Lasers with ever increasing high powers, CW as well as pulsed, have been targets for research and developments from the very invention of the laser. Availability of high powers facilitate many practical applications in industry, medicine and research in quantum electronics. This presentation will summarize some of the key advances that have occurred since early 1960's and provide a guide for what can be expected in the future.

We report substantially improved performance of high power quantum cascade lasers by utilizing epi-side down mounting that provides superior heat dissipation properties. We have obtained CW power output of 450 mW at 20°C from mid-IR QCLs. The improved thermal management achieved with epi-side down mounting has also permitted us to carry out initial lifetime tests on the mid-IR QCLs. No degradation of power output is seen even after over 300 hours of CW operation at 25°C with power output in excess of 300 mW. We believe these improvements should permit incorporation of mid-IR QCLs in reliable instrumentation.

Over the past several years, our group has endeavored to develop high power quantum cascade lasers for a variety of remote and high sensitivity infrared applications. The systematic optimization of laser performance has allowed for demonstration of high power, continuous-wave quantum cascade lasers operating above room temperature. Since 2002, the power levels for individual devices have jumped from <20 mW to >600 mW. Expanding on this development, we have able to demonstrate continuous wave operation at many wavelengths throughout the mid- and far-infrared spectral range, and have now achieved >100 mW output in the 4.0<λ<9.5 μm range.

Whereas high-power operation (> 1 W of cw output power at 200 K) has been demonstrated for quantum cascade lasers emitting at λ = 4.7-6.2 μm, those devices generally exhibited multiple longitudinal modes. Recently, a distributed-feedback quantum cascade laser operating in a single spectral mode at λ = 4.8 μm and at temperatures up to 333 K has been reported. In the present work, we provide detailed measurements and modeling of its performance characteristics. The sidemode suppression ratio exceeds 25 dB, and the emission remains robustly single-mode at all currents and temperatures tested. Cw output powers of 99 mW at 298 K and 357 mW at 200 K are obtained at currents well below the thermal rollover point. The slope efficiency and subthreshold amplified spontaneous emission spectra are shown to be consistent with a coupling coefficient of no more than κL ≈ 4-5, which is substantially lower than the estimate of 9 based on the nominal grating fabrication parameters.

We present an effective approach to calculating the low-frequency part of the spectrum of uniaxially patterned periodic structures. In this approach we ignore to zeroth-order the Bragg scattering by crystalline planes but include local field effects in first order perturbation theory. Bragg reflections are shown to be important only near points of symmetry-induced spectral degeneracy, where they can be taken into account by the degenerate perturbation theory. We apply this approach to waveguiding by thin patterned slabs embedded in a homogeneous medium. This results in an effective medium approximation, similar to the Maxwell Garnet theory but modified for the local field corrections specific to 2D geometry. Slab spectra are well described by a single frequency-independent parameter, which we call the guiding power. Simple analytic formulae are presented for both TM and TE polarizations. Comparing these formulae with similar expressions for homogeneous uniaxial slabs of same thickness, we derive the principal values of the effective homogeneous permittivity that provides identical waveguiding. We also discuss the extinction of waves due to the Rayleigh-like scattering on lattice imperfections in the slab. The TE waves that are normally better confined are scattered out more effciently, in part because of the higher scattering cross-section and in part because the better confinement leads to higher exposure of TE waves to lattice imperfections in the slab.

Subwavelength diffractive features etched into a substrate lead to form birefringence that can be utilized to produce polarization sensitive elements such as waveplates. Using etched features allows for the development of pixilated devices to be used in conjunction with focal plane arrays in polarimetric imaging systems. Typically, the main drawback from using diffractive devices is their high sensitivity to wavelength. Taking advantage of the dispersion of the form birefringence, diffractive waveplates with good achromatic characteristics can be designed. We will report on diffractive waveplates designed for minimal phase retardation error across the 2-5 micron spectral regime. The required fabrication processes of the sub-wavelength feature sizes will be discussed as well as the achromatic performance and transmission efficiency of final devices. Previous work in this area has produced good results over a subset of this wavelength band, but designing for this extended band is particularly challenging. In addition, the effect of the finite size of the apertures of the pixilated devices is of particular interest since they are designed to be used in conjunction with a detector array. The influence of small aperture sizes will also be investigated.

A pulsed distributed feedback quantum cascade laser operating near 970 cm^-1 (10.3 μm) was coupled with the technique of cavity ring-down spectroscopy, as described here for the first time. The newly constructed set-up was tested by recording three relatively weak rotational lines of the 10⁰0→00⁰1 vibrational band of CO₂ in the range from 966.75 cm^-1 to 971.5 cm^-1. The CO₂ lines were recorded by measuring the decay time of a CO₂ - N₂ mixture flowing through an open sample tube placed between the cavity ring-down mirrors. The quantum cascade laser frequency was tuned at a rate of ~ 0.071 cm^-1/K by changing the heat sink temperature in the range between -20 and 50 °C. The first results demonstrated the applicability and high sensitivity of the cavity ring-down spectroscopy - pulsed quantum cascade laser combination and encouraged us to extend our research to the study and detection of ammonia. We demonstrated that a detection limit of ammonia of ~ 25 ppbv can be attained with the current set-up. Basic instrument performance and optimization of the experimental parameters for sensitivity improvement are discussed.

In this paper we present the development and demonstration of multi-watts highbrightness vertical-external-cavity surface-emitting lasers (VECSELs). Over 10 W TEM₀₀ continuous-wave (CW) output power with high efficiency is demonstrated. Tunable multi-watts VECSELs with over 20 nm tuning range and narrow linewidth are achieved. Potential applications of tunable VECSELs are introduced.

High-speed and high-performance optical phase and amplitude modulators are critical components of many photonic systems. Semiconductor-based modulators are very attractive, since they can be monolithically integrated with other semiconductor devices. Unfortunately, the commonly used modulators based on square quantum wells have inherent properties that limit their modulation performance. We present a new class of quantum wells called "stepped quantum wells" (SQW) with extra degrees of freedom that can be used to design high performance optical modulators. We demonstrated SQW phase modulators with nearly one order of magnitude higher efficiency than their counterparts. Also, linearized modulators based on SQW with more than two orders of magnitude higher linearity than the existing semiconductor modulators are presented. Finally, high-performance surface-normal modulators based on SQWs with nearly two times better efficiency and 7 dB higher extinction ratio compared with the conventional devices with rectangular and coupled-quantum well active layers are demonstrated.

Laser diodes are not normally able to cut paper, since plain paper does not absorb light in the visible and in the Near Infrared. However, it is possible to make paper locally absorbing to the Near Infrared laser light by ink-jetting an ink formulated from Near Infrared absorbing dyes. Different inks are found suitable for the ink-jetting process using commercial printers. The absorbing characteristics of inked paper are reported and discussed. Absorption characteristics are checked to allow laser cutting using a 1 W diode. Several applications of this technology are presented and discussed, with cutting speeds up to several tens of meters per minutes.

A brief review is given about recent advances of our research group related to nanostructured semiconductors for optoelectronic applications. Semiconductor nanostructures were realised by mainly two techniques, i.e., direct patterning by lithography and etching as well as by utilizing self-organisation effects during epitaxial growth processes. By a few examples the progress is highlighted, e.g., 915 nm quantum-dot lasers for uncooled high power pump modules, ultra-broad bandwidth 1.55 μm quantum-dash lasers, ultra-short cavity quantum cascade lasers, and high-Q quantum dot microcavities as base elements for single photon emission.

Self-assembled GaN quantum dots are characterized using Raman techniques. The electrical and optical properties of these GaN quantum dots are modeled in light of optoelectronic applications. Strain-induced changes in the phononic properties of these nanostructures are modeled and the strain-induced frequency shifts are compared with Raman measurements. Acoustic phonons in colloidal GaN quantum dots are modeled using a quantized elastic continuum model. Shifts observed in the Raman signatures for different excitation wavelengths provide evidence the Raman signatures of GaN quantum dots are observed.

GaN nanotubular material is fabricated with aluminum oxide membrane in MOCVD. SEM, XRD, TEM and PL are employed to characterize the fabricated GaN nanotubular material. An aluminum oxide membrane with ordered nano holes is used as template. Gallium nitride is deposited at the inner wall of the nano holes in aluminum oxide template, and the nanotubular material with high aspect ratio is synthesized using the precursors of TMG and ammonia gas. Optimal synthesis condition in MOCVD is obtained successfully for the gallium nitride nanotubular material in this research. The diameter of GaN nanotube fabricated is approximately 200 ~ 250 nm and the wall thickness is about 40 ~ 50 nm. GaN nanotubular material consists of numerous fine GaN particulates with sizes ranging 15 to 30 nm. The composition of gallium nitride is confirmed to be stoichiometrically 1:1 for Ga and N by EDS. XRD and TEM analyses indicate that grains in GaN nanotubular material have nano-crystalline structure. No blue shift is found in the PL spectrum on the GaN nanotubular material fabricated in aluminum oxide template.

A variety of colloidal semiconductor quantum dots and related quantum-wire structures are characterized using absorption and photoluminescence measurements. The electronic properties of these structures are modeled and compared with experiment. The characterization and application of ensembles of colloidal quantum dots with molecular interconnects are considered. The chemically-directed assembly of ensembles of colloidal quantum dots with biomolecular interconnects is demonstrated with quantum dot densities in excess of 10⁺¹⁷ cm^-3. Non-charge transfer processes for switching based on dipole-dipole interactions - Forester interactions - are examined for colloidal quantum dots linked with biomolecules. Charge transport in biomolecules is studied using indirect-bandgap colloidal nanocrystals linked with biomolecules.

Here we report our recent results of InAs quantum dots grown on InP substrate by low-pressure metalorganic chemical vapor deposition (MOCVD) for the application of quantum dot infrared photodetector (QDIP). We have previously demonstrated the first InP-based QDIP with a peak detection wavelength at 6.4 μm and a detectivity of 10¹⁰cmHz^1/2/W at 77K. Here we show our recent work toward shifting the detection wavelength to the 3-5 μm middlewavelength infrared (MWIR) range. The dependence of the quantum dot on the growth conditions is studied by atomic force microscopy, photoluminescence and Fourier transform infrared spectroscopy. The device results from the MWIR InAs/InP QDIPs are discussed. Right now, the performance of the QDIPs is still far below the predicted potential, and one of the reasons is the low quantum efficiency. Possible ways to increase the quantum efficiency of QDIPs are discussed.

Quantum-dot infrared photodetectors (QDIPs) have recently been considered as strong candidates for numerous applications such as night vision, space communication, gas analysis and medical diagnosis involving middle and long wavelength infrared (MWIR and LWIR respectively) operation. This is due to their unique properties arising from their 3-dimensional confinement potential that provides a discrete density of states. They are expected to outperform quantum-well infrared photodetectors (QWIPs) as a consequence of their natural sensitivity to normal incident radiation, their higher responsivity and their higher-temperature operation. So far, most of the QDIPs reported in the literature were based on the InAs/GaAs system and were grown by molecular beam epitaxy (MBE). Here, we report on the growth of a high detectivity InGaAs/InGaP QDIP grown on a GaAs substrate using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The peak photoresponse was around 4.7μm and the peak responsivity had a value of 1.2 A/W at a peak detection bias of -0.9V at 77K. A noise current of 3.3×10^-14 A at - 0.9V bias yielded a specific peak detectivity of 1.2×10¹²cmHz^1/2/W at 77K. Peak responsivity and specific peak detectivity of 190.5mA/W and 8.3×10¹⁰ cmHz^1/2/W were still measured at 120K for a peak detection bias of -0.6V. A BLIP temperature of 200K was determined with a 45° field of view and a 300K background.

Charge carrier transport mechanism in barrier "In-macroporous silicon" structures has been investigated. Currentvoltage, capacitance-voltage, photoelectrical and noise characteristics were analyzed comparatively in structures of macroporous and single-crystal silicon. There has been designed manufacture technology of ohmic and barrier contacts on 2D macroporous silicon as well as single-crystal silicon in the same technological cycle. The contacts were found to exhibit stable characteristics during six month period of time. The saturation of the reverse current at 0.2 ≤ U ≤ 1.0 V was observed at high temperatures. The carrier transport mechanism in the investigated structures are determined by thermal activation mechanisms at room temperature and tunneling of carriers through the transient region at temperatures T ≤ 180 K. Capacitance-voltage characteristics are similar to those observed in the metal-oxide-semiconductor structures and are included capacitance of the oxide layer and the depletion region. The presence of the transient region between metal and silicon was confirmed by the photoresponse spectra of "Inmacroporous Si" structures contained two pronounced peaks at the wavelengths 0.56 and 1.1 μm. The longwavelength peak was observed for In contacts on single n-Si crystal prepared by the same method.

The Type II broken band-gap alignment in semiconductor structures wherein the conduction band minimum is in one semiconductor (e.g., InAs) and the valence band maximum is in another (e.g., GaInSb) offers certain unique advantages which can be utilized to realize band-gap engineered novel quantum electro-optic devices such as lasers and detectors. The advantages of the type II structures include reduced Auger recombination, extending the effective band-gap energy of materials wherein type I band-gap alignment would give rise to difficulties such as miscibility gap. In this paper we describe the work carried out at the Army Research Laboratory on type II semiconductor quantum electro-optic devices such as IR lasers and detectors operating in the 3-12 μm range. Specifically we will cover the progress made in GaSb based type II strained layer superlattice IR detectors and Interband Cascade IR Lasers. We will also present our recent work in self-assembled quantum dots which have type II band-gap alignment with the matrix material in which the dots are embedded.

Advances in basic infrared science and developments in pertinent technology applications have led to mature designs being incorporated in civil as well as military area defense systems. Military systems include both tactical and strategic, and civil area defense includes homeland security. Technical challenges arise in applying infrared sensor technology to detect and track targets for space and missile defense. Infrared sensors are valuable due to their passive capability, lower mass and power consumption, and their usefulness in all phases of missile defense engagements. Nanotechnology holds significant promise in the near future by offering unique material and physical properties to infrared components. This technology is rapidly developing. This presentation will review the current IR sensor technology, its applications, and future developments that will have an influence in military and civil defense applications.

Recent improvements in material quality and design have led to large improvements in the quantum efficiency (QE) of long-wave infrared (LWIR) photodiodes based on W-structured type-II superlattices (WSL), which now have achieved external QE of up to 35% on an 11.3 μm cutoff photodiode operating at 80K. While single band and dual band WSLs have been demonstrated with cutoff wavelengths out to 17 μm, the initial devices also showed significant losses of photo-excited carriers resulting in QE levels of ≤ 10%. Here we describe recent results in which these losses have been dramatically reduced by modifying the WSL barrier layers to increase the mini-band width and improve the material properties. An additional 35-55% increase in QE also resulted from the use of semitransparent Te doped n-GaSb substrates that allowed for IR reflections off the backside from the Au plated chip carrier. A series of PIN photodiodes using the improved WSL, with intrinsic regions from 1 to 4 μm thick, were used to study minority carrier transport characteristics in the new structure. As a result of the improved design and material properties, the electron diffusion length in the undoped i-region, as determined from a theoretical fit to the thickness-dependent data, was 3.5 μm, allowing for much higher collection efficiency in PIN photodiodes with intrinsic regions up to 4 μm thick.

The authors report on recent advances in the development of mid-, long-, and very long-wavelength infrared (MWIR, LWIR, and VLWIR) type-II InAs/GaSb superlattice infrared photodiodes. The residual carrier background of binary type-II InAs/GaSb superlattice photodiodes of cut-off wavelengths around 5 μm has been studied in the temperature range between 10 and 200 K. A four-point, capacitance-voltage technique on mid-wavelength and long-wavelength type-II InAs/GaSb superlattice infrared photodiodes reveal residual background concentrations around 5 × 10¹⁴ cm^-3. Additionally, recent progress towards LWIR photodiodes for focal plane array imaging applications is presented. Single element detectors with a cut-off wavelength, λ_c,50%, of 10.2 μm demonstrated detectivities of approximately 1 × 10¹¹ cmHz^1/2W^-1 and quantum efficiencies of 32% at the peak responsivity wavelength of around 7.9 μm. Furthermore, high-performance VLWIR single element photodiodes are discussed. The silicon dioxide passivation of VLWIR photodiodes is also presented, which resulted in an approximately 5 times increase of the sidewall resistivity. The latest developments in this material system lend further support for its use as a high-performance alternative for infrared optical systems compared to the current state-of-the-art imaging systems, especially those approaching the long-wavelength and very-long-wavelength infrared.

InAs/GaSb superlattices are a promising technology for long-wave and very-long-wave infrared photodetectors. Present detectors at these wavelengths are mostly built using bulk HgCdTe (MCT) alloys, where the bandgap is controlled by the mercury-cadmium ratio. In contrast, InAs/GaSb heterostructures control the bandgap by engineering the widths of the layers making up the superlattice. This approach is expected to have important advantages over MCT, notably the tighter control of bandgap uniformity across a sample and the suppression of Auger recombination. InAs/GaSb superlattices have a potential advantage in temperature of operation, uniformity and yield. To realize their inherent potential, however, superlattice materials with low defect density and improved device characteristics must be demonstrated. Here, we report on the growth and characterization of a 9.7 μm cutoff wavelength InAs/GaSb superlattice detector, with a resistance-area product of R₀A = 11 Ωcm² at 78 K, and an 8.5 μm cutoff diode with a resistance-area product of R₀A = 160 Ωcm² at 78 K. The devices are p-i-n diodes with a relatively thin intrinsic region of depth 0.5 μm as the active absorbing region. The measured external quantum efficiencies of 7.1% and 5.4 % at 7.9 μm are not yet large enough to challenge the incumbent MCT technology, but suggest scaling the intrinsic region could be a way forward to potentially useful detectors.

The optimal performance of HgTe/CdTe superlattice-based LWIR (8-12 μm cutoff wavelengths) and VLWIR (greater than 12um cutoff wavelength) photovoltaic detectors is assessed theoretically. The electronic band structures and optical absorption spectra are computed with a fourteen-band restricted-basis envelope function Hamiltonian. Auger and radiative lifetimes are computed with these accurate band structures. Vertical carrier mobilities are obtained from a Monte Carlo transport methodology. Photon detectors are modeled by solving current continuity and Poisson's equations. Predictions are compared with those for HgCdTe-alloy based detectors. We find that the superlattice-based two-color detector promise sharp rises in quantum efficiencies near the cutoff wavelengths, reflecting the quasi-2-dimensional nature of their density of states.

An uncooled infrared focal plane array (IR FPA) is a MEMS device that integrates an array of tiny thermal infrared detector pixels. An SOI diode uncooled IR FPA is a type that uses freestanding single-crystal diodes as temperature sensors and has various advantages over the other MEMS-based uncooled IR FPAs. Since the first demonstration of an SOI diode uncooled IR FPA in 1999, the pixel structure has been improved by developing sophisticated MEMS processes. The most advanced pixel has a three-level structure that has an independent metal reflector for interference infrared absorption between the temperature sensor (bottom level) and the infrared-absorbing thin metal film (top level). This structure makes it possible to design pixels with lower thermal conductance by allocating more area for thermal isolation without reducing infrared absorption. The new MEMS process for the three-level structure includes a XeF₂ dry bulk silicon etching process and a double organic sacrificial layer surface micromachining process. Employing advanced MEMS technology, we have developed a 640 x 480-element SOI diode uncooled IR FPA with 25-μm square pixels. The noise equivalent temperature difference of the FPA is 40 mK with f/1.0 optics. This result clearly demonstrates the great potential of the SOI diode uncooled IR FPA for high-end applications. In this paper, we explain the advances and state-of-the-art technology of the SOI diode uncooled IR FPA.

We report on progress in the development of a device fabrication process for type-II strained layer superlattice IR detectors, composed of InAs/GaSb or InAs/GaInSb. Steps of the process include etching the mesas, cleaning up the surface, and applying a surface passivation treatment. Certain etchants have been evaluated and calibrated. The surface has been studied with single wavelength ellipsometry and results have been compared with modeled ellipsometry values, revealing effects of surface residues and surface roughness. An initial investigation of ammonium sulfide treatment for surface passivation has been made. Initial measurements of the IR transmission of the GaSb substrate have also been made to determine how much thinning is needed for back side illuminated operation of the IR detectors.

Spin injection in metallic normal/ferromagnetic junctions is investigated taking into account the anisotropic magnetoresistance occurring in the ferromagnetic layer. On the basis of a generalized two-channel model, it is shown that there is an interface resistance contribution due to anisotropic scattering, besides spin accumulation and giant magnetoresistance. The corresponding expression of the thermoelectric power is derived and compared with the expression accounting for the thermoelectric power produced by the giant magnetoresistance. The results of this study show that, while the giant magnetoresistance and the corresponding thermoelectric power indicate the role of spin-flip scattering, the observed anisotropic magneto-thermoelectric power might be the fingerprint of interband s-d relaxation mechanisms.

We present the results of our study on the micro/nano-scale design and fabrication of optical waveguide devices, photonic devices and sensors to be integrated in the form of optical printed circuit boards (O-PCBs) for various application. Application-specific O-PCBs are composed of varied forms of optical wires and devices tailored to perform specific functions. In this paper, we present two examples of application specific O-PCB. One is an all-optical wavelength splitting triplexer module that we designed for subscriber network application and the other is a grating array that we designed for temperature-sensor application. The triplexer module consists of an array of cascaded directional couplers to split the wavelengths for passive optical network and signal distribution application and the grating array is designed for wavelength splitting and temperature sensing applications. The advantages of these devices are that they can be readily fabricated out of polymer materials by way of thermal or ultraviolet (UV) embossing (or imprinting) technique. Theoretical calculations provide design rules for these devices. The results suggest that O-PCB can be a viable and useful platform for integration of various photonic devices for sensor application.

Carbon nanotubes (CNTs) exhibit several technologically important characteristics such that metallic nanotubes can carry extremely large current densities; semiconducting nanotubes can be electrically switched on and off as field effect transistors (FETs), and so on CNT FETs with characteristics comparable to or exceeding state of the art Si based transistors have been demonstrated using a conventional FET design with high-κ ¹⁾ and SiO₂ dielectric ²⁾. In addition, CNTs have been successfully demonstrated as biological sensors with high sensitivity. It has been reported that the real time detection of single viruses ³⁾, small molecules ⁴⁾, and proteins ⁵⁾, ⁶⁾ becomes is possible with biosensors that use CNT transistors as the active transducer. For these applications of CNTs, the control of the number of CNT between electrodes is quite important technology. However, it is quite difficult and has not been realized yet. It is therefore, indispensable to control it for the future applications of CNT. In the present study, we have established the new technology to control the number of the CNT one by one during the growth of CNT by monitoring the electrical current between electrodes, which is named as "Digital Growth Process".

We have succeeded in observing the coexistence of the Coulomb charging effect and the coherent transport of the hole in a single-walled carbon nanotube (SWNT) with a length of 4.5 μm at 8.6 K. SWNT channel field-effect transistor (FET) structures were prepared with two different channel lengths of 4.5 and 1.4 μm. The samples showed p-type semiconductor characteristics under large gate and drain biases at 8.6 K. At 8.6 K, on the other hand, single-hole transistor characteristics with different Coulomb charging energies corresponding to the length of the channel were observed in each sample. Drain current peaks with different periods corresponding to the length of the channel were also observed outside of the Coulomb blockade area for the higher drain voltages in each sample. The drain current peaks are attributed to resonant tunneling of the hole through the separation of the quantum energy levels originating from coherent transport of the hole in the entire semiconductive SWNT.

DNA hybridization has sensitively been detected using carbon nanotube field-effect transistors (CNTFETs) in real time. After full-complementary DNA introduction, the source-drain current gradually increased while monitoring in real time. Full-complementary DNA with concentration as low as 1 fmol/L solution could be effectively detected. Our CNTFET-based biochip is a promising candidate for the development of an integrated, high-throughput, multiplexed DNA biosensor for medical, forensic and environmental diagnostics.

We successfully fabricated single electron transistors (SETs) operating at room temperature with carbon nanotube (CNT) channel having different island sizes. The fabrication of the CNT SETs is performed by electrical manipulation using non-contact mode atomic force microscope (AFM). We carried out cutting or nicking of CNTs by applying negative voltage between a metal-coated AFM tip and CNT. A precise control over the CNT dot size was achieved by changing the nicking distance and CNT SETs with a dot size of 15 and 22 nm were fabricated. By changing the size of the dot we could arbitrarily change the operation characteristics of the device where the period of oscillations increases as the dot size decreases.

Controlling spontaneous emission phenomena in semiconductor slabs with a two-dimensional photonic bandgap are discussed. Theoretical simulations predict that the spontaneous emission coupled to the slab modes, which is strongly confined within the slab plane, is inhibited. Simultaneously, the saved energy is redistributed to the spontaneous emission that is coupled to the vertical emission modes. The spontaneous emission control is experimentally demonstrated by measuring time-resolved photoluminescence spectra from GaInAsP quantum-well samples. Our results will open up possibilities for various applications of photonic crystals using spontaneous emission phenomena, including photonics, illuminations, displays, solar cells and even quantum-information systems.

The characteristics of organic photonic devices with various kinds of geometrical nano-structures at the interface between organic materials, and also between the organic layer and metal electrode are investigated. A cutoff frequency of more than 20 MHz was observed for single-layer heterostructure organic photodetector (OPD) by applying a reverse bias electric field under the illumination of the red repetition pulse light. The mixed-layer heterostructure OPD with high photocurrent and high speed photoresponse is suitable for the application of optical link devices. An organic light-emitting diode (OLED) with a partial doping layer at the interface of heterostructure device can be expected to improve the modulation characteristics. The existence of interface between the organic layer and Cs or CsF results in low turn-on voltage for OLEDs. To achieve the efficient electron injection, it is necessary to exist Cs layer just on the organic layer. The efficient electron injection and the low turn-on voltage result from the coexistence of MgAg and CsF at the position of approximately 1 nm from organic layer. The poly(3-hexylthiophene) device with a cathode fabricated from Ag nanoparticles shows a photoresponse and a red emission in the reverse and forward bias regions, respectively. We demonstrated the possibility of polymer OLEDs using a cathode fabricated from Ag nanoparticles by wet processing.

This paper reviews of some of the recent progress made in the development of high quality MgZnO and ZnCdO layers grown epitaxially by RF-plasma molecular beam epitaxy (MBE). We summarize optical and electrical properties of high quality Cd_xZn_1-xO alloys with Cd mole fraction from 0.02 to 0.78 and discuss phase separation phenomenon which may be present in ternary alloys. A single-crystal wurtzite structure of CdZnO alloys for this entire range of compositions was confirmed by X-ray diffraction. Compositional analysis was performed using SIMS and RBS. Strong optical emission in the 380 nm to 574 nm spectral range was achieved at RT from Cd_xZn_1-xO with various compositions, demonstrating a great potential for use in LEDs. Compositional fluctuations in a Cd_0.16Zn_0.84O films were not detected by spatially resolved CL measurements, although intensity fluctuation with features of ~0.5 μm diameter were seen on the intensity maps. Dependence of the fundamental optical band gap on the composition of Cd_xZn_1-xO alloys, band gap bowing, and the possible effect of composition micro-fluctuations in ternary Cd_xZn_1-xO alloys on the optical bandgap is also discussed. Time resolved photoluminescence shows multi-exponential decay with 21 psec. and 49±3 psec. lifetimes, suggesting that composition micro-fluctuations may be present in Cd_0.16Zn_0.84O film. High conductivity and optical transparency of the CdZnO films with high Cd-mole fraction is attractive for making high performance electrodes. We also report on crystallographic and optical properties of CdZnO/ZnO multiple quantum wells (MQW).

Recent progresses in epitaxial growth, fundamental studies of high Al content AlGaN alloys with Si and Mg doping, light polarization properties, and deep UV LEDs combined with microlens or photonic crystal structure to improve light extraction are presented. For Si doped Al_0.7Ga_0.3N, a room temperature n-type resistivity as low as 0.0075 Ω•cm has been obtained. We have also achieved n-AlN with a free electron concentration and mobility of about 1.0 x 10¹⁷cm^-3 and 2 cm²/Vs, respectively. For Mg doped Al_0.7Ga_0.3N, we have obtained a resistivity around 10⁵ Ω cm at room temperature and confirmed p-type conduction at elevated temperatures (> 700 K) with a resistivity of about 40 Ω cm at 800 K. Based on the optimized material growth, 280 nm deep UV LED with forward voltage of 6.7 V, and output power of 0.35 mW has been achieved at 20 mA. To enhance light extraction efficiency, sapphire microlens array was monolithically integrated on flip-chip bonded deep UV LED substrates; a light extraction enhancement of 55% was achieved. To improve the transverse light extraction, photonic crystal structures were incorporated into the devices, and significant light extraction enhancement was achieved.

There is a need for semiconductor based UV photodetectors to support avalanche gain in order to realize better performance and more effectively compete with existing photomultiplier tubes. However, there are numerous technical issues associated with the realization of high-quality solar-blind avalanche photodiodes (APDs). In this paper, APDs operating at 280 nm, within the solar-blind region of the ultraviolet spectrum, are investigated. The devices consist of an Al_0.38Ga_0.62N active region grown atop a high quality AlN template layer designed to allow back illumination of the devices through the sapphire substrate. These devices perform well in the unbiased mode of operation. Under the application of large reverse bias these devices show a soft breakdown starting at relatively low electric fields. The devices achieve a maximum optical gain of ~1000 at a reverse bias of ~90 Volts, which corresponds to an electric field strength of 2.5 MV/cm. The origins of this gain are discussed in detail and modeling of the devices is used to investigate the electric field build up in the multiplication region.

In recent years there has been significant activity in research and development of high sensitivity accelerometers and gyroscopes using atom interferometers. In these devices, a fringe shift in the interference of atom de Broglie waves indicates the rotation rate of the interferometer relative to an inertial frame of reference. In both optical and atomic conventional Sagnac interferometers, the resultant phase difference due to rotation is independent of the wave velocity. However, we show that if an atom interforemeter is enclosed in a Faraday cage which is at some potential, the phase difference of the counter-propagating waves is proportional to the inverse square of the particle velocity and it is proportional to the applied potential. This is due to Aharonov-Bohm effect and it can be used to increase the rotation sensitivity of atom interferometers.

Raytheon Vision Systems (RVS) is developing two-color and large format single color FPAs fabricated from molecular beam epitaxy (MBE) grown HgCdTe triple layer heterojunction (TLHJ) wafers on CdZnTe substrates and double layer heterojunction (DLHJ) wafers on Si substrates, respectively. MBE material growth development has resulted in scaling TLHJ growth on CdZnTe substrates from 10cm² to 50cm², long-wavelength infrared (LWIR) DLHJ growth on 4-inch Si substrates and the first demonstration of mid-wavelength infrared (MWIR) DLHJ growth on 6-inch Si substrates with low defect density (<1000cm^-2) and excellent uniformity (composition<0.1%, cut-off wavelength Δcenter-edge<0.1μm). Advanced FPA fabrication techniques such as inductively coupled plasma (ICP) etching are being used to achieve high aspect ratio mesa delineation of individual detector elements with benefits to detector performance. Recent two-color detectors with MWIR and LWIR cut-off wavelengths of 5.5μm and 10.5μm, respectively, exhibit significant improvement in 78K LW performance with >70% quantum efficiency, diffusion limited reverse bias dark currents below 300pA and RA products (zero field-of-view, +150mV bias) in excess of 1×103 Ωcm². Two-color 20μm unit-cell 1280×720 MWIR/LWIR FPAs with pixel response operability approaching 99% have been produced and high quality simultaneous imaging of the spectral bands has been achieved by mating the FPA to a readout integrated circuit (ROIC) with Time Division Multiplexed Integration (TDMI). Large format mega pixel 20μm unit-cell 2048×2048 and 25μm unit-cell 2560×512 FPAs have been demonstrated using DLHJ HgCdTe growth on Si substrates in the short wavelength infrared (SWIR) and MWIR spectral range. Recent imaging of 30μm unit-cell 256×256 LWIR FPAs with 10.0-10.7μm 78K cut-off wavelength and pixel response operability as high as 99.7% show the potential for extending HgCdTe/Si technology to LWIR wavelengths.

Recently, several groups have investigated the aspects of positive and negative luminescence behavior in infrared materials. Under forward bias voltage, charge carriers are injected into the active region of a p-n junction, giving rise to positive luminescence. In contrast, a p-n junction under reverse bias conditions can exhibit negative luminescence caused by a reduction of the electron-hole recombination of the device, such that the photon flux is below that of the black body emission in equilibrium. In the present work, we show measurements of both positive and negative luminescence of binary Type II InAs/GaSb superlattice photodiodes in the 3 to 13 μm spectral range. Through a radiometric calibration technique, we demonstrate temperature independent negative luminescence efficiencies of 45 % in the midwavelength (MWIR) sample from 220 K to 320 K without anti-reflective coating and values reaching 35 % in the long wavelength infrared (LWIR) spectrum sample. With the radiative recombination constant obtained in the framework of k • p theory a model is obtained to describe the temperature dependent behavior of the results near thermal equilibrium in both samples. In the long wavelength regime, we demonstrate that the dominant non-radiative recombination channel in n-type material is Auger recombination with an electron-hole-electron (CHCC) Auger recombination coefficient of C_n = 1 x 10²⁴ cm⁶s^-1. While in the mid wavelength infrared window, the primary non-radiative recombination is Shockley-Read-Hall recombination giving rise to a p-type residual background capture cross-section of σ_n = 7 x 10^-16 cm2.

For type-II superlattices with spatially indirect optical transitions across the band gap, short-period superlattices are often employed. The oscillator strength of intraband transitions, from holes states confined in one layer to electron states confined in a neighboring layer, are enhanced by increasing the wave function overlap of these states through reduced superlattice period. However, there are limits to accurately controlling an epitaxially grown semiconductor superlattice structure as the number of monolayers in each layer is decreased. For InAs/GaSb type superlattices, periods of 40Å or less are relevant to mid-infrared detection. Characterization and modeling results for a series of InAs/GaSb superlattices with periods ranging 50Å to 20Å will be presented. These results explore the break point between when thinner is better and when reducing the period no longer optimizes the superlattice optical performance.