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

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, T{sub 0}, as high as 283 K and slope-efficiency characteristic temperature coefficients, T{sub 1}, as high as 561 K, over the 20–60 °C heatsink-temperature range. These high T{sub 0} and T{sub 1} 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/cm{sup 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 ∼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 completemore » carrier-leakage suppression and high differential efficiency of the laser transition (∼90%), due to resonant extraction from the lower laser level.« less
Authors:
; ; ; ;  [1] ; ;  [2]
  1. Department of Electrical and Computer Engineering, University of Wisconsin Madison, 1415 Engineering Drive, Madison, Wisconsin 53706 (United States)
  2. Intraband, LLC, 200 N. Prospect Ave., Madison, Wisconsin 53726 (United States)
Publication Date:
OSTI Identifier:
22398887
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 106; Journal Issue: 15; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CHARGE CARRIERS; COMPARATIVE EVALUATIONS; DENSITY; DIAGRAMS; EFFICIENCY; ELECTROMAGNETIC PULSES; LASERS; LEAKAGE CURRENT; QUANTUM WELLS; REFLECTIVITY; TEMPERATURE COEFFICIENT; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0273-0400 K; THRESHOLD CURRENT; VISIBLE RADIATION; WAVEGUIDES