Nitride semiconductor quantum cascade laser

摘要

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.

主权项

1. A quantum cascade laser element comprising:
a super lattice formed by a crystal of a nitride semiconductor; the super lattice having a plurality of unit structures, each of which includes a first barrier layer; a first well layer stacked on the first barrier layer; a second barrier layer stacked on the first well layer; and a second well layer stacked on the second barrier layer, the barrier layers and the well layers having high and low potentials, respectively, relative to potentials of conduction-band electrons of the crystal, each unit structure including an energy level structure for electrons under a bias electric field in a stacking direction due to external voltage, the energy level structure having:
a mediation level that has a significant probability of finding an electron in at least one of the first well layer and the second well layer;an upper lasing level that has a significant probability of finding an electron in the first well layer; anda lower lasing level that has a significant probability of finding an electron in the second well layer, under the bias electric field, an energy value of the mediation level being close to an energy value of either the upper lasing level or the lower lasing level of one or more of the unit structure or another unit structure adjacent thereto, and is separated from an energy value of the other level by at least an energy value of a longitudinal-optical (LO) phonon of the crystal, and the energy value of the LO-phonon being greater than a photon energy for an electromagnetic wave emitted by stimulated emission from an electron that makes a transition from the upper lasing level to the lower lasing level in response to the bias electric field.