Infrared photodetection based on colloidal nanoparticles is a promising path toward low cost devices. However, mid-infrared absorption relies on interband transitions in heavy metal-based materials, which is a major flaw for the development toward mass market. In the quest of mercury-free infrared active colloidal materials, we here investigate Ag2Se nanoparticles presenting intraband transition between 3 and 15 µm. With photoemission and infrared spectroscopy, we are able to propose an electronic spectrum of the material in absolute energy scale. We also investigate the origin of doping and demonstrate that it results from a cation excess under Ag + form. We demonstrate photoconduction into this material under resonant excitation of the intraband transition. However, performances are currently quite weak with (i) a slow photoresponse (several seconds), and (ii) some electrochemical instabilities at room temperature.

Nanocrystals are promising materials for the design of low cost infrared detectors. Here we focus on HgTe colloidal quantum dots (CQDs) as an active material for detection in the extended shortwave infrared (2.5 µm as cutoff wavelength). In this paper, we propose a strategy to enhance the performances of previously reported photodiodes. In particular we integrate in this diode an unipolar barrier which role is to prevent the dark current injection to enhance the signal to noise ratio. We demonstrate that such unipolar barrier can be designed from another layer of HgTe CQDs with a wider band gap. Using a combination of IR spectroscopy and photoemission, we show that the barrier is resonant with the absorbing layer valence band, while presenting a clear offset with the conduction band. The combination of contacts with improved design and use of unipolar barrier allows us to reach a detectivity as high as 3•10 8 Jones at room temperature with 3 dB cut off frequency above 10 kHz.