Two-Dimensional Graphene-Oxide-Silicon Hybrid Photodetectors with Position-Dependent Quantum Efficiency

Graphene, a two-dimensional (2D) material known for its ultra-broadband optical absorption and compatibility with complementary metal–oxide–semiconductor (CMOS) technology, has emerged as a promising candidate for photodetection. Despite its myriad advantages, the inherent weak optical absorption (∼2.3%) and the extremely short carrier lifetime, characteristic of its single atomic layer thickness, present challenges. To surmount these, it's imperative to integrate graphene with other well-defined structures and materials, aiming for superior optical characteristics, especially in the realm of advanced nanophotonic devices. This paper delves into the fabrication and characterization of graphene-oxide-silicon (GOS) photodiodes, with a particular focus on their position-dependent quantum efficiency. By ingeniously coupling the Graphene/silicon (Gr/Si) heterojunction with the graphene/SiO₂/Si capacitor (Gr/SiO₂/Si) structure, we unveil high responsivity photodetectors that outperform the standalone graphene/Si Schottky photodiodes. Although the Gr/SiO2/Si capacitor structure is conventionally fabricated in tandem with graphene/silicon Schottky junction diodes, the precise mechanisms bolstering the augmented photocurrent generation in the hybrid structure have remained ambiguous. Our meticulous spatial photocurrent measurements demystify this phenomenon, attributing the pronounced photocurrents to photoinduced carrier multiplication in the two-dimensional electron gas (2DEG) situated in an inversion layer proximate to the SiO2/Si interface. This 2DEG, a byproduct of the Gr/SiO₂/Si field-effect structure, emerges as a cornerstone in the hybrid photodetection paradigm. Additionally, the photo-excited electron emission from the 2DEG experiences ballistic transit through a nanoscale vacuum (air) conduit, confined within the mean free path distance of air (~100 nm), culminating in its capture by the graphene electrode. This carrier transport modality deviates fundamentally from traditional graphene-centric optoelectronic applications, empowering the hybrid apparatus with heightened quantum efficiency and dynamic adaptability in both optical and electrical domains. The external (internal) quantum efficiencies of the hybrid constructs anchored on p-Si and n-Si were gauged at ~ 235% (350%) and 88% (132%), respectively. This exploration not only furnishes insights into the interplay of graphene-oxide layers on silicon substrates but also paves the path for a deeper comprehension of graphene/semiconductor hybrid apparatuses, showcasing potential for Terahertz (THz) innovations.