Compositional inhomogeneities in InGaN studied by transmission electron microscopy and spatially resolved cathodoluminescence

The structural and optical properties of InGaN epilayers grown by different molecular beam epitaxy (MBE) techniques were studied with high spatial resolution. Mappings of the local emission wavelength obtained by cathodoluminescence (CL) spectroscopy indicate lateral and spectral inhomogeneities in the luminescence of InGaN epilayers grown with continuous In and Ga fluxes. These results agree well with variations in the chemical composition in the lateral and in the growth direction seen in mappings of the local composition which were obtained by energy-dispersive X-ray (EDX) microanalysis in cross-sectional transmission electron microscopy (TEM). Possible origins of these variations are discussed. In comparison, epilayers grown with alternating deposition of (In, Ga)N and (Ga)N are more homogeneous.