Efficiency of photoconductive detectors is limited by the bulk optical properties of photoconductive materials. The absorption length is on the order of several hundred nanometers, which limits the device thickness. Optical absorption however in the photoconductive layer can be modified substantially by using the concept of hybrid cavity, which consists of nanoantennas and a Distributed Bragg Reflector. A hybrid cavity containing a GaAs photoconductive layer of just 50 nm can be used to absorb >75% of incident photons by trapping the light within the cavity. We will discuss an intuitive model, which describes the dependence of the optimum operation wavelength on the cavity thickness. We will also show that the nanoantenna size is a critical parameter, small variations of which lead to both wavelength shifting and reduced absorption in the cavity. This behavior suggests that impedance matching is key for achieving efficient absorption in the hybrid cavities.
Oleg Mitrofanov, "Hybrid cavity for photo-conductive detectors with nanoantenna arrays and distributed Bragg reflectors (Conference Presentation)," Proc. SPIE 10353, Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications 2017, 103530J (Presented at SPIE Nanoscience + Engineering: August 10, 2017; Published: 29 September 2017); https://doi.org/10.1117/12.2275566.5593159244001.
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