Low-threshold terahertz quantum-cascade lasers

Rochat, Michel; Ajili, Lassaad; Willenberg, H.; Faist, Jérôme; Beere, Harvey E.; Davies, A. G.; Linfield, E. H.; Ritchie, D. A.

doi:10.1063/1.1498861

Cited by 202 publications

(117 citation statements)

References 17 publications

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“…Lasing is observed in pulsed mode up to 64 K with a peak power level of 100 µW, compared to the 10 mW observed at 5 K. The inset shows the increase in threshold current density (J th ) with temperature. This is mostly caused by the re-duction of the upper state lifetime due to thermally activated LO-phonon scattering, rather than thermal backfilling of the lower state, as in the case of chirped superlattice THz lasers [65]. The LO-phonon based depopulation mechanism is relatively temperature insensitive, and thermal backfilling is expected to be minimal due to the large energy separation between n=4 and the collector states 2 and 1, where most for pulses of increasing width repeated at 1 kHz.…”

Section: Coated Laser Devicementioning

confidence: 99%

Terahertz quantum-cascade lasers

2007

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The development of the terahertz frequency range (1-10 THz, λ ≈ 30-300 µm) has long been impeded by the relative dearth of compact, coherent radiation sources of reasonable power. This thesis details the development of quantum cascade lasers (QCLs) that operate in the terahertz with photon energies below the semiconductor Reststrahlen band. Photons are emitted via electronic intersubband transitions that take place entirely within the conduction band, where the wavelength is chosen by engineering the well and barrier widths in multiple-quantum-well heterostructures. Fabrication of such long wavelength lasers has traditionally been challenging, since it is difficult to obtain a population inversion between such closely spaced energy levels (hω ≈ 4-40 meV), and because traditional dielectric waveguides become extremely lossy due to free carrier absorption.This thesis reports the development of terahertz QCLs in which the lower radiative state is depopulated via resonant longitudinal-optical phonon scattering. This mechanism is efficient and temperature insensitive, and provides protection from thermal backfilling due to the large energy separation (∼36 meV) between the lower radiative state and the injector. Both properties are important in allowing higher temperature operation at longer wavelengths. Lasers using a surface plasmon based waveguide grown on a semi-insulating (SI) GaAs substrate were demonstrated at 3.4 THz (λ ≈ 88 µm) in pulsed mode up to 87 K, with peak collected powers of 14 mW at 5 K, and 4 mW at 77 K.Additionally, the first terahertz QCLs have been demonstrated that use metalmetal waveguides, where the mode is confined between metal layers placed immediately above and below the active region. These devices have confinement factors close to unity, and are expected to be advantageous over SI-surface-plasmon waveguides, especially at long wavelengths. Such a waveguide was used to obtain lasing at 3.8 THz (λ ≈ 79 µm) in pulsed mode up to a record high temperature of 137 K, whereas similar devices fabricated in SI-surface-plasmon waveguides had lower maximum lasing temperatures (∼92 K) due to the higher losses and lower confinement factors.This thesis describes the theory, design, fabrication, and testing of terahertz quantum cascade laser devices. A summary of theory relevant to design is presented, 3 including intersubband radiative transitions and gain, intersubband scattering, and coherent resonant tunneling transport using a tight-binding density matrix model. Analysis of the effects of the complex heterostructure phonon spectra on terahertz QCL design are considered. Calculations of the properties of various terahertz waveguides are presented and compared with experimental results. Various fabrication methods have been developed, including a robust metallic wafer bonding technique used to fabricate metal-metal waveguides. A wide variety of quantum cascade structures, both lasing and non-lasing, have been experimentally characterized, which yield valuable information about the transport ...

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Section: Coated Laser Devicementioning

confidence: 99%

Terahertz quantum-cascade lasers

2007

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“…Such knowledge will be crucial in solving the problems of temperature dependence of the lasing characteristics of the new generations of very long wavelength ͑Terahertz͒ quantum cascade lasers reported recently. 12,13 Application of the techniques presented here to the Terahertz laser of Köhler et al 12 has shown that the coupling constant ␣ eϪl is much larger ͑ϳ47 K/kA cm Ϫ2 ͒ than in the mid-infrared devices above. This is a consequence of the increased role of electron-electron scattering in this device operating at low ͑5-50 K͒ lattice temperatures and demonstrates the greater sensitivity of the electron distribution functions to the injection current-a fact that will have to be controlled, either through reduced threshold currents or improved injector design, if high temperature operation of Terahertz lasers is to be achieved.…”

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confidence: 99%

Electron temperature and mechanisms of hot carrier generation in quantum cascade lasers

Harrison

Indjin

Kelsall

2002

Journal of Applied Physics

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A technique for calculating the temperature of the nonequilibrium electron distribution functions in general quantum well intersubband devices is presented. Two recent GaAs/Ga1−xAlxAs quantum cascade laser designs are considered as illustrative examples of the kinetic energy balance method. It is shown that at low current densities the electron temperature recovers the expected physical limit of the lattice temperature, and that it is also a function of current density and the quantised energy level structure of the device. The results of the calculations show that the electron temperature Te can be approximated as a linear function of the lattice temperature Tl and current density J, of the form Te=Tl+αe−lJ, where αe−l is a coupling constant (∼6–7 K/kA cm−2 for the devices studied here) which is fixed for a particular device.

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“…An important THz source is the quantum cascade laser (QCL), a coherent light source that can operate in the THz regime if the quantum well heterostructure is properly designed. [5][6][7][8] As it is compact, versatile and with high output power, such a device is the perfect candidate for astrophysical spectroscopic application, given that it can also fulfill other requirements like single mode and continuous wave operation. 9,10 Moreover, the fabrication of the device should be easily repeatable, meaning that it should be possible to massively fabricate it.…”

mentioning

confidence: 99%

A patch-array antenna single-mode low electrical dissipation continuous wave terahertz quantum cascade laser

Bosco

Bonzon

Ohtani

et al. 2016

Applied Physics Letters

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We introduce a double metal terahertz quantum cascade laser meant for astrophysical heterodyne measurements. The laser ridge is embedded in benzocyclobutene, and the device exhibits single mode, continuous wave operation around 4.745 THz with a peak power of almost 1.8 mW at 10 K and a power consumption of ≈1.6 W. Moreover, thanks to the integration of a top metal contact with a patch array antenna for light out-coupling the beam of the emitted light has a low-divergence single-lobe profile and an FWHM of ≈30°.

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Low-threshold terahertz quantum-cascade lasers

Cited by 202 publications

References 17 publications

Terahertz quantum-cascade lasers

Terahertz quantum-cascade lasers

Electron temperature and mechanisms of hot carrier generation in quantum cascade lasers

A patch-array antenna single-mode low electrical dissipation continuous wave terahertz quantum cascade laser

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