At present, uncooled thermal detector focal plane arrays are successfully used in string thermal imagers. However, the performance of thermal detectors is modest, they suffer from slow response and they are not very useful in applications requiring multispectral detection. In the paper, a number of concepts to improve performance of photon detectors operating at room temperature are presented. Several types of detector materials are considered: HgCdTe, Sb-based III-V ternary alloys, and type-II InAs/GaSb superlattice. Initial efforts were concentrated on photoconductors and photoelectromagnetic detectors. Recently, advanced heterojunction photovoltaic detectors have been developed. It is shown that uncooled HgCdTe photovoltaic detector can achieve detectivity of 10⁹ cmHz^1/2W^-1 at the 8-9 μm range. Potentially the devices can be assembled in large focal plane arrays. This will enable obtaining of NEDT of less than 0.1 K for staring thermal imagers operating with f/1 optics and 30s^-1 frame rate.

We formed p-GaAs/n-Si and n-GaAs/p-Si heterostructures by depositing thin-film GaAs on Si wafers with pulsed-laser deposition (PLD). For the GaAs ablation, the 532 nm emission of a Nd:YAG laser (10 Hz, 6 ns) with a fluence of 0.79-0.84 J/cm² was used. The thicknesses of the films were approximately 0.5 μm. During the deposition, the substrate was not heated and the ambient pressure was kept at 10^-6 torr. X-ray analysis showed that the films contain crystallites and by means of an atomic force microscope (AFM), it is demonstrated that the film surfaces are fairly smooth. Using a monochromatic light source and by means of electrical contacts on the top and the rear of the sample, we measured the photocurrent through the junction using lock-in technique. These measurements showed that the photocurrent spectra of the p-GaAs/n-Si diode crucially depend on the applied bias. At -0.7 V (reverse bias) the photocurrent maximum is at 930 nm, while at +0.5 V, the photocurrent maximum lies at 1056 nm. These maxima are in the vicinity to the bandgap of GaAs and Si, respectively. In other words, it is possible to switch between the spectral sensitivity of GaAs and Si via an applied electric field. The device can be either used as a photo-detector for which the sensitive wavelength range can be easily chosen by the applied bias or as hybrid multiplexer to convert two optical inputs into one electrical output.

Nanocrystal Si (nc-Si) sensitization of Er in a silica matrix to obtain high optical activity in a Si-compatible material is investigated. Er-doped silicon-rich silicon oxide (SRSO) films, which consist of nc-Si embedded inside an SiO₂ matrix, were deposited by electron-cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) using SiH₄ and O₂ with concurrent sputtering of Er followed by a high temperature anneal. For comparison, Er-free SRSO films were also deposited. Detailed investigation of processing conditions indicates that an annealing process consisting of 30 min anneal at 950°C without hydrogenation to be optimum for activation of Er. Investigation of MOS diode structure with Er-doped and Er-free SRSO films indicates that a mesa-type structure with n⁺ poly-silicon top contact, p-type substrate, and SRSO Si content of less than 40% gives the best diode performance. Er-free SRSO diodes fabricated using the optimum conditions show electroluminescence under forward bias. Er-doped SRSO diodes show photoresponse at 1.54 μm due to nanocrystal -- Er interactions, showing the promise of developing integrated, Si-based 1.54 μm light detectors for integrated microphotonic devices.

We review our recently combined study of temperature-dependent photoluminescence, absorption, and photocurrent measurements with theoretical models on PbSrSe thin films grown by molecular beam epitaxy for the key properties of PbSrSe thin films and their microstructures. The derived empirical equations for band gaps, effective masses, and refractive indices have been employed successfully in PbSrSe/PbSe multiple quantum well (MQW) mid-infrared laser systems, which opens the way for the design of IV-VI MQW mid-infrared lasers. The infrared detection of PbSrSe thin films has been demonstrated at different temperatures, where the spectral intensity and wavelength coverage are determined by the band gap and the film thickness. The bias- and frequency-dependent capacitance characteristics have also been investigated in detail.

Due to the recent experimental validations of left-handed metamaterials, negative refractive index has now become recognized as a new parameter space for the electromagnetic response of materials. Because materials with negative index behave quite differently than materials with positive index, many familiar electromagnetic phenomena must be reconsidered. Having established now the scientific basis of negative index, the effort of the community is turning toward the practical realization of both the predicted scientific phenomena and associated applications. In both of these pursuits, the ability to design, characterize and fabricate negative index materials is critical; we can consider the current status of negative refraction in some sense a materials issue, as our ability to demonstrate the predicted phenomena is linked to the quality of metamaterials we can produce. In this paper we consider several issues associated with the design and simulation of negative index metamaterials.

In the recent years, many experimental and theoretical achievements have shown that meta-materials can simulate homogeneous materials with optical index less than unity or even negative. For example, a dielectric photonic crystal, used at the edge of a band gap, can generate phenomena of ultra-refraction (positive index less than unity) or negative refraction (negative index). Some applications of these phenomena will be shown, specially the design of directive antenna in the microwaves region. More recently, experimental and theoretical studies have been published on left-handed materials. These materials, which have a permittivity and a permeability equal to -1, have been the subject of controversies about their alleged property of making perfect lenses. It will be shown that such a perfect lens cannot exist. However, this kind of meta-material could be used for making better lenses than the best classical ones, a fact which could explain some experimental results. The vital influence of the size of the elementary cell on the performance of the lens will be pointed out. Finally, it will be shown that surprisingly, a left-handed material can be interpreted as a means to go through the mirror, as Alice in the novel of Lewis Carrol...

Different approaches are reviewed to design conducting inclusions with specific microwave magnetic response. Several types of non-resonant and resonant inclusions are presented, and experimental measurements are reported. Inductive inclusions with a load made of electronic components are attractive to build sophisticated frequency response. They can be described by a simple model and a straightforward expression of the permeability as a function of the impedance of the load and the inductance of the inclusion has been derived. This model accounts for the experimental observations. The relative merits of conventional magnetic materials and artificial magnetic materials are compared through sum rules. It appears that a low frequencies, magnetic materials lead to much larger permeability levels, and combining inductive structures with a magnetic core is attractive. On the other hand, on the high frequency side including THz and optical frequencies, artificial magnetic materials may be more attractive than conventional magnetic materials.

We present results from indium antimonide and mercury cadmium telluride IR detector arrays operating at temperatures above 80K, whilst retaining high performance. Multi-layer epitaxial growth is employed to minimize thermally generated leakage currents, through the use of structures designed to control transport of charge generated outside of the active region to the diode junction and to minimize Auger generation within the active region. This enables an increase in operating temperature of a few tens of degrees in the case of background limited III-V devices, and thermoelectric operation of MCT detectors sensitive to the MWIR band. We also discuss the effects of reverse bias on diodes to actively suppress the Auger generation, and the consequent introduction of 1/f noise. Optical concentrators can be used to minimize the volume of detector material in order to gain further increases in temperature. The concentrators, based on Winston cone designs, are fabricated at each pixel by reactive ion etching directly into the detector material and its substrate, and allow a theoretical reduction in volume of a factor of up to 16. This translates into a potential additional increase in temperature of several tens of degrees.

Over the past 27 years, SCD has developed and manufactured more than 30 types of Infrared Detector, both with support from the Israeli MOD and in cooperation with institutions and companies such as the Technion, Soreq NRC, RICOR and RAFAEL. SCD's current production line includes Hg_1-xCd_xTe (MCT) devices with up to 480x6 elements operating in Time Delay and Integration (TDI) mode and InSb Focal Plane Arrays (FPAs) with up to 640x512 elements, all available in various configurations including fully integrated Detector-Dewar-Cooler (DDC) packages. Such DDCs have been designed to range from the very small to the very large. At one end the Piccolo DDC is a small, low weight and power detector, ideal for compact low cost imagers such as handheld IR cameras. At the other end, we manufacture a very long (2048x16) bi-directional TDI InSb detector designed for "whiskbroom scanning" systems. This device consists of four modules precisely butted on a single substrate, with each 512x16 module connected to a single signal processor. In 2003, SCD announced its new breakthrough Digital Read Out Integrated Circuit (ROIC) technology: Digital DDC or D³C. This readout system, with excellent performance and increased flexibility is the first in a series of new imaging solutions that SCD is developing to meet future demands of noise and power reduction, combined with greater wavelength selectivity. To continue along this path we have also been developing our new ABCS (Antimonide Based Compound Semiconductor) technology, which we first reported in 2002. The ABCS program, combining SCD's existing strengths in InSb FPA systems with new concepts in bandgap engineering and smart structure design, is aimed at multispectral IR detectors operating at higher temperatures. This review discusses some of the key trends at SCD as described above. After surveying the performance of SCD's current InSb technology, SCD's evolution towards the next generations will be described, including the achievements and potential of the D³C and ABCS systems.

This paper describes three low-cost thermoelectric infrared imaging sensors having a 1,536, 2,304, and 10,800 element thermoelectric focal plane array (FPA) respectively and two experimental automotive application systems. The FPAs are basically fabricated with a conventional IC process and micromachining technologies and have a low cost potential. Among these sensors, the sensor having 2,304 elements provide high responsivity of 5,500 V/W and a very small size with adopting a vacuum-sealed package integrated with a wide-angle ZnS lens. One experimental system incorporated in the Nissan ASV-2 is a blind spot pedestrian warning system that employs four infrared imaging sensors. This system helps alert the driver to the presence of a pedestrian in a blind spot by detecting the infrared radiation emitted from the person’s body. The system can also prevent the vehicle from moving in the direction of the pedestrian. The other is a rearview camera system with an infrared detection function. This system consists of a visible camera and infrared sensors, and it helps alert the driver to the presence of a pedestrian in a rear blind spot. Various issues that will need to be addressed in order to expand the automotive applications of IR imaging sensors in the future are also summarized. This performance is suitable for consumer electronics as well as automotive applications.

Optical technology plays an increasingly important role in numerous applications areas, including communications, information processing, and data storage. However, as optical technology develops, it is evident that there is a growing need to develop reliable photonic integration technologies. This will include the development of passive as well as active optical components that can be integrated into functional optical circuits and systems, including filters, switching fabrics that can be controlled either electrically or optically, optical sources, detectors, amplifiers, etc. We explore the unique capabilities and advantages of nanotechnology in developing next generation integrated photonic chips. Our long-range goal is to develop a range of photonic nanostructures including artificially birefringent and resonant devices, photonic crystals, and photonic crystals with defects to tailor spectral filters, and nanostructures for spatial field localization to enhance optical nonlinearities, to facilitate on-chip system integration through compatible materials and fabrication processes. The design of artificial nanostructured materials, PCs and integrated photonic systems is one of the most challenging tasks as it not only involves the accurate solution of electromagnetic optics equations, but also the need to incorporate the material and quantum physics equations. Near-field interactions in artificial nanostructured materials provide a variety of functionalities useful for optical systems integration. Furthermore, near-field optical devices facilitate miniaturization, and simultaneously enhance multifunctionality, greatly increasing the functional complexity per unit volume of the photonic system. Finally and most importantly, nanophotonics may enable easier integration with other nanotechnologies: electronics, magnetics, mechanics, chemistry, and biology.

Silicon-on-insulator is a proven technology for very large scale integration of microelectronic devices. The technology also offers the potential for development of nanophotonic devices and the ability to interface such devices to the macroscopic world. This paper will report on fabrication techniques used to form nano-structured silicon wires on an insulating structure that is amenable to interfacing nanostructured sensors with high-performance microelectronic circuitry for practical implementation. Nanostructures formed on silicon-on-sapphire can also exploit the transparent substrate for novel device geometries. This research harnesses the unique properties of a high-quality single crystal film of silicon on sapphire and uses the film thickness as one of the confinement dimensions. Lateral arrays of silicon nanowires were fabricated in the thin (5 to 20 nm) silicon layer and studied. This technique offers simplified contact to individual wires and provides wire surfaces that are more readily accessible for controlled alteration and device designs.

We discuss three unimolecular rectifiers: γ-hexadecylquinolinium tricyanoquinodimethanide, 2,6-di[dibutylamino-phenylvinyl]-1-butylpyridinium iodide and dimethylanilino-aza[C60]fullerene, and discuss the progress towards useful one-molecule electronic devices for the ultimate reduction in integrated circuit sizes.

Quantum entanglement has the potential to revolutionize the entire field of interferometric sensing by providing many orders of magnitude improvement in interferometer sensitivity. The quantum entangled particle interferometer approach is very general and applies to many types of interferometers. In particular, without nonlocal entanglement, a generic classical interferometer has a statistical-sampling shot-noise limited sensitivity that scales like 1/√N, where N is the number of particles passing through the interferometer per unit time. However, if carefully prepared quantum correlations are engineered between the particles, then the interferometer sensitivity improves by a factor of √N to scale like 1/N, which is the limit imposed by the Heisenberg Uncertainty Principle. For optical interferometers operating at milliwatts of optical power, this quantum sensitivity boost corresponds to an eight-order-of-magnitude improvement of signal to noise. This effect can translate into a tremendous science pay-off for NASA-JPL missions. For example, one application of this new effect is to fiber optical gyroscopes for deep-space inertial guidance and tests of General Relativity (Gravity Probe B). Another application is to ground and orbiting optical interferometers for gravity wave detection, Laser Interferometer Gravity Observatory (LIGO) and the European Laser Interferometer Space Antenna (LISA), respectively. Other applications are to Satellite-to-Satellite laser Interferometry (SSI) proposed for the next generation Gravity Recovery And Climate Experiment (GRACE II).

Nanotechnology development is progressing very rapidly. Several billions of dollars have been invested in nanoscience research since 2000. Pioneering nanotechnology research efforts have been primarily conducted at research institutions and centers. This paper identifies developments in nanoscience and technology that could provide significant advances in missile systems applications. Nanotechnology offers opportunities in the areas of advanced materials for coatings, including thin-film optical coatings, light-weight, strong armor and missile structural components, embedded computing, and “smart” structures; nano-particles for explosives, warheads, turbine engine systems, and propellants to enhance missile propulsion; nano-sensors for autonomous chemical detection; and nano-tube arrays for fuel storage and power generation. The Aviation and Missile Research, Development, and Engineering Center (AMRDEC) is actively collaborating with academia, industry, and other Government agencies to accelerate the development and transition of nanotechnology to favorably impact Army Transformation. Currently, we are identifying near-term applications and quantifying requirements for nanotechnology use in Army missile systems, as well as monitoring and screening research and developmental efforts in the industrial community for military applications. Combining MicroElectroMechanical Systems (MEMS) and nanotechnology is the next step toward providing technical solutions for the Army’s transformation. Several research and development projects that are currently underway at AMRDEC in this technology area are discussed. A top-level roadmap of MEMS/nanotechnology development projects for aviation and missile applications is presented at the end.

Very high power continuous-wave quantum cascade lasers are demonstrated in the mid-infrared (3 - 6 μm) wavelength range. λ~6 μm high-reflectivity coated QCLs are demonstrated producing over 370 mW continuous-wave power at room temperature with continuous-wave operation up to 333 K. Advanced heterostructure geometries, including the use of a thick electroplated gold, epilayer-side heat sink and a buried-ridge heterostructure are demonstrated to improve laser performance significantly when combined with narrow laser ridges. Recent significant improvements in CW operation are presented and include the development if narrow (9 μm-wide) ridges for high temperature CW operation. GasMBE growth of the strain-balanced λ~6 μm QCL heterostructure is discussed. X-ray diffraction measurements are presented and compared to computer simulations that indicate excellent layer and compositional uniformity of the structure.

We consider the application of mid-infrared (MIR) wavelength quantum cascade lasers (QCL) as sources for free-space optical communications. QCL’s possess high modulation bandwidth and excellent optical performance in the atmospherically transparent MIR spectral range. In order to investigate this potential application area, we have performed a series of comparative evaluations on analog and digital free-space optical links operating in the near-infrared (NIR) (830nm, 1300nm and 1550nm) and mid-infrared (8μm). The measurements were made using well controlled atmospheric conditions in the 65ft long Pacific Northwest National Laboratory’s Aerosol Wind Tunnel Research Facility using water vapor, oil vapor and dust as the scattering media. We measured the transmitted intensity as a function of the density of scatterers in the tunnel. We also performed bit error rate analysis of signals transmitted at the DS-3 data rate. The QCL link consistently showed a higher performance level when compared to the NIR links for water fog, oil fog and dust scattering.

Quantum cascade lasers (QCLs) provide a viable infrared laser source for a new class of laser transmitters capable of meeting the performance requirements for a variety of national security and civilian applications. The high output power, small size, and superb stability and modulation characteristics of QCLs make them amenable for integration as transmitters into ultra-sensitive, ultra-selective point sampling and remote short-range chemical sensors. This paper reports on the current development in infrared photonics that provides a pathway for QCL transmitter miniaturization. This research has produced infrared waveguide-based optical components in chalcogenide glass using both direct-laser writing and holographic exposure techniques. We discuss here the design and fabrication concepts and capabilities required to produce integrated waveguides, waveguide couplers, and other photonic devices.

Defects in photonic crystals (PCs) can support localized light modes with extremely small mode volumes. Depending on the symmetry of the PC, and the means of fabrication of the PC, extremely high quality factors (Q) are also possible. The combination of high Q and small mode volume should allow us to observe strong coupling between the cavity and quantum dot (QD) emitters that are strategically embedded within the cavity. This, in turn, has important implications for a variety of optical phenomena, such as single-photon sources. We describe the fabrication of PCs formed within membranes (180 nm thick) of GaAs, of either triangular or square lattice symmetry. The structures incorporate InAs QDs, grown monolithically with the PC material by Molecular Beam Epitaxy (MBE). We have observed emission from the smallest volume cavities (i.e. single-hole defects) in both the triangular and square lattice structures. The cavities have lattice constants ranging from 0.25 - 0.40 μm, and Q factors as high as 8500. To improve the probability of coupling a single QD to a cavity mode, we have developed a lithographic positioning technique capable of aligning a cavity to a feature on the surface within 50 nm, adequate to overlap a QD with a cavity mode. We will report on the progress achieved thus far with these structures and the challenges remaining to achieve strong coupling with specific QDs.

This paper investigates the properties of homoepitaxial growth of ZnO. High quality bulk ZnO crystals have been produced by melt growth techniques in addition to ZnO thin films grown by Metalorganic Chemical Vapor Deposition (MOCVD) on bulk ZnO substrates (Zinc side and Oxygen side). The photoluminescence showed the dominance of strong and narrow band due to the band edge emissions for undoped ZnO. UV transmission showed sharp transition indication good crystal quality. High resolution x-ray diffraction measurements (HRXRD) along with rocking curve showed excellent crystal quality with full width at half maximum values close to 100 arc seconds.

A review of the current literature on plasma etching of ZnO is presented. The etch rates as a function of etch conditions in Cl₂-based BCl₃-based and CH₄-based and related chemistries are reviewed. Resultant surface morphology, anisotropy, surface stoichiometry and band edge photoluminescence results are also discussed.

Chalcogenide glasses are formed by combining chalcogen elements with IV-V elements. Among the family of glasses, As₂S₃, and As₂Se₃ are important infrared (IR) transparent materials for a variety of applications such as IR sensors, waveguides, and photonic crystals. With the promise of accessibility to any wavelengths between 3.5 and 16 μm using tunable quantum cascade lasers (QCL) and chalcogenides with IR properties that can be compositionally adjusted, ultra-sensitive, solid-state, photonic-based chemical sensing in mid-wave IR region is now possible. Pacific Northwest National Laboratory (PNNL) has been developing quantum cascade lasers (QCLs), chalcogenides, and all other components for an integrated approach to chemical sensing. Significant progress has been made in glass formation and fabrication of different structures at PNNL. Three different glass-forming systems, As-S, As-S-Se, and As-S-Ag have been examined for this application. Purification of constituents from contaminants and thermal history are two major issues in obtaining defect-free glasses. We have shown how the optical properties can be systematically modified by changing the chemistry in As-S-Se system. Different fabrication techniques need to be employed for different geometries and structures. We have successfully fabricated periodic arrays and straight waveguides using laser-writing and characterized the structures. Wet-chemical lithography has been extended to chalcogenides and challenges identified. We have also demonstrated holographic recording or diffraction gratings in chalcogenides.

This paper is an overview of research in my group over the past 10 to 15 years. Our work has explored the synthesis, assembly, nanostructure characterization, and optical properties of a wide variety of semiconductor quantum dots in II-VI, III-V, and other systems. Our early work was aimed at applications in photonics and fiber optics but more recently we have worked on biomolecular engineering with quantum dots for immunoassays and related interests. The chosen hosts for the quantum dots are glasses, polymers and sol-gel prepared xerogels. The synthesized quantum dot nanocomposites have been most commonly characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and high resolution transmission electron microscopy (HRTEM). Absorption and photoluminescence (PL) spectroscopy data are also reported on selected quantum dot samples. A short summary of ongoing research in our laboratory on magnetic iron oxide nanocrystals for biological applications is also presented.

The formation of self-assembled ZnO nanoclusters using diblock copolymers for self-assembly is reviewed and the development of the ZnO nanoclusters within two different copolymer systems -- poly styrene-acrylic acid and poly styrene methacrylic acid, with block repeat unit ratios of 159/63 and 318/78, respectively, are reported. Different copolymer systems were used to observe the size dependence of the nanoclusters on the molecular block lengths of the copolymers. The synthesis scheme of the nanoclusters relied on the thermodynamically driven microphase separation of the diblock copolymers in solid phase due to immiscibility of the covalently bonded polymers in the copolymer. The scheme involved the formation of ZnCl₂ nanoclusters on Si and SiO₂ surfaces by doping of the copolymer systems with ZnCl₂ in liquid phase at room temperature and application of the doped solution onto the surfaces by spin-on casting, followed by conversion to ZnO nanoclusters using a new dry technique of ozone exposure. The dry method effectively converted ZnCl₂, without any loss of ZnO during conversion and with better conversion rate than the wet chemical method developed previously. XPS verified the conversion to ZnO and AFM showed the spherical morphology of the nanoclusters. Technique was developed using RIE for obtaining stand-alone nanoclusters on both surfaces.

Photoluminescence (PL) and electron paramagnetic resonance (EPR) are high-resolution techniques used to study donors and acceptors in optoelectronic materials. Zinc oxide (ZnO), with a room-temperature band gap of 3.37 eV, has significant potential for applications ranging from light emission to sensors and detectors. The low-temperature near-edge PL of ZnO is rich in detail, with sharp-line emissions from bound excitons related to various donors and acceptors. Strong phonon couplings in this material produce a series of LO and TO phonon sidebands at slightly lower energies. Donor-acceptor pair and electron-acceptor recombinations related to nitrogen (E_A = 209 meV) and lithium (E_A ~ 0.6 eV) are detected. Copper and iron impurities show characteristic luminescence spectra in the visible. Thermal anneals in air induce significant changes in the PL spectra. Complementary information can be obtained from EPR and photoinduced EPR experiments performed at low temperature. In ZnO, EPR spectra have been observed from neutral nitrogen acceptors, neutral copper acceptors, neutral lithium acceptors, hydrogenic shallow donors, as well as deeper donors such as nickel and iron. In previous work, EPR spectra have been assigned to singly ionized oxygen vacancies and singly ionized zinc vacancies in electron-irradiated crystals.

The incorporation and electrical activity of nitrogen as an acceptor in ZnO has been investigated. Low temperature Metalorganic Vapor Phase Epitaxy (MOVPE) growth, using diallylamine as nitrogen precursor, yields to incorporation of nitrogen in the range 10¹⁶-10²¹ cm^-3. The electrical activity of nitrogen is demonstrated through the increased compensation of the natural donors with doping level. Close Space Vapor transport (CSVT) and Chemical Vapor Transport (CVT) are found to be less efficient for nitrogen incorporation. This suggests that the use of high temperature growth is a limiting factor for nitrogen incorporation in ZnO. Ex-situ techniques have been tried for both electrical activation and nitrogen incorporation in ZnO. High pressure annealing under oxygen pressure shows a conversion to p-type on nitrogen doped samples grown by MOVPE. Finally, diffusion of nitrogen was carried out on undoped MOVPE layers under high pressure conditions stemming from the decomposition of NH₄NO₃. Conversion to p-type conductivity was observed in a systematic way with measured hole concentrations up to 6.5.10¹⁷ cm^-3. These results suggest that ex-situ treatment can be a practical way to realize p-type ZnO layers.

High temperature Hall effect and resistivity measurements have been made on undoped, high purity semi-insulating (HPSI) 4H SiC samples. Both physical vapor transport and high temperature chemical vapor deposition grown samples have been investigated. Resistivity measurements before and after annealing at temperatures up to 1800°C are also reported. Hall and resistivity results are compared with low temperature photoluminescence results. The thermal activation energies for HPSI material taken from temperature dependent resistivity measurements varied from 0.9 to 1.5 eV. Hall effect measurements were made on several HPSI. In all cases the material was found to be n-type and the measured carrier concentration activation energies agreed within a few tens of percent with the resistivity activation energies. Mixed conduction analysis of the data suggests that the hole concentration was negligible in all of the samples studied. This suggests that the defects responsible for the semi-insulating properties have deep levels located in the upper half of the bandgap.

The spin state of holes bound to Mn acceptors in GaMnAs is investigated by optical spectroscopy. Concentrations of Mn from 10¹⁷ to 10¹⁹ cm^-3 were studied as a function of magnetic field and temperature. The photoluminescence from recombination of electrons with holes bound in the Mn-acceptor complex (MAC) displays multiple spectral peaks. The circular polarization of these peaks increases with increasing magnetic field and saturates at ρ ≈ 1/3. This value of polarization is expected from modeling the addition of spin angular momentum and interband optical transition matrix elements.

The recent advances in the experimental work on the Type II InAs/GaSb superlattices necessitate a modeling that can handle arbitrary layer thickness as well as different types of interfaces in order to guide the superlattice design. The empirical tight-binding method (ETBM) is a very good candidate since it builds up the Hamiltonian atom by atom. There has been a lot of research work on the modeling of Type II InAs/GaSb superlattices using the ETBM. However, different groups generate very different accuracy comparing with experimental results. We have recently identified two major aspects in the modeling: the antimony segregation and the interface effects. These two aspects turned out to be of crucial importance governing the superlattice properties, especially the bandgap. We build the superlattice Hamiltonian using antimony segregated atomic profile taking into account the interface. Our calculations agree with our experimental results within growth uncertainties. In addition we introduced the concept of Ga_xIn_1-x type interface engineering, which will add another design freedom especially in the mid-wavelength infrared range (3~7 μm) in order to reduce the lattice mismatch.

The nonlinear optical response for index-matched, non-absorbing immiscible phases (liquid-solid, liquid-liquid, solid-solid) has been determined by means of open aperture z-scan measurements. In mixtures where one constituent shows a relatively high optical nonlinearity, rapid and reversible transformation to a light-scattering state is observed under conditions where a critical incident light fluence is exceeded. This passive broadband response is induced by a transient change in the dispersive part of the refractive index, and is based upon the Christiansen-Shelyubskii filter that at one time was used as a means to monitor the temperature of glass melts. Modeling studies are used to simulate scattering intensities in such textured composites as a function of composition, microstructure, and constituent optical properties. Results provide a rational approach to the selection of materials for use in these limiters. Challenges to preparing dispersed phase mixtures and their response to 532 nm nanosecond pulsed laser irradiation are described.

Hybrid photonic crystal (PhC) and conventional waveguide (CWG) structures have been proposed to achieve ultracompact waveguide bends and splitters with very high efficiency (>99.0%). Such elements are enablers to realize large scale planar lightwave circuits (PLCs) with low index contrast waveguide materials such as silica and polymers. In this paper, we first discuss high efficiency 90 degree bends and splitters and then show how these can be used to create compact ring resonators. These in turn can be used as building blocks for add/drop filters, band pass filters, wavelength division multi-/demultiplexers, and all optical switches.

I review light production from quantum dot nanocrystals embedded in a semiconducting polymer. Integrable optoelectronics is facilitated in this processible material system - one which may conveniently be combined with silicon electronics, passive optics, and RF platforms. Synthetic conditions determine nanocrystal diameter and thereby tune, through the quantum size effect, the spectrum of optical emissions from the quantum dots. We show that it is possible to span across and beyond the 1.3-1.6 μm spectrum of optical communications. Nonradiative recombination from the nanocrystals’ surface is addressed by choosing stabilizing, passivating organic ligands which nevertheless permit energy transfer from polymer to nanocrystals.

A multi-channel free-space micro-optical module for dense MCM-level optical interconnections has been designed and fabricated. Extensive modeling proves that the module is scalable with a potential for multi-Tb/s.cm2 aggregate bit rate capacity while alignment and fabrication tolerances are compatible with present-day mass replication techniques. The micro-optical module is an assembly of refractive lenslet-arrays and a high-quality micro-prism. Both components are prototyped using deep lithography with protons and are monolithically integrated using vacuum casting replication technique. The resulting 16-channel high optical-grade plastic module shows optical transfer efficiencies of 46% and inter-channel cross talks as low as -22 dB, sufficient to establish workable multi-channel MCM-level interconnections. This micro-optical module was used in a feasibility demonstrator to establish intra-chip optical interconnections on a 0.6μm CMOS opto-electronic field programmable gate array. This opto-electronic chip combines fully functional digital logic, driver and receiver circuitry and flip-chipped VCSEL and detector arrays. With this test-vehicle multichannel on-chip data-communication has been achieved for the first time to our knowledge. The bit rate per channel was limited to 10Mb/s because of the limited speed of the chip tester.

This paper summarizes experiments using a modelocked laser to produce a fast-rising, low-jitter electrical signal for clocking CMOS circuits. A simple integrating optical-to-electrical conversion scheme using two photodiodes is used to minimize jitter, area and electrical power consumption. This scheme is called receiver-less because there is no receiver to introduce unwanted skew, jitter and electrical power consumption. Receiver-less optical clock injection to a single CMOS circuit with < 6 ps rms jitter has been demonstrated. To scale the receiver-less concept low capacitance detectors are necessary. Transit-time limited rise times from low capacitance monolithic silicon CMOS photo-detectors have been simulated using 425 nm short pulses. The utility of this 'receiver-less' scheme is examined for larger clock distribution networks and varying photodiode capacitances.

Semiconductor lasers can be used simultaneously as optical sources and optical sensors, as they are extremely sensitive to a small amount of coherent optical feedback. We present a survey on experimental results on optical feedback in semiconductor lasers and on different approaches to describe its effect on the laser properties. We show that for long and moderate long external cavities (hundreds of meters down to centimeters) the Lang-Kobayashi delay model, multiple delays and multimode delay rate equation models are in very good agreement with experiments on edge emitting lasers (EELs) and vertical-cavity surface-emitting lasers (VCSELs). We present examples of frequency and polarization mode hopping, periodic and quasiperiodic behavior, different routes to chaos, regular pulse packages, high frequency pulsations and stochastic and coherence resonance, that all have been experimentally and numerically demonstrated. Suitable models for studying laser diodes subject to optical feedback from extremely short external cavity, or ESEC (of the order of the wavelength) are the composite cavity and the multimode butt coupling models that either consider the field amplitudes after multiple reflections in the external cavity (EC) as stationary or treat the whole compound cavity at once. Numerical and experimental studies showed that optical feedback in ESEC leads to detectable change of the laser output power or the voltage drop over the laser for a small change of either the phase or the optical feedback strength. As an example, we discuss experimental and numerical results on spectral and polarization properties of VCSELs subject of insensitive optical feedback from ESEC. The wavelength and the current of polarization switching between the two linearly polarized fundamental modes of the VCSEL are periodically modulated with the external cavity length. High contrast polarization switching is thus possible for quarter-wavelength change of external cavity length. In the case of EEL we experimentally demonstrate that with changing the length of the EC the emitted power, the wavelength and the laser voltage are periodically modulated. We explain the longitudinal mode-hopping between the neighboring composite cavity modes followed by large jumps at the external cavity frequency splitting as a result of the spectral modulation of the effective losses of the composite cavity system.

Optical absorption and transient photobleaching in solutions of surfactant encapsulated and DNA wrapped single-walled carbon nanotubes (SWNTs) are studied. Optical transitions between van Hove singularities are red shifted in solutions of DNA wrapped SWNTs compared with transitions in solutions of sodium dodecyl sulfate (SDS) encapsulated SWNTs. This red shift may be due to changes in the local surrounding dielectric constant and corresponding changes in charge screening. Transient photobleaching at the E₁₁ transition of semiconducting SWNTs is observed in both solutions of SDS encapsulated SWNTs and DNA wrapped SWNTs in response to optical excitation at corresponding E₂₂ transitions, and the saturation of photobleaching at high excitation intensities greater than 500 W cm^-2 is studied. It is found that the photobleaching intensity does not saturate as significantly in solutions of DNA wrapped SWNTs as in solutions of SDS isolated SWNTs. Lastly, using degenerate, delayed pump-probe characterization, the temporal relaxation of excited charge carriers is investigated. Measured decays are characterized by both fast and slow processes. The slow decay time constant across the band gap of semiconducting SWNTs is fit to 120 ps for SDS encapsulated SWNTs and 73 ps for DNA wrapped SWNTs.

The potential of high power extraction from AlGaN-based ultraviolet light emitting diodes (UV-LEDs) is described. Improvements of UV-LEDs are shortly introduced from the viewpoints of nitride epitaxial growth, heterostructure optical characteristics based on the internal polarization field, and p-n junction design. The UV light extraction enhancement by utilizing the GaN-free transparent UV-LED structure and highly efficient UV-LEDs fabricated by introducing a high-quality AlN template on sapphire substrate are described. The maximum output powers are 8.6 mW and 5.5 mW at an injection current of less than 150 mA, at the emission wavelength of 350 nm and 340 nm, respectively. The highest external quantum efficiencies are 2.2 and 1.7%, respectively. The application to white lighting and the potential of the high-flux UV-extraction utilizing bulk AlN substrate are also investigated.

We demonstrate high power AlGaN based ultraviolet light-emitting diodes (UV LEDs) with an emission wavelength of 280 nm using an asymmetric single quantum well active layer configuration on top of a high-quality AlGaN/AlN template layer grown by metalorganic chemical vapor deposition (MOCVD). An output power of 1.8 mW at a pulsed current of 400 mA was achieved for a single 300 μm × 300 μm diode. This device reached a high peak external quantum efficiency of 0.24% at 40 mA. An array of four diodes produced 6.5 mW at 880 mA of pulsed current. We also demonstrate high output power operation of AlGaN-based UV LEDs at a short wavelength of 265 nm. An output power of 2.4 mW at a pulsed current of 360 mA was achieved for a single diode. A packaged array of four diodes produced 5.3 mW at 700 mA of pulsed current. The DC output power is 170 μW at 250 mA.

We fabricated high power ultraviolet (UV) light emitting diodes (LEDs), whose emission wavelength is around 365 nm. We found that, in order to improve the external quantum efficiency (η_ex) of UV LEDs, it is very important to reduce the optical self-absorption and the threading dislocation density (TDD) of epi-layers. Therefore, at first, UV LEDs epi-layers were grown on high-quality GaN templates (TDD = 2x 10⁸/cm²) with sapphire substrates, and then the GaN templates and the sapphire substrates were removed by using laser-induced lift-off and polishing techniques. As a result, we obtained the low self-absorption and low TDD UV LEDs. When this UV LED was operated at a forward-bias pulsed current of 500 mA at room temperature (RT), the peak wavelength, the output power (P_o), the forward voltage (V_f) and the η_ex were 365 nm, 410 mW, 5.3 V, 24%, respectively. Moreover, at a forward-bias direct current of 500 mA at RT, P_o, V_f and η_ex were 360 mW, 5.0 V, 21%, respectively.

For the realization of 250-350 nm band deep ultraviolet (UV) emitters using group III-nitride materials, it is required to obtain high-efficiency UV emission and hole conductivity for wide-bandgap (In)AlGaN. For achieving high-efficiency deep UV emission, it is quite effective to use In segregation effect which has been already used for InGaN blue emitting devices. We have demonstrated high-efficiency UV emission by introducing several percent of In into AlGaN in the wavelength range of 300-360 nm at room temperature with an In segregation effect. The emission fluctuation in the submicron region due to In segregation was clearly observed for the quaternary InAlGaN epitaxial layers. An internal quantum efficiency as high as 15% was estimated from quaternary InAlGaN based single quantum well (SQW) at around 350 nm at room temperature. Such a high efficiency UV emission can be obtained even on high threading dislocation density buffers. Also, hole conductivity was obtained for high Al content (>53%) Mg-doped AlGaN by using alternative gas flow growth process in metal-organic vapor phase epitaxy (MOVPE). Using these techniques we fabricated 310 nm band deep UV light-emitting diodes (LEDs) with quaternary In_xAl_yGa_1-x-yN active region. We achieved output power of 0.4 mW for a 308 nm LED and 0.8 mW for a 314 nm LED under room temperature pulsed operation.

We report AlGaN-based back-illuminated solar-blind p-i-n photodetectors with a record peak responsivity of 150 mA/W at 280 nm, corresponding to a high external quantum efficiency of 68%, increasing to 74% under 5 volts reverse bias. Through optimization of the p-AlGaN layer, we were able to remove the out-of-band negative photoresponse originating from the Schottky-like p-type metal contact, and hence significantly improve the degree of solar-blindness. We attribute the high efficiency of these devices to the use of very-high quality AlN and Al_0.87Ga_0.13N/AlN superlattice material, a highly conductive Si-In co-doped Al_0.5Ga_0.5N layer, and the elimination of the negative photoresponse through improvement of the p-type AlGaN.

Spin-angular momentum transfer (or spin-transfer for short) describes the angular momentum exchange between a spin-polarized current and a ferromagnetic conductor. When the conductor dimensions are reduced to around 100nm or below, the spin-angular momentum transfer effect becomes significant compared to the current-induced magnetic field. This paper describes some recent spin-transfer experimental findings in sub-100nm current-perpendicular spin-valve systems consisting of Co-Cu-Co nanopillars. The spin-transfer current is shown to cause a magnetic reversal of the thinner magnetic layer inside the nanopillar. The reversal is experimentally shown to reach sub-nanosecond speed. The effect of spin-transfer is best understood in terms of its modification to the effective Landau-Lifshiz-Gilbert damping coefficient, either increasing or decreasing its value depending on the direction and magnitude of the spin-polarized current. For sufficiently large spin-current, the net damping coefficient may change sign, resulting in amplification of magnetic precession, leading to a magnetic reversal. At finite temperatures, the effect of spin-transfer is to either increase or decrease the thermal agitation of the nanomagnet. A quantitative model is developed that adequately describes the finite temperature experimental observations of the dynamic spin-transfer effect.

In the model case of a III-V semiconductor, we calculate the evanescent waves and the associated energies throughout the forbidden band gap, taking into account the electron spin. Starting with simple pictures, step by step we include more bands and, finally, the calculation is performed using a k.p technique within a 30-band model. We show that no evanescent state associated with a purely imaginary wave vector may exist in some simple directions. In general, the evanescent wave functions have to involve complex wave vectors associating non-collinear propagation and attenuation directions. Such waves only exist in limited wave-vector and energy domains and these properties have deep consequences on tunneling phenomena.

Evidence abounds that we are reaching the carrying capacity of the earth -- engaging in deficit spending. The amount of crops, animals, and other biomatter we extract from the earth each year exceeds wth the earth can replace by an estimated 20%. Additionally, signs of climate change are precursors of things to come. Global industrialization and the new technologies of the 20th century have helped to stretch the capacities of our finite natural system to precarious levels. Taken together, this evidence reflects a fraying web of life. Sustainable development and natural capitalism work to reverse these trends, however, we are often still wedded to the notion that environmental conservation and economic development are the 'players' in a zero-sum game. Engineering and its technological derivatives can also help remedy the problem. The well being of future generations will depend to a large extent on how we educate our future engineers. These engineers will be a new breed -- developing and using sustainable technology, benign manufacturing processes and an expanded array of environmental assessment tools that will simultaneously support and maintain healthy economies and a healthy environment. The importance of environment and sustainable development cosiderations, the need for their widespread inclusion in engineering education, the impediments to change, and the important role played by ABET will be presented.