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Highly temperature insensitive, low threshold-current density (λ=8.7-8.8 μm) quantum cascade lasers
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DOI：10.1063/1.4917499.png)
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Abstract
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By stepwise tapering, both the barrier heights and quantum-well depths in the active regions of 8.7-8.8 mu m-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, T-0, as high as 283K and slope-efficiency characteristic temperature coefficients, T-1, as high as 561 K, over the 20-60 degrees C heatsink-temperature range. These high T-0 and T-1 values reflect at least a factor of four reduction in carrier-leakage current compared to conventional 8-9 mu m-emitting QCLs. Room temperature, pulsed, threshold-current densities are 1.58 kA/cm(2); 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 similar to 1.3 x 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 mu m-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 (similar to 90%), due to resonant extraction from the lower laser level. (c) 2015 AIP Publishing LLC.
Keywords:
CONTINUOUS-WAVE
HIGH-PERFORMANCE
EFFICIENCY
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