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

J. D. Kirch, C. C. Chang, C. Boyle, L. J. Mawst, D. Lindberg, T. Earles, D. Botez*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)


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.

Original languageEnglish
Article number151106
JournalApplied Physics Letters
Issue number15
Publication statusPublished - 2015 Apr 13
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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