Optimization of charge carrier extraction in colloidal quantum dots short-wave infrared photodiodes through optical engineering

Colloidal quantum dots (QDs) have attracted scientific interest for infrared (IR) optoelectronic devices due to their bandgap tunability and the ease of fabrication on arbitrary substrates. In this work, short-wave IR photodetectors based on lead sulfide (PbS) QDs with high detectivity and low dark current is demonstrated. Using a combination of time-resolved photoluminescence, carrier transport, and capacitance-voltage measurements, it is proved that the charge carrier diffusion length in the QD layer is negligible such that only photogenerated charges in the space charge region can be collected. To maximize the carrier extraction, an optical model for PbS QD-based photodiodes is developed, and through optical engineering, the cavity at the wavelength of choice is optimized. This universal optimization recipe is applied to detectors sensitive to wavelengths above 1.4 mu m, leading to external quantum efficiency of 30% and specific detectivity (D*) in the range of 10(12) Jones

Thin-film quantum dot photodiode for monolithic infrared image sensors

Imaging in the infrared wavelength range has been fundamental in scientific, military and surveillance applications. Currently, it is a crucial enabler of new industries such as autonomous mobility (for obstacle detection), augmented reality (for eye tracking) and biometrics. Ubiquitous deployment of infrared cameras (on a scale similar to visible cameras) is however prevented by high manufacturing cost and low resolution related to the need of using image sensors based on flip-chip hybridization. One way to enable monolithic integration is by replacing expensive, small-scale III-V-based detector chips with narrow bandgap thin-films compatible with 8- and 12-inch full-wafer processing. This work describes a CMOS-compatible pixel stack based on lead sulfide quantum dots (PbS QD) with tunable absorption peak. Photodiode with a 150-nm thick absorber in an inverted architecture shows dark current of 10(-6) A/cm(2) at 2 V reverse bias and EQE above 20% at 1440 nm wavelength. Optical modeling for top illumination architecture can improve the contact transparency to 70%. Additional cooling (193 K) can improve the sensitivity to 60 dB. This stack can be integrated on a CMOS ROIC, enabling order-of-magnitude cost reduction for infrared sensors

FABRICATION AND CHARACTERIZATION OF LARGE-AREA FLEXIBLE CAPACITIVE MICROMACHINED ULTRASOUND TRANSDUCERS

This work was funded by an SB PhD fellowship of the Research Foundation-Flanders [FWO, 1S27524N]. The authors would like to thank Tsung-Chieh Sun for his assistance in cleanroom processing, Clement Leruth for scanning electron microscopy (SEM), and Francois Berghmans for running the automatic prober

Monolithic near infrared image sensors enabled by quantum dot photodetector

status: publishe