Complex Oxide Thin Films for Surface-Phonon-Polariton-Based Infrared Optoelectronics

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 they are more challenging to integrate with conventional III-V-based semiconductors used in infrared optoelectronics. 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 (PLD), 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, 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 with an order of magnitude improvement in responsivity versus a device with a simple optical grating. Our results demonstrate that integrating oxide materials with conventional semiconductors is a viable approach to enhancing infrared detector technology, offering a competitive alternative to other nanophotonics methods.