Optical spectroscopy of single InAs/InP quantum dots around λ=1.55 μm

We discuss the preparation and spectroscopic characterisation of a single InAs/InP quantum dot suitable for long-distance quantum key distribution applications around λ=1.55 μm. The dot is prepared using a site-selective growth technique which allows a single dot to be deposited in isolation at a controlled spatial location. Micro-photoluminescence measurements as a function of exciton occupation are used to determine the electronic structure of the dot. Biexciton emission, shell filling and many-body re-normalization effects are observed for the first time in single InAs/InP quantum dots.     

Monte-Carlo calculations of cloud returns for ground-based and space-based LIDARS

A Monte-Carlo model is described which has been developed for calculation of multiply scattered LIDAR returns. Results are shown for the common problem selected by the MUSCLE (MUltiple SCattering LIDAR Experiments) group for intercomparison, which represents a typical ground-based cloud-sensing scenario. This is contrasted with returns from the same cloud sensed by a space-based LIDAR, where multiple-scattering effects are much greater. The magnitude of multiple-scattering effects is seen to be largely determined by the optical depth across the receiver field of view at the cloud.     

Glass-forming liquids,anomalous liquids,and polyamorphism in liquids and biopolymers

Summary Glass formation in nature and materials science is reviewed and the recent recognition of polymorphism within the glassy state, polyamorphism, is discussed. The process by which the glassy state originates during the continuous cooling or viscous slowdown process, is examined and the three canonical characteristics of relaxing liquids are correlated through the fragility. The conversion of strong liquids to fragile liquids by pressure-induced coordination number increases is discussed, and then it is shown that for the same type of system it is possible to have the same conversion accomplished via a first-order transition within the liquid state. The systems in which this can happen are of the same type which exhibit polyamorphism, and the whole phenomenology can be accounted for by a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The concept of complex amorphous systems which can lose a significant number of degrees of freedom through weak first-order transitions is then used to discuss the relation between native and denatured hydrated proteins, since the latter have much in common with plasticized chain polymer systems. Finally, we close the circle by taking a short-time-scale phenomenon given much attention by protein physicists,viz., the onset of an anomaly in the Debye-Waller factor with increasing temperature, and showing that for a wide variety of liquids, including computer-simulated strong and fragile ionic liquids, this phenomenon is closely correlated with the experimental glass transition temperature. This implies that the latter owes its origin to the onset of strong anharmonicity in certain components of the vibrational density of states (evidently related to the boson peak) which then permits the system to gain access to its configurational degrees of freedom. The more anharmonic these vibrational components, the closer to the Kauzmann temperature will commence the exploration of configuration space and, for a given configurational microstate degeneracy, the more fragile the liquid will be. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Two-mode fibre spatial-mode converter using periodic coredeformation

Efficient conversion between the LP₀₁ and LP₁₁ modes in a two-mode fibre is achieved by periodically ablating the fibre surface with a CO₂ laser and then annealing the fibre with an electric arc. The resulting periodic core deformation produces 99% mode conversion over a 37 nm bandwidth around 1540 nm and 0.38 dB insertion loss     

The impact of single-wafer processing on semiconductor manufacturing

In this paper, we have described the importance of single-wafer processing (SWP) in semiconductor manufacturing. As compared to batch processing, reduced cycle time, better control of surface and interface properties, and reduced defect densities are some of the attractive features of SWP. We have provided the example of new SWP tools that have the answers to address virtually all process integration issues in dealing with new materials as well as conventional materials in ultra small dimensions. Driven by reduced I/O pitches, and emergence of system-on-chip, system-in-package or system-on-package as the driver of semiconductor growth, SWP tools have started to play an important role in the surface cleaning in IC assembly and packaging. Global acceptance of SWP in manufacturing can address the supply chain problem of the semiconductor industry.     

Simulating IC reliability with emphasis on process-flaw relatedearly failures

A Monte-Carlo reliability simulator for integrated circuits (IC) that incorporates the effects of process flaws, material properties, the mask layout, and use conditions is presented. The mask layout is decomposed into distinct objects, such as contiguous metal runs, vias, contacts, and gate-oxides, for which user-defined distributions are used for determining the failure probability. These distributions are represented by a mixture of defect-related and wearout-related distributions. The failure distributions for nets (sets of interconnected layout objects) are obtained by combining the distributions of their component objects. System reliability is obtained by applying control variate sampling to the logic network which is comprised of all nets. The effects of k-out-of-n substructures within the reliability network are accounted for. The methodology is illustrated by the effect of particulate-induced defects on metal runs and vias in a simple test circuit. The results qualitatively verify the methodology and show that predictions which incorporate failures due to process flaws are appreciably more pessimistic than those obtained from current practice     

Demonstration of an ion-implanted, wavelength-shifted quantum-well laser

A technique for fabricating many different wavelength lasers on the same wafer has been developed. High energy ion implantation was used to selectively blue shift the emission wavelength of an InP-based quantum well laser structure. This structure was then processed into fully functional broad-area lasers whose current threshold was unaffected by the implantation process, indicating extremely high material quality after bandgap-shifting. This process has the potential for the integration of not only different wavelength lasers, but also other devices, such as waveguides, detectors, modulators, etc., on a single wafer.