  Silicon photonics faces a persistent challenge in extending photodetection
capabilities beyond the 1.6 um wavelength range, primarily due to the lack of
appropriate epitaxial materials. Colloidal quantum dots (QDs) present a
promising solution here, offering distinct advantages such as infrared
wavelength tunability, cost-effectiveness, and facile deposition. Their unique
properties position them as a potential candidate for enabling photodetection
in silicon photonics beyond the conventional telecom wavelength, thereby
expanding the potential applications and capabilities within this domain. In
this study, we have successfully integrated lead sulfide (PbS) colloidal
quantum dot photodiodes (QDPDs) onto silicon waveguides using standard process
techniques. The integrated photodiodes exhibit a remarkable responsivity of 1.3
A/W (with an external quantum efficiency of 74.8%) at a wavelength of 2.1 um, a
low dark current of only 106 nA and a bandwidth of 1.1 MHz under a -3 V bias.
To demonstrate the scalability of our integration approach, we have developed a
compact 8-channel spectrometer incorporating an array of QDPDs. This
achievement marks a significant step toward realizing a cost-effective
photodetector solution for silicon photonics, particularly tailored for a wide
range of sensing applications around the 2 um wavelength range.
