Low-flux long-wave infrared FPAs developments at LETI for science applications

For several years, CEA-LETI has worked on the development of IR MCT detectors for low flux applications in scientific imaging. MCT has remarkable material properties that allow for highly performing detection, with high QEs and minimal dark currents. Currently, both Teledyne US and LETI-Lynred in France achieve dark currents in the range of a fraction of e/s/pixel for NIR imaging, utilizing the p-on-n extrinsic diode structure, for astronomy applications. As part of the NEOCAM project, Teledyne has demonstrated the ability to extend the cut-off wavelength to significantly longer wavelengths (10.3μm and recently 13μm) while keeping the dark current in the e/s range. Furthermore, LETI is presently enhancing its p-on-n technology to satisfy the demanding specifications of low-flux applications. Achieving very low dark current leakage and large diode polarisation plateaus is required to achieve SFD input stage ROIC operation and to reach such low dark current values. This entails the mitigation of tunnelling currents that appear in low-gap materials. In this report, we present the production of a 15μm pitch TV-size prototype array that operates in the LW range (8μm @ 35K). Dark current values as low as 0.5 e/s/pixel have been measured below 40K, and will be discussed.