Patent ID: 9001858
Filing Date: 2015-04-07
Classification: H01S

Abstract:
1. A quantum cascade laser (QCL) element having a semiconductor superlattice sandwiched by a pair of electrodes, wherein the semiconductor superlattice has an active region that emits electromagnetic waves of a first frequency in a THz range during application of an external voltage for operation through the pair of electrodes, wherein the active region has a plurality of unit structures each of which is stacked with one another to form a multi-layered structure, wherein each unit structure is made of first to fourth well layers that are stacked in this order and are separated from one another by at least one barrier layer, wherein an energy level structure for an electron in one unit structure of the active region during application of a first bias electric field by the external voltage comprises, at least: wherein, during application of a second bias electric field that is weaker than the first bias electric field, an unnecessary upper lasing level and an unnecessary lower lasing level are separated by an energy difference that is equivalent to a photon energy value corresponding to one of electromagnetic waves of frequencies different from the first frequency and whose wavefunctions for an electron have an overlap integral value with each other of 0.15 or less, wherein the unnecessary lasing upper level is either of the reception level or the depopulation level in the upstream unit structure and is one that will have a high probability of existence of an electron in the first well layer during application of the second bias electric field, and wherein the unnecessary lower lasing level is either of the upper lasing level or the lower lasing level and is one that will have a high probability of existence of an electron in the second well layer during application of the second bias electric field, whereby stimulated emissions of photons are suppressed for electromagnetic waves at frequencies different from the first frequency.