Technology Development of Extended Spectral Response for SWIR Detectors

SELEX ES Ltd with STFC ATC

Project Funded in the CEOI-ST EO9 Call for Mission and Technology Studies in preparation for future ESA Earth Explorer Missions

Fast Track Project

In response to the latest funding call from the Centre for Earth Observation Instrumentation and Space Technology (CEOI-ST), Selex ES is proposing a technology development activity in preparation for the ESA Earth Explorer 9 (EE9) Mission Proposals. The objective of this programme of work is to de-risk and mature the performance of NIR and SWIR cooled infrared detectors over an extended spectral range which is critical for a number of proposed earth observation missions such as TRUTHS and Tropical Carbon Mission. These missions are seeking a single detector solution to cover a spectral range from <1 micron to 2.5 microns in order to address the spectral features of interest. Development of detectors with the required performance will provide a return on the investment made in these programmes by the UK, through exploitation of our leading edge IR detector capability and avoid the need to use detectors which are subject to ITAR restrictions. This work will support detector proposals for earth observation and science missions and will advance the existing technology developments towards a higher TRL, which will de-risk the intended flight programmes.

Selex ES has invested over many years in its MOVPE growth on GaAs substrates to bring it to the point where it provides world leading performance and offers particular benefits to large format arrays through its low cost capabilities. Selex ES devices with cut-off wavelengths required for the programmes above have demonstrated good performance using a standard diode design as implemented on a range of detectors. In order to achieve the requirement for improved quantum efficiency at lower cut-on wavelengths, we have supplemented ESA funding on current NIR and SWIR large format detector development programmes with company funding to develop novel structures. Characterisation of these devices has been undertaken in collaboration with the UK ATC. This work has demonstrated improvements in the spectral performance for both conventional and avalanche photodiode designs in MCT. In addition, recent work jointly funded by Selex ES and CEOI successfully radiation tested the cell design implemented in large format silicon CMOS read out integrated circuits (ROICs). This includes our 2k x 2k device, which is the basis for the largest MCT device in Europe developed through ESA TRP programme. Together these developments have enhanced the TRL of the array level products.

We are now proposing to undertake further design, manufacture, and characterisation of novel MCT photodiode structures as part of the drive towards achieving uniform and high quantum efficiency across the wavelength range of interest. This work exploits the capabilities of the MOVPE technology to extend the cut-on to lower wavelengths and achieve this with high and uniform quantum efficiency through adjustment of the diode structure such that the transport properties of the photo-generated charge carriers are uniform across the waveband of interest. We propose to take the lessons from the preceding activities and apply these to two new designs to investigate the relative merits of the different structures. We have selected the smaller format Saphira ROIC with world leading low noise performance, developed for ESO wavefront sensing applications, as the most appropriate vehicle for demonstrating these MCT developments based on cost and performance. The resulting MCT designs would then be applied to arrays using existing and future ROICs such as the NIR and SWIR large format devices.

Once the MCT material has been designed, grown, processed and diced, it will be hybridised to the Saphira ROIC and screen tested at Selex ES to select the best device. Detailed characterisation will be undertaken at the UK Astronomy Technology Centre in Edinburgh using their existing test set up established for the Saphira device.