Quantum dots and nanowires for photonics applications

We review our results on integrated photonic devices fabricated using InGaAs quantum-dots. Selective-area metal organic chemical vapor deposition (MOCVD) is used to grow the active region with quantum dots emitting at different wavelengths for fabrication of the integrated devices. We will also review the structural and optical properties of III-V nanowires, and axial and radial nanowire heterostructures grown by MOCVD. In addition to binary nanowires, such as GaAs, InAs, and InP, we have demonstrated ternary InGaAs and AlGaAs nanowires. Core-shell nanowires consisting of GaAs cores with AlGaAs shells, and core-multishell nanowires with several alternating shells of AlGaAs and GaAs, exhibit strong photoluminescence. Axial segments of InGaAs have been incorporated within GaAs nanowires to form GaAs/InGaAs nanowire superlattices.

Fast O2 measurement using modified UEGO sensors in the intake and exhaust of a diesel engine

Recent work has investigated the use of O2 concentration in the intake manifold as a control variable for diesel engines. It has been recognised as a very good indicator of NOX emissions especially during transient operation, however, much of the work is concentrated on estimating the O2 concentration as opposed to measuring it. This work investigates Universal Exhaust Gas Oxygen (UEGO) sensors and their potential to be used for such measurements. In previous work it was shown that these sensors can be operated in a controlled pressure environment such that their response time is of the order 10ms. In this paper, it is shown how the key causes of variation (and therefore potential sources of error) in sensor output, namely, pressure and temperature are largely mitigated by operating the sensors in such an environment. Experiments were undertaken on a representative light duty diesel engine using modified UEGO sensors in the intake and exhaust system. Results from other fast emissions measuring equipment are also shown and it is seen that the UEGO sensors are capable of giving an accurate measurement of O2 and EGR. Copyright © 2013 SAE International.

Electroluminescence analysis and simulation of the effects of injection and temperature on carrier distribution in InGaN-based light-emitting diodes with color-coded quantum wells

This paper reports on an extensive analysis of the electroluminescence characteristics of InGaN-based LEDs with color-coded structure, i.e., with a triple quantum well structure in which each quantum well has a different indium content. The analysis is based on combined electroluminescence measurements and two-dimensional simulations, carried out at different current and temperature levels. Results indicate that (i) the efficiency of each of the quantum wells strongly depends on device operating conditions (current and temperature); (ii) at low current and temperature levels, only the quantum well closer to the p-side has a significant emission; (iii) emission from the other quantum wells is favored at high current levels. The role of carrier injection, hole mobility, carrier density and non-radiative recombination in determining the relative intensity of the quantum wells is discussed in the text. © 2013 The Japan Society of Applied Physics.

Dicke superradiance in GaN quantum wells

We numerically modeled the spatio-temporal dynamics of Dicke superradiance in GaN/InGaN heterostructure quantum wells in a ridge waveguide cavity. Model predictions envisage ultrashort pulses of intensities superior to what can be obtained in mode-locked lasers. ©2010 IEEE.

Sensors based on SAW and FBAR technologies

Over the last few years a number of sensing platforms are being investigated for their use in drug development, microanalysis or medical diagnosis. Lab-on-a-chip (LOC) are devices integrating more than one laboratory functions on a single device chip of a very small size, and typically consist of two main components: microfluidic handling systems and sensors. The physical mechanisms that are generally used for microfluidics and sensors are different, hence making the integration of these components difficult and costly. In this work we present a lab-on-a-chip system based on surface acoustic waves (for fluid manipulation) and film bulk acoustic resonators (for sensing). Coupling surface acoustic waves into liquids induces acoustic streaming and motion of micro-droplets, whilst it is well-known that bulk acoustic waves can be used to fabricate microgravimetric sensors. Both technologies offer exceptional sensitivity and can be fabricated from piezoelectric thin films deposited on Si substrates, reducing the fabrication time/cost of the LOC devices. © 2013 SPIE.

A single FBAR-based temperature and pressure sensors

A novel temperature and pressure sensor based on a single film bulk acoustic resonator (FBAR) is designed. This FBAR support two resonant modes, which response opposite to the change of temperature. By sealed the back cavity of a back-trench membrane type FBAR with silicon wafer, an on-chip single FBAR sensor suitable for measuring temperature and pressure simultaneously is proposed. For unsealed device, the experimental results show that the first resonant mode has a temperature coefficient of frequency (TCF) of 69.5ppm/K, and the TCF of the second mode is -8.1ppm/K. After sealed the back trench, it can be used as a pressure sensor, the pressure coefficient of frequency (PCF) for the two resonant mode is -17.4ppm/kPa and -6.1 ppm/kPa respectively, both of them being more sensitive than other existing pressure sensors. © 2013 Trans Tech Publications Ltd, Switzerland.

Efficient decoy-state quantum key distribution with quantified security

We analyse the finite-size security of the efficient Bennett-Brassard 1984 protocol implemented with decoy states and apply the results to a gigahertz-clocked quantum key distribution system. Despite the enhanced security level, the obtained secure key rates are the highest reported so far at all fibre distances.

High bit rate quantum key distribution with 100 dB security

We report the operation of a gigahertz clocked quantum key distribution system featuring high composable and quantifiable security while maintaining more than 1 Mbit/s secure key rate over a 50 km quantum channel. © OSA 2013.

Graphene SOI CMOS sensors for detection of PPB levels of NO2 in air

There is considerable demand for sensors that are capable of detecting ultra-low concentrations (sub-PPM) of toxic gases in air. Of particular interest are NO2 and CO that are exhaust products of internal combustion engines. Electrochemical (EC) sensors are widely used to detect these gases and offer the advantages of low power, good selectivity and temporal stability. However, EC sensors are large (1 cm3), hand-made and thus expensive ($25). Consequently, they are unsuitable for the low-cost automotive market that demands units for less than $10. One alternative technology is SnO2 or WO3 resistive gas sensors that are fabricated in volume today using screen-printed films on alumina substrates and operate at 400°C. Unfortunately, they suffer from several disadvantages: power consumption is high 200 mW; reproducibility of the sensing element is poor; and cross-sensitivity is high. © 2013 IEEE.

Model for quantum efficiency of guided mode plasmonic enhanced silicon Schottky detectors

Plasmonic enhanced Schottky detectors operating on the basis of the internal photoemission process are becoming an attractive choice for detecting photons with sub bandgap energy. Yet, the quantum efficiency of these detectors appears to be low compare to the more conventional detectors which are based on interband transitions in a semiconductor. Hereby we provide a theoretical model to predict the quantum efficiency of guided mode internal photoemission photodetector with focus on the platform of silicon plasmonics. The model is supported by numerical simulations and comparison to experimental results. Finally, we discuss approaches for further enhancement of the quantum efficiency.

Fabrication and integration of horizontally aligned carbon nanotube C60 films for UV sensors

Carbon nanotubes (CNTs) are promising for microsystems applications, yet few techniques effectively enable integration of CNTs with precise control of placement and alignment of the CNTs at sufficiently high densities necessary for compelling mechanical or electrical performance. This paper explores new methods for scalable integration of dense, horizontally aligned (HA) CNTs with patterned electrodes. Our technique involves the synthesis of vertically aligned (VA) CNTs directly on a conductive underlayer and subsequent mechanical transformation into HA-CNTs, thus making electrical contact between two electrodes. We compare elasto-capillary folding and mechanical rolling as methods for transforming VA-CNTs, which lead to distinctly different HA-CNT morphologies and potentially impact material and device properties. As an example application of this novel CNT morphology, we investigate fabrication of electrically addressable CNT-C60 hybrid thin films that we previously demonstrated as photodetectors. We synthesize these assemblies by crystallizing C60 from dispersion on HA-CNT thin-film scaffoldings. HA-CNTs fabricated by rolling result in relatively low packing density, so C 60 crystals embed inside the HA-CNT matrix during synthesis. On the other hand, C60 crystallization is restricted to near the surface of HA-CNT films made by the elasto-capillary process. © 2013 IEEE.

Exploring the use of sensors to measure behavioral interactions: an experimental evaluation of using hand trajectories.

Humans appear to be sensitive to relative small changes in their surroundings. These changes are often initially perceived as irrelevant, but they can cause significant changes in behavior. However, how exactly people's behavior changes is often hard to quantify. A reliable and valid tool is needed in order to address such a question, ideally measuring an important point of interaction, such as the hand. Wearable-body-sensor systems can be used to obtain valuable, behavioral information. These systems are particularly useful for assessing functional interactions that occur between the endpoints of the upper limbs and our surroundings. A new method is explored that consists of computing hand position using a wearable sensor system and validating it against a gold standard reference measurement (optical tracking device). Initial outcomes related well to the gold standard measurements (r = 0.81) showing an acceptable average root mean square error of 0.09 meters. Subsequently, the use of this approach was further investigated by measuring differences in motor behavior, in response to a changing environment. Three subjects were asked to perform a water pouring task with three slightly different containers. Wavelet analysis was introduced to assess how motor consistency was affected by these small environmental changes. Results showed that the behavioral motor adjustments to a variable environment could be assessed by applying wavelet coherence techniques. Applying these procedures in everyday life, combined with correct research methodologies, can assist in quantifying how environmental changes can cause alterations in our motor behavior.

Room temperature single-photon detectors for high bit rate quantum key distribution

We report room temperature operation of telecom wavelength single-photon detectors for high bit rate quantum key distribution (QKD). Room temperature operation is achieved using InGaAs avalanche photodiodes integrated with electronics based on the self-differencing technique that increases avalanche discrimination sensitivity. Despite using room temperature detectors, we demonstrate QKD with record secure bit rates over a range of fiber lengths (e.g., 1.26 Mbit/s over 50 km). Furthermore, our results indicate that operating the detectors at room temperature increases the secure bit rate for short distances. © 2014 AIP Publishing LLC.