Periodic Reporting for period 3 - SWIRup (HOT III-V II-VI Focal Plane Arrays for Space Applications in the Upper SWIR Band) Reporting period: 2021-07-01 to 2022-07-31 Summary of the context and overall objectives of the project One of the most difficult challenges in the future is to manage greenhouse effect and natural disasters. This requires spectroscopic imaging for remote sensing of greenhouse gases. The most known is the on-going ESA Anthropogenic CO2 monitoring mission (CO2M: Copernicus Space Component Expansion) that have been identified by the European Commission as a priority. There are also needs for high-resolution earth observations in geological applications, land degradation studies, vegetation conditions, ground biomass or separation between snow, cloud & ice. All these applications require a real-time monitoring from space. The core sensor of the current optical payload of these satellites is a HgCdTe N/P detector cooled to 150 K. This cryogenic temperature is a penalty which restricts its use. For many applications, the penalty is even greater when several small satellites must be used to deliver the required data.SWIR imaging technologies are also widely used in airborne, laboratory and industry, via hyperspectral imaging systems. Example applications of SWIR hyperspectral imaging include mineral mapping, urban planning, quality control in food, military target detection, search and rescue, micro-plastic detection and classification, medical, and forestry.The key technology common to SWIR satellites and hyperspectral imagers is the Focal Plane Arrays (FPA) of the imager. FPA, which is part of the hybrid circuit family is constituted of a detection circuit hybridized on a Read-Out Integrated Circuit (ROIC). The small satellite European roadmap requires cheaper satellite. Then improvements within the detection circuit, especially for the SWIR bands, are necessary. To meet this objective, all SWIR camera integrators desire a detector technology capable of a higher operating temperature (HOT), as close as possible to room temperature: 240-290 K would be a convenient range which avoids the use of cooling system. Then, satellite power consumption and mass would be significantly decreased.To increase the operating temperature, SWIRup project will concentrate on the improvement of the detection circuits, which are the common part of the FPAs.The strategy selected for this project consists to push forward and to compare two sensor materials:- Adapt the top state-of-the-art InGaAs III-V sensor material from 1,7µm to at least 2,3 µm, with a dark current level offering the possibility to operate the detector at the targeted temperature. This technology corresponds to InGaAs/GaAsSb super-lattice (type 2) lattice matched to InP substrate.- Improve the HgCdTe P/N technology which is actually the European reference solution for SWIR detectors (see ASTEROID H2020 project).The SWIRup consortium will develop, manufacture and test different detector prototype of the 2 technological chains identified previously with the goal to reach a TRL 5 level. At the end of the project, a system demonstration will be performed in Norway with an existing spectrometer to acquire realistic scenes in hyper spectral. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far Detector specification has been completed by Thales Alenia Space to comply with a large panel of SWIR instruments that can be used in harsh space or conventional terrestrial environments.For III-V detector technologies, the work began with designs of Type-II superlattice (T2SL) carried out by III-V Lab and University of Sheffield(USFD). Despite using different simulation software, similar designs were reached by the 2 partners.Following the design work, III-V Lab carried out the first round of wafer growths (bulk InGaAs and T2SL wafers). Using these wafers, device fabrication was carried out by III-V Lab and USFD, which encountered issues with device fabrication in the first FPA lot. These issues were identified and have been rectified. A new ultimate wafer batch have been manufacturing.The final performance (dark current-voltage and photoresponse) could not be assessed as the wafers processing is not finshed yet, as well the associated FPA characterisations and environmental tests. However, preliminary results are encouraging since photoluminescence measurements indicated cutoff of 2 wafers at 2.2 µm and 2.5 µm repectively. Holes localization effects in the T2SL photodiodes shall be reduced by lattice strained compensation, which makes expect higher quantum efficiency. The InGaAs is large enough to achieve flat band conditions in the T2SL stack to reduce the dark current, and thin enough to optimize collection at lower bias conditions. A smoother valence band offset is introduced for that aim also. The definition of the II-VI epilayers growth was conducted by CEA/LETI. n-doped, Hg1-xCdxTe epilayers on 47x48mm CZT substrates have been grown. Three level of In donor concentration has been selected. After optimization of the epitaxial process, a set of 4 LPE layers with optimal characteristics has been grown. Their cutoff wavelength are close to the target (2.4 µm). MCT FPA and test chips masks have been procured and the fabrication of the MCT detection circuits wafers ended during RP1. Tests at wafer level have revealed the presence of current excess for all diode designs on all wafers, which is due to current leakage between photodiodes at passivation level.After E-O characterization on test chip constituted of 84 diodes, a technological correction which aim was to cut the conduction channel between photodiodes has been applied and some detections circuits have been hybridized on the ROIC. The test means developed for the level 1 electro-optical characterization of the FPAs has been used to make dark current measurement. The conclusion is that the correction does not solve completely the crosstalk issue but remains interesting for fine characterisations. 1 FPA has been delivered to TAS.Laboratory cryostat and Video Acquisition System (VAS) have been defined by TAS, then designed and manufactured by the STFC engineering team, and recently delivered to TAS. The VAS has been validated coupled with the TAS test benches, on a standard SNAKE detector. In particular TAS demonstrated its novel MTF measurement method based on titled LSF (Line Spread Function). However no time was left to characterize the delivered II-VI FPA. The assembly of the SWIRup dedicated spectrometer initiated at NEO during the second period of the project, could be finished as well as no III-V FPA was available.The website ‘swirup.eu’ was updated by USFD. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) T2SL are proposed as solution for versatile solutions in the full infrared spectral range. SWIRup provides a deep understanding of T2SL performances transport based on holes as minority carriers. Localization has not been detailed so accurately before.At the end of the project, at least one and probably two hot detector technologies (with a limitation at 2,1 µm for the III V one) will be available to answer to the SWIR spectral region needs. Compared to the existing TRL 9 SWIR detector technologies (HgCdTe N/P), the operating temperature actually between 150 and 200 K, can be increased at a level compatible with a standard thermal control using small passive radiators. Then, the implementation of SWIR channels will be easier that it is currently, which means smaller and less expensive systems while reducing power consumption and increasing the possibility of greenhouse gases monitoring. View of the head board of the VAS, integrated inside the cryostat View of the main board of the VAS, including four 16 bits video chains 3 D view of a detector breaboard in the final configuration PCB packaging used to support one detector chip and to address interconnexion function Wafer of HgCdTe manufactured by CEA/LETI for the II VI detector breadboards 3D view of the laboratory cryostat under development in the system demonstration configuration SWIR MTF test bench developped by TAS with VAS and cryostat delivered by STFC
