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

Simultaneous in situ measurements of small-scale structures in neutral, plasma, and atomic oxygen densities during the WADIS sounding rocket project

In this paper we present an overview of measurements conducted during the WADIS-2 rocket campaign. We investigate the effect of small-scale processes like gravity waves and turbulence on the distribution of atomic oxygen and other species in the mesosphere-lower thermosphere (MLT) region. Our analysis suggests that density fluctuations of atomic oxygen are coupled to fluctuations of other constituents, i.e., plasma and neutrals. Our measurements show that all measured quantities, including winds, densities, and temperatures, reveal signatures of both waves and turbulence. We show observations of gravity wave saturation and breakdown together with simultaneous measurements of generated turbulence. Atomic oxygen inside turbulence layers shows two different spectral behaviors, which might imply a change in its diffusion properties. © 2019 Author(s)

Noise in InAs/GaSb type-II superlattice photodiodes

The noise behavior of InAs/GaSb superlattice photodiodes for high-performance thermal imaging in the mid- and longwavelength infrared atmospheric windows at 3-5 µm and 8-12 µm is complex and up to now not very well understood. In order to characterize these devices we have developed a noise measurement setup with a noise current resolution in the femtoampère range. First, we show that, when sidewall leakage is absent, InAs/GaSb superlattice photodiodes with a low dark current very close to the generation-recombination limited dark current level of the bulk behave according to the well-known shot noise expression. Next, we investigate a set of 18 large-area diodes with a bandgap in the midwavelength infrared regime, which show an increased dark current depending linearly on the applied reverse bias. For these diodes the common shot noise model generally fails to describe the noise experimentally observed in the white part of the noise spectrum. Instead, we find that McIntyre's excess noise model for electron-initiated avalanche multiplication processes fits our data remarkably well for the entire set of diodes, which covers about three orders of magnitude in dark current and a wide range of reverse bias voltage. Thus, to explain the mechanism leading to the increased reverse dark current and observed excess noise we tentatively suggest that primary electrons originating from Shockley-Read-Hall states within the space charge region might initiate avalanche multiplication processes within high electric field domains localized around sites of macroscopic crystallographic defects

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

Dual-color InAs/GaSb superlattice focal-plane array technology

Within a very few years, InAs/GaSb superlattice technology has proven its suitability for high-performance infrared imaging detector arrays. At the Fraunhofer Institute for Applied Solid State Physics (IAF) and AIM Infrarot-Module GmbH, efforts have been focused on developing mature fabrication technology for dual-color InAs/GaSb superlattice focal-plane arrays for simultaneous, colocated detection at 3 µm to 4 µm and 4 µm to 5 µm in the mid-wavelength infrared atmospheric transmission window. Integrated into a wide-field-of-view missile approach warning system for an airborne platform, a very low number of pixel outages and cluster defects is mandatory for bispectral detector arrays. Process refinements, intense root-cause analysis, and specific test methodologies employed at various stages during the process have proven to be the key for yield enhancements

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