Development and simulated environment testing of β-(Al)Ga2O3-based photodetectors for space-based observation of the Herzberg continuum
Résumé
With the advent of “New Space” and the explosion of nanosatellite missions, an extended latitude is offered for the emergence of innovative technological devices such as novel compact solid state UVC sensors. In this context, β-Ga2O3-based photodetectors are emerging as very promising candidates to overcome current technological limits for UVC detection in Space. Indeed, monitoring UVC solar radiation, and more specifically the Herzberg continuum (200-242nm), is fundamental to understand its’ impact on the earth’s climate and build better chemistry-climate models [1]. It is also, however, extremely challenging to achieve due to the harsh operating environment including large thermal variations, high energy particles, ionizing radiation and filter contamination due to satellite outgassing. The Ultra Wide Band Gap semiconductor, β-Ga2O3 (Eg ~ 4.9eV at 253nm), is intrinsically solar blind, radiation-hard and thermally-robust. Furthermore, the authors have recently shown that the bandgap can be engineered upwards through Al alloying so as to obtain optical transitions from 253 down to 200nm [2,3]. This allows the realization of β-Ga2O3-based photodetectors with peak operating wavelengths which capture the Herzberg continuum selectively and thus, dispenses with the need for short pass filters. Therefore, these β-Ga2O3-based photodetectors are excellent candidates to monitor the Herzberg continuum from Space. Hence, they have been selected to be integrated on the INSPIRE-Sat 7 (International Satellite Program in Research and Education) nanosatellite (“2U” CubeSat) which will monitor the Herzberg continuum on a low Earth orbit, following a prototype mission UVSQ-Sat (INSPIRE-Sat 5) successfully launched in January 2021 [4]. This work presents the realization of β-Ga2O3-based photodetectors going from the wafer to the final packaged sensors including device architecture development, photolithography, contacting, probing, singulation, packaging, stringent robustness testing (in a simulated environment) and performance binning, so as to obtain the final flight model photodetectors.