Appl. Phys. Lett. 100, 041109 (2012)

The only semiconductor lasers currently capable of accessing mid-infrared wavelengths above 2.3 μm — a range that is particularly important for trace-gas optical detection — are those based on GaSb. Alternative InP-based devices, which offer the benefits of being cheaper, exhibiting lower thermal conductivity and relying on more established technology, are limited to an upper wavelength of around 1.75 μm. Stephan Sprengel and co-workers have now demonstrated room-temperature lasing at 2.55 μm in an InP-based GaInAs/GaAsSb type-II quantum-well laser operating in pulsed mode. The device employs compressive strain in both the GaInAs and GaAsSb regions, together with carrier confinement provided by electron- and hole-blocking layers made from AlAsSb and AlGaInAs, respectively. Whereas previous attempts exploited superlattice active regions, the device demonstrated by Sprengel and co-workers employs W-shaped active regions to benefit fully from the reduced density of states of the quantum confinement. The researchers also demonstrated continuous-wave lasing at 2.31 μm for temperatures of up to 0 °C. Although the device is still in the early stages of development, the researchers say that growth optimization and additional advances in design are expected to improve laser performance and extend operation further into the mid-infrared.