Abstract
Quantum-cascade lasers, which are obtained by molecular-beam epitaxy, emit at wavelengths of 5.0 mu m at 77 K and 5.2 mu m at 300 K and are based on a design with four quantum wells in the active region with vertical transitions and strain-compensated superlattices with high-efficiency injection and a short lifetime of the ground state are fabricated. The typical thresholds for lasing at 300 K were in the range 4-10 kA/cm(2). The maximum emission power was as high as similar to 1 W, the maximum lasing temperature was similar to 450 K, and the maximum characteristic temperature T-0 approximate to 200 K. The use of a modified process of postgrowth treatment made it possible to reproducibly obtain high-quality devices.