Imaging detection of CO 2 using a bispectral type-II superlattice infrared camera

Abstract Bispectral infrared (IR) cameras provide additional spectral information in contrast to common monospectral devices, which merely measure the integrated intensity of IR radiation. A bispectral IR camera has been manufactured from InAs/GaSb type-II superlattices. The two detector channels range from 3 -4 µm and 4 -5 µm, respectively. Thus, this camera is very sensitive to the spectral signature of carbon dioxide at approximately 4.3 µm and can be used for remote imaging of CO2

Defect density reduction in InAs/GaSb type II superlattice focal plane array infrared detectors

InAs/GaSb short-period superlattices (SL) have proven their large potential for high performance focal plane array infrared detectors. Lots of interest is focused on the development of short-period InAs/GaSb SLs for mono- and bispectral infrared detectors between 3 - 30 µm. InAs/GaSb short-period superlattices can be fabricated with up to 1000 periods in the intrinsic region without revealing diffusion limited behavior. This enables the fabrication of InAs/GaSb SL camera systems with very high responsivity, comparable to state of the art CdHgTe and InSb detectors. The material system is also well suited for the fabrication of dual-color mid-wavelength infrared InAs/GaSb SL camera systems. These systems exhibit high quantum efficiency and offer simultaneous and spatially coincident detection in both spectral channels. An essential point for the performance of two-dimensional focal plane infrared detectors in camera systems is the number of defective pixel on the matrix detector. Sources for pixel outages are manifold and might be caused by the dislocation in the substrate, the epitaxial growth process or by imperfections during the focal plane array fabrication process. The goal is to grow defect-free epitaxial layers on a dislocation free large area GaSb substrate. Permanent improvement of the substrate quality and the development of techniques to monitor the substrate quality are of particular importance. To examine the crystalline quality of 3'' and 4''GaSb substrates, synchrotron white beam X-ray topography (SWBXRT) was employed. In a comparative defect study of different 3'' GaSb and 4'' GaSb substrates, a significant reduction of the dislocation density caused by improvements in bulk crystal growth has been obtained. Optical characterization techniques for defect characterization after MBE growth are employed to correlate epitaxially grown defects with the detector performance after hybridization with the read-out integrated circuit

High operating temperature InAs/GaSb type-II superlattice detectors on GaAs substrate for the long wavelength infrared

We report on the development of InAs/GaSb type-II superlattice infrared photodetectors for operation under temperatures reachable with thermoelectric cooling. We investigate optically immersed, laterally operated photoconductors with a cutoff wavelength around 10 μm at an operating temperature of 200 K. The identification of a suitable superlattice composition, the growth of a linearly graded metamorphic buffer layer and the transfer of the device concept from GaSb to GaAs are motivated and described. We show that immersion lens technology even for non-doping optimized devices enables a peak spectral detectivity above 6×109 cm Hz0.5W−1 at 195 K, approaching the performance of commercially available HgCdTe-based photoconductors

Infrared photodetector development at Fraunhofer IAF

Fraunhofer IAF can look back on many years of expertise in developing high-performance infrared photodetectors. Since pioneering the InAs/GaSb type-II superlattice detector development, extensive capabilities of epitaxy, process technology, and device characterization of single element detectors and camera arrays for the mid- and longwave infrared (MWIR and LWIR) have been established up to the level of small-scale production. Bispectral MWIR/MWIR and MWIR/LWIR cameras based on type-II superlattices or HgCdTe are key topics at Fraunhofer IAF. Recently, we started the development of InGaAs-based short-wave infrared (SWIR) photodetectors for low-light-level applications. In this contribution, we report on materials and technology development for SWIR p-i-n and avalanche photodiodes (APDs), covering detector design, epitaxial growth, process technology, and most recent electro-optical characterization results of focal plane arrays as well as single element detectors