Design and Fabrication of Strain-Balanced nBn Dual-Band LWIR/LWIR Focal Plane Arrays Based on InAsSb/InAsType-II Superlattices

The infrared spectral range is of particular interest for remote planetary sensing of gaseous molecules, such as H2O, CO2, CH4, N2O, CO, NH3, and many other compounds. Infrared thermography can also be used to accurate measure minute variations in surface temperatures. High performance infrared focal plane arrays (FPAs) allow rapid acquisition of a 2D surface maps--indispensable in planetary sciences. By using two different cut-off detectors integrated into a single FPA to simultaneously image a planet we can avoid atmospheric effect and much more accurately map minute variations in the surface temperature, or gain a clearer picture of the atmospheric composition. In recent years, Type-II InAs/GaSb superlattices have experienced significant development—we have played a pioneering role in the rapid development of that technology. However, the full potential of Type-II superlattice has not been fully explored and alternate superlattice architectures hold great promise; one of the most promising is gallium free InAsSb/InAs Type-II superlattices. In this project, we propose to study strain-balanced nBn InAs1-xSbx/InAs Type-II superlattice-based photodetectors and mini-arrays for LWIR/LWIR dual-band detection. Using this new superlattice structure, it is expected to achieve longer minority carrier lifetime. Longer minority carrier lifetime results in lower dark current, lower noise, higher operation temperature, and higher quantum efficiency. Applying this superlattice design to dual-band LWIR/LWIR FPAs, it is expected to achieve higher quantum efficiency, lower dark current, higher specific detectivity (D*) and reduced Noise Equivalent Temperature Difference (NETD). This work will form the basis of the Phase II work in which we will use this new superlattice structure to develop and deliver LWIR/LWIR dual-band FPAs for planetary sciences.

LWIR is of special interest to NASA for planetary observation missions. The LWIR wavelength region is also an ideal wavelength to look at other planets, or look back at the earth from space, and accurately map minute variations in the surface and/or atmospheric temperatures. Furthermore, by using simultaneous measurements from two different LWIR wavelengths (i.e. a two-color camera) it is possible to better isolate the surface temperature from that of the atmosphere or vice versa. Using the infrared emission of the planetary body or active illumination via a laser source it is also possible to carefully look at the atmospheric absorption and perform chemical spectroscopy. Many molecules such as H2O, CO2, CH4, N2O, CO, NH3 have absorption lines in the infrared and the ability to compositionally map the concentrations of these and many other molecules. The large-format two color cameras we will be developing and delivering in Phase II of this program will be able to provide high resolution mapping of planetary bodies.

IR imaging sensors also find their use in commercial applications such as satellite imaging, weather modelling, geophysics, geology, remote environmental (pollution) IR monitering, law enforcement, search and rescue, firefighting, and emergency response. For its part, the Optoelectronics Industry Development Association estimates that the current infrared imaging market for military and law enforcement applications is about US$3 billion. The development of higher performance LWIR imagers and two color LWIR/LWIR imagers based on Type-II superlattices has the potential to eliminate the n eed 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.

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