Reduced Defect Densities in Cubic GaN Epilayers with AlGaN/GaN Superlattice Underlayers Grown on (001) GaAs Substrates by Metalorganic Vapor Phase Epitaxy

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The effects of AlxGa1-xN/GaN superlattice (SL) insertion on the structural homogeneity, photoluminescence (PL) lifetime ($\tau_{\text{PL}}$), 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 ($V_{\text{Ga}}$)-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.
2004-03-15