Plasmon enhancement of the electric field in mid-infrared Ge/Si quantum-dot photodetectors with different thicknesses of the active region

The spatial distribution of the electric field in Ge/Si photodetector heterostructures coated with a gold film containing a regular two-dimensional array of subwavelength apertures is calculated by the finite-element method. The array period and aperture diameter are 1.2 and 0.7 $\mu$m, respectively. The efficiency of field enhancement is determined for different thicknesses of the active region occupied by quantum dots. It is demonstrated that the field-enhancement factor for an electromagnetic wave incident on the structure from the side of the substrate is $\sim$3.5 times larger than that for a wave incident from the opposite side. In the first case, the field-enhancement factor varies nonmonotonically with the thickness of the active region.