Thin-Film Photodetector Optimization for High-Performance Short-Wavelength Infrared Imaging

Abstract

In this letter, we present a small pixel pitch image sensor optimized for high external quantum efficiency in short-wavelength infrared (SWIR). Thin-film photodiodes based on PbS colloidal quantum dot (CQD) absorber allow us to exceed the spectral limitations of silicon’s absorption while maintaining the benefits of CMOS technology. By monolithically integrating PbS CDQ thin films with CMOS readout arrays, high-pixel density SWIR image sensors can be achieved. To overcome the remaining disadvantages of the CQD-based image sensors over their bulk III-V semiconductor counterparts (lower sensitivity and reduced linearity), the thin-film photodiode stack is adapted towards the used readout circuit. A prototype image sensor with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$768\times 512$ </tex-math></inline-formula> resolution of 5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> pitch pixels is fabricated by using a modified 130 nm CMOS process for readout IC, together with the new CQD thin-film photodiode on top. Thanks to the optimized photodiode stack and co-integration process, the prototype image sensor shows less than 5% linearity error while having 40% external quantum efficiency in SWIR, which enables acquisition of high-quality images.