Well-width dependence of the linewidth enhancement factor of wurtzite InGaN/GaN quantum-well lasers

The well-width dependence of the linewidth enhancement factor, αe, of (0001)-oriented wurtzite (WZ) InGaN/GaN QW structures is investigated theoretically using the non-Markovian gain model with many-body effects. In the range of the peak gain below 1000 cm-1, the linewidth enhancement factor rapidly decreases with increasing peak gain. This can be explained by the fact that the differential gain, dg/dN, rapidly increases with increasing peak gain while the differential refractive index change, d(δne)/dN, is nearly constant irrespective of the peak gain. Also, in the range of small peak gain, the QW structure with a thin well width is found to have a larger linewidth enhancement factor than that with thick well width because the d(δne)/dN for the QW structure with a thin well width is larger than that for the QW structure with a thick well width. However, in the range of large peak gain above 3500 cm-1, the QW structure with a thick well width has a larger linewidth enhancement factor than that with a thin well width. These results can be explained by the peak gain dependences of dg/dN and d(δne)/dN.