InAs Colloidal Quantum Dot Photodiode Stack for CMOS-Integrated Infrared Imaging

Heavy-metal-free III-V semiconductor-based colloidal quantum dots (CQDs), such as InAs, are promising candidates for near- and short-wave infrared detection. However, up-to-date research efforts remain mainly limited to wavelengths below 1100 nm due to challenges in synthesis, junction formation, and passivation for large diameter InAs quantum dots. Systematic investigations into device design, reverse dark current mechanisms, and trap distributions in larger InAs quantum dots remain limited. Here, we report a thin-film PIN heterojunction colloidal InAs (1200 nm) photodiode stack with amorphous indium gallium zinc oxide and copper(I) iodide transport layers. To the best of our knowledge, the device exhibits one of the lowest reported dark current densities of 4.7 μA/cm² at -1 V and 298 K, which decreases to 3.6 nA/cm² at 220 K. Temperature-dependent current-voltage characteristics and activation energy analysis confirm thermally driven dark current increasing with applied field. Impedance spectroscopy reveals the dominant deep trap states within the InAs CQD layer, being tail states of the conduction band that reach down to ∼0.4 eV below the band edge, with a density of ∼2 × 10¹⁶ cm^-3. The temperature-induced increase in carrier density and reduction in built-in potential within the depleted InAs layer reflect trap filling and Fermi level pinning in the N and P layers. The trapping-detrapping induced noise reduces the specific detectivity (D*) at -1 V by 1.97 orders at 1 Hz and by 1.52 orders of magnitude at 10 Hz relative to the shot-noise-limited baseline. At frequencies ∼ ≥500 Hz the D* approaches the calculated limit of 2.5 × 10¹¹ Jones. Finally, we demonstrate infrared imaging by monolithically integrating the photodiode with a Si read-out IC, enabling imaging beyond the spectral range of CMOS sensors.