Linewidth enhancement factor of wurtzite GaN/AlGaN quantum-well lasers with spontaneous polarization and piezoelectric effects

Spontaneous and piezoelectric polarization effects on the linewidth enhancement factor alpha(e) of (0001)-oriented wurtzite (WZ) GaN/AlGaN quantum-well (QW) lasers are investigated using a many-body self-consistent (MB-SC) model. The results are compared with those of a many-body flat-band (MB-FB) model and a free-carrier flat-band (FC-FB) model ignoring spontaneous and piezoelectric polarization. The MB-FB model shows a significant increase of ae at the peak gain position at high carrier densities compared to that of the FC-FB model. This is because the refractive index change at high carrier densities increases with the inclusion of the Coulomb enhancement effect. With the inclusion of the internal field, the differential gain and the differential index change (dg/dN and -d(deltan(e))/dN) are reduced compared to those for the MB-FB model, because the optical matrix elements of the MB-SC model decrease with the inclusion of the internal field. In the case of a well width of 30 Angstrom A, the MB-SC model has a smaller ae factor than that of the MB-FB model. On the other hand, in the case of a well width of 50 Angstrom A, the MB-SC model has a larger ae factor than that of the MB-FB model at a larger peak gain because the reduction rate of dg/dN is larger than that of -d(deltan(e))/dN for a larger peak gain.