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Broadband antireflection (AR) optical coatings covering the ultraviolet (UV) to infrared (IR) spectral bands have many potential applications for various NASA systems. The performance of these systems is significantly limited by signal loss due to reflection off substrates and optical components. Tunable nanoengineered optical layers offer omnidirectional suppression of light reflection/scattering with increased optical transmission to enhance detector and system performance particularly over IR band wavelengths. Nanostructured AR coatings enable the realization of optimal AR coatings with high laser damage thresholds and reliability in extreme low temperature environments and under launch conditions for various NASA applications. We are developing and advancing high-performance AR coatings on GaSb and various other substrate types for spectral bands ranging from UV to LWIR. The nanostructured AR coatings enhance transmission of light through optical components and detector devices by greatly minimizing reflection losses over range of incidence angles, providing substantial improvements over more conventional thin film AR coating technologies. In this paper, we review our latest developments in high performance nanostructurebased AR coatings, focusing primarily on recent efforts in designing and fabricating AR coatings for the LWIR spectral band for performance improvements in airborne and space detector applications.

Broadband antireflection (AR) optical coatings covering the ultraviolet (UV) to infrared (IR) spectral bands have many potential applications for various NASA systems. The performance of these systems is substantially limited by signal loss due to reflection off substrates and optical components. Tunable nanoengineered optical layers offer omnidirectional suppression of light reflection/scattering with increased optical transmission to enhance detector and system performance. Nanostructured AR coatings enable realization of optimal AR coatings with high laser damage thresholds and reliability in extreme low temperature environments and under launch conditions for various NASA applications. We are developing and advancing high-performance AR coatings on various substrates for spectral bands ranging from the UV to IR. The nanostructured AR coatings enhance the transmission of light through optical components and devices by significantly minimizing reflection losses, providing substantial improvements over conventional thin film AR coating technologies. The optical properties of the AR coatings have been measured and fine-tuned to achieve high levels of performance. In this paper, we review our latest work on high performance nanostructure-based AR coatings, including recent efforts in the development of the nanostructured AR coatings for UV band applications.

Broadband antireflection (AR) optical coatings covering the ultraviolet (UV) to infrared (IR) spectral bands have many potential applications for various NASA systems. The performance of these systems is substantially limited by signal loss due to reflection off substrates and optical components. Tunable nanoengineered optical layers offer omnidirectional suppression of light reflection/scattering with increased optical transmission to enhance detector and system performance. Nanostructured AR coatings enable realization of optimal AR coatings with high laser damage thresholds and reliability in extreme low temperature environments and under launch conditions for various NASA applications. We are developing and advancing high-performance AR coatings on various substrates for spectral bands ranging from the UV to IR. The nanostructured AR coatings enhance the transmission of light through optical components and devices by significantly minimizing reflection losses, providing substantial improvements over conventional thin film AR coating technologies. The optical properties of the AR coatings have been measured and fine-tuned to achieve high levels of performance. In this paper, we review our latest work on high performance nanostructure-based AR coatings, including recent efforts in the development of the nanostructured AR coatings for UV band applications.

Infrared (IR) technology plays a critical role in various military and civilian applications including target acquisition, surveillance, night vision, and target tracking. IR sensors and systems operating from the short-wave infrared (SWIR) to long-wave infrared (LWIR) spectra are being developed for defense and commercial system applications. Performance of these IR systems is substantially limited by signal loss due to reflection off the IR substrates and optical components. Optical coatings with high antireflection (AR) characteristics can overcome this limitation and thus enhance the performance of IR systems. We are developing and advancing high-performance antireflection (AR) coatings for a wide range of spectral bands on various substrates for a variety of defense and commercial applications. The AR coatings enhance the transmission of light through optical components and devices by significantly minimizing reflection losses, providing substantial improvements over conventional thin-film AR coating technologies. The optical properties of ARcoated optical components and sensor substrates have been measured and fine-tuned to achieve high levels of performance. In this paper, we review our latest work on robust nanostructure-based AR coatings, including recent efforts in the development of the nanostructured AR coatings on silicon and CdZnTe substrates as well as on ZnSe lenses.

Sensors and imaging systems operating from visible to long-wave infrared (LWIR) spectrum are being developed for a variety of defense and commercial systems applications. Signal losses due to the reflection of incident signal from the surface of sensors and optical components limits the performance of image sensing systems. Antireflection (AR) coating technology overcomes this limitation and enhance the performance of image sensing systems. Magnolia is actively working on the development and advancement of ultra-high-performance AR coatings for a wide variety of defense and commercial applications. Nanostructured AR coatings fabricated via a scalable self-assembly process are shown to enhance the optical transmission through transparent optical components and sensor substrates by minimizing reflection losses in the spectral band of interest to less than one percent, a substantial improvement over conventional thin-film AR coating technology. Step-graded AR structures also exhibit excellent omnidirectional performance and have recently been demonstrated in various IR spectral bands.

Oblique-angle deposition is used to fabricate indium tin oxide (ITO) optical coatings with a porous, columnar nanostructure. Nanostructured ITO layers with a reduced refractive index are then incorporated into antireflection coating (ARC) structures with a step-graded refractive index design, enabling increased transmittance into an underlying semiconductor over a wide range of wavelengths of interest for photovoltaic applications. Low-refractive index nanostructured ITO coatings can also be combined with metal films to form an omnidirectional reflector (ODR) structure capable of achieving high internal reflectivity over a broad spectrum of wavelengths and a wide range of angles. Such conductive high-performance ODR structures on the back surface of a thin-film solar cell can potentially increase both the current and voltage output by scattering unabsorbed and emitted photons back into the active region of the device.

Electro-optical/infrared (EO/IR) sensors and photovoltaic power sources are being developed for a variety of defense and commercial applications. One of the critical technologies that will enhance both EO/IR sensor and photovoltaic module performance is the development of high quality nanostructure-based antireflection coatings. In this paper, we review our work on advanced antireflection structures that have been designed by using a genetic algorithm and fabricated by using oblique angle deposition. The antireflection coatings are designed for the wavelength range of 250 nm to 2500 nm and an incidence angle between 00 and 400. These nanostructured antireflection coatings are shown to enhance the optical transmission through transparent windows over a wide band of interest and minimize broadband reflection losses to less than one percent, a substantial improvement over conventional thin-film antireflection coating technologies.

Electro-optical/infrared nanosensors are being developed for a variety of defense and commercial systems applications. One of the critical technologies that will enhance EO/IR sensor performance is the development of advanced antireflection coatings with both broadband and omnidirectional characteristics. In this paper, we review our latest work on high quality nanostructure-based antireflection structures, including recent efforts to deposit nanostructured antireflection coatings on large area substrates. Nanostructured antireflection coatings fabricated via oblique angle deposition are shown to enhance the optical transmission through transparent windows by minimizing broadband reflection losses to less than one percent, a substantial improvement over conventional thin-film antireflection coating technologies. Step-graded antireflection structures also exhibit excellent omnidirectional performance, and have recently been demonstrated on 6-inch diameter substrates.

The scalability of nanostructured, self-assembled antireflection (AR) coatings has been demonstrated on 6-inch glass and silicon wafers. Ultra-high transmittance through these large-area coatings has been confirmed by measuring the short circuit current of a CIGS-based thin film photovoltaic (PV) device placed below the large-area AR-coated glass wafer. At normal light incidence, the light transmitted through the AR coated glass wafer yields 5% more short-circuit current compared to the uncoated glass wafer. At off-angle incidence, the light transmitted through the AR-coated wafer yields nearly 20% higher short-circuit current compared to light transmitted through an uncoated glass wafer. The large-area AR coating preserves ultra-high transmittance over a wide range of incident angles and has the potential to enhance PV device performance from dawn to dusk.

Flexible photovoltaic cells with a specific power of more than 275 W/kg have been demonstrated by depositing copper indium gallium diselenide (CIGS) absorber layers on ultra lightweight and highly durable titanium foil. Advanced device designs employing nanostructured optical coatings and exploiting optical cavity effects provide a pathway to further increase power-generating capability. Single-junction CIGS devices can potentially outperform multi-junction III-V structures in some environments, including under high air mass terrestrial spectrums.

Oblique-angle deposition of indium tin oxide (ITO) is used to fabricate optical thin-film coatings with a porous, columnar nanostructure. Indium tin oxide is a material that is widely used in industrial applications because it is both optically transparent and electrically conductive. The ITO coatings are fabricated, using electron-beam evaporation, with a range of deposition angles between 0 degrees (normal incidence) and 80 degrees. As the deposition angle increases, we find that the porosity of the ITO film increases and the refractive index decreases. We measure the resistivity of the ITO film at each deposition angle, and find that as the porosity increases, the resistivity increases superlinearly. A new theoretical model is presented to describe the relationship between the ITO film's resistivity and its porosity. The model takes into account the columnar structure of the film, and agrees very well with the experimental data.

Ultra-high, omnidirectional transmittance through a coated glass window is demonstrated over the entire accessible portion of the solar spectrum. The average broadband transmittance has been increased to greater than 98.5% at normal incidence, and exceeds 97.8% at all wavelengths between 440 nm and 1800 nm, significantly outperforming conventional MgF 2 coated glass. The measured improvement in transmittance results from coating the window with a new class of materials consisting of porous SiO 2 nanorods. The step-graded antireflection structure also exhibits excellent omnidirectional performance, enabling average broadband transmittance in excess of 96% at incident angles as high as 70°.

Photon absorption, and thus current generation, is hindered in conventional thin-film solar cell designs, including quantum well structures, by the limited path length of incident light passing vertically through the device structure. Optical scattering into lateral waveguide structures provides a physical mechanism to dramatically increase photocurrent generation through in-plane light trapping. However, the insertion of wells of high refractive index material with lower energy gap into the device structure often results in lower voltage operation, and hence lower photovoltaic power conversion efficiency. In this work, we demonstrate that the voltage output of an InGaAs quantum well waveguide photovoltaic device can be increased by employing a novel III-V material structure with an extended wide band gap emitter heterojunction. Analysis of the light IV characteristics from small area test devices reveals that nonradiative recombination components of the underlying dark diode current have been reduced, exposing the limiting radiative recombination component and providing a pathway for realizing solar-electric conversion efficiency of 30% or more in single-junction cells.

SiGe based focal plane arrays offer a low cost alternative for developing visible- near-infrared focal plane arrays that will cover the spectral band from 0.4 to 1.6 microns. The attractive features of SiGe based foal plane arrays take advantage of silicon based technology that promises small feature size, low dark current and compatibility with the low power silicon CMOS circuits for signal processing. This paper discusses performance characteristics for the SiGe based VIS-NIR Sensors for a variety of defense and commercial applications using small unit cell size and compare performance with InGaAs, InSb, and HgCdTe IRFPA's. We present results on the approach and device design for reducing the dark current in SiGe detector arrays. The electrical and optical properties of SiGe arrays at room temperature are discussed. We also discuss future integration path for SiGe devices with Si-MEMS Bolometers.

Next Generation EO/IR focal plane arrays using nanostructure materials are being developed for a variety of Defense and Homeland Security Sensor Applications. Several different nanomaterials are being evaluated for these applications. These include ZnO nanowires, GaN Nanowires and II-VI nanowires, which have demonstrated large signal to noise ratio as a wide band gap nanostructure material in the UV band. Similarly, the work is under way using Carbon Nanotubes (CNT) for a high speed detector and focal plane array as two-dimensional array as bolometer for IR bands of interest, which can be implemented for the sensors for homeland security applications. In this paper, we will discuss the sensor design and model predicting performance of an EO/IR focal plane array and Sensor that can cover the UV to IR bands of interest. The model can provide a robust means for comparing performance of the EO/IR FPA's and Sensors that can operate in the UV, Visible-NIR (0.4- 1.8μ), SWIR (2.0-2.5μ), MWIR (3-5μ), and LWIR bands (8-14μ). This model can be used as a tool for predicting performance of nanostructure arrays under development. We will also discuss our results on growth and characterization of ZnO nanowires and CNT's for the next generation sensor applications. We also present several approaches for integrated energy harvesting using nanostructure based solar cells and Nanogenerators that can be used to supplement the energy required for nanostructure based sensors.

Ultra-high, broadband transmittance through coated glass windows is demonstrated over a wide range of incident angles. Near perfect 100% transmittance through a glass substrate has been achieved over select spectral bands, and the average transmittance increased to over 97% for photons incident between 0° and 75° with wavelengths between 400 nm and 1600 nm. The measured improvements in transmittance result from coating the windows with a new class of materials consisting of porous SiO2 nanorods.

EO/IR Nanosensors are being developed for a variety of Defense and Commercial Systems Applications. These include UV, Visible, NIR, MWIR and LWIR Nanotechnology based Sensors. The conventional SWIR Sensors use InGaAs based IR Focal Plane Array (FPA) that operate in 1.0-1.8 micron region. Similarly, MWIR Sensors use InSb or HgCdTe based FPA that is sensitive in 3-5 micron region. More recently, there is effort underway to evaluate low cost SiGe visible and near infrared band that covers from 0.4 to 1.6 micron. One of the critical technologies that will enhance the EO/IR sensor performance is the development of high quality nanostructure based antireflection coating. Prof. Fred Schubert and his group have used the TiO2 and SiO2 graded-index nanowires / nanorods deposited by obliqueangle deposition, and, for the first time, demonstrated their potential for antireflection coatings by virtually eliminating Fresnel reflection from an AlN-air interface over the UV band. This was achieved by controlling the refractive index of the TiO2 and SiO2 nanorod layers, down to a minimum value of n = 1.05, the lowest value so far reported In this paper, we will discuss our modeling approach and experimental results for using oblique angle nanowires growth technique for extending the application for UV, Visible and NIR sensors and their utility for longer wavelength application. The AR coating is designed by using a genetic algorithm and fabricated by using oblique angle deposition. The AR coating is designed for the wavelength range of 400 nm to 2500 nm and 0° to 40° angle of incidence. The measured average optical transmittance of an uncoated glass substrate between 1000 nm and 2000 nm is improved from 92.6% to 99.3% at normal incidence by using a two-layer nanostructured AR coating deposited on both surfaces of the glass substrate.