Low-Threshold GaSb-Based Interband Cascade Lasers Emitting at 4.5 μm

We present low-threshold high-performance interband cascade lasers (ICLs) emitting at $4.5~\mu$ m at room temperature (RT). The broad-area ICL device had a RT threshold input power density of 782 W/cm ${}^{\mathbf {2}}$ and a threshold current density of 163 A/cm ${}^{\mathbf {2}}$ that is substantially lower than the previous record of 220 A/cm ${}^{\mathbf {2}}$ for ICLs with emitting wavelengths beyond $4\mu$ m. For continuous-wave (CW) operation, the narrow-ridge device with epi-down mounting and a high-reflection coating on the back facet, exhibited threshold current and power densities of only 220 A/cm ${}^{\mathbf {2}}$ and 1056 W/cm ${}^{\mathbf {2}}$ at $20~^{\circ }$ C, respectively, and delivered a maximum power of 33 mW at the same temperature. The same narrow-ridge device also operated in CW mode at temperatures up to $78~^{\circ }$ C, which is $12~^{\circ }$ C higher than the previously reported maximum operating temperature for ICLs in the wavelength region beyond $4~\mu$ m.