Two-well terahertz quantum-cascade laser with direct intrawell-phonon depopulation

Kumar, Sushil; Chan, Chun Wang Ivan; Hu, Qing; Reno, John L.

doi:10.1063/1.3243459

Cited by 77 publications

(95 citation statements)

References 15 publications

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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: 80%

“…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][6][7][8] , as well as finding optimized QCL designs [9][10][11][12][13][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 .…”

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confidence: 99%

“…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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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%

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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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“…The resonanttunneling is due to the strongly anticrossed doublet of lower radiative subbands 3 and 4, which leads to selective transport of the electrons in the lower radiative subband to the wide injector wells. The tunneled electrons then emit LO-phonons on a sub-ps time-scale owing to the [17] . Moduli-squared wavefunctions are vertically displaced in the GaAs/Al0.15Ga0.85As superlattice according to their energies.…”

Section: Resonant-phonon Depopulation Schemementioning

confidence: 99%

Quantum cascade lasers operating from 1.4 to 4 THz (Invited Paper)

Kumar¹

2011

Chin. Opt. Lett.

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The development of teranertz (THz) quantum cascade lasers (QCLs) has progressed considerably since their advent almost a decade ago. THz QCLs operating in a frequency range from 1.4 to 4 THz with electron-phonon scattering mediated depopulation schemes are described. Several different types of GaAs/AlGaAs superlattice designs are reviewed. Some of the best temperature performances are obtained by the so-called resonant-phonon designs that are described. Operation above a temperature of 160 K has been obtained across the spectrum for THz QCLs operating at ν > 1.8 THz. The maximum operating temperature of previously reported THz QCLs has empirically been limited to a value of ∼ ω/kB. A new design scheme for THz QCLs with scattering-assisted injection is shown to surpass this empirical temperature barrier, and is promising to improve the maximum operating temperatures of THz QCLs even further.

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“…However, so far, no room temperature operation has ever been reported and the search for improvement is intensive [4][5][6] . The Free Carrier Absorption (FCA) is a plausible source of losses for far-IR and THz lasers [7][8][9] .…”

Section: Introductionmentioning

confidence: 99%

Free-carrier absorption in asymmetric double quantum well structures due to static scatterers in the in-plane polarization

Ndebeka-Bandou¹,

Carosella²,

Ferreira³

et al. 2014

Phys. Rev. B

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We report on the computation of the free carrier absorption induced by static scatterers in cascade structures when the electromagnetic wave propagates along the growth axis. We find that a Drudelike tail exists for this polarization. The absorption is found larger than when the wave propagates in the layer plane. Also intra-subband scattering is found more efficient than inter-subband scattering. The alloy scattering is found to be particularly efficient.

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Two-well terahertz quantum-cascade laser with direct intrawell-phonon depopulation

Cited by 77 publications

References 15 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

Quantum cascade lasers operating from 1.4 to 4 THz (Invited Paper)

Free-carrier absorption in asymmetric double quantum well structures due to static scatterers in the in-plane polarization

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