Design and simulation of losses in Ge/SiGe terahertz quantum cascade laser waveguides

Gallacher, K. et al. (2020) Design and simulation of losses in Ge/SiGe terahertz quantum cascade laser waveguides. Optics Express, 28(4), pp. 4786-4800. (doi: 10.1364/OE.384993)

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The waveguide losses from a range of surface plasmon and double metal waveguides for Ge/Si1−xGex THz quantum cascade laser gain media are investigated at 4.79 THz (62.6 μm wavelength). Double metal waveguides demonstrate lower losses than surface plasmonic guiding with minimum losses for a 10 μm thick active gain region with silver metal of 21 cm−1 at 300 K reducing to 14.5 cm−1 at 10 K. Losses for silicon foundry compatible metals including Al and Cu are also provided for comparison and to provide a guide for gain requirements to enable lasers to be fabricated in commercial silicon foundries. To allow these losses to be calculated for a range of designs, the complex refractive index of a range of nominally undoped Si1−xGex with x = 0.7, 0.8 and 0.9 and doped Ge heterolayers were extracted from Fourier transform infrared spectroscopy measurements between 0.1 and 10 THz and from 300 K down to 10 K. The results demonstrate losses comparable to similar designs of GaAs/AlGaAs quantum cascade laser plasmon waveguides indicating that a gain threshold of 15.1 cm−1 and 23.8 cm−1 are required to produce a 4.79 THz Ge/SiGe THz laser at 10 K and 300 K, respectively, for 2 mm long double metal waveguide quantum cascade lasers with facet coatings.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Paul, Professor Douglas and REW, Kirsty and Gallacher, Dr Kevin
Authors: Gallacher, K., Ortolani, M., Rew, K., Ciano, C., Baldassarre, L., Virgillio, M., Scalari, G., Faist, J., Di Gaspare, L., De Seta, M., Capellini, G., Grange, T., Birner, S., and Paul, D.J.
College/School:College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
Journal Name:Optics Express
Publisher:Optical Society of America
ISSN (Online):1094-4087
Copyright Holders:Copyright © 2020 The Optical Society
First Published:First published in Optics Express 28(4):4786-4800
Publisher Policy:Reproduced under a Creative Commons License
Data DOI:10.5525/gla.researchdata.950

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
301516Far-infrared Lasers Assembled using SiliconDouglas PaulEuropean Commission (EC)766719ENG - Electronics & Nanoscale Engineering
171911Engineering Quantum Technology Systems on a Silicon PlatformDouglas PaulEngineering and Physical Sciences Research Council (EPSRC)EP/N003225/1ENG - Electronics & Nanoscale Engineering