Tailoring Spectrally Flat Infrared Photodetection with Thickness-Controlled Nanocrystalline Graphite

Graphene, a zero-gap semiconductor, absorbs 2.3% of incident photons in a wide wavelength range as a free-standing monolayer, whereas 50% is expected for similar to 90 layers. Adjusting the layer number allows the tailoring of the photoresponse; however, controlling the thickness of multilayer graphene remains challenging on the wafer scale. Nanocrystalline graphene or graphite (NCG) can instead be grown with controlled thickness. We have fabricated photodetectors from NCG that are spectrally flat in the near-infrared to shortwavelength infrared region by tailoring the layer thicknesses. Transfer matrix simulations were used to determine the NCG thickness for maximum light absorption in the NCG layer on a silicon substrate. The extrinsic and intrinsic photoresponse was determined from 1100 to 2100 nm using chromatic aberrationcorrected photocurrent spectroscopy. Diffraction-limited hyperspectral photocurrent imaging shows that the biased photoresponse is unipolar and homogeneous across the device area, whereas the short-circuit photoresponse gives rise to positive and negative photocurrents at the electrodes. The intrinsic photoresponses are wavelength-independent, indicative of bolometric and electrothermal photodetection.

Automated summary

In this study, photodetectors were fabricated from nanocrystalline graphene or graphite (NCG) with tailored layer thicknesses, achieving spectrally flat characteristics in the near-infrared to shortwavelength infrared region. The photodetectors exhibited homogeneous and unipolar biased photoresponse, with positive and negative photocurrents at the electrodes during short-circuit photoresponse.