On‐Chip Colloidal Quantum Dot Photodetectors With a Complementary Metal–Oxide–Semiconductor‐Compatible Architecture for Near‐Infrared Light Sensing and Electrical Signal Amplification

Solution‐processed semiconductors with tunable optical absorption and compatibility with complementary metal–oxide–semiconductor technology offer an attractive route for near‐infrared (NIR) photodetection. Colloidal quantum dots (CQDs) are promising candidates due to their solution processability and superior optoelectronic properties. Although CQD/Si heterojunction photodiodes extend the photoresponse of silicon beyond its intrinsic absorption limit, their photocurrent is typically limited, often requiring external operational amplifiers for signal readout. Here, we demonstrate a PbS CQD photodiode‐integrated silicon bipolar junction transistor (BJT) that enables intrinsic electrical amplification of the NIR photoresponse. Device simulations show that optical absorption in the CQD layer generates a photovoltage at the CQD/Si heterojunction, which drives the transistor into the active regime and produces an amplified collector voltage. Proof‐of‐concept experiments using PbS CQD/Si photodiodes coupled to a commercial npn BJT confirm current amplification and a linear dependence of the output voltage on the incident optical power.