Improvement of Terahertz Photoconductive Antenna using Optical Antenna Array of ZnO Nanorods

Mohammad Bashirpour,Seyed Ehsan Hosseininejad,Mohammad Neshat,Mohammadreza Kolahdouz,Matin Forouzmehr

doi:10.1038/s41598-019-38820-3

Mohammad Bashirpour, Seyed Ehsan Hosseininejad + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-38820-3

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Journal: Scientific Reports	Publication Date: Feb 5, 2019
Citations: 41	License type: open-access

Affiliation: University of Tehran, Yazd University

Abstract

An efficient terahertz (THz) photoconductive antenna (PCA), as a major constituent for the generation or detection of THz waves, plays an essential role in bridging microwave-to-photonic gaps. Here, we propose an impressive approach comprising the use of arrayed zinc oxide nanorods (ZnO NRs) as an optical nanoantenna over an anti-reflective layer (silicon nitride) in the antenna gap to boost the photocurrent and consequently the THz signal. The numerical approach applied in investigating the optical behavior of the structure, demonstrates a significant field enhancement within the LT-GaAs layer due to the optical antenna performing simultaneously as a concentrator and an antireflector which behaves as a graded-refractive index layer. ZnO NRs have been fabricated on the PCA gap using the hydrothermal method as a simple, low cost and production compatible fabrication method compared to other complex methods used for the optical nanoantennas. Compared to the conventional PCA with a traditional antireflection coating, the measured THz power by time domain spectroscopy (TDS) is increased more than 4 times on average over the 0.1–1.2 THz range.

Highlights

Devices e.g. solar cells[25], photodetectors[26], or light emitting diodes[27], the antireflection coating (ARC) plays a critical role
A solver based on the Finite element method (FEM) was applied to investigate the electrical and optical behavior of the proposed structure through combining Maxwell’s equations with the drift-diffusion/Poisson equations[31]
The numerical results show that the calculated photocurrent of the proposed structure experiences a 2.5-fold and 6-fold increase compared to the conventional photoconductive antenna (PCA) with and without ARC, respectively (Fig. 4a)

Summary

Optical Antenna Array of ZnO

Mohammad Bashirpour[1], Matin Forouzmehr[1], Seyed Ehsan Hosseininejad[1,2], Mohammadreza Kolahdouz 1 & Mohammad Neshat[1]. Many efforts have been devoted to increase the laser pulse coupling into LT-GaAs substrates, and to improve the performance of the PCA; such as using antireflection coating on LT-GaAs8, distributed Bragg reflector made of AlAs:AlGaAs stacks located under the LT-GaAs layer[9], three dimensional nanoplasmonic structure[10], double layer nanoplasmonic structure[11,12], recessed electrode and recessed nanoplasmonic array, nano-spaced electrodes[13], optical plasmonic nanoantenna[14,15], plasmonic nanostructure[16,17,18,19,20] and else[21,22,23] Most of these methods require electron beam lithography which raises the cost and time of fabrication significantly. The optical power enhancement results in more photocarrier generation, and so higher power for terahertz emission

Device Structure and Design

Results and Discussion

Additional Information