Ayman Karar

High-responsivity plasmonics-based GaAs metal-semiconductor-metal photodetectors

We report the experimental characterization of high-responsivity plasmonics-based GaAsmetal-semiconductor-metalphotodetector (MSM-PD) employing metal nano-gratings. Both the geometry and light absorption near the designed wavelength are theoretically and experimentally investigated. The measured photocurrent enhancement is 4-times in comparison with a conventional single-slit MSM-PD. We observe reduction in the responsivity as the bias voltage increases and the input light polarization varies. Our experimental results demonstrate the feasibility of developing a high-responsivity, low bias-voltage high-speed MSM-PD.

Optical absorption enhancement of hybrid-plasmonic-based metal-semiconductor-metal photodetector incorporating metal nanogratings and embedded metal nanoparticles

We propose and numerically demonstrate a high absorption hybrid-plasmonic-based metal semiconductor metal photodetector (MSM-PD) comprising metal nanogratings, a subwavelength slit and amorphous silicon or germanium embedded metal nanoparticles (NPs). Simulation results show that by optimizing the metal nanograting parameters, the subwavelength slit and the embedded metal NPs, a 1.3 order of magnitude increase in electric field is attained, leading to 28-fold absorption enhancement, in comparison with conventional MSM-PD structures. This is 3.5 times better than the absorption of surface plasmon polariton (SPP) based MSM-PD structures employing metal nanogratings and a subwavelength slit. This absorption enhancement is due to the ability of the embedded metal NPs to enhance their optical absorption and scattering properties through light-stimulated resonance aided by the conduction electrons of the NPs.

Metal Nano-Grating Optimization for Higher Responsivity Plasmonic-Based GaAs Metal-Semiconductor-Metal Photodetector

To improve the responsivity of the metal semiconductor metal photodetector (MSM-PD), we propose and demonstrate the use of sub-wavelength slits in conjunction with nano-structured the metal fingers that enhance the light transmission through plasmonic effects. A 4-finger plasmonics-based GaAs MSM-PD structure is optimized geometrically using a 2-D Finite Difference Domain (FDTD) method and developed, leading to more than 7-times enhancement in photocurrent in comparison with the conventional MSM-PD of similar dimensions at a bias voltage as low as 0.3 V. This enhancement is attributed to the coupling of the surface plasmon polaritons (SPPs) with the incident light through the nano-structured metal fingers. This work paves the way for the development of high-responsivity, high-sensitivity, low bias-voltage high-speed MSM-PDs and CMOS-compatible GaAs-based optoelectronic devices.

Design of high-sensitivity plasmonics-assisted GaAs metal-semiconductor-metal photodetectors

In this paper, we use the finite difference timedomain (FDTD) method to optimize the light absorption of an ultrafast plasmonic GaAs metal-semiconductor-metal photodetector (MSM-PD) employing metal nano-gratings. The MSM-PD is optimized geometrically, leading to improved light absorption near the designed wavelength of GaAs through plasmon-assisted electric and magnetic field concentration through a subwavelength aperture. Simulation results show up to 10-times light absorption enhancement at 867 nm due to surface plasmon polaritons (SPPs) propagation through the metal nano-grating, in comparison to conventional MSM-PD.

Impact of Nanograting Phase-Shift on Light Absorption Enhancement in Plasmonics-Based Metal-Semiconductor-Metal Photodetectors

The finite difference time-domain (FDTD) method is used to simulate the light absorption enhancement in a plasmonic metal-semiconductor-metal photodetector (MSM-PD) structure employing a metal nanograting with phase shifts. The metal fingers of the MSM-PDs are etched at appropriate depths to maximize light absorption through plasmonic effects into a subwavelength aperture. We also analyse the nano-grating phase shift and groove profiles obtained typically in our experiments using focused ion beam milling and atomic force microscopy and discuss the dependency of light absorption enhancement on the nano-gratings phase shift and groove profiles inscribed into MSM-PDs. Our simulation results show that the nano-grating phase shift blue-shifts the wavelength at which the light absorption enhancement is maximum, and that the combined effects of the nano-grating groove shape and phase shift degrade the light absorption enhancement by up to 50%.

Absorption enhancement of MSM photodetector structure with a plasmonic double grating structure

We present finite difference time domain simulation to analyze the optical absorption enhancement of metal-semiconductor-metal photo detectors employing double plasmonic grating structures. Simulation results show that the combination of a subwavelength aperture and double nano-structured metal grating results in up to 25 times enhancement in optical absorption, in comparison to MSM photodetector structures employing only a subwavelength aperture. This improvement of the absorption enhancement is due to the coupling out function of the bottom grating structure which distributes the light to both side of the subwavelength aperture.

Groove shape-dependent absorption enhancement of 850 nm MSM photodetectors with nano-gratings

Finite difference time-domain (FDTD) analysis is used to investigate the light absorption enhancement factor dependence on the groove shape of the nano-gratings etched into the surfaces of metal-semiconductor-metal photodetector (MSM-PD) structures. By patterning the MSM-PDs with optimized nano-gratings a significant improvement in light absorption near the design wavelength is achieved through plasmon-assisted electric field concentration effects. Simulation results show about 50 times light absorption enhancement for 850 nm light due to improved optical signal propagation through the nano-gratings.

Metal-semiconductor-metal (MSM) photodetectors with plasmonic nanogratings*

We discuss the light absorption enhancement factor dependence on the design of nanogratings inscribed into metal-semiconductor-metal photodetector (MSM-PD) structures. These devices are optimized geometrically, leading to light absorption improvement through plasmon-assisted effects. Finite-difference time-domain (FDTD) simulation results show ~50 times light absorption enhancement for 850 nm light due to improved optical signal propagation through the nanogratings. Also, we show that the light absorption enhancement is strongly dependent on the nanograting shapes in MSM-PDs.

Impact of metal nano-grating phase-shift on plasmonic MSM photodetectors

In this paper, finite difference time-domain (FDTD) method is used to simulate the light absorption enhancement in a plasmonic metal-semiconductor-metal photodetector (MSM-PD) structure employing a metal nano-grating with phase-shifts. The metal fingers of the MSM-PDs are etched with appropriate depths to maximize light absorption through plasmonic effects into a subwavelength aperture. Simulation results show that the nano-grating phase-shift red-shifts the wavelength at which the light absorption enhancement maximum, and that the combined effects of the nano-grating groove shape and the nano-grating phase-shift, degrade the light absorption enhancement by up to 50%.

Plasmonic-based GaAs balanced metal-semiconductor-metal photodetector with high common mode rejection ratio

We propose and demonstrate a plasmonic-based GaAs balanced metal-semiconductor-metal photodetector (BMSM-PD) structure. A dual-beam FIB/SEM is employed for the fabrication of the metal nano-gratings and slits of the B-MSMPD. A common mode rejection ratio (CMRR) value less than 25 dB at 830nm wavelength, dependent on the applied bias, is measured. This adequate CMRR value indicates that the BMSM-PD structure substantially suppresses laser intensity noise, making it suitable for ultra-high-speed optical telecommunication systems. In addition, this work paves the way for the monolithic integration of B-MSM-PDs into large scale semiconductor circuits.