Effect of incidence and sidewall taper angles on plasmonic metal–semiconductor–metal photodetector enhancements

We investigate an interdigitated nanograting structure on a GaAs substrate for plasmonic metal–semiconductor–metal photodetector applications. This computational work has studied the effects that the taper angle of the nanograting sidewall and the light wave angle of incidence have on the optical and current enhancements in the device. The study, involving two types of taper angle structures—positive and negative—showed that both taper angle directions can generate more optical and electrical enhancements than perfectly vertical wall structures for light incident at both the Brewster angle and the normal incident angle. The enhanced electric field value at the optimum positive taper angle is ∼22% and ∼120% greater than the negative taper angle and vertical wall structure, respectively. In addition, the total weighted optical enhancement value for the optimal positive taper angle structure is ∼65% and ∼120% greater than the optimal negative taper angle and vertical wall structure, respectively. This work demonstrates that the increased enhancements are due to the nanoscale focusing of light and impedance matching. The incident wave angle along with the taper angle can significantly promote these enhancements, especially at the Brewster angle.