Broadband THz lasing from a photon-phonon quantum cascade structure

Scalari, Giacomo; Amanti, Maria I.; Walther, Christoph; Terazzi, Romain; Beck, Mattias; Faist, Jérôme

doi:10.1364/oe.18.008043

Cited by 72 publications

(60 citation statements)

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“…Here, we see that the phonon extraction has been complemented by a secondary extraction mechanism; tunnelling into state number 4 ′ with subsequent phonon emission landing on the ul or i state of the next period, as indicated by the calculated phonon scattering rates (see Supplementary material, Table 1). This resonance is also present in previous 2-well structures 10,30 , where it is detrimental since it has significant overlap with continuum states. This is similar to the situation in Ref.…”

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confidence: 58%

“…As a starting point, we choose the shortest possible structure based on two quantum wells per period 10,30 , in order to maximize the gain per unit length; with fewer active states per period, more carriers are expected to concentrate on the upper laser level (ul). In addition, we limit the escape of carriers into continuum states by employing barriers with a high (25%) AlAs concentration [12][13][14]20 .…”

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confidence: 99%

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Two-well quantum cascade laser optimization by non-equilibrium Green's function modelling

Franckié

Bosco

Beck

et al. 2018

Applied Physics Letters

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We present a two-quantum well THz intersubband laser operating up to 192 K. The structure has been optimized with a non-equilibrium Green's function model. The result of this optimization was confirmed experimentally by growing, processing and measuring a number of proposed designs. At high temperature (T > 200 K), the simulations indicate that lasing fails due to a combination of electron-electron scattering, thermal backfilling, and, most importantly, re-absorption coming from broadened states.Terahertz quantum cascade lasers (QCLs) 1 are interesting candidates for a wide variety of potential applications 2,3 . However, to date, their operation is limited to ∼200 K 4 and the necessity of cryogenic cooling hinders a widespread use of these devices. In the last decade, significant scientific effort has been directed towards identifying the main temperaturedegrading mechanisms 5-8 , as well as finding optimized QCL designs 9-14 . The degrading mechanisms include thermal backfilling 3,15 , thermally activated LO phonon emission [6][7][8]16 , increased broadening [17][18][19] , and carrier leakage into continuum states 20 . When numerically optimizing a design, it is important to take all of these effects into consideration, in order to ensure a close correspondence between the model and the real device. Combined with the fact that the optimization parameters are typically trade-offs for one another, the task is very complex. Here, typically simpler rate equation or density matrix models are used in order to more quickly sweep the parameter space 21-23 , while more advanced models, such as non-equilibrium Green's functions (NEGF) or Monte-Carlo, are used to validate and analyze the final designs 13,[24][25][26] . In contrast, in this work we will employ an advanced model directly at the optimization stage. Specifically, we shall use a NEGF model 27 , capable of accurately simulating experimental devices 13,26,28 and including the most general treatment of scattering, from all relevant processes.The goal of the optimization is to achieve the highest possible operating temperature. Thus, the gain of the active medium should be maximized at high lattice temperature, and simultaneously the external losses minimized. The key figures for gain are inversion, oscillator strength, and line width 29 . These are mainly controlled by the doping density, the energy difference E ex between the lower laser level ll and the extractor state e, and the width of the two barriers: the laser and injection barriers. Population inversion increases with doping, although a too high level promotes detrimental effects, such as electron-electron scattering. E ex , which is chosen to be close to the LO phonon resonance E LO in order to have a short ll lifetime, and the laser frequency ω are mainly determined by the well widths. The laser barrier width determines the oscillator strength, which at the same time affects inversion; a more vertical transition

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confidence: 99%

Two-well quantum cascade laser optimization by non-equilibrium Green's function modelling

Franckié

Bosco

Beck

et al. 2018

Applied Physics Letters

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“…Here, we study the first realized structure KumarAPL2009B 34 as well as the broadband laser ScalariOE2010. 35 Both lasers were processed with metalmetal (MM) waveguides and the latter showed high power output when parts of the upper metal contact were removed.…”

Section: A 2-well Designsmentioning

confidence: 99%

Simulating terahertz quantum cascade lasers: Trends from samples from different labs

Winge

Franckié

Wacker

2016

Journal of Applied Physics

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We present a systematic comparison of the results from our non-equilibrium Green's function formalism with a large number of AlGaAs-GaAs terahertz quantum cascade lasers previously published in the literature. Employing identical material and simulation parameters for all samples, we observe that discrepancies between measured and calculated peak currents are similar for samples from a given group. This suggests that the differences between experiment and theory are partly due to a lacking reproducibility for devices fabricated at different laboratories. Varying the interface roughness height for different devices, we find that the peak current under lasing operation hardly changes, so that differences in interface quality appear not to be the sole reason for the lacking reproducibility.

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“…Since their initial demonstration in 2002, terahertz quantum cascade lasers have developed remarkably [15,16], with various propositions for the active region design [17]. The number of wells per period has been reduced, starting from the superlattice-based structure that comprised 7 wells (the first demonstration) [18], down to two-well diagonal design [3,17].…”

Section: Introductionmentioning

confidence: 99%

“…The number of wells per period has been reduced, starting from the superlattice-based structure that comprised 7 wells (the first demonstration) [18], down to two-well diagonal design [3,17]. Also, the upconversion of THz QCL radiation in the near-IR region, using nonlinear intracavity mixing, has been reported [19].…”

Section: Introductionmentioning

confidence: 99%

Magnetic field effects on THz quantum cascade laser: A comparative analysis of three and four quantum well based active region design

Daničić¹,

Radovanović

Milanović

et al. 2016

Physica E: Low-dimensional Systems and Nanostructures

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ReuseUnless 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. TakedownIf 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. Abstract. We consider the influence of additional carrier confinement, achieved by application of strong perpendicular magnetic field, on inter Landau levels electron relaxation rates and the optical gain, of two different GaAs quantum cascade laser structures operating in the terahertz spectral range. Breaking of the in-plane energy dispersion and the formation of discrete energy levels is an efficient mechanism for eventual quenching of optical phonon emission and obtaining very long electronic lifetime in the relevant laser state. We employ our detailed model for calculating the electron relaxation rates (due to interface roughness and electron-longitudinal optical phonon scattering), and solve a full set of rate equations to evaluate the carrier distribution over Landau levels. The numerical simulations are performed for threeand four-well (per period) based structures that operate at 3.9THz and 1.9THz, respectively, both implemented in GaAs/Al0.15Ga0.85As. Numerical results are presented for magnetic field values from 1.5 T up to 20 T, while the band nonparabolicity is accounted for. Magnetic field effects on IntroductionQuantum Cascade Lasers (QCLs) have become important light sources for infrared spectroscopy within the last decade, especially when it comes to new structures operating in the terahertz (THz) region, suggesting numerous applications, such as chemical sensing, infrared imaging, non-invasive medical diagnostics and optical communications [1][2][3][4][5][6][7][8][9][10][11][12][13]. These devices are designed in such a manner so as to have electronic subbands defined as the upper and the lower laser level, electric pumping along the growth direction, as well as periodic repetition of active elements, which enhances the light amplification. Because of the specific properties of intersubband transitions, dynamical behavior is very different from that of inter-band lasers. The first and most important feature of intersubband transitions is very fast non-radiative scattering, proceeding on a time scale of few picoseconds [6]. THz frequencies belong to the quite under-utilized part of the electromagnetic spectrum, despite their significant application potential. This is mostly due to...

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Broadband THz lasing from a photon-phonon quantum cascade structure

Cited by 72 publications

References 19 publications

Two-well quantum cascade laser optimization by non-equilibrium Green's function modelling

Two-well quantum cascade laser optimization by non-equilibrium Green's function modelling

Simulating terahertz quantum cascade lasers: Trends from samples from different labs

Magnetic field effects on THz quantum cascade laser: A comparative analysis of three and four quantum well based active region design

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