High-performance, homogeneous broad-gain quantum cascade lasers based on dual-upper-state design

Fujita, Kazuue; Edamura, Tadataka; Furuta, Shunsuke; Yamanishi, Masamichi

doi:10.1063/1.3455102

Cited by 73 publications

(33 citation statements)

References 15 publications

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“…In order to verify the anticrossed two upper state conditions, we have fabricated the devices based on the anticrossed DAU to single-lower-state design and confirmed broad and symmetric EL spectra like the 8 m DAU laser case. 8 The energy separation ͑anticrossing gap͒ between two upper states is designed to be large enough E 43 ϳ 25 meV to obtain broader gain-width. The emission wavelength is chosen to be ϳ6.8 m to avoid a large optical absorption.…”

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confidence: 99%

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High-performance quantum cascade lasers with wide electroluminescence (∼600 cm−1), operating in continuous-wave above 100 °C

Fujita¹,

Furuta²,

Sugiyama³

et al. 2011

Applied Physics Letters

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The authors report high temperature continuous-wave ͑cw͒ operations of broad-gain quantum cascade lasers based on the anticrossed dual-upper-state to multiple-lower-state design. The devices exhibit extremely wide electroluminescence ͑Ͼ600 cm −1 ͒ and subthreshold amplified spontaneous emission ͑ϳ570 cm −1 ͒ spectra at room temperature. Despite showing such broad electroluminescence spectra, the high-reflection coated, buried heterostructure lasers operating at 6.8 m demonstrate a low threshold current density of ϳ1.5 kA/ cm 2 and a high power of Ͼ500 mW with a high slope efficiency of ϳ1.6 W / A in cw mode at 300 K. The maximum cw operating temperature of above 100°C is achieved.Quantum cascade ͑QC͒ lasers 1 are promising light sources for many chemical sensing applications in the midinfrared spectral range. For industrial application, broadband wavelength tuning of external-cavity QC lasers with very broad gain-width ͑⌬ / 0 Ͼ 0.3͒ has been demonstrated. 2,3 For instance, a five wavelength stack laser 2 demonstrates a wide wavelength tuning of 432 cm −1 and another two wavelength stack laser 3 also did a tuning range of 292 cm −1 both at room temperature. The latter laser was achieved cw operation above room temperature by using the combination of junction down mounting with diamond heat-sink and buried hetero structure.However, for multiple-stack approach, it may raise problems such as inhomogeneous spectral behavior owing to spatial heterogeneity of active region 4 in which it takes a longer time ͑Ͼ1 ps͒ for electron transfer between spatially separated wavelength stacks. The following fact was clarified on longitudinal mode-stability in bipolar lasers. When the intraband relaxation time is longer than 3 ϫ 10 −13 s, the gain shows strong nonuniformity across the spectral or energy distributions and at the same time the gain of some resonating modes is increased; 5 this hinders the single mode operation under wavelength tuning. Although the short relaxation lifetime 1 ϫ 10 −13 s in cases of bipolar lasers is reported, 6 even shorter relaxation times would be required for modestability in QC lasers due to very high stimulated emission rates. 7 On this issue, in an identical-stack ͑homogeneous cascade͒ QC laser, depression of electron population in a upper subband, induced by stimulated emissions can be compensated quickly by relaxation from other subbands in the same space, in an anticrossed dual-upper-state ͑DAU͒ design 8 because of sufficient spatial overlapping of wave functions of both subbands. Thus, gain spectrum of an identical-stack DAU QC laser would be viewed as spectrally homogeneous one. Obviously, an inherently broad and spectrally homogeneous gain profile of the laser medium with translational symmetry is preferable for single mode operation in the external cavity application of QCLs. Recently we have reported broad-gain ͑⌬ / 0 ϳ 0.4, ϳ500 cm −1 full width at half maximum, FWHM͒ and temperature insensitive ͑T 0 ϳ 510 K͒ operations of QC lasers based on the active region with translational symmetry....

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“…The 40-period active region was used as the emitting region and the waveguide structure is almost same as that in Ref. 8. After the growth, the wafer was processed into buried hetero structure.…”

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confidence: 99%

High-performance quantum cascade lasers with wide electroluminescence (∼600 cm−1), operating in continuous-wave above 100 °C

Fujita¹,

Furuta²,

Sugiyama³

et al. 2011

Applied Physics Letters

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“…Very high T 0 and T 1 values have been reported from 8-9 lm QCLs with unconventional upper-state(s) populating mechanisms; 16,[20][21][22] however, at a price in J th and/or g s . Indirect-pump devices 20 have provided high T 0 values: 243 K and 303 K, but they had high J th values of 2.7 and 3.3 kA/cm 2 , respectively.…”

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confidence: 94%

Highly temperature insensitive, low threshold-current density (λ = 8.7–8.8 μm) quantum cascade lasers

Kirch

Chang

Boyle

et al. 2015

Applied Physics Letters

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By stepwise tapering, both the barrier heights and quantum-well depths in the active regions of 8.7–8.8 μm-emitting quantum-cascade-laser (QCL) structures, virtually complete carrier-leakage suppression is achieved. Such step-taper active-region-type QCLs possess, for 3 mm-long devices with high-reflectivity-coated back facets, threshold-current characteristic temperature coefficients, T0, as high as 283 K and slope-efficiency characteristic temperature coefficients, T1, as high as 561 K, over the 20–60 °C heatsink-temperature range. These high T0 and T1 values reflect at least a factor of four reduction in carrier-leakage current compared to conventional 8–9 μm-emitting QCLs. Room temperature, pulsed, threshold-current densities are 1.58 kA/cm2; values comparable to those for 35-period conventional QCLs of similar injector-region doping level. Superlinear behavior of the light-current curves is shown to be the result of the onset of resonant extraction from the lower laser level at a drive level of ∼1.3× threshold. Maximum room-temperature slope efficiencies are 1.23 W/A; that is, slope efficiency per period values of 35 mW/A, which are 37%–40% higher than for same-geometry conventional 8–9 μm-emitting QCLs. Since the waveguide-loss coefficients are very similar, we estimate that the internal differential efficiency is at least 30% higher than in conventional QCLs. Such high internal differential efficiency values reflect the combined effect of nearly complete carrier-leakage suppression and high differential efficiency of the laser transition (∼90%), due to resonant extraction from the lower laser level.

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“…Multiple quantum well structure is a low-dimensional semiconductor nanostructure which is coupled through the external world by means of resonant tunneling; and based on this physical insight, several novel electronic [31,32] and photonic [30][31][32][33] devices are fabricated which is far superior to their bulk counterparts. The analysis of resonant tunneling diodes was carried out with submicron-sized mesa structures along with contacts at both the terminals in order to measure the current-voltage characteristics in the bistable regime at room temperature.…”

Section: Introductionmentioning

confidence: 99%

“…Stöhr et al [29] experimentally characterized electro-optical modulators and switches based on MQW-structure. It can also be used for making quantum cascade laser (QCL) [30], resonant tunneling diode (RTD) [31], resonant tunneling transistor (RTT) [32], quantum well infrared photodetectors (QWIP) [33], etc., which have greater eiciency compared to their bulk counterparts. QCLs are preferred for broadband tuning, RTD and RTT for digital circuits and negative resistance devices.…”

Section: Introductionmentioning

confidence: 99%

Electronic Band Structure of Quantum Cascade Laser

Deyasi¹

2017

Quantum Cascade Lasers

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Multiple quantum well structure is the subject of theoretical and experimental research over the last two decades due to the possibility of making novel electronic and optoelectronic devices. The phenomenon of resonant tunneling makes it a prime candidate for all tunneling-based quantum devices with one-dimensional coninement. THz laser design using multilayered low-dimensional semiconductor structure is one such example, where miniband formation and its energy diference with lowest quantum state play crucial factor in governing device performance. Quantum cascade laser (QCL) is one of such candidate, which speaks in favor of research using multiple-quantum-well (MQW) structure. In the proposed chapter, transmission coeicient of multiple quantum-well structure is numerically computed using propagation matrix technique, and its density of states is calculated in the presence and absence of electric ield applied along the direction of quantum coninement. Absorption coeicient is also calculated for its possible application as optical emiter/detector. Based on the electronic and photonic properties investigated, electronic band structure of the quantum cascade laser (formed using the MQW structure) is computed. Formation of miniband is tailored with variation of external bias is shown.

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High-performance, homogeneous broad-gain quantum cascade lasers based on dual-upper-state design

Cited by 73 publications

References 15 publications

High-performance quantum cascade lasers with wide electroluminescence (∼600 cm−1), operating in continuous-wave above 100 °C

High-performance quantum cascade lasers with wide electroluminescence (∼600 cm−1), operating in continuous-wave above 100 °C

Highly temperature insensitive, low threshold-current density (λ = 8.7–8.8 μm) quantum cascade lasers

Electronic Band Structure of Quantum Cascade Laser

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