Narottam Das

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.

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.

Light absorption enhancement in metal-semiconductor-metal photodetectors using plasmonic nanostructure gratings

In this paper, we adopt the finite difference time-domain (FDTD) method to optimize the absorption of a novel metal-semiconductor-metal photodetector (MSM-PD) structure based on the use of a double-layer nanostructured metal grating. The metal fingers of the MSM-PDs are etched with appropriate depths to maximize light absorption through plasmonic effects. Simulation results show 40 times enhancement in 980nm light trapping due to extraordinary optical signal propagation through the nanostructured double-metal grating, in comparison to conventional MSM-PDs.

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.

Design and development of silver nanoparticles to reduce the reflection loss of solar cells

In this paper, we investigate the design and fabrication of silver nano-particles using thin film deposition in conjunction with thermal annealing. We also predict the performance of conical shaped subwavelength grating structure developed using dry and isotropic etching of semiconductor substrates. Several silver (Ag) thin films of different thicknesses are deposited on semiconductor substrates and annealed at different temperatures. Adequate nanoparticle distribution of 200 nm average diameter is successfully fabricated on Si and GaAs substrates using 10nm thick Ag thin films annealed at 523 K. Moreover, the Finite-Difference Time Domain (FDTD) method is used to optimize the grating height and period size of the SWG structure for minimizing the reflection of semiconductor devices over the solar spectrum.

Numerical analysis of wavelength conversion based on semiconductor optical amplifier integrated with microring resonator notch filter

In this paper, we numerically investigate the wavelength conversion using semiconductor optical amplifier (SOA) integrated with microring resonator. In the model all nonlinear effects, which can appear in picosecond and subpicosecond pulse regime, are taken into account. It is shown that with three coupled microring resonators, output four-wave mixing (FWM) signal generated by the SOA can be filtered perfectly. Moreover, it is demonstrated that microring resonator can be used for modifying the output FWM signal shape and spectrum. The output time bandwidth product is also enhanced by this technique.

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%.

Investigation of input pulsewidth, medium loss and gain effect on the output pulse characteristics of semiconductor optical amplifiers

We have analysed the output pulse characteristics of semiconductor optical amplifier (SOA). They can be modified due to the variation of input parameters, such as, gain, input pulsewidth and internal loss imposed by the medium. In our model, the effect of self-phase modulation (SPM) has taken into consideration to improve the accuracy of simulation results. The proper output pulse characteristics can be achieved by controlling the mentioned parameters. We used a simplified nonlinear Schrodinger equation (SNSE) to model the behaviour of SOAs. The SNSE is solved using the finite-difference beam propagation method (FDBPM).