Spectrally Adjustable Narrowband Photonic Device Based on Heat‐Driven Amorphous‐to‐Crystal Transformation of Si

Highly demanding modern IR nanophotonic devices with spectrally sharp resonances often require precise fabrication methods or precisely controllable material responses to ensure appropriate spectral performance. In this context, photonic architectures based on low‐loss thermo‐optical materials have recently shown the possibility of yielding narrowband‐resonance spectra and present accurate spectral adjustability in the order of a few tens of nanometers. Another way to adopt the temperature‐driven optical effect of Si is demonstrated by achieving wide‐band and highly precise spectral adjustability of the IR resonance wavelength in multilayered ultranarrowband photonic devices based on Si/SiO 2 distributed Bragg reflectors. This new approach is based on controlling the continuous and irreversible amorphous‐to‐crystal transformation of Si, yielding a colossal shift in the refractive index of Si, which results in wide‐band spectral adjustability of the resonance wavelength of the fabricated devices by up to 100 nm. This design strategy can be adopted for other high‐refractive‐index materials such as Ge to achieve spectrally selective photonic devices with ultrafine wavelength tunability operating in the IR to near‐infrared regions, such as narrowband thermal emitters and spectroscopic sensors.