Vertical field enhanced nanostructure for quantum well infrared photodetector through Germanium subwavelength arrays

Finite-difference-time-domain (FDTD) computer simulations reveal interesting features of Germanium (Ge) subwavelength nanostructures designed in x-y plane on substrate of InP with normal incidence, which can be applied in quantum well infrared photodetector (QWIP). Unlike the mechanism of excellent near field effects through periodic metallic nanostructures, large intensity of Ez field is achieved at near-infrared range by subwavelength arrays of Ge which has no surface plasmons (SPs). The evanescent Ez field generated along the surface of Ge is interpreted due to waveguide mode interference of coupled scattering. The existence of the enhanced field is confirmed by comparing the Fourier transform infrared (FTIR) spectra of real-fabricated samples with simulation outcomes. Positions of resonant peaks obtained in experiment are in good agreement with those of simulation.