Transport in ITO Nanocrystals with Short- to Long-Wave Infrared Absorption for Heavy-Metal-Free Infrared Photodetection

Nanocrystals are often described as interesting materials for the design of low-cost optoelectronic devices, especially in the infrared range. However, the driving materials reaching infrared absorption generally contain heavy metals (Pb and Hg) with a high toxicity. An alternative strategy to achieve infrared transition is the use of doped semiconductors presenting intraband or plasmonic transition in the short-, mid-, and long-wave infrared. This strategy may offer more flexibility regarding the range of possible candidate materials. In particular, significant progress has been achieved for the synthesis of doped oxides and for the control of their doping magnitude. Among them, tin doped indium oxide (ITO) is the one providing the broadest spectral tunability. Here we test the potential of such ITO nanoparticles for photoconduction in the infrared. We demonstrate that In2O3 nanoparticles present an intraband absorption in the mid-infrared range which is transformed into a plasmonic feature as doping is introduced. We have determined the cross section associated with the plasmonic transition to be in the 1–3 × 10–13 cm2 range. We have observed that the nanocrystals can be made conductive and photoconductive thanks to a ligand exchange using a short carboxylic acid, leading to a dark conduction with n-type character. We present evidence that the observed photoresponse in the infrared is the result of a bolometric effect.