Electrical and optical characterization of quantum dots PbS/TiO₂ based heterojunction as a SWIR detector and a proposed design of PbS/TiO₂-PeLED as a SWIR to visible upconversion device

In this work we present the electrical and optical characterizations of a Short Wavelength Infrared (SWIR) photodetector, which consists of tandem FTO/TiO₂/PbS colloidal quantum dot (CQD) layers. The TiO₂/PbS hetero-structure can be operated either as a standalone detector or as the SWIR absorption section of a SWIR to visible up-conversion device (SWVUCD) when visible photo-emission layer is attached to infrared absorption layer such as this heterojunction. The results reveal the existence of the PbS CQD's bandgap operating in the SWIR spectral range as well as exhibit mixed photovoltaic and photoconductive characteristics. The optical characteristics of the different grown layers were analyzed by photoluminescence and absorption methods. The current density - voltage (J-V) curve at forward bias shows a crossover effect, however, no rollover effect has been observed. The latter indicates that there is no Schottky barrier component in this structure. We have concluded that in our case the energy bandgap of the PbS CQD is 0.93 eV where a defects states level with energy of 0.83 eV in the bandgap is evident. Finally, we propose and discuss a possible architecture of such a SWIR photosensitive hetero-structure wafer bonded to a Perovskite LED in order to form an imaging SWVUCD. Such a SWVUCD, when attached to a visible CMOS sensor, can serve as a low cost SWIR based detector for eye-safe Laser Imaging Radar (LiDAR) and for SWIR night vision applications. Such an architecture is favorable over current technologies with regard to manufacturing costs, preparation complexity, power consumption, size and weight.