Surface Plasmon-Enhanced Absorption in Metal Grating Coupled Terahertz Quantum Well Photodetectors

Effects of surface plasmon polaritons (SPPs) on the absorption efficiencies of metal-grating-coupled terahertz quantum well photodetectors (QWPs) are theoretically investigated. The thin top contact layers of the devices are utilized to support the SPPs, and the metal gratings couple p-polarized incident light into SPP modes. The electric fields related to the SPP modes have large components in the quantum well growth direction and are mostly localized in the multi-quantum-well regions of the terahertz QWPs. The dependences of the resonant absorption behaviors on the device parameters are systematically studied. A maximum value of about 30-fold enhancement of inter-sub-band absorption efficiency is achieved in comparison with that of a traditional 45-degree facet coupling scheme. Our proposed metal-grating-coupled terahertz QWPs is expected to significantly improve the device performance.