The infrared radiative properties of one heavily doped silicon complex grating and its corresponding four modified complex gratings with attached features at transverse magnetic wave incidence were numerically investigated by employing the finite-difference time-domain method.For the complex grating,by properly choosing the carrier concentration and geometry,it exhibited a broadband absorptance peak at wavelengths between 7 and 12μm resulting from the excitation of surface plasmon polaritons.As for the four modified complex gratings,though absorptance spectra of the gratings almost remained unchanged, their locations shifted towards longer wavelengths.Meanwhile,the spectral absorptance peaks of two modified complex gratings were wider than that of the grating without attached features.Such broadened peaks could be partly attributed to the cavity resonance within the grating structures demonstrated by the electromagnetic fields and Poynting vectors plots.Finally,through comparing the spectral absorptances of complex gratings with two symmetrical square features in three sizes,it was shown that the peak wavelength shifted toward longer wavelengths with enlarged feature size.This work theoretically laid a foundation for the optimized design and application of the infrared detector with high performance. The infrared radiative properties of one heavily doped silicon complex grating and its corresponding four modified complex gratings with attached features at transverse magnetic wave incidence were numerically investigated by employing the finite-difference time-domain method. For the complex grating, by properly choosing the carrier concentration and geometry, it exhibited a broadband absorptance peak at wavelengths between 7 and 12 μm resulting from the excitation of surface plasmon polaritons. As for the four modified complex gratings, though absorptance spectra of the gratings almost unchanged unchanged, their locations shifted towards longer wavelengths. Meanwhile, the spectral absorptance peaks of two modified complex gratings were wider than that of the grating without attached features. Chu broadened peaks could be partly attributed to the cavity resonance within the grating structures demonstrated by the electromagnetic fields and Poynting vectors plots. Finally, through comparing the s pectral absorptances of complex gratings with two symmetrical square features in three sizes, it was shown that the peak wavelength shifted toward longer wavelengths with enlarged feature size. This work is theoretically laid a foundation for the optimized design and application of the infrared detector with high performance.