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

Microscopic calculations of the absorption and luminescence spectra are pre sented for wide bandgap Ga1-xInxN/GaN quantum well Systems. Whereas structu res with narrow well widths exhibit the usual excitation-dependent bleachin g of the exciton resonance without shifting spectral position, a significan t blueshift of the exciton peak is obtained for wider quantum wells. This b lueshift, which is also present in the excitation-dependent luminescence sp ectra, is attributed to the interplay between the screening of a strain ind uced piezoelectric field and the density dependence of many-body Coulomb ef fects. 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. Th e resulting decrease in spontaneous emission loss is predicted to lead to i mproved threshold properties in wide quantum well lasers.