Propagation of surface plasma waves in metal films perforated with n × n lattices of holes (n = 2 to 72).

The propagation of surface plasma waves (SPWs) in 90 nm-thick Au films perforated with n × n square lattices of circular holes, referred to as n-metal photonic crystals (n-MPCs), is investigated. The hole period was set to 3 µm with n = 2, 4, 6, 8, 12, 18, 24, 36, and 72. For each n-MPC, the total number of holes was conserved to 5184 (= 72 × 72), which were grouped to form an Mn × Mn (Mn = 72/n) array of lattices, evenly spaced on 384 × 384 µm. The n-MPCs were individually integrated on semi-insulating GaAs substrates. In the transmission through them, the primary peak by the SPW excited at the n-MPC/GaAs interface exhibits clear variation with n in its wavelength and intensity. It begins to appear for n ∼ 4 and its intensity is increased with n but saturated for n∼ > 36 with Fano lineshape. These imply the SPW excitation is significantly affected by the boundary and number of holes in each lattice. Such lattice size-dependent transmission is compared with the absorption of the quantum dot infrared photodetectors identically coupled to the n-MPCs. In the absorption, the saturation of the peak intensity is observed for n∼ > 24, lower than the ∼36 in the transmission. Their difference is characterized with the SPW propagation and decay that critically depend on the dielectric properties of devices as well as the number of holes and boundaries of each lattice in plasmonic excitation.