higher energy band gap than the quantum well structure 15 a for example when the quantum well structure is formed of in x1 ga 1 x1 n the polarization relaxation layer 15 b may be formed of gan or in x2 ga 1 x2 n x 1 gt x 2 that has a relatively low in content further the polarization relaxation layer 15 b is a very thin film as compared with a general quantum barrier layer for example approximately 30 to 100 u00e5 specifically the polarization relaxation layer 15 b used in this embodiment has a very slight thickness so that the electrons and the holes injected into the active layer 15 can tunnel through the polarization relaxation layer 15 b without taking it as a quantum barrier for this operation a thickness t a of the polarization relaxation layer 15 b is preferably 15 u00e5 or less further the thickness t a of the polarization relaxation layer 15 b is preferably 7 u00e5 or more to obtain sufficient polarization relaxation in this embodiment there are two polarization relaxation layers 15 b the quantum well structure 15 a is structurally divided into three regions by the two polarization relaxation layers 15 b however as described above in quantum mechanics since the polarization relaxation layer 15 b does not.