Indium incorporation at In_xGa_1-xN relaxed self-assembled nanostructures on Si substrates

In this work, we report on self-assembling of In_xGa_1-xN nanostructures under strong nitrogen-rich conditions on Si (111) substrates by molecular beam epitaxy. In-situ analysis of the reflection high-energy electron diffraction patterns allowed to follow the strain evolution of the films as well as to monitor the morphological changes related to the In incorporation. Scanning electron microscopy and atomic force microscopy images of the samples evidenced the growth of different nanostructures such as nanocolumns and nanowalls depending on the In content. X-ray diffraction (XRD) measurements allowed to determine the indium concentration while Rutherford backscattering spectrometry (RBS) was used to obtain the composition and thickness of the films and to explore the way in which In and Ga atoms are incorporated in the In_xGa_1-xN ternary alloy. XRD and RBS complementary analysis suggests that phase separation, occurring at the higher indium concentration, induces both the In and Ga rich phases segregation towards the external surface of the growths. Therefore, the columnar surface arrangement observed on the extreme binary compounds is transformed into separated nanowalls as the indium content increases. The probable origin of this morphology change is discussed. A shift towards lower energies of the low temperature photoluminescence spectra was observed for increased In concentration and a value of the bowing band gap parameter of about 3 was estimated using the extrema binary compounds and the intermediated indium concentration samples.