Antenna enhanced quantum dot infrared photodetectors.

摘要

Similar to conventional microwave antennas, optical antennas are playing increasingly important roles in photonic devices covering visible, near infrared (IR), mid-wave and long-wave infrared (MWIR/LWIR), through terahertz (THz) operating frequency regimes. However, due to the ultra-high frequency (30 THz at the wavelength of 10 microm) of electromagnetic (EM) waves in the optical spectral regimes, it is difficult to directly collect electromagnetic waves-generated current through optical antennas. Nevertheless, one can still achieve most of the antenna functionalities through surface plasmonic resonance in metallic antennas, including conversion (i.e. transmission or receiving) between free-space EM waves and localized field, strong EM field enhancement and localization beyond the diffraction limit, and directivity (gain) in transmission or receiving. Such plasmonic optical antennas offer effective tools for numerous applications, including light emission, beam control, beam shaping, sensing and imaging.;For light sensing and imaging applications, the effective light collection and the strong light focusing effect of plasmonic optical antennas not only enhances the photoresponsivity of a photodetector through effective light collection, but also enables high-resolution light sensing and imaging well beyond the diffraction limit of light.;However, due to the surface confinement of plasmonic waves, plasmonic optical antennas interact with photodetectors through their near-field EM components. Therefore, to fully exploit the advantages of plasmonic optical antennas, it is critical to have close interacting antennas and photodetector structures.;In this study, we report a full wavelength dipole antenna integrated with a LWIR quantum dot infrared photodetector (QDIP). We investigate directivity, the polarization dependency of the antenna-coupled QDIP as well as the performance of the device under back-side and front side illumination configurations. The study of back-side illumination configuration for antenna-coupled QDIPs has the great importance of being compatible with the state of the art focal plane array (FPA) fabrication and testing.;We also investigate how different parameters such as the gap size, the period, and the length of the antennas can enhance the photocurrent response of antenna-coupled QDIP. Enhancements of 2-12 times, depending on the size, the period, and orientation of these antennas are being reported. The simulation results strongly support the measured data.