Revealing Additional Size-Dependent Defect Suppression Channels Governing Detectivity in InAs Colloidal Quantum Dot Photodiodes

Abstract

Indium arsenide (InAs) colloidal quantum dot (CQD) photodiodes combine tunable bandgaps with solution processing, offering a versatile platform for infrared detection. Using high-dynamic-range external quantum efficiency (HDR-EQE) measurements, we probe defect signatures and quantify their impact on performance. Analysis of Urbach tails and Gaussian sub-bandgap states shows that trap densities decrease with increasing nanocrystal size, exceeding predictions from simple surface-to-volume scaling and underscoring the influence of surface chemistry on bandedge disorder. These defect states affect the dark saturation current (J0), enabling us to estimate their contribution to detectivity and noise. The results connect nanocrystal size, defect population, and device performance, distinguishing intrinsic trap-mediated effects from extrinsic loss channels. We find that while intrinsic defects play a role, today’s InAs CQD photodiodes are primarily limited by contact and interface properties, highlighting these as key targets for further improvement.