Leaky-mode effects in plasmonic-coupled quantum dot infrared photodetectors

The effects of a heavily doped GaAs top contact layer on a plasmonics-integrated InAs quantum dot infrared photodetector (QDIP) are investigated. A metal photonic crystal (MPC), a 100 nm-thick gold film perforated with a 2.5 μm-period, 2-dimensional square hole array, is employed as a plasmonic coupler. The MPC is fabricated on QDIPs with identical structures except for the thickness (0.1 and 1.3 μm) of the top contact layer (doping concentration ∼2 × 1018 cm−3). For the lowest order surface plasma wave (SPW) resonance, the resonance wavelength undergoes a blue shift of 0.27 μm from 8.26 μm, and the responsivity and detectivity drop by ∼50% for the thicker contact layer. These effects are explained by leaky mode characteristics resulting from the free-carrier-reduced dielectric constant in the contact region that impacts the SPW resonance.