Microscopic theory of optical nonlinearities and spontaneous emission lifetime in group-III nitride quantum wells

Microscopic calculations of the absorption and luminescence spectra are presented for wide bandgap Ga_1-xIn_xN/GaN quantum well systems. Whereas structures with narrow well widths exhibit the usual excitation-dependent bleaching of the exciton resonance without shifting spectral position, a significant blueshift of the exciton peak is obtained for wider quantum wells. This blueshift, which is also present in the excitation-dependent luminescence spectra, is attributed to the interplay between the screening of a strain induced piezoelectric field and the density dependence of many-body Coulomb effects. The calculations also show an over two orders of magnitude increase in the spontaneous electron-hole-pair lifetime with well width, due to the reduction of the electron-hole wave function overlap in the wider wells. The resulting decrease in spontaneous emission loss is predicted to lead to improved threshold properties in wide quantum well lasers.