THz emitter based on InAs-GaSb coupled quantum wells: New prospects for THz photonics

We suggest a new structure for THz generation based on coupled quantum wells of InAs-GaSb. This structure uniquely combines the advantages of both the p-n junction laser and the cascade laser. Actual generation results from optical transitions between the e3 and e2 levels in InAlAs quantum well, and resonant with them effective band gap between the conduction band of InAs and the valence band of GaSb quantum well, el-hh1. The separation between el and e2 equals to LO phonon energy that provides population inversion between e3 and e2. We consider two ways of structure design that differ by the carrier dispersion: W-shaped dispersion of the carriers in ground states and regular V-shaped dispersion. All these structures bring in the advantages of the system with equidistant levels, i.e., good temperature characteristics and high probability of radiative transition leading to low threshold current compared to alternative designs. We present a comparative analysis of various mechanisms of carrier relaxation (LO phonons and electron - electron scattering) and point out an optimal band structure favoring high efficiency of THz emitter. Corresponding band structure calculations supply one with the range of quantum well parameters providing all the features presented above.