Davies, AG

Dean, P

Kundu, I

Li, L

Linfield, EH

White Rose Research Online

This is a repository copy of High-power GaAs/AlGaAs quantum cascade lasers with emission in the frequency range 4.7–5.6 THz.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/104741/Version: Accepted VersionProceedings Paper:Li, L, Kundu, I, Dean, P et al. (2 more authors) (2016) High-power GaAs/AlGaAs quantum cascade lasers with emission in the frequency range 4.7–5.6 THz. In: UNSPECIFIED International Quantum Cascade Lasers School and Workshop, 04-09 Sep 2016, Cambridge, UK. . eprints@whiterose.ac.ukhttps://eprints.whiterose.ac.uk/Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. High-power GaAs/AlGaAs quantum cascade lasers withemission in the frequency range 4.7–5.6 THzLianhe Li*, Iman Kundu, Paul Dean, Edmund H. Linfield, and A. Giles DaviesSchool of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom*l.h.li@leeds.ac.uk1. IntroductionTerahertz (THz) frequency radiation has many potential applications, ranging from imaging and chemical sensingthrough to high-speed and high-capacity optical wireless communications. However, one of the principal challengesis to develop compact, low-cost, efficient THz sources. In this respect, the development of the THz frequencyquantum cascade laser (QCL) has provided a potential solid-state solution. Since their first demonstration in 2002,THz QCLs, based on the GaAs materials system, have become important compact sources of coherent radiation inthe 1.2–5.4 THz band, with maximum operating temperatures of 199.5 K and peak pulsed output powers >1 Wbeing demonstrated [1–3].THz waves in the 5–12 THz frequency range are of interest for applications such as high-resolution spectroscopy ofgaseous species and the study of shallow donor transitions in isotopically enriched semiconductors [4, 5]. However,owing to strong absorption caused by electron-longitudinal optical (LO) phonon interactions in GaAs materials, it isdifficult to develop GaAs-based THz QCLs in this frequency range. Indeed, deteriorating device performance hasbeen observed as the emission frequency is increased beyond 5 THz [2, 3]. To date, the highest emission frequencyobserved from GaAs-based THz QCLs is 5.4 THz. However, this device only worked in pulsed mode, with amaximum operating temperature of 55 K and a maximum peak output power of 6 mW at 5 K [2]. As an alternative,group III-nitride semiconductors, having much larger LO phonon energies than those in GaAs, have been proposedand examined as potential materials for THz QCLs. However, owing to the relative immaturity of this materialsystem, lasing action has not yet been observed at temperatures above ~5 K [6].Here, we demonstrate GaAs/AlGaAs THz QCLs emitting over a spectral range of 4.7–5.6 THz. The devices operatein pulsed mode with a maximum working temperature of 107 K, and a peak output power from a single facet inexcess of 170 mW at 10 K.2. Experimental detailsThe QCL active region design is based on a bound-to-continuum transition with a single-well injector, similar tothose reported in Refs. 1 and 7, but with rescaled layer thicknesses to enable higher frequency emission. The QCLstructure was grown by solid-source molecular beam epitaxy on a semi-insulating GaAs substrate. After growth, theQCL wafer was processed into surface-plasmon ridge waveguide structures using standard photolithography and wetchemical etching techniques before the substrate was thinned to ~165 µm. For measurement, devices were cleavedand indium-soldered onto copper sub-mounts. They were characterized in pulsed mode, with a repetition rate of10 kHz and a duty cycle of 2 %, in a liquid-helium continuous-flow cryostat. The radiation was collected from asingle facet and the average power was measured using an absolute terahertz power meter (Thomas Keating). Peakoutput power was then calculated from the measured average power and duty cycle. Unlike some earlier reports,neither a light-pipe nor a Winston core was used to improve collection efficiency from the devices. Furthermore, nocorrection was made to account for the collection efficiency or for absorption in the polyethylene windows, althoughthese factors have been considered elsewhere [8-10].3. Results and discussionsFig. 1 shows the LIV curves of an as-cleaved Fabry-Përot (FP) cavity device with a ridge width of 150 µm and acavity length of 1.8 mm at different heatsink temperatures (left panel). Also shown are typical lasing spectra fromthe same device with different injection currents at 10 K (right panel). The device operates with a maximumtemperature of 107 K. At 10 K, a peak output power of ~170 mW is obtained from a single facet. Even at 77 K, thedevice still delivers a peak output power of ~50 mW. If a larger dimension device is fabricated, then the peak outputpower should be much higher, as shown in Ref. 1. The device emits over a spectral range of 4.7–5.6 THz withdominant peaks at ~5 THz. It should be noted that this broadband emission is observed across almost the wholeinjection current dynamic range. For example, the highest emission frequency of ~5.6 THz is preserved withincreasing injection current up to the peak maximum, and additionally, it is still observed even with a workingtemperature of 90 K (data not shown). To the best of our knowledge, this is the highest frequency emission observedto date from GaAs/AlGaAs THz QCLs. To obtain single mode emission, after characterization of the FP-cavitydevice, a photonic lattice (PL) with only 20 defect sites was patterned on the ridge of the same device using afocused ion beam (FIB) [11]. The device emits a single mode of 4.98 THz at 10 K (inset to right panel) with amaximum working temperature of 88.5 K and a peak output power up to 33.5 mW (data not shown). Since there issufficient gain, with further refinement and optimization of the PL design and processing, it should in principle befeasible to engineer single mode emission of ~5.6 THz from this QCL structure.4. References[1] L. H. Li, L. Chen, J. Zhu, J. Freeman, P. Dean, A. Valavanis, A. G. Davies, and E. H. Linfield, “Terahertz quantum cascade lasers with >1W output powers,” Electron. Lett., 50, 309 (2014).[2] M. Wienold, B. Röben, X. Lü, G. Rozas, L. Schrottke, K. Biermann, and H. T. Grahn, “Frequency dependence of the maximum operatingtemperature for quantum-cascade lasers up to 5.4 THz”, Appl. Phys. Lett., 107, 202101 (2015).[3] C. W. I. Chan, Q. Hu, J. R. Reno, “Ground state terahertz quantum cascade lasers”, Appl. Phys. Lett., 101, 151108 (2012).[4] K. Fukunaga, Y. Ogawa, S. Hayashi, I. Hosako, “Terahertz spectroscopy for art conservation”, EICE Electron. Express 4, 258 (2007).[5] A. J. Mayur, M. Dean Sciacca, A. K. Ramdas, and S. Rodriguez, “Redetermination of the valley-orbit (chemical) splitting of the 1s groundstate of group-V donors in silicon,” Phys. Rev. B 48, 10893 (1993).[6] W. Terashima and H. Hirayama, “Terahertz frequency emission with novel quantum cascade laser designs”, SPIE newsroom,http://spie.org/newsroom/technical-articles/6058-terahertz-frequency-emission-with-novel-quantum-cascade-laser-designs[7] M. I. Amanti, G. Scalari, et al., “Bound-to-continuum terahertz quantum cascade laser with a single-quantum-well phononextraction/injection stage,” New J. Phys. 11, 125022 (2009).[8] L. Ajili, G. Scalari, J. Faist, H. Beere, E. H. Linfield, and A. G. Davies, “High power quantum cascade lasers operating at そ؄87 and130たm,” Appl. Phys. Lett., 85, 3986 (2014). [9] http://www.tydexoptics.com/products/thz_optics/thz_materials/[10] M. S. Vitiello, G. Scamarcio, V. Spagnolo, S. S. Dhillon, and C. Sirtori, “Terahertz quantum cascade lasers with large wall-plugefficiency,” Appl. Phys. Lett., 90, 191115 (2007).[11] I. Kundu, P. Dean, A. Valavanis, L. Chen, L. Li, J. E. Cunningham, E. H. Linfield, and A. G. Davies, “Discrete Vernier tuning in terahertzquantum cascade lasers using coupled cavities,” Opt. Express, vol. 22, no. 13, 16595 (2014).Fig. 1 Left panel: LIV curves of an as-cleaved FP-cavity device with a ridge width of 150 µm and a cavity length of1.8 mm at different heatsink temperatures. The power only takes emission from a single facet into account. No correction ismade for the collection efficiency or for absorption in the polyethylene windows. Right panel: Typical lasing spectra for thesame device with different injection currents at 10 K. Inset: the typical lasing spectrum at 10 K of a PL laser fabricated bypost-packaging FIB processing of the same device.

High-power GaAs/AlGaAs quantum cascade lasers with emission in the frequency range 4.7–5.6 THz

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High-power GaAs/AlGaAs quantum cascade lasers with emission in the frequency range 4.7–5.6 THz

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