Free-carrier screening of polarization fields in wurtzite GaN/InGaN laser structures

The free-carrier screening of macroscopic polarization fields in wurtzite G aN/InGaN quantum well lasers is investigated via a self-consistent tight-bi nding approach. We show that the high carrier concentrations found experime ntally in nitride laser structures effectively screen the built-in spontane ous and piezoelectric polarization fields, thus inducing a "field-free'' ba nd profile. Our results explain some heretofore puzzling experimental data on nitride lasers, such as the unusually high lasing excitation thresholds and emission blue shifts for increasing excitation levels. (C) 1999 America n Institute of Physics. [S0003-6951(99)00314-9].