Abstract: A terahertz quantum cascade laser (THz-QCL) element operable at an unexplored frequency is obtained. A crystal of a nitride semiconductor is used to fabricate a repeated set of unit structures into a super lattice. Each unit structure includes a first barrier layer, a first well layer, a second barrier layer, and a second well layer disposed in this order. An energy level structure for electrons under a bias electric field has a mediation level, an upper lasing level, and a lower lasing level. The energy value of the mediation level is close to the energy value of either an upper lasing level or a lower lasing level, each belonging to either the unit structure or the other unit structure adjacent thereto, and is separated from the energy value of the other level by at least the energy value of a longitudinal-optical (LO) phonon exhibited by the crystal.

Abstract: A terahertz quantum cascade laser (THz-QCL) element operable at an unexplored frequency is obtained. A crystal of a nitride semiconductor is used to fabricate a repeated set of unit structures into a super lattice. Each unit structure includes a first barrier layer, a first well layer, a second barrier layer, and a second well layer disposed in this order. An energy level structure for electrons under a bias electric field has a mediation level, an upper lasing level, and a lower lasing level. The energy value of the mediation level is close to the energy value of either an upper lasing level or a lower lasing level, each belonging to either the unit structure or the other unit structure adjacent thereto, and is separated from the energy value of the other level by at least the energy value of a longitudinal-optical (LO) phonon exhibited by the crystal.