Abstract-Enhanced terahertz emission bandwidth from photoconductive antenna by manipulating carrier dynamics of semiconducting substrate with embedded plasmonic metasurface

Arkabrata Bhattacharya, Dipa Ghindani, and S. S. Prabhu

Schematic showing the fabricated PCA on SI-GaAs substrate. Inset shows the embedded metasurface in the photoconductive gap of the PCA. The TiO2 antireflection coating has not been shown here. (b) SEM image of the fabricated devices. The First and the third devices have nanostructured PC gap, while the second and the fourth are bare PCAs for reference.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-21-30272

In this article, we demonstrate a technique to enhance the Terahertz (THz) emission bandwidth from photo-conductive antenna (PCA) based on semiconducting substrates by manipulating the surface carrier dynamics of the semiconductor. Bandwidths in PCAs are limited by the decay of the photogenerated charge carriers, which in case of SI-GaAs is in the orders of 50 picoseconds. We show, with an embedded design of plasmonic meta-surface in the photoconductive gap of a PCA, it is possible to enhance the emission bandwidths by more than 50 percent. This is due to the fact that these nano-structures act as local recombination sites for the photogenerated carriers, effectively reducing the carriers’ lifetime. Additionally, the defect sites reduce the terminal current, thereby reducing the Joule heating in the device. Furthermore, the meta-surface also facilitates higher in-coupling of the exciting infrared light on to the PCA, thereby increasing the optical-to-THz conversion efficiency of the device.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Enhanced optical-to-THz conversion efficiency of photoconductive antenna using dielectric nano-layer encapsulation

Abhishek Gupta, Goutam Rana, Arkabrata Bhattacharya, Abhishek Singh, Ravikumar Jain, Rudheer D. Bapat, S. P. Duttagupta,   S. S. Prabhu,

https://aip.scitation.org/doi/abs/10.1063/1.5021023


Photoconductive antennas (PCAs) are among the most conventional devices used for emission as well as detection of terahertz (THz) radiation. However, due to their low optical-to-THz conversion efficiencies, applications of these devices in out-of-laboratory conditions are limited. In this paper, we report several factors of enhancement in THz emission efficiency from conventional PCAs by coating a nano-layer of dielectric (TiO2) on the active area between the electrodes of a semi-insulating GaAs-based device. Extensive experiments were done to show the effect of thicknesses of the TiO2 layer on the THz power enhancement with different applied optical power and bias voltages. Multiphysics simulations were performed to elucidate the underlying physics behind the enhancement of efficiency of the PCA. Additionally, this layer increases the robustness of the electrode gaps of the PCAs with high electrical insulation as well as protect it from external dust particles.

Abstract-Terahertz diffraction enhanced transparency probed in the near field

Alexei Halpin, Niels van Hoof, Arkabrata Bhattacharya, Christiaan Mennes, and Jaime Gomez Rivas

https://journals.aps.org/prb/accepted/ba076O10Q0913a31a24c61171bda23fbf5c1b5280

Electromagnetically induced transparency in metamaterials allows to engineer structures which transmit narrow spectral ranges of radiation while exhibiting a large group index. Implementation of this phenomenon frequently calls for strong near-field coupling of bright (dipolar) resonances to dark (multipolar) resonances in the meta-molecules comprising the metamaterials. The sharpness and contrast of the resulting transparency windows thus depends strongly on how closely these meta-moleucles can be placed to one another, placing constraints on fabrication capabilities. In this manuscript we demonstrate that the reliance on near-field interaction strength can be relaxed, and the magnitude of the electromagnetic induced transparency enhanced, by exploiting the long range coupling between meta-molecules in periodic lattices. By placing dolmen structures resonant at THz frequencies in a periodic lattice, we show a significant increase of the transparency window when the in-plane diffraction is tuned to the resonant frequency of the meta-molecules, as confirmed by direct mapping of the THz near-field amplitude across a lattice of dolmens. Through the direct interrogation of the dark resonance in the near-field we show the interplay of near- and far-field couplings in optimizing the response of planar dolmen arrays via diffraction induced transparency.