Crystal orientation effects on many-body optical gain of wurtzite InGaN/GaN quantum well lasers

The crystal orientation effects on the optical gain of wurtzite (WZ) InGaN/GaN quantum wells QWs) with piezoelectric (PZ) and spontaneous (SP) polarizations are investigated using the non-Markovian gain model with many-body effects. These results are also compared with those of WZ GaN/AlGaN QW structures. The reductive effect of the average hole effective mass on crystal angle is much dominant in the InGaN/GaN QW structure than in the GaN/AlGaN QW structure. On the other hand, both InGaN/GaN and GaN/AlGaN QW structures show similar dependences of the matrix element on crystal orientation. The optical gain of the WZ InGaN/GaN QW structure is found to largely increase with crystal angle compared to that of the WZ GaN/AlGaN QW structure. On the other hand, in the case of the GaN/AlGaN QW structure, the improvement of the optical gain is relatively small compared to that of the WZ InGaN/GaN QW structure. This is attributed to the increase in the quasi-Fermi level separation due to the large reduction of the hole effective mass of WZ InGaN/GaN QW structures.