Graphene/Si Heterostructure with an Organic Interfacial Layer for a Self-Powered Photodetector with a High ON/OFF Ratio

Photodetectors (PDs) are widely used in various fields of military and daily life especially for imaging, telecommunications, sensing, and so on. Therefore, high performance and low power consumption are of crucial importance for PDs with high detectivity and fast response speed. Self-powered PDs have the advantage of low cost, which can be fabricated by the direct contact of graphene and silicon (Si). However, the graphene/Si Schottky structure suffers from the interface trap states and low Schottky junction barrier. Such drawbacks reduce the response speed and increase the noise current, which eventually hinder high-performance applications of PDs. In this study, 2,2′,7,7′-tetrakis­(N,N′-di-p-methoxyphenylamine)-9,9′-spirobiuorene (spiro-OMeTAD) was selected as an interfacial layer due to its suitable molecular orbital positions and excellent optical properties. The fabricated graphene/Si heterostructure PD with a spiro-OMeTAD interfacial layer showed an extremely high ON/OFF ratio over 10⁷ at 0 V bias and a fast response of ∼5.1 μs. Moreover, it also exhibited a high specific detectivity of ∼8.7 × 10¹⁰ Jones, which was many-fold higher than the PD without the interfacial layer. Furthermore, the responsivity was obtained as 0.355 A/W at 532 nm illumination with 145 μW power. Hence, these results show a flexible approach to improve the performance of graphene/Si heterostructure-based PDs by using an organic interfacial layer.