Low-threshold photonic crystal laser

We have fabricated photonic crystal nanocavity lasers, based on a high-quality factor design that incorporates fractional edge dislocations. Lasers with InGaAsP quantum well active material emitting at 1550 nm were optically pumped with 10 ns pulses, and lased at threshold pumping powers below 220 µW, the lowest reported for quantum-well based photonic crystal lasers, to our knowledge. Polarization characteristics and lithographic tuning properties were found to be in excellent agreement with theoretical predictions

Near-field scanning optical microscopy of photonic crystal nanocavities

Near-field scanning optical microscopy was used to observe high-resolution images of confined modes and photonic bands of planar photonic crystal (PPC) nanocavities fabricated in active InGaAsP material. We have observed the smallest optical cavity modes, which are intentionally produced by fractional edge dislocation high-Q cavity designs. The size of the detected mode was roughly four by three lattice spacings. We have also observed extended dielectric-band modes of the bulk PPC surrounding the nanocavity by geometrically altering the bands in emission range and eliminating localized modes out of the emission range

Near-field scanning optical microscopy of photonic crystal high-Q nanocavities

Near-field scanning optical microscopy (NSOM) was used to observe high-resolution images of planar photonic crystal nanocavities fabricated in active InGaAsP material. We have observed the smallest optical cavity modes and dielectric band modes

Laterally Coupled Quantum-Dot Distributed-Feedback Lasers

InAs quantum-dot lasers that feature distributed feedback and lateral evanescent- wave coupling have been demonstrated in operation at a wavelength of 1.3 m. These lasers are prototypes of optical-communication oscillators that are required to be capable of stable single-frequency, single-spatial-mode operation. A laser of this type (see figure) includes an active layer that comprises multiple stacks of InAs quantum dots embedded within InGaAs quantum wells. Distributed feedback is provided by gratings formed on both sides of a ridge by electron lithography and reactive-ion etching on the surfaces of an AlGaAs/GaAs waveguide. The lateral evanescent-wave coupling between the gratings and the wave propagating in the waveguide is strong enough to ensure operation at a single frequency, and the waveguide is thick enough to sustain a stable single spatial mode. In tests, the lasers were found to emit continuous-wave radiation at temperatures up to about 90 C. Side modes were found to be suppressed by more than 30 dB

Near-field scanning optical microscopy of photonic crystal high-Q nanocavities

Near-field scanning optical microscopy (NSOM) was used to observe high-resolution images of planar photonic crystal nanocavities fabricated in active InGaAsP material. We have observed the smallest optical cavity modes and dielectric band modes

Nanophotonics based on planar photonic crystals

By creating different types of defects in the photonic crystal lattice, various nanophotonics components, such as cavities and waveguides, can be realized. The quest for a compact and efficient nano-cavity, with high quality factor (Q) and small mode volume (V/sub mode/), has been a central part of research in integrated optics. Recently, we have proposed a systematic method to design optical nano-cavities that satisfy both of these requirements. The cavity consists of a defect hole that is smaller than surrounding holes arranged in the triangular lattice photonic crystal. In order to test our design we have fabricated high-Q cavities in the InGaAsP material system

Multi-State Memory and Logic Designs Using Multi-Quantum Channel Nano-FETs

In this dissertation, implementation of multi value logic using a novel algebra and Spatial Wavefunction Switched Field Effect Transistor (SWSFET) has been explored. The quantum mechanical simulations, characteristics of the fabricated SWS structures are discussed. The novel device and quaternary algebra has been used to implement multi-value logic. The designs of quaternary SRAM cells, basic logic gates and arithmetic cells are presented. In addition, mixed signal architectures using SWSFET are explored. Simulations for the memory, logic and mixed signal designs are presented. BSIM3 equivalent channel models were used for SWSFET. Cadence Spectre Simulator and Advanced Design Simulator were used as the simulation tools. Quaternary to binary and binary to quaternary conversion circuits are also designed and presented. This helps the quaternary and binary circuits to co-exist on the same die. Multi Valued Logic (MVL) has been in research for many decades. MVL offers benefits and opportunities but it has its own challenges. Quaternary SRAM using SWSFET reduces the number of transistors needed by 75%. Similar savings are shown for implementing quaternary logic when compared to implementation using CMOS based binary logic. In addition, significant reduction in gate delays is achieved by implemented logic using quaternary algebra. Also, logic implementation using quaternary algebra leads to about 50% reduction in interconnect metal density for data signals. This is helpful in reducing the congestion in metal signal routing layers. Metal density, number of metal layers and pressure to use low resistivity materials have added to the die cost over recent years. Implementing MVL in main stream microprocessor needs further research in designs tools. In addition, the fabrication and transistor design need to be optimized to tune MVL based designs

High Temperature Thermoelectric Properties Of Nano-Bulk Silicon And Silicon Germanium

Point defect scattering via the formation of solid solutions to reduce the lattice thermal conductivity has been an effective method for increasing ZT in state-of-the-art thermoelectric materials such as Si -Ge, Bi2Te 3-Sb2Te3 and PbTe-SnTe. However, increases in ZT are limited by a concurrent decrease in charge carrier mobility values. The search for effective methods for decoupling electronic and thermal transport led to the study of low dimensional thin film and wire structures, in particular because scattering rates for phonons and electrons can be better independently controlled. While promising results have been achieved on several material systems, integration of low dimensional structures into practical power generation devices that need to operate across large temperature differential is extremely challenging. We present achieving similar effects on the bulk scale via high pressure sintering of doped Si and Si-Ge nanoparticles. The nanoparticles are prepared via high energy ball milling of the pure elements. The nanostructure of the materials is confirmed by powder X-ray diffraction and transmission electron microscopy. Thermal conductivity measurements on the densified pellets show a drastic reduction in the lattice contribution at room temperature when compared to doped single crystal Si. The combination of low thermal conductivity and high power factor leads to an unprecedented increase in ZT at 1275 K by a factor of 3.5 in n-type nanobulk Si over that of single crystalline samples. Experimental results on both n-type and p -type Si are discussed in terms of the impact of the size distribution of the nanoparticles, doping impurities and nanoparticle synthesis processes. © 2009 Materials Research Society