Design of a Unipolar Barrier for a Nanocrystal-Based Short-Wave Infrared Photodiode

Nanocrystals are promising materials for the design of low-cost, infrared (IR) 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 cutoff wavelength). In this paper, we propose a strategy to enhance the performances of previously reported photodiodes. In particular, we integrate in this diode a unipolar barrier, whose role is to reduce the dark current injection and subsequently 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 a 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.