Optical gain characteristics of AlGaN/AlN quantum well structures grown on GaN substrate for ultraviolet TM light source

Optical gain characteristics of ultraviolet AlGaN/AlN quantum well (QW) structures grown on GaN substrate were investigated using the multiband effective-mass theory and non-Markovian model with the many-body effect. The TE-polarized optical gain peak of the QW structure on AlN substrate gradually increases with increasing Al composition and begins to decrease rapidly when the Al composition exceeds 0.6. On the other hand, the QW structure on GaN substrate shows that the TE-polarized optical gain peak continuously decreases with increasing Al composition and the TM-polarized optical gain peak begins to increase at much lower Al composition than that of the QW structure on AlN substrate. As a result, the QW structure on GaN substrate shows that the critical Al composition switching from TE to TM polarization is much smaller than that of the QW structure on AlN substrate. Also, the TM-polarized gain peak of the QW structure on GaN substrate is found to be much larger than that of the QW structure on AlN substrate.