Intrinsic microstrains and cathodoluminescence in epitaxial GaN films

Intrinsic strain along the c-axis of the lattice, epsilon(zz) = delta c/c, rms fluctuation (epsilon(zz)) of this strain (microstrain), rms axis-tilt f luctuations [epsilon(zx)] and [epsilon(xz)] for the a- and c-axes, block si ze in the directions parallel and normal to the sample surface and other st ructural characteristics have been studied on epitaxial GaN films grown by molecular beam epitaxy on Al2O3 and GaAs substrates. The intensities of bou nd-exciton (3.45 eV) and donor-acceptor luminescence (blue (3.26 eV) and ye llow (2.30-2.67 eV)) have been measured as functions of excitation density and correlated to the structural characteristics. A recombination and defec t-nucleation model is proposed to explain the fall in the luminescence inte nsity with increasing [epsilon(xz)], observed for the first time.