We describe the progress made in the development of type-II interband casca
de lasers emitting in the midinfrared (3.8-3.9 mu m) spectral region. Three
nominally similar molecular beam epitaxy growths on substrates from differ
ent vendors show qualitatively different electrical and optical properties.
The devices tested show significant improvements over previously reported
results with respect to differential external quantum efficiency (similar t
o 500%), peak power (>4 W/facet), peak power conversion efficiency (similar
to 7%), maximum operating temperature (217 K), and continuous-wave operati
on.