Solution-processed MoS ₂ quantum dot/GaAs vertical heterostructure based self-powered photodetectors with superior detectivity

Abstract

The characteristics of a novel 0D/3D heterojunction photodetector fabricated using solution-processed colloidal MoS₂ quantum dots (QDs) on GaAs is presented. MoS₂ QDs with a dimension of ∼2 nm, synthesized by a standard sono-chemical exfoliation process with 2D layers have been used for the purpose. The microscopic and spectroscopic studies confirmed the formation of semiconducting (2H phase) MoS₂ QDs. The photodetectors were fabricated using n-GaAs substrates with two different doping concentrations resulting in n-n heterojunctions between n-type 0D MoS₂ QDs and bulk n-GaAs. The devices fabricated using GaAs with a higher doping concentration, showed an increase in the reverse current of the order of ∼10² upon illumination, while the same with a lower doping concentration showed an increase of the order of ∼10³. All the heterojunction photodetector devices show a broadband operation over the visible wavelength range of 400-950 nm, with a peak responsivity of the devices being observed at 500 nm. The peak responsivity and detectivity are found to be ∼400 mA W^-1 and ∼4 × 10¹² Jones, respectively, even without any external applied bias, which are useful for self-powered photodetection. The results indicate that colloidal MoS₂/GaAs based hybrid heterostructures provide a platform for fabricating broadband photodetectors by using highly absorbing MoS₂ QDs, which may show the pathway towards next-generation optoelectronic devices with superior detection properties.