In situ real time ellipsometry monitoring during GaN epilayers processing

The surface nitridation of GaAs and sapphire substrates and the growth of GaN buffer layers in a remote r.f. plasma MOCVD apparatus are investigated in real time by in situ spectroscopic ellipsometry. Substrates are at first in situ cleaned by H2 plasmas, then are nitrided by N2 or N2–H2 plasmas at low temperature and afterwards the GaN buffer layer growth by GaMe3 and N2–H2 plasmas is performed at T=600°C. The role of the surface temperature on the nitridation depth, on the substrate/GaN interface composition and morphology is highlight by ellipsometry. Also, the initial stage of the GaN buffer growth is described in terms of nucleation, Ga-enrichment and of GaN/GaAs interface degradation.