Tailoring of colloidal quantum dot layer thickness for highly efficient short-wavelength infrared photodiode

Abstract

Colloidal quantum dots (CQDs) have emerged as promising materials for thin film photodiodes (TFPDs) in the short-wavelength infrared detection range, offering an alternative to III–V and HgCdTe-based TFPDs. However, optimizing the structure of CQD-based TFPDs remains a challenge, as it involves a delicate balance between reducing dark currents and enhancing carrier extraction efficiency. In this study, we explore the influence of varying the thickness of CQD layers to achieve a highly efficient photodiode. Our investigations reveal a continuous reduction in the dark current as the CQD layers become thicker, but we observe fluctuation in the external quantum efficiency (EQE). To shed light on this relationship between dark current density (Jdark) and EQE, we conduct capacitance measurements and employ optical simulations. From the capacitance measurements, they demonstrate an increased depletion width with varying CQD thickness, apart from layers exceeding 500 nm in thickness. Leveraging optical simulations, we propose an optimal thickness for CQD-based TFPDs and compare its EQE performance. The optimized CQD-based TFPD exhibits a Jdark of 4.1 μA/cm2 and EQE of 56.5%, and the highest specific detectivity, based on the assumption of shot noise dominance, is 1.78 × 1012 Jones at a wavelength of 1420 nm.