New optical coupling structure of high light absorption quantum well infrared photodetectors

A new optical coupling structure of high optical absorption quantum well infrared photodetectors is reported, in which 4 periods of Al_0.15Ga_0.85As/GaAs QWs was integrated with double gold films and a sandwiched structure of metal-QWs-metal gratings has been adopted. Normal incident light can be coupled and trapped in the dielectric layer in the form of transverse electromagnetic waves, when the structure is optimized. Therefore, the light absorption of quantum wells is greatly enhanced when the light travels back and forth in the dielectric layer. Numerical simulations are made via 2D finite-difference time-domain (FDTD) method, yielding consistent results with experiments, which shows the photocurrent response increase of 21 times to the 45 degree mesa photodetector. At the same time, we observe the Rabi splitting.