Two research groups have reported independent approaches to the fabrication of the first electrically injected indium phosphide (InP)-based diode lasers on silicon. Such lasers, if practical, would help to usher in low-cost but extremely rapid data transmission. In both approaches, the light from the lasers was coupled into silicon-on-insulator (SOI) waveguides on silicon chips. In the method developed by a group from Intel (Santa Clara, CA) and the University of California–Santa Barbara (Santa Barbara, CA), an oxide layer a few nanometers thick is created on the InP component, which is heated and pressed against the SOI, bonding them. The silicon serves as the continuous-wave laser cavity, which is 800 µm long. The technology should make data-transmission speeds of 20 to 40 Gbit/s over distances of tens of feet possible, says Intel. Contact Barbara Bronson Gray at bbgray@engineering.ucsb.edu.
In the approach taken by researchers at Ghent University (Ghent, Belgium) and the Technical University Eindhoven (Eindhoven, The Netherlands), an InP-based laser structure is bonded to SOI with an adhesive called DVS-BCB. A polymer waveguide adiabatically couples 0.9 mW of 1550 nm laser light (via tapering) into an SOI waveguide. In this setup, the laser (if made shorter) can be used as a photodetector with a responsivity of 0.23 A/W. Contact Gunther Roelkens at Gunther.Roelkins@intec.Ugent.be.
Researchers are actively involved in the exploitation of electro-optic and nonlinear effects that produce zero-index and negative-index materials. By embedding aligned nematic liquid crystals with coated dielectric nanospheres, researchers at Pennsylvania State University (University Park, PA) have demonstrated the possibility of creating a new type of metamaterial with a refractive index that is tunable from negative, through zero, to positive values.
The material properties of this new metamaterial are predicted using Maxwell Garnet mixing-rule equations for a medium with three regions: the host liquid crystal, the nanosphere outer shell, and the nanosphere core. Though these materials are nonmagnetic with relative permeability equal to 1, the combination of the permittivities at the appropriate resonances in conjunction with the electric- or magnetic-field-induced permittivity change in the liquid-crystal host material enables the refractive-index tun-ability over a wide dynamic range from the visible to the microwave region. Contact Iam Choon Khoo at ick1@psu.edu.
Single-crystal semiconductor materials such as silicon (Si) and gallium arsenide have previously been transferred to flexible polymers to create thin-film transistors (TFTs) on plastic; however, the process is limited and cumbersome. Researchers at the University of Wisconsin-Madison (Madison, WI) have instead developed a simpler, more versatile transfer technique that allows them to create strained-silicon TFTs with high drive current and high transconductance, making them excellent candidates for use in displays, solar cells, and biosystem implants.
The TFT active layer is formed as a thin membrane on silicon-on-insulator (SOI) substrates. Both strained- and unstrained-silicon
TFTs are fabricated in a similar process using a sandwich structure of Si and silicon-germanium alloy. Photolithography is used to pattern the membrane, which is then transferred (using a “dry” printing method) to a flexible polyethylene substrate onto which a layer of photoresist has been applied that serves as both an adhesive and as the gate-dielectric layer for the TFTs. Contact Zhenqiang Ma at mazq@engr.wisc.edu.
References:
mailto:bbgray@engineering.ucsb.edu
Archives