Depth resolved studies of indium content and strain in InGaN layers

A depth resolved study of optical and structural properties in wurtzite InG aN/GaN bilayers grown by MOCVD on sapphire substrates is reported. Depth re solved cathodoluminescence (CL). Rutherford backscattering spectrometry (RB S) and high resolution X-ray diffraction (HRXRD) were used to gain an insig ht into the composition and strain depth profiles. It is found that both qu antities can vary considerably over depth. Two representative samples are d iscussed. The first shows a CL peak shift to the blue when the electron bea m energy is increased. Such behaviour conforms to the In/Ga profile derived from RBS, where a linear decrease of the In mole fraction from the near su rface (approximate to0.20) down to the near GaN/InGaN interface (approximat e to0.14) region was found. The other sample discussed shows no depth varia tions of composition. However. the strain changes from nearly pseudomorphic , close the GaN interface, to an almost relaxed state close to the surface. This discrete variation of strain over depth. originates a double XRD and CL peak related to InGaN.