Optical Gain in GaN Quantum Well Lasers with Quaternary AlInGaN Barriers

Optical gain in GaN quantum-well (QW) lasers with quaternary AlInGaN barriers lattice-matched to GaN is investigated on the basis of the multiband effective-mass theory and is compared with that of conventional GaN/AlGaN QW structures. GaN/AlInGaN QW lasers are expected to have enhanced optical gain compared with GaN/AlInGaN QW lasers. However, the optical gain is shown to be reduced markedly with increasing band gap of the AlInGaN barrier. This is because the spontaneous polarization effect is increased significantly for the QW structures with a larger AlInGaN band gap. We find that the threshold current density of the GaN/AlInGaN QW structure can be reduced using a quarternary AlInGaN barrier.