Broadening mechanisms and self-consistent gain calculations for GaN quantum cascade laser structures

Wang, Ke; Grange, Thomas; Lin, Tsung‐Tse; Wang, Li; Jéhn, Zoltán; Birner, Stefan; Yun, Joosun; Terashima, Wataru; Hasegawa, Hideki

doi:10.1063/1.5029520

Cited by 20 publications

(19 citation statements)

References 37 publications

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“…To overcome this limitation, QCLs based on crystals having large optical phonon energy such as GaN or ZnO have recently been proposed 10 . As an alternative strategy, non-polar material systems are attractive because of their weaker e-phonon interaction.…”

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confidence: 99%

Room temperature operation of n-type Ge/SiGe terahertz quantum cascade lasers predicted by non-equilibrium Green's functions

Grange

Stark

Scalari

et al. 2019

Applied Physics Letters

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n-type Ge/SiGe terahertz quantum cascade laser are investigated using non-equilibrium Green's functions calculations. We compare the temperature dependence of the terahertz gain properties with an equivalent GaAs/AlGaAs QCL design. In the Ge/SiGe case, the gain is found to be much more robust to temperature increase, enabling operation up to room temperature. The better temperature robustness with respect to III-V is attributed to the much weaker interaction with optical phonons. The effect of lower interface quality is investigated and can be partly overcome by engineering smoother quantum confinement via multiple barrier heights.Terahertz (THz) quantum cascade lasers (QCLs) have been demonstrated with different III-V materials including GaAs/AlGaAs 1 , InGaAs/AlInAs 2,3 , InGaAs/GaAsSb 4 and InAs/AlAsSb 5 .In the past decade however, relatively small progress has been reported to increase the maximum operating temperature (presently 200 K) despite substantial efforts of design optimization 6-8 . The rationale for the quenching of THz laser emission above this temperature is due to the very effective electron-phonon (e-phonon) interaction, typical of III-V materials. Indeed in polar lattices the longitudinal optical (LO) phonons induce a long-range polarization field which strongly couples to the charge carriers (Fröhlich interaction). The THz transitions are typically designed to be well below the optical phonon energy (30-36 meV), so that at low temperature the upper laser state is protected against scattering by emission of LO-phonons. With increasing temperature however, the thermally activated electrons in the subband of the upper lasing state gain enough in-plane kinetic energy to access this scattering channel 9 . This non-radiative relaxation of carriers reduces the population inversion and is responsible for quenching of the laser emission with increasing temperature as the gain drops below the cavity losses. This fast non-radiative channel cannot easily be overcome by design engineering, as there is a necessary trade-off between selectivity and speed of the carrier injection in such closely spaced energy levels.To overcome this limitation, QCLs based on crystals having large optical phonon energy such as GaN or ZnO have recently been proposed 10 . As an alternative strategy, non-polar material systems are attractive because of their weaker e-phonon interaction. Indeed in these crystals the e-phonon coupling is controlled by the deformation potential which due to its short range is much less effective than the Fröhlich interaction. SiGe alloys fulfill this requirement and also have the great advantage of being non-toxic materials fully compatible with silicon technology. Among different configurations (electron or hole based, Si or Ge rich regimes) 11-14 , theoretical studies have indicated n-type Ge/SiGe heterostructures where charge transport is associated to L electrons, as the most promising architecture 15-17 . Experimentally, sharp THz absorption peaks, related to intersubband transitions in n-typ...

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confidence: 99%

Room temperature operation of n-type Ge/SiGe terahertz quantum cascade lasers predicted by non-equilibrium Green's functions

Grange

Stark

Scalari

et al. 2019

Applied Physics Letters

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“…In contrast, it is more challenging for the methods of rate equations, Monte Carlo, or density-matrix to address such leakage current. Electron-electron interactions are treated as an elastic approximation 34 . Non-elastic (electron-phonon interactions) and elastic (charged impurity, interface roughness) scatterings are also considered in this package, and for alloy disorders, since Al 0.04 Ga 0.96 As is used for phonon well, the alloy scattering involved in transport is as a function dependent on its position.…”

Section: Methodsmentioning

confidence: 99%

Short-period scattering-assisted terahertz quantum cascade lasers operating at high temperatures

Wang

Lin

Wang

et al. 2019

Sci Rep

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Operating at high temperatures in the range of thermoelectric coolers is essential for terahertz quantum cascade lasers to real applications. The use of scattering-assisted injection scheme enables an increase in operating temperature. This concept, however, has not been implemented in a short-period structure consisting of two quantum wells. In this work, based on non-equilibrium Green’s function calculations, it emphasizes on the current leakage and parasitic absorption via high-energy states as fundamental limitations in this scheme with short-period. A new design concept employing asymmetric wells composition is proposed to suppress these limitations. A peak gain of 40 cm −1 at 230 K is predicted in the GaAs/AlGaAs semiconductor material system with an emission frequency of 3.5 THz.

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“…where θ(z) is a unit step function. Acoustic phonon modes arising in a multilayer AlN/GaN RTS are obtained by solving the equation of motion for the elastic displacement of the medium of the RTS layers, which, taking into account (1), (2), can be presented as: For the case of the investigated RTS, we assume that the propagation of acoustic phonons occurs within the Ox axis. Since for an arbitrarily chosen RTS p-th layer, it is uniform in the plane Oxy, and the elastic displacement vector u i (r, t) is independent on coordinate y, this makes it possible to search for solutions of equation (…”

Section: Analytical Solutions Of Equations For the Elastic Displacemementioning

confidence: 99%

“…Modern quantum cascade lasers (QCL) [1][2][3] and detectors (QCD) [4][5][6] of the near and mid infrared ranges of electromagnetic waves use plane multilayer nanostructures based on double GaN, AlN and triple AlGaN compounds of nitride semiconductor materials as their active elements. The characteristic feature of the mentioned materials is the possibility of nanodevices operation based on them in a wide temperature range and the generation of a constant electric field caused by the piezoelectric effect in the nanostructure layers.…”

Section: Introductionmentioning

confidence: 99%

Acoustic phonons in multilayer nitride-based AlN/GaN resonant tunneling structures

2020

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The study of physical processes associated with acoustic phonons in nitride-based nanosystems is of great importance for the effective operation of modern nanoscale devices. In this paper, a consistent theory of acoustic phonons arising in multilayer nitride-based semiconductor resonant tunneling structures, that can function as a separate cascade of a quantum cascade laser or detector is proposed. Using the physical and geometric parameters of a typical nanostructure, the spectrum of various types of acoustic phonons and the corresponding normalized components of the elastic displacement vector are calculated. It has been established that the spectrum of acoustic phonons of a multilayer nanostructure consists of two groups of the shear phonons dependencies and three groups of dependencies for a mixed spectrum of flexural and dilatational phonons. The dependencies of the acoustic phonons spectrum of the nanostructure and the components of the elastic displacement vector on its geometric parameters are studied. It has been established that for the components of the displacement vector u 2 for shear phonons have a decrease in the absolute values of their maxima with increasing of energy level number. The components u 1 and u 3 of flexural and dilatational phonons behave respectively as symmetric and antisymmetric functions relatively the center of an separate selected layer of the nanostructure. The proposed theory can be further applied to study the interaction of electrons with acoustic phonons in multilayer resonant tunneling structures.

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Broadening mechanisms and self-consistent gain calculations for GaN quantum cascade laser structures

Cited by 20 publications

References 37 publications

Room temperature operation of n-type Ge/SiGe terahertz quantum cascade lasers predicted by non-equilibrium Green's functions

Room temperature operation of n-type Ge/SiGe terahertz quantum cascade lasers predicted by non-equilibrium Green's functions

Short-period scattering-assisted terahertz quantum cascade lasers operating at high temperatures

Acoustic phonons in multilayer nitride-based AlN/GaN resonant tunneling structures

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