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We present theoretical and experimental analysis of photocarrier kinetics in quantum dot (QD) solar cells. The measurements of the J–V characteristics reveal strong effects of QD charging by selective doping of the interdot space on the solar cell characteristics. We demonstrate that charging of QDs significantly increases electron coupling to sub-bandgap photons, provides effective harvesting of IR energy, and serve as an effective tool for manipulating the potential profile at the micro- and nanoscale. The potential well for electrons in InAs QDs is substantially deeper than that for holes and, due to major differences between the effective masses of electrons and holes, the electron level spacing is substantially larger than the level spacing for holes. Therefore, QDs act as deep traps for electrons but shallow traps for holes. Filling of QDs under illumination is determined by a condition of equality of electron and hole capture rates which is realized via strong exponential dependence of the capture rates on the potential barrier around a charged dot. Without adequate doping of the QD medium, QDs are filled by electrons from the n-doped junction area and deteriorate the solar cell performance. However, selective n-doping of the QD medium results in micro- and nanoscale potential profiles favorable for photovoltaic conversion. Potential barriers around charged QDs decrease the photoelectron capture processes and suppress recombination processes via QDs. The filling of QDs predominantly from dopants in the QD medium allows one to maintain the microscale potential profile analogous to that in the best conventional single-junction solar cells.

We present computational and experimental results of dust particles that can be tuned to preferentially reflect or emit IR radiation within the 8–14 μm band. The particles consist of thin metallic subwavelength gratings patterned on the surface of a simple quarter wavelength cavity. This design creates distinct IR absorption resonances by combining the plasmonic resonance of the grating with the natural resonance of the cavity. We show that the resonance peaks are easily tuned by varying either the geometry of the grating or the thickness of the cavity. Here, we present a computational design algorithm along with experimental results that validate the design methodology.

Nanoscale engineering of band profile and potential profile provide effective tools for the management of photoelectron processes in quantum dot (QD) photovoltaic devices. We investigate the QD devices with various 1-μm InAs /GaAs QD media placed in a 3-μm base GaAs p-n junction. We found that n-charging of quantum dots (QDs) create potential barriers around QDs. QD growth between ultrathin AlGaAs layers leads to the formation of AlGaAs “fence” barriers, and reduces the wetting layers (WLs). The barriers around QDs and reduction of the wetting layer substantially suppress recombination processes via QDs. The n-doping of interdot space in QD media enhances electron extraction from QDs. All of our QD devices show short-circuit current, J SC , higher than that of the reference cell, but smaller open-circuit voltage, V OC .. In the QD devices, the short circuit currents increase by ~0.1 mA/cm 2 per dot layer. J SC reaches 28.4 mA/cm 2 in the device with QD media that combines dot charging, fence barriers, and WL reduction.

We have designed and characterized an infrared spectrometer, which uses a linear array of quantum grid infrared photodetectors (QGIPs) as its spectral sensing elements. Each QGIP element shares the same detector material but has a different grid geometry. The detector material, which is based on a binary superlattice design, provides an 8–14 μm broadband absorption medium for the spectrometer. The geometry of the grid, which is the light coupling structure under normal incidence, selects individual absorption wavelength for each element. Using a linear array of QGIPs of different geometries, multiple wavelengths can be detected simultaneously, and the array thus forms a spectrometer. Multicolor infrared imaging can then be achieved by integrating such QGIPs in unit cells of a two-dimensional array.

We report on the realization of a GaAs type-I quantum dot solar cell with a record 29.9 mA/cm2 short circuit current density and we compare it to a reference bulk GaAs solar cell.

Novel approach to control of photoelectron processes is based on nanoscale engineering of 3D potential profile employing quantum dots with built-in charge (Q-BIC). Charging of quantum dots creates local potential barriers around single dots, if dots are arbitrary distributed in the medium, and collective barriers around dot clusters, rows etc, if quantum dots form specific structures. Manipulations with potential barriers provide an effective tool for suppression of fast capture processes of photocarriers by quantum dots. This allows one to increase the photocarrier lifetime and to reduce the recombination losses. The charging of dots also enhances the electron coupling to infrared radiation and multi-step absorption of sub-gap photons. Q-BIC nanomaterials have a number of attractive features to be used in photovoltaic and sensing applications.

We present theoretical and experimental results of electron kinetics and transport in quantum dot structures with potential barriers created around dots via intentional or unintentional doping. Monte Carlo simulations demonstrate that photoelectron capture is substantially enhanced in strong fields and electron kinetics can be controlled by potential barriers. Therefore, by creating potential barriers around dots, we found that our novel quantum dots with built-in charge (Q-BIC) solar cells and infrared (IR) photodectors enhance electron intersubband transitions and suppress fast electron capture processes. These factors lead to a 60% increase in the photocurrent of the Q-BIC solar cells (without degradation of the open circuit voltage) and ~25 times increase in the photoresponse of the Q-BIC photodetectors.

This report describes the highlights and summary of the year 2, quarter four (Y2Q4) progress for the 6.2 project Improved Sensitivity Low-Cost Uncooled IR Detector Focal-Plane Arrays. This work occurred during the January 2010 May 2010 time period. The program goals for Y2Q4 corresponded to the continued expansion of our barium titanium oxide (BaTiO3) nanomaterial synthesis capabilities and deposition methods; laser-induced pyroelectric phase conversion studies and nanoscale characterization of the pyroelectric activation process; and fabrication of infrared (IR) test heterostructures for pyroelectrical analysis, along with the development of a technique for generating the requisite IR absorbing layer.

We investigated the effects of doping on the photovoltaic efficiency in a GaAs reference cell, and in undoped, n-doped, and p-doped InAs/GaAs quantum-dot (QD) solar cells. We found that the photovoltaic efficiency of the undoped QD solar cell is almost the same as that of the reference cell. However, the efficiency improves monotonically with increasing inter-dot ndoping, while p-doping deteriorates the photovoltaic conversion. We observed a 50 % increase in photovoltaic efficiency in the device n-doped to provide approximately six electrons per dot as compared with the undoped QD cell. In this QD solar cell, the short circuit current density increases to 24.30 mA/cm 2 compared with 15.07 mA/cm 2 in the undoped QD solar cell without deterioration of the open circuit voltage. To identify the physical mechanisms that provide this improvement, we investigated the spectral characteristics of the photovoltaic response and photoluminescence of our QD solar cells. We found that the electron capture into QDs is substantially faster than the hole capture, which leads to an accumulation of electrons in QDs. The electrons trapped in dots enhance IR transitions. The built-in-dot electron charge together with charged dopants outside the dots creates potential barriers, which suppress the fast electron capture processes and at the larger scale form a potential profile which precludes degradation of the open circuit voltage. All of these factors lead to the enhanced harvesting of IR energy and a radical improvement of the QD solar cell efficiency. Higher efficiencies are anticipated with further increase of doping level and at higher radiation intensity. This makes the QD solar cells promising candidates for use with concentrators of solar radiation.

Diminished performance due to poor chemical and electrical surface stability of InAs/GaSb SL photodetectors continues to be a major hurdle to the realization of the theoretically predicted high performance of this material system. Improved epitaxial growth conditions have yielded improvements in material quality over the past several years. However, surface instability resulting in electrical shunt pathways across the junction, and diminished device performance over time is still a major limiting factor for application of InAs/GaSb SL in long-wavelength infrared detectors. This study focuses on a two-step approach towards the successful surface passivation of long-wavelength InAs/GaSb superlattice structures. Two distinct sulfide chemical surface treatments were applied to inhibit the formation of native surface oxides and satisfy dangling bonds. This was followed by the application of a robust SU8-2 dielectric treatment on the mesa sidewalls to inhibit sulfide layer degradation and oxidation of the surface over time. A variable area diode analysis (VADA) technique employing diodes of variable diameter (40-400um) enabled the investigation of surface resistivity as a result of different passivation treatments. Temperature dependent studies of the dark current were used to understand the dominating current mechanisms.

This report describes the highlights and summary of the year two, quarters two and three progress for the 6.2 project Improved Sensitivity Low-Cost Uncooled IR Detector Focal-Plane Arrays. This work occurred during the August 2009 January 2010 time period. The program goals for year 2-quarters 2&3 corresponded to the continued expansion of our BaTiO3 nanomaterial synthesis capabilities and deposition methods, laser-induced pyroelectric phase conversion studies and nanoscale characterization of the pyroelectric activation process, and fabrication of IR test heterostructures for pyroelectrical analysis, along with the development of a technique for generating the requisite IR absorbing layer.

We report a 50% increase in power efficiency for our novel InAs/GaAs quantum dot with built-in charge (Q-BIC) solar cells. We found that n-doping the inter-dot space of a quantum dot solar cell (QDoSC) increases the short circuit current density from 15.07 mA/cm2 in undoped QDoSC to 24.30 mA/cm2 in the device doped to provide approximately six electrons per dot. To identify the physical mechanisms that provide this significant improvement, we investigate the photovoltaic response and its spectral characteristics in GaAs reference cell, undoped, n-doped, and p-doped QDoSCs. We found that the photovoltaic efficiency of the undoped QDoSC is almost the same as that of the reference cell. The efficiency monotonically improves with increasing n-doping, while the p-doping deteriorates the photovoltaic conversion. Studies of the photoluminescence of p- and n-doping show that the photoelectron capture into QDs is substantially faster than the hole capture, which leads to an accumulation of electrons in QDs. The built-in-dot electron charge enhances electron inter-subband QD transitions, suppresses the fast electron capture processes, and together with charged donors, forms the potential profile which precludes degradation of the open circuit voltage. All of these factors lead to the enhanced harvesting of IR energy and to a radical improvement of the QDoSC efficiency. Even higher efficiencies are anticipated for higher n-doping levels.

In this paper we present computational and experimental results of dust particles that can be tuned to preferentially reflect or emit IR radiation within the 8-14 μm band. The particles consist of thin metallic subwavelength gratings patterned on the surface of a simple quarter wavelength cavity. This design creates distinct IR absorption resonances by combining the plasmonic resonance of the grating with the natural resonance of the cavity. We will show that the resonance peaks are easily tuned by varying either the geometry of the grating or the thickness of the cavity. Here, we present a computational design algorithm along with experimental results that validate the design methodology.

The program goals for year 2-quarter 1 (Y2Q1) Institute for Collaborative Biotechnologies project 'Lower Cost Uncooled IR Detector Focal Plane Arrays' included (1) the continued expansion of our barium titanium oxide (BaTiO3) nanomaterial synthesis capabilities and deposition methods, (2) laser-induced pyroelectric phase conversion studies and spectroscopic end-point control scheme, and (3) comprehensive material characterization studies, along with electrical property characterization of BaTiO3 thin films. This report covers progress that took place in the three month period from May 1, 2009-July 30, 2009.

Infrared (IR) photon detectors based on III-V semiconductor quantum structures such as type-II superlattices [1] and quantum well infrared photodetectors (QWIPs) [2] require atomically flat interfaces, which are achieved through expensive, high-vacuum growth techniques such as molecular beam epitaxy (MBE). These structures are fabricated into detector arrays which are bump-bonded to Silicon (Si) Read-Out Integrated Circuits (ROICs). IR detector applications involving high resolution and fast refresh rates use highly sensitive photon detectors which require external cooling; making them bulky, expensive, and therefore impractical for equipping each soldier on the battlefield [3]. Uncooled thermal detectors tend to be lower cost, but the challenge is in developing materials that are thermally compatible with Si readout electronics. Thermal detectors convert incident radiation to heat. When a pyroelectric material is subjected to a temperature change, a dipole is induced, which sets up an electric potential. The resulting pyroelectric current can be read by the Si electronics. IR detectors based on perovskite oxides such as Barium Titanate (BaTiO 3 ) are of interest in part because of their lack of need for cryogenic cooling, which makes them relatively more affordable and operationally simpler than cooled photon detector systems. Using a biologically-inspired low-temperature nanoparticle deposition technique, direct-write laser phase conversion, and micro-electro-mechanical systems (MEMS) fabrication techniques, we are working towards an uncooled IR focal plane array (FPA) process compatible with monolithic integration of the detector pixels directly onto ROICs.

Pyroelectric infrared (IR) detectors based on perovskite oxides are of interest in part because of their lack of need for cooling, which makes them relatively more affordable and operationally simpler than cooled photon detector systems. We are investigating two methods for low-cost growth of perovskite oxide thin films, namely, a bio-inspired, low-temperature synthesis method and a modified industry-standard metalorganic solution deposition (MOSD) method. Subsequent to film synthesis, we utilize direct-write laser phase conversion and micro-electro-mechanical systems (MEMS) fabrication for development of an uncooled IR focal plane array (FPA). Film growth, crystallization and MEMS processes are compatible with monolithic integration of the detector pixels directly onto Si readout integrated circuits (ROICs).

At the time of immediate breast reconstruction with submuscular implants, 76 consecutive patients (89 breasts) were randomized into two groups. One received a gel-saline, double-lumen implant with 40 cc of saline added to the outer lumen, while the other received the same implant plus 40 cc of saline and 16 mg methyl prednisolone (40 mg%). Patients were followed for a minimum of 3 years. The groups, which were matched for patient age and implant size, were evaluated at 3, 12, 24, and 36 months for capsular contracture, steroid atrophy, and other complications. With completion of the double-blind study, the patients with submuscular gel-saline implants with only saline added had an overall capsular contracture rate of 38 percent at 3 months, 38 percent at 12 months, and 44 percent at 24 and 36 months. Those with methyl prednisolone had an overall capsular contracture rate of 14 percent at 3 months, and this remained unchanged through the end of the study. The rates of all other complications were comparable. Methyl prednisolone in a dose of 16 mg in 40 cc saline (concentration 40 mg%), when used in the outer lumen of a double-lumen gel-saline implant in a submuscular pocket, is both safe and efficacious in reducing the risk of capsular contracture for a minimum of 3 years in patients undergoing immediate breast reconstruction with submuscular mammary implants.

We report the results of a study of the temperature-dependent photoluminescence (PL) and leakage current characteristics of a set of type II idium arsenide (InAs)-gallium antimonide (GaSb) superlattice (SL) photodiode structures. We find that the PL efficiency of high-quality structures is determined by Shockley-Read and trap-assisted tunneling nonradiative recombination processes. Our results suggest a possible correlation between trap-assisted tunneling in some SL structures and an anomalous decrease in the PL efficiency with increasing temperature over the range 40-78 K, and provide insight into the effect of defects and SL homogeneity on the PL and transport characteristics of the photodiodes.

Effects of concentrated solar radiation on photovoltaic performance are investigated in well-developed GaAs quantum dot (QD) solar cells with 1-Sun efficiencies of 18%–19%. In these devices, the conversion processes are enhanced by nanoscale potential barriers and/or AlGaAs atomically thin barriers around QDs, which prevent photoelectron capture to QDs. Under concentrated radiation, the short circuit current increases proportionally to the concentration and the open circuit voltage shows the logarithmic increase. In the range up to hundred Suns, the contributions of QDs to the photocurrent are proportional to the light concentration. The ideality factors of 1.1–1.3 found from the VOC-Sun characteristics demonstrate effective suppression of recombination processes in barrier-separated QDs. The conversion efficiency shows the wide maximum in the range of 40–90 Suns and reaches 21.6%. Detailed analysis of I-V-Sun characteristics shows that at low intensities, the series resistance decreases inversely proport...

The Large Binocular Telescope (LBT) features dual 8.4 m diameter mirrors in a common elevation-over-azimuth mount. The LBT moves in elevation on two large crescent-shaped C-rings that are supported by radial hydrostatic bearing pads located near the four corners of the rectangular azimuth frame. The azimuth frame, in turn, is supported by four hydrostatic bearing pads and uses hydrodynamic roller bearings for centering. Each axis is gear driven by four large electric motors. In addition to precision optical motor encoders, each axis is equipped with Farrand Inductosyn strip encoders which yield 0.005 arcsecond resolution. The telescope weighs 580 metric tons and is designed to track with 0.03 arcsecond or better servo precision under wind speeds as high as 24 km/hr. Though the telescope is still under construction, the Mount Control System (MCS) has been routinely exercised to achieve First Light. The authors present a description of the unique, DSP-based synchronous architecture of the MCS and its capabilities.

We are investigating the structural, electrical, and infrared optical properties of a new material system comprising undoped self-assembled quantum dots having a type II band alignment with the matrix material in which they are embedded. This material system is fundamentally different from conventional type I quantum dots that must be doped and that rely on intersubband transitions for infrared photoresponse. Type II quantum dots would operate in photovoltaic mode with infrared photoresponse arising from electron-hole pair production involving 3-dimensionally-confined states in the dots and quantum well states in the matrix material. This paper emphasizes the structural characterization of molecular beam epitaxy (MBE)-grown InSb quantum dots grown in an In0.53Ga0.47As matrix lattice matched to an InP substrate.

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.

We demonstrate that longitudinal-optical phonons in type-II InAs/GaSb quantum wells can be used to up-convert photoluminescence. Such a phenomenon could be used to achieve laser-induced cooling of lattices.

We have studied the coupling between the InAs quantum dots and coupled quantum wells strained by the InAs quantum dots (i.e. coupled-quantum-well dots) by measuring photoluminescence spectra. By comparing the photoluminescence spectra of the coupled-quantum-well dots in which either the narrow well or wide well is grown next to the InAs quantum dots, we have evidenced the spatially inhomogeneous strains applied by the InAs quantum dots on the coupled quantum wells. Moreover, we have also investigated the three coupling regimes, i.e. when the dot level is higher than, lower than, and aligned to the lowest quantum-well transition. Based on our measurements, we conclude that the optical properties for the coupled-quantum-well dots have been significantly improved over the quantum dots.

We have demonstrated that type-II InAs/GaSb superlattices exhibit anomalously strong band-filling effects. By varying the width of the barrier or well, we have investigated the effects from 2-D quantum wells to quasi-3-D superlattices.

We report on the fabrication of quantum grid infrared photodetector (QGIP) arrays and demonstrate their feasibility for use as multi-channel long wavelength infrared spectrometers. The quantum well infrared photodetector (QWIP) material structure was designed to exhibit broadband absorption in the wavelength range of 7 μm to 16 μm. By fabricating QGIP devices with this QWIP material, scattering of light at an individual wavelength of interest within the material absorption range can create narrow band detection in each device. Arrays of QGIP devices with varying geometry, each tailored to respond to a discrete wavelength were fabricated. Details of the epi-growth, processing steps taken to fabricate required device features for narrow band absorption of the QGIP devices, and characterization methods will be discussed.

We have studied coupling between InGaAs/GaAs coupled quantum wells and self-assembled InAs quantum dots by measuring the linewidths, peak energies and peak intensities of photoluminescence peaks for different pump powers and lateral locations

In an effort to develop materials that are sensitive to mid and far infrared radiation, we examine InAs quantum dot/GaAs matrix multilayer structures grown by molecular beam epitaxy (MBE). Customized electrical and optical properties result from nanoscale-level manipulation of the dots' physical dimensions. The MBE growth temperature can be set to yield dots having the desired lateral dimension; however this leads to dots of insufficient vertical height. It is therefore necessary to grow the dots in a manner that allows independent control of the lateral and vertical dimensions. In this experiment, the vertical dimension is controlled by growing the dots in a multilayer structure with GaAs matrix layers. An initial layer of InAs quantum dots was grown on top of GaAs, followed by a few seconds short growth of GaAs, and then followed by the growth of another layer of InAs dots. The GaAs laterally surrounds, but does not bury, the InAs quantum dots. When the second layer of InAs dots is grown, they tend to self-organize directly on top of the exposed first layer of dots. We then grew a third layer of dots in the same manner. This effectively results in a pseudo-single layer of dots of the desired height which is then completely buried in GaAs. The goal is to develop structures that can be integrated into high operating temperature quantum dot infrared detectors (QDIPs) that have maximum sensitivity, robustness, and portability.

Quantum dots (QDs) provide photovoltaic conversion of below-bandgap photons due to multistep electron transitions. QDs also increase conversion efficiency of the above-bandgap photons due to extraction of electrons from QDs via Coulomb interaction with hot electrons excited by high-energy photons. Nanoscale potential profile (potential barriers) and nanoscale band engineering (AlGaAs atomically thin barriers) allow for suppression of photoelectron capture to QDs. To study these kinetic effects and to distinguish them from the absorption enhancement due to light scattering on QDs, we investigate long, 3-μm base GaAs devices with various InAs QD media with 20 and 40 QD layers. Quantum efficiency measurements show that, at least at low doping, the multistep processes in QD media are strongly affected by the wetting layer (WL). The QD media with WLs provide substantial conversion of below-bandgap photons and for devices with 40 QD layers the short circuit current reaches 29.2 mA/cm2. The QD media with band-engineered AlGaAs barriers and reduced wetting layers (RWL) enhance conversion of high-energy photons and decrease the relaxation (thermal) losses.

This paper provides the design details for a new two-color quantum-well infrared photodetector for use in advanced thermal imaging. The single pixel experimental data used in the evolution of this design is discussed in significant detail. Using the knowledge gained from extensive measurements comparing miniband transport with bound-to-quasi-bound QWIPs and also double and triple coupled-well QWIPs with the more conventional single-well QWIPs, a two-color design is presented. The detector design provides for a lattice-matched growth and superior response in the MWIR spectral region, while keeping the dark currents from the LWIR portion of the detector to a minimum. The architecture will allow for the MWIR and LWIR stacks to be biased separately and also for the signals to be read independently.

We report on results of laboratory and field tests of dual- band MWIR/LWIR focal plane arrays (FPAs) produced under the Army Research Laboratory's Multidomain Smart Sensor Federated Laboratory program. The FPAs were made by DRS Infrared Technologies using the HgCdTe material system and by BAE Systems using QWIP technology. The HgCdTe array used the DRS HDVIPTM process to bond two single-color detector structures to a 640 X 480-pixel single-color read-out integrated circuit (ROIC) to produce a dual-band 320 X 240 pixel array. The MWIR and LWIR pixels are co-located and have a high fill factor. The images from each band may be read out either sequentially (alternating frames) or simultaneously. The alternating frame approach must be used to produce optimal imagery in both bands under normal background conditions. The QWIP FPA was produced using MBE-grown III-V materials. The LWIR section consisted of GaAs quantum wells and AlGaAs barriers and the MWIR section used InGaAs quantum wells with AlGaAs barriers. The detector arrays were processed with three ohmic contacts for each pixel allowing for independent bias control over both the MWIR and LWIR sections. The arrays were indium bump-bonded to an ROIC (specifically designed for two color operation) which puts out the imagery from both bands simultaneously. The ROIC has variable gain and windowing capabilities. Both FPAs were tested under similar ambient conditions with similar optical components. The FPAs were subjected to a standard series of laboratory performance tests. The relative advantages and disadvantages of the two material systems for producing medium-format dual-band FPAs are discussed.

Infrared sensor technology is critical to many commercial and military defense applications. Traditionally, cooled infrared material systems such as indium antimonide, platinum silicide, mercury cadmium telluride, and arsenic doped silicon (Si:As) have dominated infrared detection. Improvement in surveillance sensors and interceptor seekers requires large size, highly uniform, and multicolor IR focal plane arrays involving medium wave, long wave, and very long wave IR regions. Among the competing technologies are the quantum well infrared photodetectors based on lattice matched or strained III-V material systems. This paper discusses cooled IR technology with emphasis on QWIP and MCT. Details will be given concerning device physics, material growth, device fabrication, device performance, and cost effectiveness for LWIR, VLWIR, and multicolor focal plane array applications.

A comparison is presented between two GaAs/AlGaAs quantum well infrared photodetector (QWIP) designs: the miniband transport (MBT) and the bound-to-quasibound (BTQB). Two QWIP test arrays were prepared, designed to have the same peak operating wavelength, doping density, barrier thickness, and excited state binding energy. The detectors are long wavelength infrared (LWIR), each having about a 9.1-microns-peak wavelength. The detector array test structures used edge coupling to remove the grating or optical coupling structure effects from the detector response characteristics. Extensive bias and spectral-dependent blackbody response and specific detectivity data will be presented. The data show that MBT and BTQB QWIPs offer comparable performance.

We describe here a study of Mini-Band Transport (MBT) Quantum Well Infrared Photodetector (QWIP) samples in which the binding energy of photoexcited electrons is systematically varied. Each sample has been characterized electrically and radiometrically. Results are reported for variation of absorption spectra, spectral response, IV characteristics, blackbody responsivity, detector noise, and detectivity vs. binding energy for dark current limited mode of operation.

Quantum dots acquire built-in charge due to selective n-doping of the interdot space. The quantum dots with built-in charge (Q-BIC) increase electron coupling to IR radiation and suppress photoelectron capture, which in turn decrease the recombination via quantum dots. To investigate effects of the built-in-dot charge on recombination processes and device performance, the light and dark I–V characteristics and their temperature dependences of Q-BIC solar cells are measured. Employing the diode model, the data are analyzed in terms of the ideality factor, shunt resistance, and reverse saturation current. The authors compare the n-doped Q-BIC solar cells with the GaAs p-i-n reference cell, undoped, and p-doped devices. The analysis provides a qualitative description of the effect of doping on carrier kinetics and transport. The authors show that n-doping substantially reduces the recombination via quantum dots.

We have studied the effects of AlGaAs energy barriers surrounding self-assembled InAs quantum dots in a GaAs matrix on the properties of solar cells made with multiple quantum dot layers in the active region of a photodiode. We have compared the fenced dot samples with conventional InAs/GaAs quantum dot solar cells and with GaAs reference cells. We have found that, contrary to theoretical predictions, the AlGaAs fence layers do not enhance the transport properties of photogenerated carriers but instead suppress the extraction of the carriers excited in the dots by light with wavelengths longer than the cutoff wavelength of the GaAs matrix material. Both the standard quantum dots and the fenced dots were found to give solar cell performance comparable to the GaAs reference cells for certain active region thicknesses but neither showed enhancement due to the longer wavelength absorption or improved carrier transport.

The rejuvenation technique of malar imbrication, which avoids dissection in the plane of the seventh cranial nerve, is presented to address the author's altered priorities in midfacial rejuvenation. These priorities target volumetric over tension-based goals in a manner that is simpler, safer, and more sculpturally effective than existing techniques. Volumetric manipulations in the subperiosteal and subcutaneous planes also bring substantial rejuvenation to the periorbital and perioral regions, without lip or lower lid incisions. Fourteen of the 172 patients (8 percent) who underwent consecutive procedures for primary facial rejuvenation suffered temporary upper lip paresis. Other complications were infrequent and limited. One patient underwent reoperation for asymmetry. Increased postoperative swelling and recovery are a necessary consequence of the subperiosteal component, just as increased operative time attends the wide undermining of the subcutaneous component. Despite these liabilities, the author recommends adding volumetric resculpture to the existing conventional tools of soft-tissue displacement under tension and topical resurfacing in pursuit of safer, more effective, and more natural rejuvenation of the aging face.

We have measured the radiometric properties of two midwave infrared photodiode arrays (320×256pixel2 format) fabricated from the same wafer comprising a thin (0.24μm), not intentionally doped InAs∕GaSb superlattice between a p-doped GaSb layer and a n-doped InAs layer. One of the arrays was indium bump bonded to a silicon fanout chip to allow for the measurement of properties of individual pixels, and one was bonded to a readout integrated circuit to enable array-scale measurements and infrared imaging. The superlattice layer is thin enough that it is fully depleted at zero bias, and the collection efficiency of photogenerated carriers in the intrinsic region is close to unity. This simplifies the interpretation of photocurrent data as compared with previous measurements made on thick superlattices with complex doping profiles. Superlattice absorption coefficient curves, obtained from measurements of the external quantum efficiency using two different assumptions for optical coupling into the chip, bracke...

An improved understanding of the vascular supply of the layers of the temporal fossa has increased the potential of this region for new and ingenious reconstructive techniques. Separate and independently vascularized layers of this region include hair-bearing scalp, glabrous skin, tempororoparietal fascia (and galea aponeurotica), temporalis muscle and fascia, and pericranium. Island flaps of glabrous skin and scalp provided esthetically appropriate tissue to cover a variety of defects. The malleable bulk of the subcutaneous fascial layers were combined with skin grafts to restore thin lining, and used as a vascularized bed for cartilage grafts in otherwise unsatisfactory recipient sites. Illustrative cases from our 5-year clinical experience are presented to demonstrate various combinations of the temporoparietal fascial pedicle with tissues from the temporal region to reconstruct the eyebrows, eyelids, orbits, cheeks, and lips.

To assess the relative effect of natural versus experimental influenza illness on pulmonary function, we compared 43 normal adults with documented nonpneumonic influenza A infection during three outbreaks, 1974 (A/Port Chalmers/74), 1975 (A/Port Chalmers/74), and 1976 (A/Victoria/75) to 24 normal volunteers following nasal inoculation with wild-type influenza A/England/42/72, A/Scotland/74 or A/Victoria/75. In naturally acquired illness, abnormalities in small airway functiion and transiently increase airway reactivity were observed. In contrast, no such dysfunction was observed in experimentally induced illness. This group manifested milder illness and significantly shorter duration of cough.

Costal cartilage irregularities are a major component of most congenital thoracic-wall deformities. A significant number of patients with these cartilage irregularities may either refuse major reconstruction or in fact have disorders of insufficient magnitude to justify such endeavors. In patients undergoing augmentation mammaplasty, recontouring or sculpturing of these abnormal costal cartilages may correct or improve the underlying chest-wall deformity and thus enhance the final aesthetic result. This method has had application in mild to moderate asymmetrical cases of both pectus excavatum and pectus carinatum, thoracic hypoplasia (Poland's syndrome), isolated cartilage deformities, and spinal scoliosis. In our hands, the combination of cartilage sculpturing with submuscular augmentation mammaplasty is performed as an outpatient local anesthetic procedure requiring not more than 90 minutes.

For evaluation of heterologous protection by live attenuated influenza virus vaccine, 42 healthy volunteers with low titers of or no antibody to A/Scotland/74 (H3N2) and A/Victoria/3/75 (H3N2) influenza viruses were given live attenuated A/Scotland/74 (H3N2) virus vaccine or placebo by the intranasal route with no resultant vaccine-related illness. Seventeen of 21 vaccine recipients and none of 21 placebo recipients developed antibody conversion. Thirty-seven days after administration of vaccine or placebo, all subjects were challenged intranasally with wild-type A/Victoria/3/75 influenza virus. Five placebo recipients and no vaccine recipients developed moderately severe illness, whereas 10 vaccine recipients and three placebo recipients developed no illness (p less than 0.025). Although 16 of 21 vaccine recipients fulfilled criteria of infection with the challenge virus, shedding of virus was significantly less frequent, less prolonged, and of significantly lower magnitude than that in the placebo recipients. Thus, live attenuated influenza virus vaccine showed a significant protective effect against illness following challenge with heterologous wild-type virus. The protective effect and the negligible side effects of this vaccine merit consideration of its use in a large-scale field trial.

We present a composite flap based on the musculature of the anterolateral thorax that allows immediate reconstruction of the mandible through the interposition of vascularized bony fifth rib. While the vascular pedicle remains the pectoral branch of the thoracoacromial artery, the pectoralis major muscle can be spared largely intact. The lateral position of the composite rib segment ensures a purely bony composition, while the lateral skin island remains largely hairless. Despite the unfavorable conditions of massive tumor size and prior irradiation attending the clinical cases presented, the complication rate was acceptable, with only one flap loss, and this followed technical error.

Two groups of consecutive patients from two different plastic surgical practice populations were evaluated to determine psychosocial differences between those who underwent immediate (n = 25) versus delayed (n = 38) breast reconstruction. Psychological assessment consisted of a standardized symptom inventory (BSI) and a specially designed self-report questionnaire investigating reactions unique to mastectomy and reconstruction. Both groups were extremely equivalent with regard to sociodemographic data, with the typical subject being a well-educated and employed Caucasian wife. Verbal reports of physical complaints revealed no significant differences between the two groups except for difficulty with arm movement, which was statistically higher for the immediate group (p = 0.006.). This difference most likely was due to the axillary dissection being performed simultaneously at the time of reconstruction. The relationship between timing of reconstruction and self-reported distress over the mastectomy experience revealed that only 25 percent of the women who underwent immediate repair reported "high distress" in recalling their mastectomy surgery compared with 60 percent of the delayed reconstruction group (p = 0.02). In reference to the two scales measuring psychological symptoms, a general trend was present, with the delayed group scoring higher (although not statistically significantly) on 9 of our 12 scales. Ninety-six percent of the immediate group and 89 percent of the delayed group reported satisfaction with results.(ABSTRACT TRUNCATED AT 250 WORDS)

USE of indwelling arterial cannulas has become standard practice for monitoring of systemic arterial pressure and sampling of arterial blood in critically ill patients.1 A recent article implicates clots formed at the tip of a Scribner shunt as being responsible for cerebrovascular accidents when these clots were flushed retrograde into the central arterial circulation.2 That study included a calculation of the theoretical volume of flush solution necessary to cause cerebral embolization, but had no confirmatory measurements. The occurrence of sudden unexplained neurologic deficits in patients with indwelling radial arterial cannulas prompted the present study. The purpose was to determine a . . .