Dynamics of bound-exciton luminescences from epitaxial GaN

Free- and bound-exciton luminescences of GaN epitaxial layers grown by a sublimation technique on 6H-SiC substrates were investigated using time-integrated and time-resolved photoluminescence measurements at low temperatures. Lifetimes were determined for the donor-bound exciton at 3.4722 eV and for two acceptor-bound excitons with energies of 3.4672 eV and 3.459 eV. On the basis of our results we obtain an upper Limit of the free-exciton oscillator strength of 0.0046 for GaN. Luminescences between 3.29 eV and 3.37 eV are identified as due to excitons deeply bound to centers located near the substrate-epilayer interface. Free excitons are captured by these centers within 20 ps. (C) 1996 American Institute of Physics.