The presence of dark current, signal charge which is not due to photons, has been a performance limiter for image sensors. There has been a 5000x decrease over 40 years and there is the assumption that this trend will continue. However, the decrease has been accompanied by a change of the nature of the generation mechanism as is seen in characterization data related to voltages and temperature. The present limiting root cause of dark current needs to be determined to guide further improvement. It is also interesting to speculate on the ultimate limitation of dark current in defect-free silicon.
Dan McGrath, Steve Tobin, Vincent Goiffon, Pierre Magnan, Alexandre Le Roch, "Dark Current Limiting Mechanisms in CMOS Image Sensors" in Proc. IS&T Int’l. Symp. on Electronic Imaging: Image Sensors and Imaging Systems, 2018, pp 354-1 - 354-8, https://doi.org/10.2352/ISSN.2470-1173.2018.11.IMSE-354