Formation and nitridation of InGa composite droplets on Si(1 1 1): In-situ study by high resolution X-ray photoelectron spectroscopy

We demonstrate applying synchrotron radiation based high resolution X-ray photoelectron spectroscopy as a versatile in-situ tool to study the step-wise formation and nitridation of indium gallium (InGa) composite droplets on Si(1 1 1)7 × 7. This includes analysis of initial interactions of Ga and In with Si(1 1 1)7 × 7, and characterization of formation and nitridation of InGa droplets. The results show that after stabilization of Si(1 1 1)7 × 7 structure with Ga and In at 750 °C and formation of Ga nanodroplets as the bases, the InGa composite droplets (In:Ga ≈ 3:1) were formed at RT and 200 °C in a coverage range 3-14 monolayers. The nitridation efficiency and structure of the droplets/Si(1 1 1) with NH ₃ were temperature dependent. At or below 350 °C, the droplets were hardly nitridated. At 670 °C, the nitridation of InGa was more completed, which however caused an unavoidable nitridation of Si surface. The optimum nitridation occurred around 480 °C and proceed in a 2D mode. Further simultaneous growth and nitridation of the InGa droplets on the 2D nitridated surface at 400 °C resulted in a complex surface composition and structure. An ex-situ atomic force microscopy reveals both the aligned metallic droplet-island assemblies and the fractured nitridated island bases with small droplets on top for the final surface.