Reduced defect densities in cubic GaN epilayers with AlGaN/GaN superlattice underlayers grown on (001) GaAs substrates by Metalorganic vapor phase epitaxy

The effects of Al_xGa_1-xN/GaN superlattice (SL) insertion on the structural homogeneity, photoluminescence (PL) lifetime (τ_PL), and defect densities were studied in cubic (c-) GaN epilayers on (001) GaAs substrates grown by low-pressure metalorganic vapor phase epitaxy. Values of the full-width at half maximum (FWHM) of both the (002) X-ray diffraction peak and near-band-edge excitonic PL peak were significantly decreased by the insertion of appropriate short-period AlGaN/GaN SLs between the c-GaN epilayer and the c-GaN template layer prepared on a substrate- decomposition-shielding GaN layer deposited at a low temperature. The density or size of Ga-vacancy (V_Ga)-related defects in the c-GaN epilayer was significantly reduced. Simultaneously, the value of excitonic PL lifetime at 293 K was improved from approximately 20 ps to 230 ps, indicating a tremendous reduction of the nonradiative defect density.