With my research, we strive to enhance the quantum efficiency of long wave infrared (LWIR) (8 µm to 12 µm) photodetectors by light trapping metastructures. Infrared (IR) photodetectors have numerous applications, from space-based earth-observations to surveillance and gas detection at industrial sites. We are focusing on photodetectors made from the type-II superlattice (T2SL) material system, a III-V quantum structure material with cut-off wavelengths covering a large part of the IR spectrum. T2SL have gained much attention since the beginning of the new millennium thanks to its growth uniformity and bandgap design flexibility, enabling T2SL photodetectors with high production yield and high operating temperatures compared to competing technologies. However, T2SL with cut-off wavelengths in the LWIR regime has weaker absorption compared to the mid-wave and short-wave T2SL, limiting the quantum efficiency of LWIR T2SL photodetectors. By integration of light trapping metastructures in the photodetector we aim to enhance the field inside the absorbing material and thus increase the detector’s quantum efficiency.

Metastructures manipulate light by subwavelength arrangements and the interaction can have different physical origins. One of these phenomena is based on the coupling between light and collective charge oscillations in a conductor, called surface plasmon polaritons (SPP). When light couple to SPPs at a metal-dielectric interface, the wave propagates along the interface. Perpendicular to the interface, the field is strongly enhanced but evanescent. If the absorbing material is placed close to the metal-dielectric interface, the on-resonance field enhancement will boost the detector’s quantum efficiency. Other light-trapping mechanisms are also investigated, either in combination with SPP coupling or as an individual effect. The research involves FEM simulations, photodetector fabrication and performance measurements.

The research is a collaboration between Faculty of Engineering (LTH) at Lund University, Halmstad University and IRnova. IRnova is a state-of-the-art developer and producer of high-performance IR photodetectors based on quantum well and T2SL technology. The company has more than 20 years of experience in the field and is based in Kista, Stockholm. Halmstad University provides simulation expertise, while LTH supports the project with profound knowledge in nanostructures.