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High-performance graphene-HgCdTe detector technology has been developed combining the best properties of both materials for mid-wave infrared (MWIR) detection and imaging. The graphene functions as a high mobility channel that whisks away carriers before they can recombine, further contributing to detection performance. Comprehensive modeling on the HgCdTe, graphene, and the HgCdTe-graphene interface has aided the design and development of this MWIR detector technology. Chemical doping of the bilayer graphene lattice has enabled p-type doping levels in graphene for high mobility implementation in high-performance MWIR HgCdTe detectors. Characterization techniques, including SIMS and XPS, confirm high boron doping concentrations. A spin-on doping (SOD) procedure is outlined that has provided a means of doping layers of graphene on native substrates, while subsequently allowing integration of the doped graphene layers with HgCdTe for final implementation in the MWIR photodetection devices. Successful integration of graphene into HgCdTe photodetectors can thus provide higher MWIR detector efficiency and performance compared to HgCdTe-only detectors. New earth observation measurement capabilities are further enabled by the room temperature operational capability of the graphene-enhanced HgCdTe detectors and arrays to benefit and advance space and terrestrial 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 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.

High performance detector technology is being developed for sensing over the mid-wave infrared (MWIR) band for NASA Earth Science, defense, and commercial applications. The graphene-based HgCdTe detector technology involves integration of graphene with HgCdTe photodetectors allowing higher performance detection over 2-5 μm compared with photodetectors using only HgCdTe material. The graphene layer functioning as a high mobility channel reduces recombination of photogenerated carriers in the detector to further enhance performance. Graphene bilayers on Si/SiO2 substrates have been doped with boron using a spin-on dopant (SOD) process. The p-doped graphene is then transferred onto HgCdTe substrates for high mobility layers in MWIR photodetectors. Various characterization techniques including Raman spectroscopy and secondary-ion mass spectroscopy (SIMS) have analyzed dopant levels and properties of the graphene throughout various stages of development to qualify and quantify the graphene doping and transfer. The objective of this work is demonstration of graphene-based HgCdTe room temperature MWIR detectors and arrays through modeling, material development, and device optimization. The primary driver for this technology development is enablement of a scalable, low cost, low power, and small footprint uncooled MWIR sensing technology capable of measuring thermal dynamics with better spatial resolution for applications such as remote sensing and earth observation.

Recent experimental investigations in Bi-Layer Graphene (BLG) have shown interesting and useful electrical behavior that can be leveraged in building novel device applications. One such behavior being carrier multiplication effects within the BLG. We propose to use a heterostructure of BLG-CdTe-HgCdTe as a detector structure that marries this effect along with the unique bandalignment of the heterostructure which suggest an Ohmic contact for the electrons but a Schottky barrier for the holes. Using a dissipative quantum transport model, namely the Non-Equilibrium Green’s Functions with self-consistent Born approximation accounting for electron-electron and electron-phonon interactions, we calculate energy and position resolved electron and hole currents through these heterostructure and discover a 20X ratio of electron-to-hole ratio in an illustrative simulation which demonstrates the potential for reducing the hole contribution to dark current and modulating the recombination mechanisms and therefore the lifetime of the carriers in the heterostructure.

Front-illuminated p-i-n GaN-based ultraviolet (UV) avalanche photodiodes (APDs) were grown by metalorganic chemical vapor deposition (MOCVD) on 25 mm dia. bulk Ammono® n-GaN substrate having a low etch pit density (EPD) less than 5 × 104 [cm-2] and processed into 6×6 APD arrays. The devices employed N-ion implantation to achieve sidewall passivation. Evaluation of these 6×6 arrays will help to confirm the uniformity of the epitaxial materials and device processing. The maximum avalanche gain reached ~ 3×105 at the breakdown (current limited). The dark current density was 10-9 A/cm2 at reverse bias up to -20 V and the APDs exhibited a reverse breakdown voltage of 81 ± 1 V for all 36 devices without any leaky devices, confirming a high uniformity of the growth and fabrication processes.

In this work, we use contrast image processing to estimate the concentration of multi-wall carbon nanotubes (MWCNT) in a given network. The fractal dimension factor (D) of the CNT network that provides an estimate of its geometrical complexity, is determined and correlated to network resistance. Six fabricated devices with different CNT concentrations exhibit D factors ranging from 1.82 to 1.98. The lower D-factor was associated with the highly complex network with a large number of CNTs in it. The less complex network, having the lower density of CNTs had the highest D factor of approximately 2, which is the characteristic value for a two-dimensional network. The electrical resistance of the thin MWCNT network was found to scale with the areal mass density of MWCNTs by a power law, with a percolation exponent of 1.42 and a percolation threshold of 0.12 &mu, g/cm2. The sheet resistance of the films with a high concentration of MWCNTs was about six orders of magnitude lower than that of less dense networks, an effect attributed to an increase in the number of CNT&ndash, CNT contacts, enabling more efficient electron transfer. The dependence of the resistance on the areal density of CNTs in the network and on CNT network complexity was analyzed to validate a two-dimension percolation behavior.

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.

Detection of ultraviolet (UV) bands offers increased spatial resolution, small pixel sizes, and large format arrays, thus benefitting a variety of NASA, defense, and commercial applications. AlxGa1-xN semiconductor alloys, which have attracted much interest for detection in the UV spectral region, have been shown to enable high optical gains, high sensitivities with the potential for single-photon detection, and low dark current performance in ultraviolet avalanche photodiodes (UV-APDs). We are developing GaN/AlGaN UV-APDs with large pixel sizes that demonstrate consistent and uniform device performance and operation. These UV-APDs are fabricated through high quality metal organic chemical vapor deposition (MOCVD) growth on lattice-matched, low dislocation density GaN substrates with optimized material growth and doping parameters. The use of these low defect density substrates is a critical element to realizing highly sensitive UV-APDs and arrays with suppressed dark current and jitter under high electric fields. Optical gains of 5×106 and greater with enhanced quantum efficiencies over the 320-400 nm spectral range have been demonstrated, enabled by a strong avalanche multiplication process. We are additionally using device technology developed for high voltage GaN p-i-n rectifier devices to enable advanced Geiger-mode UVAPDs with single-photon counting capability. This technology provides extremely low leakage currents in the reverse bias range near avalanche breakdown, a necessary requirement for stable Geiger-mode operation. The variable-area GaN/AlGaN UV-APD detectors and arrays being developed enable advanced sensing performance over UV bands of interest with high resolution detection for NASA Earth Science 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.

Graphene-HgCdTe heterostructure based mid wave IR (MWIR) detectors are being designed for NASA Earth Science applications. Combining Density Functional Theory (DFT) based calculations of the bandstructure with carrier generation and transport model of this detector, we study the essential physics of this novel detector design and project its performance. Combining the best of both these materials can yield high performance and superior detection capabilities.

Strained InGaAs (In = 8%) quantum wells (QW) were inserted into the intrinsic region of n-i-p InGaP/GaAs heterojunction solar cells, with thin (1 nm to 4nm) GaAs barriers separating the QWs. This design exhibited improved carrier collection from the QWs as compared to thicker barrier designs, as well as almost no degradation in Voc from control devices without QWs. Champion devices incorporating three layers of strained InGaAs QWs exhibited conversion efficiencies of >26%, exceeding that of the control, with corresponding short circuit current of 30.22 mA/cm2 and open circuit voltage of 1.03V under 1-sun AM1.5G solar spectrum.

Germanium offers many benefits over groups III-V materials when used for infrared detection. Most importantly, germanium is compatible with Complementary Metal Oxide Semiconductor (CMOS) manufacturing which allows for a low-cost, high-throughput device, and it does not require cooling, which many III-V devices do. With the deposition of germanium directly on silicon, there will be a thermally induced strain due to the difference in thermal expansion coefficients between the two materials. When a biaxial tensile strain is present, the direct bandgap of germanium is lowered to ~0.77 eV and is capable of absorbing longer wavelengths. We have used a two-step deposition process to create a strained germanium film in order to fabricate a photodetector device. Our device has a dark current of 1.35 nA and a photocurrent of 22.5 nA at 1570 nm wavelength. Next, we developed a model in order to compare theoretical results with experimental results. The results indicate that the model is in close agreement with our measured data, and we are therefore able to use it to model future devices.

Electro-optic infrared technologies and systems operating from ultraviolet (UV) to long-wave infrared (LWIR) spectra are being developed for a variety of defense and commercial systems applications. Loss of a significant portion of the incident signal due to reflection limits the performance of electro-optic infrared (IR) sensing systems. A critical technology being developed to overcome this limitation and enhance the performance of sensing systems is advanced antireflection (AR) coatings. Magnolia is actively involved in the development and advancement of nanostructured AR coatings for a wide variety of defense and commercial applications. Ultrahigh AR performance has been demonstrated for UV to LWIR spectral bands on various substrates. The AR coatings enhance the optical transmission through optical components and devices by significantly minimizing reflection losses, a substantial improvement over conventional thin-film AR coating technologies. Nanostructured AR coatings have been fabricated using a nanomanufacturable self-assembly process on substrates that are transparent for a given spectrum of interest ranging from UV to LWIR. The nanostructured multilayer structures have been designed, developed and optimized for various optoelectronic applications. The optical properties of optical components and sensor substrates coated with AR structures have been measured and the process parameters fine-tuned to achieve a predicted high level of performance. In this paper, we review our latest work on high quality nanostructure-based AR coatings, including recent efforts on the development of nanostructured AR coatings on IR substrates.

Nanostructured quantum well and quantum dot III–V solar cells provide a pathway to implement advanced single-junction photovoltaic device designs that can capture energy typically lost in traditional solar cells. To realize such high-efficiency single-junction devices, nanostructured device designs must be developed that maximize the open circuit voltage by minimizing both non-radiative and radiative components of the diode dark current. In this work, a study of the impact of barrier thickness in strained multiple quantum well solar cell structures suggests that apparent radiative efficiency is suppressed, and the collection efficiency is enhanced, at a quantum well barrier thickness of 4 nm or less. The observed changes in measured infrared external quantum efficiency and relative luminescence intensity in these thin barrier structures is attributed to increased wavefunction coupling and enhanced carrier transport across the quantum well region typically associated with the formation of a superlattice under a built-in field. In describing these effects, a high efficiency (>26% AM1.5) single-junction quantum well solar cell is demonstrated in a device structure employing both a strained superlattice and a heterojunction emitter.

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.

The shorter wavelengths of the ultraviolet (UV) band enable detectors to operate with increased spatial resolution, variable pixel sizes, and large format arrays, benefitting a variety of NASA, defense, and commercial applications. AlxGa1-xN semiconductor alloys, which have attracted much interest for detection in the UV spectral region, have been shown to enable high optical gains, high sensitivities with the potential for single photon detection, and low dark current performance in ultraviolet avalanche photodiodes (UV-APDs). We are developing GaN/AlGaN UV-APDs with large pixel sizes that demonstrate consistent and uniform device performance and operation. These UV-APDs are fabricated through high quality metal organic chemical vapor deposition (MOCVD) growth on lattice-matched, low dislocation density GaN substrates with optimized material growth and doping parameters. The use of these low defect density substrates is a critical element to realizing highly sensitive UV-APDs and arrays with suppressed dark current under high electric fields.Optical gains greater than 5X10 (exp 6) with enhanced quantum efficiencies over the 350-400 nm spectral range have been demonstrated, enabled by a strong avalanche multiplication process. Furthermore, we are developing 6X6 arrays of devices to test high gain UV-APD array performance at ~355 nm. These variable-area GaN/AlGaN UV-APD detectors and arrays enable advanced sensing performance over UV bands of interest with high resolution detection for NASA Earth Science applications.

A high-performance graphene-based HgCdTe detector technology is being developed for sensing over the mid-wave infrared (MWIR) band for NASA Earth Science, defense, and commercial applications. This technology involves the integration of graphene into HgCdTe photodetectors that combines the best of both materials and allows for higher MWIR(2-5 m) detection performance compared to photodetectors using only HgCdTe material. The interfacial barrier between the HgCdTe-based absorber and the graphene layer reduces recombination of photogenerated carriers in the detector. The graphene layer also acts as high mobility channel that whisks away carriers before they recombine, further enhancing the detector performance. Likewise, HgCdTe has shown promise for the development of MWIR detectors with improvements in carrier mobility and lifetime. The room temperature operational capability of HgCdTe-based detectors and arrays can help minimize size, weight, power and cost for MWIR sensing applications such as remote sensing and earth observation, e.g., in smaller satellite platforms. The objective of this work is to demonstrate graphene-based HgCdTe room temperature MWIR detectors and arrays through modeling, material development, and device optimization. The primary driver for this technology development is the enablement of a scalable, low cost, low power, and small footprint infrared technology component that offers high performance, while opening doors for new earth observation measurement capabilities.

Epitaxial reflector structures can potentially boost both the current and voltage output of III-V quantum well solar cells. While conventional distributed Bragg reflector (DBR) structures can provide high peak reflectivity, their bandwidth performance is limited. Here more complex AlAs/Al0.1Ga0.9As multi-layer structures are considered. In particular, composite chirped DBR structures with varying optical thickness are simulated and optimized. The larger bandwidth of an optimized chirped DBR is projected to outperform a conventional DBR as the GaAs base layer of a recently demonstrated high-efficiency InGaAs quantum well solar cell structure is thinned. Thin GaAs subcells incorporating both quantum wells and epitaxial back reflectors are of interest for enhancing the radiation tolerance of III-V multi-junction devices.

Quantum wells can improve solar cell conversion efficiency by extending infrared absorption and, in some cases, by suppressing radiative recombination to lower the dark current and increase the operating voltage. In this study, the effect of strained InGaAs/GaAs QWs incorporated in an InGaP-GaAs heterojunction based single junction solar cell has been investigated. The performance of 3-layer In 0.08 Ga 0.92 As/GaAs QWs incorporated in the intrinsic region of the nip deive with varying barrier thicknesses have been compared. The heterojunction design along with a wider bandgap InAlP front window allows superior absorption and low dark current. Despite the incorporation of QWs, minimal to no V oc loss has been observed compared to the baseline design without QWs, which can be attributed to suppressed radiative emission from the devices. All designs exhibit low-dark current characteristics, while the best QW cell conversion efficiency of >26% has been obtained with short circuit current of 30.22 mA/cm2 and open circuit voltage of 1.03V under 1-sun AM1.5G solar spectrum.

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.

Front-illuminated GaN p-i-p-i-n separate-absorption and multiplication avalanche photodiode (SAM-APD) epitaxial structures were grown by metalorganic chemical vapor deposition (MOCVD) on n-type bulk GaN substrates and fabricated into 4×4 arrays with a large detection area of 100×100 μm2. The SAM-APD array showed a uniform distribution of dark current density of JDark

GaN p-i-n ultraviolet avalanche photodiodes (UV-APDs) were fabricated from epitaxial structures grown on low-dislocation-density free-standing GaN substrates to form $4\times 4$ UV-APD arrays with a device size of $75\times 75~\mu \text{m}^{{ {2}}}$ . The devices in the UV-APD array showed a uniform and reliable distribution of breakdown voltage ( $V_{\text {BR}}$ ) and leakage current density. The average $V_{\text {BR}}$ of the 16 devices in one of the UV-APD arrays was 96±0.6 V, and the average dark current density ( $J_{R\_{}{\text {Dark}}}$ ) and photocurrent density ( $J_{R\_{}{\text {Photo}}}$ ) were measured to be (6.5±1.8) $\times 10^{-7}$ and (5.7±1.1) $\times 10^{{\text {-6}}}$ A/cm $^{{{2}}}$ at the reverse bias voltage of $V_{R}=48$ V (50% of the average onset point of $V_{\text {BR}}$ ), respectively. The reliable device performance was confirmed by performing multiple reverse bias $I$ – $V$ scans for the selected devices in the UV-APD array. We also observed the significantly enhanced spectral responsivity from the 142 to 5485 mA/W due to the strong carrier impact ionization at high reverse bias.

Nanostructured quantum well and quantum dot solar cells are being widely investigated as a means of extending infrared absorption and enhancing photovoltaic device performance. In this work, we describe the impact of nanostructured layer number on the performance of flexible, high-voltage InGaAs/GaAs quantum well solar cells. Multiple quantum well structures are observed to have a higher short circuit current but a lower open circuit voltage than similar single quantum well structures. Analysis of the underlying dark diode characteristics indicate that these high-voltage structures are limited by radiative recombination at high bias levels. The results of this study suggest that future development efforts should focus on maximizing the current generating capability of a limited number of nanostructured layers and minimizing recombination within the nanostructured absorber.

Electro-optical detection in ultraviolet (UV) and near-infrared (NIR) bands has distinct advantages for various applications. UV/NIR wavelengths are desired for a variety of NASA, defense and commercial applications. While UV and NIR detection technologies are governed by similar physical principles, a major differentiating factor lies in the choice of detector materials. Using the GaN/AlGaN material system, we are developing avalanche photodiodes (APDs) as discrete devices with high gains and responsivities. These devices, based on high crystalline quality metal organic chemical vapor deposition (MOCVD) growth on lattice-matched GaN substrates, demonstrate uniform and reliable distribution of breakdown voltage and leakage currents with gains of above 106. For NIR detection we have employed epitaxial layer deposition of germanium on silicon for room temperature operation. This development is focused on demonstrating very low noise performance as a result of low dislocation densities and dark currents. Both these material/device technologies can be adapted to create arrays of detectors for a variety of applications. The primary objective in developing these sensing and imaging technologies is to advance the state-of-the-art to benefit diverse UV/NIR applications for NASA, defense, and commercial applications.

Infrared (IR) technology plays a critical role in a wide range of terrestrial and space applications. IR sensing technologies and systems operating from the near-infrared (NIR) to long-wave infrared (LWIR) spectra are being developed for a variety of defense and commercial system applications. However, the performance of IR systems can be significantly limited by signal losses due to reflections from the IR substrates. Optical coatings with high antireflection (AR) characteristics can overcome this limitation and yield substantial enhancement in IR system performance. Magnolia is actively working on the development and advancement of ultrahigh performance AR coatings for a wide variety of defense and commercial applications. These nanostructured AR coatings have been demonstrated for ultraviolet (UV) to LWIR spectral bands on various substrates. The AR coatings enhance the transmission of light through optical components and devices by significantly minimizing reflection losses, providing substantial improvement over conventional thin film AR coating technologies. Nanostructured AR coatings have been fabricated using a tunable self-assembly process on substrates transparent for a given spectra of interest ranging from the UV to LWIR. The nanostructured multilayer coatings have been designed, developed and optimized for various optoelectronic applications. The optical properties of AR-coated optical and IR components and sensor substrates have been measured and fine-tuned to achieve a high level of performance. In this paper, we review our latest work focusing on high quality nanostructure-based AR coatings, including recent efforts to develop of the nanostructured coatings on IR-transparent substrates.

SiGe offers a low-cost alternative to conventional infrared sensor material systems such as InGaAs, InSb, and HgCdTe for developing near-infrared (NIR) photodetector devices that do not require cooling and can operate with relatively low dark current. As a result of the significant difference in thermal expansion coefficients between germanium (Ge) and silicon (Si), tensile strain incorporated into SiGe detector devices through specialized growth processes can extend their NIR wavelength range of operation. We have utilized high throughput, large-area complementary metal-oxide semiconductor (CMOS) technology to fabricate Ge based p-i-n (PIN) detector devices on 300 mm Si wafers. The two-step device fabrication process, designed to effectively reduce the density of defects and dislocations arising during deposition that form recombination centers which can result in higher dark current, involves low temperature epitaxial deposition of Ge to form a thin p+ seed layer, followed by higher temperature deposition of a thicker Ge intrinsic layer. Phosphorus was then ion-implanted to create devices with n+ regions of various doping concentrations. Secondary ion mass spectroscopy (SIMS) has been utilized to determine the doping profiles and material compositions of the layers. In addition, electrical characterization of the I-V photoresponse of different devices from the same wafer with various n+ region doping concentrations has demonstrated low dark current levels (down to below 1 nA at -1 V bias) and comparatively high photocurrent at reverse biases, with optimal response for doping concentration of 5 × 1019 cm-3.

Flexible copper indium gallium diselenide (CIGS) solar cells on lightweight substrates can deliver high specific powers. Flexible lightweight CIGS solar cells are also primary candidates for building-integrated panels. In all applications, CIGS cells can greatly benefit from the application of broadband and wide-angle AR coating technology. The AR coatings can significantly improve the transmittance of light over the entire CIGS absorption band spectrum. Increased short-circuit current has been observed after integrating AR coated films onto baseline solar panels. NREL’s System Advisor Model (SAM) has predicted up to 14% higher annual power output on AR integrated vertical or building-integrated panels. The combination of lightweight flexible substrates and advanced device designs employing nanostructured optical coatings together have the potential to achieve flexible CIGS modules with enhanced efficiencies and specific power.

The impact of nanostructured broadband antireflection (AR) coatings on solar panel performance has been projected for a broad range of panel tilt angles at various locations. AR coated films have been integrated on test panels and the short-circuit current has been measured for the entire range of panel tilts. The integration of the AR coatings resulted in an increase in short-circuit current of the panels by eliminating front sheet reflection loss for a broad spectrum of light and wide angle of light incidence. The short-circuit current enhancement is 5% for normal light incidence and approximately 20% for off-angle light incidence. The National Renewable Energy Laboratory (NREL) System Advisor Model (SAM) predicts that this AR coating can yield at least 6.5% improvement in solar panel annual power output. The greatest enhancement, approximately 14%, is predicted for vertical panels. The AR coating’s contributions to vertical mount panels and building-integrated solar panels are significant. This nanostructured broadband AR coating thus has the potential to lower the cost per watt of photovoltaic solar energy.

Type-II strained-layer superlattices (T2SLs) are receiving increased interest as mid-wave infrared (MWIR) and long-wave infrared detector absorbers due to their potential Auger suppression and ability to be integrated into complex device structures. Although T2SLs show promise for use as infrared detectors, further investigation into the effects of high energy particle radiation is necessary for space-based applications. In this presentation, the effects of both 4.5 MeV and 63 MeV proton radiation on the carrier lifetime of MWIR InAs/InAsSb T2SLs will be shown. The 63 MeV proton radiation study will focus on the carrier lifetime of MWIR InAs/InAsSb T2SL samples of varying donor density. These results reveal a Shockley-Read-Hall (SRH) lifetime associated with a radiation induced defect level, which is not dependent on the donor density of the T2SL. Using 4.5 MeV proton radiation, the dependence of carrier lifetime on relative trap density in MWIR T2SLs samples is studied by varying the particle fluence. A comparison of these two radiation studies shows similar lifetime effects that will be discussed in detail. These results give insight into the viability of Ga-free T2SLs for space applications.

Infrared (IR) sensing technologies and systems operating from the near-infrared (NIR) to long-wave infrared (LWIR) spectra are being developed for a variety of defense and commercial systems applications. Reflection losses affecting a significant portion of the incident signal limits the performance of IR sensing systems. One of the critical technologies that will overcome this limitation and enhance the performance of IR sensing systems is the development of advanced antireflection (AR) coatings. Magnolia is actively involved in the development and advancement of ultrahigh performance AR coatings for a wide variety of defense and commercial applications. Ultrahigh performance nanostructured AR coatings have been demonstrated for UV to LWIR spectral bands using various substrates. The AR coatings enhance the optical transmission through optical components and devices by significantly minimizing reflection losses, a substantial improvement over conventional thin-film AR coating technologies. Nanostructured AR coatings are fabricated using a tunable self-assembly process on substrates that are transparent for a given spectrum of interest ranging from UV to LWIR. The nanostructured multilayer structures have been designed, developed and optimized for various optoelectronic applications. The optical properties of the AR-coated optical components and sensor substrates have been measured and fine-tuned to achieve a predicted high level of performance of the coatings. In this paper, we review our latest work on high quality nanostructure-based AR coatings, including recent efforts towards the development of nanostructured AR coatings on IR-transparent substrates.

SiGe p-i-n photodetectors have been fabricated on 300 mm (12”) diameter silicon (Si) wafers utilizing high throughput, large-area complementary metal-oxide semiconductor (CMOS) technologies. These Ge photodetectors are designed to operate in room temperature environments without cooling, and thus have potential size and cost advantages over conventional cooled infrared detectors. The two-step fabrication process for the p-i-n photodetector devices, designed to minimize the formation of defects and threading dislocations, involves low temperature epitaxial growth of a thin p+ (boron) Ge seed/buffer layer, followed by higher temperature deposition of a thicker Ge intrinsic layer. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated uniform layer compositions with well defined layer interfaces and reduced dislocation density. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was likewise employed to analyze the doping levels of the p+ and n+ layers. Current-voltage (I-V) measurements demonstrated that these SiGe photodetectors, when exposed to incident visible-NIR radiation, exhibited dark currents down below 1 μA and significant enhancement in photocurrent at -1 V. The zero-bias photocurrent was also relatively high, showing a minimal drop compared to that at -1 V bias.

Image sensing technologies and systems operating from the ultraviolet (UV) to long-wave infrared (LWIR) spectral range are being developed for a variety of defense and commercial systems applications. Reflection loss of a significant portion of the incident signal limits the performance of image sensing systems. One of the critical technologies that will overcome this limitation and enhance image sensor performance is the development of advanced antireflection (AR) coatings. In this paper, we review our latest work on high-quality nanostructure-based AR structures, including recent efforts to deposit nanostructured AR coatings on substrates transparent to infrared (IR) radiation. Nanostructured AR coatings fabricated via a scalable self-assembly process are shown to enhance the optical transmission through transparent optical components by minimizing reflection losses in the spectral band of interest to less than one percent, a substantial improvement over conventional thin-film AR coating technologies. Step-graded AR structures also exhibit excellent omnidirectional performance, and have recently been demonstrated in medium wavelength and long wavelength IR spectral bands.

Wurtzite Zn1−xMgxO nanowires (NWs) are grown using metalorganic chemical vapor deposition technique with the highest Mg mole fraction of 0.29. The physical structure of the NWs remains invariant with increasing Mg incorporation while the diameters and lengths vary in the range 40–180 nm and 0.5–1.5 μm, respectively. Room temperature photoluminescence shows near band edge emission associated with free exciton emission that shifts to shorter wavelength with an increase in the Mg mole fraction. Hall measurement shows that electron mobility decreases with increasing Mg concentration. Revised elastic constants are suggested to explain the observed decrease in the lattice volume at a low Mg mole fraction.Wurtzite Zn1−xMgxO nanowires (NWs) are grown using metalorganic chemical vapor deposition technique with the highest Mg mole fraction of 0.29. The physical structure of the NWs remains invariant with increasing Mg incorporation while the diameters and lengths vary in the range 40–180 nm and 0.5–1.5 μm, respectively. Room temperature photoluminescence shows near band edge emission associated with free exciton emission that shifts to shorter wavelength with an increase in the Mg mole fraction. Hall measurement shows that electron mobility decreases with increasing Mg concentration. Revised elastic constants are suggested to explain the observed decrease in the lattice volume at a low Mg mole fraction.

A comparison of ZnO nanowires (NWs) and nanorods (NRs) grown using metalorganic chemical vapor deposition (MOCVD) and hydrothermal synthesis, respectively, on p-Si (100), GaN/sapphire, and SiO2 substrates is reported. Scanning electron microscopy (SEM) images reveal that ZnO NWs grown using MOCVD had diameters varying from 20 nm to 150 nm and approximate lengths ranging from 0.7 μm to 2 μm. The NWs exhibited clean termination/tips in the absence of any secondary nucleation. The NRs grown using the hydrothermal method had diameters varying between 200 nm and 350 nm with approximate lengths between 0.7 μm and 1 μm. However, the NRs grown on p-Si overlapped with each other and showed secondary nucleation. x-Ray diffraction (XRD) of (0002)-oriented ZnO NWs grown on GaN using MOCVD demonstrated a full-width at half-maximum (FWHM) of 0.0498 (θ) compared with 0.052 (θ) for ZnO NRs grown on similar substrates using hydrothermal synthesis, showing better crystal quality. Similar crystal quality was observed for NWs grown on p-Si and SiO2 substrates. Photoluminescence (PL) of the NWs grown on p-Si and SiO2 showed a single absorption peak attributed to exciton–exciton recombination. ZnO NWs grown on GaN/sapphire had defects associated with oxygen interstitials and oxygen vacancies.

The field of ultraviolet (UV) photonics at wavelengths λ

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.

Optical sensing technology is critical for optical communication, defense and security applications. Advances in optoelectronics materials in the UV, Visible and Infrared, using nanostructures, and use of novel materials such as CNT and Graphene have opened doors for new approaches to apply device design methodology that are expected to offer enhanced performance and low cost optical sensors in a wide range of applications. This paper is intended to review recent advancements and present different device architectures and analysis. The chapter will briefly introduce the basics of UV and Infrared detection physics and various wave bands of interest and their characteristics [1, 2] We will cover the UV band (200-400 nm) and address some of the recent advances in nanostructures growth and characterization using ZnO/MgZnO based technologies and their applications. Recent advancements in design and development of CNT and Graphene based detection technologies have shown promise for optical sensor applications. We will present theoretical and experimental results on these device and their potential applications in various bands of interest.