On the Suitable Choice of Metal for HgTe Nanocrystal-Based Photodiode: To Amalgam or Not to Amalgam

HgTe,thanks to its unique spectral tunability in the infrared,is the only material able to cover near-, short-, and mid-wave infrared.Current best devices rely on electrodes made from transparent conductiveoxides and gold, but so far, none of these completely fit for theintended purpose. Gold is not compatible with Si foundries, and transparentconductive oxides are highly lossy in this spectral range, limitingelectrode transparency. Metal-based electrodes appear as good alternativecandidates but require further investigations. While obvious constraintsof work function get raised, chemical stability appears equally important.Here, we screen the use of Au, Al, Ag, and Zn as possible metals andreveal that in the case of Ag, dramatic transformations of Ag andHgTe are observed. Especially, a cation exchange procedure can occurover a solid-state film without intentional heating of the sample.This process has then been studied by combining both structural andelectronic probes. This work points out the importance of the carefulchoice of surrounding electrodes in the case of HgTe since the observedmechanism is likely not limited to Ag. On the other hand, both Auand Al appear stable toward this transformation.