High-power continuous-wave midinfrared type-II “W” diode lasers

A type-II “W” diode laser with five quantum well periods and emitting at $\lambda \approx 3.5\mu \mathrm{m}$ operated in cw mode to $T=218\mathrm{K}$ . A second device produced more than $500\mathrm{mW}$ of cw power at $80\mathrm{K}$ . The threshold current density at $T=78\mathrm{K}$ was $31\mathrm{A}∕{\mathrm{cm}}^2$ , and pulsed operation was observed to $317\mathrm{K}$ . Improvements over previous single-stage devices for this wavelength range may be attributed in part to high growth quality and also to the incorporation of transition regions that smooth discontinuities in the conduction-band profile.