High-performance dual-mode ultra-thin broadband CdS/CIGS heterojunction photodetector on steel

Abstract

An ultra-thin CdS/CIGS heterojunction photodiode fabricated on steel firstly exhibits dual-mode broadband photodetection from ultraviolet to near infrared spectrum. In the photovoltaic mode, the CIGS photodiode, working as a self-driven photodetector, shows an outstanding photodetection capability (under a light power density of 20 µW cm -2 at 680 nm), reaching a record detectivity of ∼4.4×10 12 Jones, a low noise equivalent power ( NEP ) of 0.16 pW Hz -1/2 and a high I light /I dark ratio of ∼10 3 , but a relatively low responsivity of ∼0.39 A W -1 and an external quantum efficiency ( EQE ) of ∼71%. Working under the same illumination but in the photoconductive mode (1 V reverse bias), the responsivity and EQE are significantly enhanced to 1.24 A W -1 and 226%, respectively, but with a relatively low detectivity of 7×10 10 Jones and a higher NEP of 10.1 pW Hz -1/2 . To explain these results, a corrected photoconductive gain ( G ) model indicates that minority electrons could be localized in the defects, surface states and depletion region of the CIGS photodiode, causing excess hole accumulation in the ultra-thin CIGS photodiode and thus high EQE over 100% ( G over 1).