Terahertz photoconductive emitter with dielectric-embedded high-aspect-ratio plasmonic grating for operation with low-power optical pumps

D V Lavrukhin,I A Glinskiy,I E Spector,Y G Goncharov,A E Yachmenev,D S Ponomarev,M Shur,K I Zaytsev,T Otsuji,M Skorobogatiy,M Ryzhii,R A Khabibullin

doi:10.1063/1.5081119

Abstract

We report on the design, optimization and fabrication of a plasmon-assisted terahertz (THz) photoconductive antenna (PCA) for THz pulse generation at low-power optical pumps. The PCA features a high aspect ratio dielectric-embedded plasmonic Au grating placed into the photoconductive gap. Additionally, Si3N4-passivation of the photoconductor and the Al2O3-antireflection coating are used to further enhance antenna performance. For comparative analysis of the THz photocurrents, THz waveforms and THz power spectra we introduced the THz photocurrent δi and the THz power enhancement δTHz factors, which are defined as ratios between the THz photocurrents and the THz power spectra for the plasmon-assisted and conventional PCAs. We demonstrated superior performance of the plasmon-assisted PCA δi=30 and δTHz=3 ⋅ 103 at the lowest optical pump power of P=0.1 mW. Nevertheless the increase to P=10 mW lead to monotonically decrease in the both values to δi=2 and δTHz=102 due to screening effects. These results demonstrate a strong potential of the plasmonic PCA for operation with low-power lasers, thus, opening opportunities for the development of portable and cost-effective THz spectrometers and imaging systems.

Highlights

The PCAemitters and photoconductive antenna (PCA)-detectors using different geometries of metal and dielectric nanoantennas, such as silver nano-islands or arrays of nanoscale apertures,15–17 fractal antennas,18 monopole or dipole plasmonic gratings with either low or high aspect ratios,10,11,19–24 plasmonic nanocavities based on Bragg reflectors,25 metal colloidal particles deposited onto the photoconductive substrate,26 or even all-dielectric gratings,27 demonstrated impressive performance enhancement compared to the conventional PCAs
We report on a plasmon-assisted THz PCA that enhances the THz pulse generation and operates with low-power optical pumps
We demonstrated superior performance of the plasmon-assisted PCA which THz photocurrent and THz power spectrum were 30 and 3 · 103 higher than those of a conventional PCA at the lowest optical pump power of P=0.1 mW, confirming that our plasmonic PCA is well suited for operation with low-power lasers

Summary

Introduction

An approach for boosting the THz PCAs performance using plasmonic or dielectric nanoantennas incorporated into a photoconductive gap has been proposed.10,11 In such PCAs, strong confinement of the optical pump excitation at the semiconductor/nanoantenna interface leads to enhancement of the light matter interaction, and to improvement of the antenna thermal efficiency.12–14 The PCAemitters and PCA-detectors using different geometries of metal and dielectric nanoantennas, such as silver nano-islands or arrays of nanoscale apertures,15–17 fractal antennas,18 monopole or dipole plasmonic gratings with either low or high aspect ratios,10,11,19–24 plasmonic nanocavities based on Bragg reflectors,25 metal colloidal particles deposited onto the photoconductive substrate,26 or even all-dielectric gratings,27 demonstrated impressive performance enhancement compared to the conventional PCAs.

Results

Conclusion