Advantages of GaSb/AlSb LO phonon depopulation terahertz quantum cascade laser on GaAs substrate

A terahertz quantum cascade laser (THz-QCL) using a resonant longitudinal optical (LO) phonon depopulation scheme was successfully demonstrated by MIT´s group. We fabricated QCL structures from both a GaAs/AlGaAs material system and a GaSb/AlSb system using this scheme. The characteristics of these QCLs were compared experimentally. A smaller threshold electric field was expected for the GaSb/AlSb QCL because GaSb has smaller LO phonon energy than that of GaAs. Experimental results indicated that the threshold electric field of the GaSb/AlSb QCL was 3.2 kV/cm. These results mean that the GaSb/AlSb QCL is suitable for low input power operation. Furthermore, the GaSb/AlSb QCL on a GaAs substrate provides high optical confinement without a complicated fabrication process