Design of Unipolar Barrier for Nanocrystal Based Short Wave Infrared Photodiode

International audience; 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 short-wave infrared (2.5 µm as cut-off 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 3·108 Jones at room temperature with 3 dB cut off frequency above 10 kHz.