Michael E. Flatte

Carrier recombination dynamics in a (GaInSb/InAs)/AlGaSb superlattice multiple quantum well

We have used the 830 nm, subpicosecond output of a mode‐locked Ti:sapphire laser, together with subpicosecond 3.55 μm pulses from a synchronously pumped optical parametric oscillator, to perform room‐temperature, time‐resolved, differential transmission measurements on a multiple quantum well structure with AlGaSb barriers and GaInSb/InAs superlattice wells. From these measurements, we have determined a Shockley–Read–Hall rate of 2.4×108 s−1 and an Auger coefficient of 7×10−27 cm6/s. In addition, we estimate the carrier capture efficiency into the wells to be ∼52% and have demonstrated that carrier cooling, cross‐well transport, and capture are complete within ∼10 ps after excitation.

Electronic structure engineering of MWIR emitters

Applications of continuous-wave room-temperature semiconductor laser diodes emitting in the mid-infrared (MWIR) range of wavelengths (from 2-5 microns) will be extensive. The achievement of CW room-temperature operation of MWIR semiconductor lasers has proved to be elusive. Physical processes which degrade laser performance, such as Auger recombination (which increases the threshold current) and intersubband absorption (which increases the internal loss) increase rapidly with decreasing band gap in bulk semiconductors. Thus the threshold current at room temperature can be expected to be dominated by intrinsic Auger recombination processes. As a result, the active region performance cannot be improved simply by growing cleaner material - the material itself must be designed for better performance. Several strategies have been proposed to reduce Auger recombination and internal loss in MWIR materials through the design of superior heterostructure active regions (electronic structure engineering). These strategies include the use of strain and quantum confinement to improve the balancing between conduction and valence densities of states. This type of band-edge engineering was previously developed for near-IR laser active regions, and has proved successful in improving laser performance. A new level of electronic structure engineering is possible in the MWIR through the use of the InAs-GaInSb-AlAsSb material system. The band offsets in this material system exceed three times the MWIR energy gap, and thus allow extensive tailoring of heterostructure materials to reduce the availability of final states for intersubband absorption and Auger recombination.

Ultrafast measurements of electronic and optical properties of mid-IR, strain-balanced, superlattice laser materials

We describe measurements and calculations of the density and temperature dependence of Auger recombination and the density dependent absorption (or gain) spectra in a 4-/spl mu/m band gap multilayer superlattice designed for Auger suppression. We use these results to estimate threshold current densities, characteristic temperatures, and linewidth enhancement factors in this optimized, mid-IR laser active region.