Role of internal loss in limiting type-II mid-IR laser performance

We report an experimental and theoretical investigation of internal losses in optically pumped type-II lasers with InAs/GaSb/Ga1−xInxSb/GaSb superlattice active regions. Whereas the losses are found to be moderate at 100 K (11–14 cm−1), they increase rapidly with increasing temperature (to 50–120 cm−1 at 200 K). Comparison with a detailed numerical simulation shows that the internal losses play a much more important role than Auger recombination or carrier/lattice heating in limiting the laser performance at high temperatures. Calculations of the temperature-dependent intervalence absorption cross sections show that losses of the magnitude observed experimentally can easily occur if one does not take special care to avoid resonances in all regions of the Brillouin zone. Practical design guidelines are presented. The superlattice lasers yield maximum peak output powers of up to 6.5 W per facet at 100 K and 3.5 W per facet at 180 K, threshold incident pump intensities as low as 340 W/cm2 at 100 K, and Shockley–Read lifetimes >30 ns at 100 K. The Auger coefficients are suppressed (⩽1.6×10−27 cm6/s at T=260 K) despite the intervalence resonances which produce the high internal losses.