Complex oxide thin films towards surface-phonon-polariton-based infrared optoelectronics [Invited]

Infrared nanophotonics offers enormous potential for enhancing infrared optoelectronic technologies, due to the ability to confine light to deeply sub-wavelength dimensions. One of the limitations of traditional nanophotonics approaches is the inherent losses present in the plasmonic materials that are conventionally used. Surface phonon polaritons offer a lower-loss alternative but are more difficult to integrate with conventional III-V-based semiconductors used for infrared optoelectronics. In this work, we examine the properties of complex oxides, which can be grown directly onto III-V semiconductors for the purpose of infrared light detection. We grow films of both SrTiO₃ and BaTiO₃ on GaAs using pulsed laser deposition, and examine their properties using a combination of X-ray diffraction, atomic force microscopy, transmission electron microscopy, and infrared reflectance spectroscopy. We find that the films grown exhibit good crystallinity with smooth, uniform surfaces, and with occasional minor misoriented grains. Their optical properties indicate higher losses than perfect single crystal substrates, but by less than a factor of two, with phonon Q factors of 18-60, which is favorable when compared with plasmonic materials. We then conduct numerical simulations, which show that these films can be used to create surface phonon polariton infrared detectors that outperform similar metallic gratings by a factor of four. Our results show that the integration of oxide materials with conventional semiconductors is a viable route to improving infrared detector technology, competitive with other nanophotonics approaches.