Finite-Difference Time-Domain Simulations of Photon-Trapping Nanohole Arrays for Enhanced Optical Absorption in Ultrahigh-Speed GaAs Photodetectors

Although GaAs-based photodetectors have been the dominant technology in optical communication for decades, the application of submicrometer absorbers for ultrahigh bandwidth, beyond 100 Gbps, is challenged due to low responsivity. Ultrahigh speed and efficient 0.5 μm thick GaAs PIN photodiode integrated with submicron photon-trapping (PT) structures are investigated via numerical simulations. The PT structure is designed in an insulator layer such as silicon dioxide (SiO2) and hafnium oxide (HfO2) with various patterns (square and hexagonal), shapes (cylindrical and funnel), and dimensions (thickness, period, and diameter) in order to explore and optimize the effect of parameters on photon absorption enhancement. The proposed device of 0.5 μm thin-film GaAs without antireflection coatings or back reflector layers, as conventional techniques for absorption enhancement, exhibits more than 55% external quantum efficiency of ∼0.38 A/W at 850 nm. The data transfer rate can be as high as 100 Gbps nonreturn-to-zero with no equalization.