Spatial Distribution of Impulse Bandwidth of a Graphene/Silicon Schottky Photodetector

Graphene/Silicon (Gr/Si) Schottky photodetector combines the maturity of silicon technology with the excellent optoelectronic properties of graphene, offering advantages such as broad spectral coverage, high response speed, high sensitivity, and excellent environmental stability. It is well-suited for applications like ultrafast photodetection, broadband imaging, and integrated optoelectronic chips. Recently, it is revealed that the photoresponse bandwidth exhibits inhomogeneous distribution across its relatively large photosensitive area. To investigate the factors causing this non-uniformity, we conducted high-resolution scanning of the in-plane impulse response τ_FWHM (τ_FWHM is the width of the temporal response pulse) with a 2 ns excitation pulse for Gr/Si devices. Interestingly, for devices with large lateral dimension, there is always a well-defined ‘slow response’ region away from the contact. We verified through photocurrent mapping that these inhomogeneous response time distributions are of intrinsic nature and we attribute the observed slow component to arise from the time for holes to drift out of the graphene plane. Our experimental approach, i.e., scanning the in-plane τ_FWHM or impulse bandwidth 0.35/τ_FWHM, provides insights into the working mechanism of Gr/Si Schottky photodetectors and offers a complementary approach for characterizing semiconductor heterointerfaces.