InAs-GaSb laser: Prospects for efficient THz emission
  We suggest to use InAs/GaSb coupled quantum wells for THz lasing. In these heterostructures THz lasing is based not on intersubband but on interband transitions. Crucial advantages of this design in comparison with intersubband lasers are (i) a large value of the interband dipole matrix element and (ii) easier maintaining of population inversion. These advantages lead to a gain of two orders of magnitude higher than for intersubband lasing. Even higher gain can be obtained in special design InAs/GaSb W-structures where a hybridization gap of 1-3THz is formed and optical density of states is singular. 
L.D. Shvartsman and B. Laikhtman