Impact of substrate characteristics on performance of large area plasmonic photoconductive emitters.

Nezih T Yardimci,Hari P Nair,Erica M Krivoy,Seth R Bank,Rodolfo Salas,Mona Jarrahi

doi:10.1364/oe.23.032035

Abstract

We present a comprehensive analysis of terahertz radiation from large area plasmonic photoconductive emitters in relation with characteristics of device substrate. Specifically, we investigate the radiation properties of large area plasmonic photoconductive emitters fabricated on GaAs substrates that exhibit short carrier lifetimes through low-temperature substrate growth and through epitaxially embedded rare-earth arsenide (ErAs and LuAs) nanoparticles in superlattice structures. Our analysis indicates that the utilized substrate composition and growth process for achieving short carrier lifetimes are crucial in determining substrate resistivity, carrier drift velocity, and carrier lifetime, which directly impact optical-to-terahertz conversion efficiency, radiation power, radiation bandwidth, and reliability of large area plasmonic photoconductive emitters.

Highlights

Photoconductive emitters are widely used in time-domain terahertz imaging and spectroscopy systems for generating pulsed terahertz radiation [1,2,3,4,5,6,7,8,9,10,11,12,13]
Since the major portion of the generated terahertz radiation from the large area plasmonic photoconductive emitters is due to the ultrafast photocurrent fed to the nanoantenna arrays [17], similar radiation spectral shapes are obtained from the emitter prototypes fabricated on the low temperature grown (LT)-GaAs, ErAs:GaAs, and LuAs:GaAs substrates
The terahertz output power and device characteristics are measured under identical conditions for large area plasmonic photoconductive emitters fabricated on LT-GaAs, and superlattice structures of ErAs:GaAs and LuAs:GaAs with different rare-earth arsenide (RE-As) deposition and superlattice period thicknesses

Summary

Introduction

Photoconductive emitters are widely used in time-domain terahertz imaging and spectroscopy systems for generating pulsed terahertz radiation [1,2,3,4,5,6,7,8,9,10,11,12,13]. They are required to have high dark resistivity levels to allow device operation under high bias voltages in order to drift the photocarriers at saturation velocities while maintaining low dark current and thermal dissipation levels. Large area plasmonic photoconductive emitters fabricated on semi-insulating (SI) GaAs substrates offer the highest optical-to-terahertz conversion efficiencies and terahertz radiation power levels at 800 nm optical pump wavelengths [17] because of a higher carrier mobility and drift velocity compared to short carrier lifetime photo-absorbing semiconductor substrates such as low temperature grown (LT) GaAs. large area plasmonic photoconductive emitters fabricated on short carrier lifetime substrates such as LT-GaAs offer lower thermal dissipation and better reliability by recombining the slow photocarriers that do not contribute to efficient terahertz generation. We study the use of various short carrier lifetime photo-absorbing semiconductor substrates in large area plasmonic photoconductive emitters to gain a deeper understanding of the impact of the substrate properties on terahertz radiation characteristics

Material growth and device fabrication

Experimental characterization and analysis

Conclusion