Mid-Wave Infrared Graphene Photodetectors With High Responsivity for On-Chip Gas Sensors

On-chip integration of mid-wave infrared (MWIR) absorption spectroscopy gas sensors is a powerful approach to massproducing compact and inexpensive devices and systems. Moreover, this approach opens new horizons for sophisticated applications in environmental monitoring, quality control, and Internet-of-Things networks. Nonetheless, further development of integrated photonic devices that can operate at the MWIR band is essential. Towards that end, we propose an MWIR graphene photodetector that is integrated into silicon-on-sapphire (SOS) slot waveguides for on-chip absorption spectroscopy applications. This configuration boosts the electric field distribution of the guided mode, which enhances the effective absorption of graphene. In addition, the presence of the guided mode in the slotted air region permits significant interaction with the analyte gas, which is a significant advantage for absorption spectroscopy. The sensing performance of the device is quantified by investigating its minimum detectable concentration of the three most prevalent greenhouse gases in the U.S.: carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Numerical results reveal that sub-ppb detection of these gases is achievable at the chip scale. These promising findings pave the way for the emergence of novel designs of portable, inexpensive, and highly sensitive sensors that are integrated into miniaturized electronic–photonic chipsets.