High Photocurrent in Gated Graphene-Silicon Hybrid Photodiodes

TL;DR

This paper investigates the spatial distribution and physical mechanisms of photocurrent generation in graphene-silicon hybrid photodiodes, revealing high photocurrents under SiO2 regions due to inversion layers, aiding in the design of efficient optoelectronic devices.

Contribution

It provides a detailed physical model explaining photocurrent generation in G/Si devices, highlighting the role of inversion layers and threshold voltage effects.

Findings

Higher photocurrents observed under SiO2 regions adjacent to Schottky junctions.

A threshold voltage is necessary to observe significant photocurrent.

Formation of an inversion layer in Si explains the large photocurrents.

Abstract

Graphene/silicon (G/Si) heterojunction based devices have been demonstrated as high responsivity photodetectors that are potentially compatible with semiconductor technology. Such G/Si Schottky junction diodes are typically in parallel with gated G/silicon dioxide (SiO$_2$)/Si areas, where the graphene is contacted. Here, we utilize scanning photocurrent measurements to investigate the spatial distribution and explain the physical origin of photocurrent generation in these devices. We observe distinctly higher photocurrents underneath the isolating region of graphene on SiO$_2$ adjacent to the Schottky junction of G/Si. A certain threshold voltage (V$_T$) is required before this can be observed, and its origins are similar to that of the threshold voltage in metal oxide semiconductor field effect transistors. A physical model serves to explain the large photocurrents underneath SiO$_2$ by the formation of an inversion layer in Si. Our findings contribute to a basic understanding of graphene / semiconductor hybrid devices which, in turn, can help in designing efficient optoelectronic devices and systems based on such 2D/3D heterojunctions.