The trade-off between the enhanced signal-to-noise ratio and reduced light absorption in thin-film photodetectors is
the main issue for improving device performance. Nanoscale patterning of metal/dielectric interface can couple incident
light into surface plasmon polaritons (SPPs) modes, leading to the enhanced absorption. However, due to the nature of
resonant excitation of SPPs, it is difficult to realize broadband absorption enhancement. In this study, we propose a novel
device structure to achieve absorption enhancement over the whole spectral response range of the thin-film In0.53Ga0.47As
photodetector. Numerical simulation shows that both the preferential forward scattering of InP cylinder and grating
coupled waveguide modes contribute to the broadband absorption enhancement.
In this paper, metallic back structure with one dimensional periodic nano-ridge is attached to the capping layer of the In0.53Ga0.47As photodetector with 100 nm absorption layer. We present finite difference time domain (FDTD) simulation to analyze the optical absorption enhancement of the photodetector. By comparing with the photodetector with planar metallic film, simulation results show that by introducing the nanostructure a 2.8 times and a 3 times absorption enhancements can be achieved under transverse magnetic (TM) and transverse electric (TE) polarized plane wave illuminations, respectively. Increasing the period of the nanostructure, the absorption enhancement peak positions exhibit a red shift. In addition, the optimization of the metal grating height and width is also crucial for maximizing the absorption enhancement. The absorption enhancements are well explained by surface plasmon polaritons and Rayleigh Anomalies phenomena. Solid simulation and theoretical results are both presented with good agreement with each other.