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 lime by in situ spectroscopic ellipsometry. Substrates are at first in situ cleaned by H-2 plasmas, then are nitrided by N-2 or N-2-H-2 plasmas at low temperature and afterwards the GaN buffer layer growth by GaMe3 and N-2-H-2 plasmas is performed at T = 600 degrees 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.