Description: In recent years, Type-II superlattices have experienced significant development. However, the full potential of Type-II superlattice has not been fully explored and alternate superlattice architectures hold great promise. Despite demonstration of SWIR photodetectors based on this material system, there has been no report about Type-II superlattice-based photodetectors that have been sensitive to visible light. We propose to develop Type-II superlattice-based photodetectors and focal plane arrays for NASA's imaging and spectroscopy applications in the spectral band from visible to extended short-wavelength infrared (0.4–2.5 um) with a very low dark current density. In mid- and long-wavelength infrared spectral bands, Type-II superlattice-based photodetectors already offers performance comparable to the state-of-the-art mercury cadmium telluride but at a fraction of the cost due to the leveraging of commercial growth and process equipment. Our goal is to extend that benefit into the short-wavelength infrared. Using the best material currently available and a novel bandgap-engineering design and process, we will fabricate photodetectors and, ultimately, focal plane arrays.In Phase I, we are going to demonstrate photodetector designs based on Type-II superlattices, which can cover spectral range between 0.4 to 2.5 um with a very low dark current density (<10^(-11) A/cm2) at temperatures below 100 K.. In Phase II, we are going to continue reduction of the dark current density to <10^(-13) A/cm2-level at temperatures below 100K. Then, we will use the optimized device design to develop and deliver 1K×1K imagers to NASA for planetary sciences.

Benefits: Visible-SWIR photodetectors are of special interest to NASA for planetary observation missions. The Visible-SWIR imagers can be used to study the world's ecosystems and provide critical information on natural disasters such as volcanoes, wildfires and drought. Visible-SWIR imaging will be able to identify the type of vegetation that is present and whether the vegetation is healthy. It can provide a benchmark on the state of the worlds ecosystems against which future changes can be assessed. Moreover this imaging method can assess the pre-eruptive behavior of volcanoes and the likelihood of future eruptions as well as the carbon and other gases released from wildfires. The data from Visible-SWIR imagers can be used for a wide variety of studies primarily in the Carbon Cycle and Ecosystem and Earth Surface and Interior focus areas. The large-format Visible-SWIR cameras, with ultra-low dark current, we will be developing and delivering in Phase II of this program will be able to provide high resolution mapping of planetary bodies.

The key applications of visible-SWIR imaging are listed below: * Mineral exploration, resource management, and environmental monitoring. * In agriculture for monitoring the development and health of crops. * In geology for rapidly mapping nearly all minerals of commercial interest * For ecology, surveillance, and historical manuscript research * For research in areas such as nano-drug delivery and nano-toxicology * For use in many research areas, such as vegetation research, forensics, life sciences, food analysis, and mineral research. * FTIR imaging microscopy * Gas imaging (e.g. for the petrochemical industry) * Security and surveillance (day and night) * Missile defense * Space-based situational awareness The development of high-performance visible-SWIR imagers based on Type-II superlattices has the potential to eliminate the need for expensive mercury-cadmium-telluride materials and thus the potential to significantly reduce the operational cost of these sensors and thus potentially open up new lower cost commercial applications.