Study of buffer and epitaxy technology in two-step growth of aluminium nitride

AlN (aluminium nitride) films were prepared by metalorganic chemical vapor deposition (MOCVD) on c -plane sapphire (α-Al 2 O 3 ) substrates. By means of studying the traces of in-situ optical reflectivity, it was found that the AlN nucleation layer showed a specific (0001) lattice orientation, which differed from the GaN nucleation layer on (0001) sapphire substrates. The AlN buffer suffered the compressive stress at the initial stage of nucleation. And the compressive strain was relaxed gradually along with the thickness of buffer increasing and consequently annealing. Optical transmission spectra revealed that in the process of growing AlN epilayers, higher V/III ratio could improve the crystal quality but reduce the growth rates. In addition, proper doping of silane (SiH 4 ) could improve the surface morphology of AlN film.