Extremely Slow Relaxation Process of a Yellow-Luminescence-Related State in GaN Revealed by Two-Wavelength Excited Photoluminescence

摘要

In addition to detection of nonradiative recombination centers by a below-gap excitation (BGE) technique at steady state, we have studied the time-response of both donor-acceptor pair luminescence and yellow luminescence (YL) in GaN after switching off the BGE light. An extremely slow recovery of YL with a time constant of up to 28 s was observed, which is interpreted as a relaxation process of electrons from the state chosen by a BGE energy of 1.17 eV. The dependence of recovery time on the BGE energy and on the above-gap and below-gap excitation power densities became clear for the first time; it reflects the carrier recombination dynamics including YL among below-gap states.