A detailed numerical study of subwavelength nanogratings behavior to enhance the light absorption characteristics in plasmonic-based metal-semiconductor-metal photodetectors (MSM-PDs) is performed by implementation of 2D finite-difference time-domain (FDTD) algorithm. Due to the structure design and changes in the device physical parameters, various devices with different geometries are simulated and compared. Parameters like nano-grating height and duty cycle (DC) are optimized for rectangular and taper subwavelength metal nanogratings on GaAs substrate and their impact on light absorption below the diffraction limits are confirmed. The calculated light enhancement is ~32.7-times for an optimized device in comparison with a conventional MSM-PD. This enhancement is attributed to the plasmonic effects in the near-field region. 1. Introduction Periodic nanostructures can produce an efficient light transmission and absorption by excitation of surface plasmons (SPs) [1] and their potential practice (or application) in optical communication system has made them an interesting type of devices [2]. The continuing progress in plasmonic interaction with nanostructures and their outstanding design instruction in metal-semiconductor-metal photodetectors (MSM-PDs) has developed a unique context for future-generation optoelectronic systems, such as, optical fiber communication systems, high speed chip-to-chip interconnects, and high-speed sampling [3]. The conventional MSM-PD is a symmetrical device which is equivalent to two back-to-back connected Schottky diodes on a semiconductor substrate [4], such as GaAs which as a direct band gap semiconductor collects and emits photons more efficiently than indirect semiconductors such as Si and Ge [5]. To create a Schottky junction, some essential properties must be satisfied, such as type and quality of metal and semiconductor along with the shape and size of the interface [6]. A significant amount of illumination on top of a conventional MSM-PD is reflected, and the light absorption is reduced considerably in device’s active region. Fabrication of nanogratings on top of the metal fingers on conventional MSM-PDs can avoid the unwanted reflection and exhibit notable light transmission. By tailoring the electrodes structure surface with metal nanogratings, MSM-PDs can be modified for the light absorption, and the modification process strongly depends on the corrugation parameters. Recently, different shapes of one-dimensional (1D) nanostructured surfaces have been developed in which noble metals, such as gold (Au), are used
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