Bandwidth Characteristics of a Graphene/Silicon Schottky-Junction Photodetector

Graphene/silicon (Gr/Si) heterostructure has emerged as a promising approach for high-performance broadband photodetectors. However, it is often the case that devices of similar structures exhibit bandwidths that differ by orders of magnitude. Moreover, the relatively large photosensitive area combined with multiple operation modes make it imperative to understand the in-plane bandwidth characteristics of such devices. Here, we conducted a thorough investigation of the in-plane bandwidth distribution and the focal-condition-dependent bandwidth characteristics in an exemplar Gr/Si Schottky-junction photodetector with a large lateral dimension ( $\sim 640~\mu $ m). It is found that the bandwidth as deduced by the 0.35/ $\tau _{\mathrm {FWHM}}$ method can better depict the high-frequency transient response of the device than the more conventional S21 bandwidth. Additionally, influence of illumination area and excitation power density on the response time has been characterized. Our study helps clarify two commonly used bandwidth figures of merit, and suggests that more analysis of the in-plane bandwidth characteristics may lead to updated design guidelines for photosensitive devices.