Near-infrared photodetection in nanocarbon materials

The conversion of light into electricity is at the heart of solar cells and photodetectors and in other optoelectronic devices used in telecommunication systems. In particular, near-infrared (NIR) photodetection is very relevant for applications in night vision, remote sensing, food inspection, and surveillance. Novel materials that enable broadband NIR photodetection are sought, and the emerging class of nanocarbon and other 2D materials hold promise for large device photoresponsivities, high-speed detection, spectral control of the photoresponse, ease of integration, and waferscale fabrication. In this thesis, two types of nanocarbon materials have been explored for broadband NIR photodetection: nanocrystalline graphene (NCG) and single-walled carbon nanotubes (SWCNTs) networks. Graphene is a gapless 2D semi-metal with wavelength-independent light absorption with only 2.3% of the incident photons in a wide wavelength range. The growth of multi-layer graphene with predefined thickness for increased absorption has not yet been realized. To this end, nanocrystalline graphite (NCG), synthesized with a defined thickness on a silicon wafer, is introduced as a material for near-infrared to short-wavelength infrared (SWIR) photodetection. A broadband spectrally flat photoresponse was obtained in the NIR-SWIR spectral region, and the detected photocurrents were attributed to a temperature-induced bolometric effect. The SWCNT networks with a diameter distribution tailored for the near-infrared photodetection are grown using chemical vapor deposition (CVD) process on SiO2/p-Si substrates. The SWCNT networks are complementarily characterized using multi-wavelength resonant Raman spectroscopy and scanning photocurrent spectroscopy. The photocurrent data confirms a broadband optical response to the near-infrared light indicating a large diameter distribution in the CNT network. Devices are fabricated in a transistor geometry to study the spatial photoresponse distribution under different biasing schemes in the 1100 nm – 1800 nm spectral region, and the resulting photoresponse is discussed in terms of the photodetection mechanisms. During the course of this thesis, the photocurrent data were obtained with an in-house developed aberration-corrected scanning photocurrent setup. In order to enhance light-matter interaction in nanocarbon materials, the so-called plasmonic-photonic (PPhC) structures with optical resonances in visible-nIR spectrum were fabricated and characterized to investigate Raman enhancement in graphene. The local enhancements in the PPhCs were understood from the complementary near-field and far-field simulations optical simulations