atomically thin Mo(1-x)W(x)S2 (0 ≤ x ≤ 1) ternary compounds have been grown on 2-inch c-plane sapphire substrates with high uniformity by sulfurizing thin Mo(1-x)W(x) layers that were deposited at room temperature using a co-sputtering technique. Atomic force microscopy (AFM), Raman scattering, and optical absorbance spectroscopy (OAS) studies reveal that the Mo(1-x)W(x)S2 films consist of crystallites of two-to-four monolayers in thickness. X-ray photoelectron spectroscopy (XPS) shows that the core levels of Mo3d and W4f shift to lower binding energies while that of S2p shifts to higher ones with the increase in W compositions, which can be related to the larger electron affinity of W (0.

Piezotronic effect on the transport properties of GaN nanobelts for active flexible electronics.

The transport properties of GaN nanobelts (NBs) are tuned using a piezotronic effect when a compressive/tensile strain is applied on the GaN NB. This is mainly due to a change in Schottky barrier height (SBH). A theoretical model is proposed to explain the observed phenomenon.

Interplay of processing, morphological order, and charge-carrier mobility in polythiophene thin films deposited by different methods: comparison of spin-cast, drop-cast, and inkjet-printed films.

The dependence of morphology and polymer-chain orientation of regioregular poly(3-hexylthiophene) (rrP3HT) thin films on processing conditions have been widely studied. However, their possible variation across the film thickness direction remains largely unknown. We report here a marked difference in the optical dielectric (n,k) spectra between the top and bottom interfaces of spin-cast (sc) rrP3HT films deposited from chlorobenzene solutions.

A New Method for Lift-off of III-Nitride Semiconductors for Heterogeneous Integration.

The release and transfer of GaN epilayers to other substrates is of interest for a variety of applications, including heterogeneous integration of silicon logic devices, III-V power devices and optical devices. We have developed a simple wet chemical etching method to release high-quality epitaxial III-nitride films from their substrates. This method builds on a nanoepitaxial lateral overgrowth (NELO) process that provides III-Nitride films with low dislocation densities.

Gallium arsenide (GaAs) island growth under SiO(2) nanodisks patterned on GaAs substrates.

We report a growth phenomenon where uniform gallium arsenide (GaAs) islands were found to grow underneath an ordered array of SiO(2) nanodisks on a GaAs(100) substrate. Each island eventually grows into a pyramidal shape resulting in the toppling of the supported SiO(2) nanodisk. This phenomenon occurred consistently for each nanodisk across a large patterned area of approximately 50 x 50 microm(2) (with nanodisks of 210 nm diameter and 280 nm spacing).

High-density arrays of InGaN nanorings, nanodots, and nanoarrows fabricated by a template-assisted approach.

Dense, crystalline arrays of InGaN nanorings, nanodots, and nanoarrows have been fabricated on GaN substrates by template-assisted nano-area selective growth. To create the nanostructures, we have used nanoporous anodic alumina films as templates to pattern nanopores in an SiO2 transfer layer, and then used this patterned SiO2 layer as a template for nitride growth by metalorganic chemical vapor deposition. We have varied the diameter of the deposited nitride nanostructures from 35 to 250 nm by changing the initial anodic alumina template structure.

Symmetrical 1x2 digital photonic splitting switch with low electrical power consumption in SiGe waveguides.

A symmetrical digital photonic splitting switch with a low insertion loss and a low driving voltage is developed using carrier injection in a silicon-germanium material for optical communication systems and networks at a wavelength of 1.55 mum. The switch structure has been improved based on a traditional 1x2 Y-shaped configuration by using two widened carrier injection regions.