Controlling the electronic properties of silicon nanowires with functional molecular groups.

Attachment of a simple polar molecule, terpyridine, to the surfaces of Si nanowires with diameters ranging from 7-100 nm was investigated with two terminal conductivity measurements, a unique single nanowire photoelectron spectroscopy, and theoretical analysis. Our experiments reveal the details of molecule-nanowire bonding and charge transfer, diameter dependent Fermi level shifts, and acid attachment leading to conductivity in the cylindrical molecular nanolayer surrounding the nanowire.

Measurement of carrier mobility in silicon nanowires.

We report the first direct capacitance measurements of silicon nanowires (SiNWs) and the consequent determination of field carrier mobilities in undoped-channel SiNW field-effect transistors (FETs) at room temperature. We employ a two-FET method for accurate extraction of the intrinsic channel resistance and intrinsic channel capacitance of the SiNWs. The devices used in this study were fabricated using a top-down method to create SiNW FETs with up to 1000 wires in parallel for increasing the raw capacitance while maintaining excellent control on device dimensions and series resistance. We found that, compared with the universal mobility curves for bulk silicon, the electron and hole mobilities in nanowires are comparable to those of the surface orientation that offers a lower mobility.

Ultra-compact high order ring resonator filters using submicron silicon photonic wires for on-chip optical interconnects.

Ultra-compact 5(th) order ring resonator optical filters based on submicron silicon photonic wires are demonstrated. Out-of-band rejection ratio of 40dB, 1dB flat-top pass band of 310GHz with ripples smaller than 0.4dB, and insertion loss of only (1.8+/-0.5)dB at the center of the pass band are realized simultaneously, all within a footprint of 0.0007mm(2) on a silicon chip.

Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator.

Silicon p(+)-i-n(+) diode Mach-Zehnder electrooptic modulators having an ultra-compact length of 100 to 200 mum are presented. These devices exhibit high modulation efficiency, with a V(pi)L figure of merit of 0.36 V-mm. Optical modulation at data rates up to 10 Gb/s is demonstrated with low RF power consumption of only 5 pJ/bit.

Optical modulation using anti-crossing between paired amplitude and phase resonators.

An optical modulator design based upon anti-crossing between coupled silicon microrings with independent amplitude and phase functionality is presented. The device exhibits over 25x improvement in sensitivity to an input drive signal when compared with previously studied microring modulators based on control of waveguide-resonator coupling. The new design also demonstrates an ON-OFF contrast of 14 dB, and has an ultra-compact footprint of 0.003 mm(2). The observed sensitivity enhancement suggests that this modulator may be driven directly by digital CMOS electrical signals with less than 1 V amplitude.

Mode conversion losses in silicon-on-insulator photonic wire based racetrack resonators.

Two complimentary types of SOI photonic wire based devices, the add/drop (A/D) filter using a racetrack resonator and the Mach-Zehnder interferometer with one arm consisting of an identical resonator in all-pass filter (APF) configuration, were fabricated and characterized in order to extract the optical properties of the resonators and predict the performance of the optical delay lines based on such resonators. We found that instead of well-known waveguide bending and propagation losses, mode conversion loss in the coupling region of such resonators dominates when the air gap between the racetrack resonator and access waveguide is smaller than 120nm. We also show that this additional loss significantly degrades the performance of the optical delay line containing cascaded resonators in APF configuration.