Blue photoluminescence activated by surface states in GaN grown by molecular beam epitaxy

We have studied the broad blue band, which emerges in the photoluminescence (PL) spectrum of c-plane GaN layers after etching in hot H3PO4 and subsequ ent exposure to air. This band exhibited a 100 meV blueshift with increasin g excitation intensity and a thermal quenching with activation energies of 12 and 100 meV. These observations led us to suggest that surface states ma y be formed on etched surfaces and cause bandbending, which leads to a shif t in transition energy with excitation. The blue PL is related to transitio ns from the shallow donors filled with nonequilibrium electrons to the surf ace states, which capture the photogenerated holes. The observed irreversib le bleaching of the blue luminescence may be attributed to the metastable n ature of the surface states or to the oxygen desorption. (C) 2001 American Institute of Physics.