Compositional pulling effects in InxGa1-x/GaN layers: A combined depth-resolved cathodoluminescence and Rutherford backscattering/channeling study - art. no. 205311

A depth-resolved study of the optical and structural properties of wurtzite InGaN/GaN bilayers grown by metallorganic chemical vapor deposition on sap phire substrates is reported. Depth-resolved cathodoluminescence (CL) and R utherford backscattering spectrometry (RBS) were used to gain an insight in to the compositional profile of a 75-nm thick InGaN epilayer in the directi on of growth. CL acquired at increasing electron energies reveals a peak sh ift of about 25 meV to the blue when the electron beam energy is increased from 0.5 to similar to7 keV, and shows a small shift to lower energies betw een similar to7 and 9 keV. For higher accelerating voltages the emission en ergy peak remains constant. This behavior can be well accounted for by a li near variation of In content over depth. Such an interpretation conforms to the In/Ga profile derived from RBS. where a linear decrease of the In mole fraction from the near surface (similar to0.20) down to the near GaN/InGaN interface (similar to0.14) region fits the random spectra very well. Furth ermore, by measuring the tetragonal distortion at different depths, using R BS/channeling. it is shown that regions of higher In content also appear to be more relaxed. This result suggests that strain hinders the incorporatio n of In atoms in the InGaN lattice, and is the driving force for the compos itional pulling effect in InGaN films.