Near‐Infrared Photoresponse of Ge/Si Quantum Dot Waveguide Photodiodes Enhanced by Al Plasmonic Metastructures

The near‐infrared photoresponse in Ge/Si photodiodes with Ge quantum dots grown on a silicon‐on‐insulator substrate and integrated with two types of 2D metal metastructures on the surface of the photodiodes has been studied. The first type consisted of a regular grid of holes in an Al film, the second was a periodic array of Al disks. Metal metastructures make it possible to convert external electromagnetic radiation into surface plasmon modes at the Al–Si boundary. In the region of telecommunication wavelengths, a multiple photocurrent enhancement was found in comparison with a sample without plasmonic structures. Measurements of the angular dependences of the photocurrent were used to determine the dispersion of the excited optical modes. It was found that the resonant increase in the photocurrent by about two times relative to a bare sample without plasmonic metal is due to the generation of a surface plasmon‐polariton wave mode for a perforated Al film and a localized surface plasmon for an array of Al disks. According to the computational results, the maximum increase in the photoresponse up to 5 times for both types of metastructures is provided by hybrid planar waves, which are a superposition of waveguide and plasmonic modes.