Initial GaN Growth Research Articles

Initial growth of GaN on α-Al2O3(0001) by molecular beam epitaxy

The sapphire surface, used for growth of GaN by molecular beam epitaxy, was studied by reflection high-energy electron diffraction during the in situ pretreatment and initial growth. We investigated the effect of Ga cleaning, nitridation, and growth of the AlN nucleation layer on the lattice constant. One Ga-cleaning cycle restored the surface with a higher diffraction density. Nitridation changed the lattice constant instantaneously. The lattice constant was restored if the nitridation was switched off. For the AlN nucleation layer, the first monolayer was strained, followed by first a rapid and then a slow relaxation.

MBE growth of different hexagonal GaN crystal structures on vicinal (100) GaAs substrates

GaN thin films of different hexagonal crystal structures have been grown by radio-frequency nitrogen plasma source molecular beam epitaxy (RFMBE) on vicinal (100) GaAs substrates. Polycrystalline hexagonal material occurred for high temperature (630°C) nitridation of the GaAs surface or low temperatures of the initial GaN buffer layer deposition. On the contrary, initial GaN growth at 540°C gave hexagonal single crystals with [0001] axis either inclined at approximately 43° from the growth axis or aligned parallel to it. The GaN orientation depended on the annealing or not, respectively, of the initial low temperature buffer layer.

Initial growth of GaN on sapphire(0 0 0 1) using an amorphous buffer layer formed at room temperature by RF-MBE

The two-step growth process of GaN layer on sapphire using a buffer layer deposited at room temperature has been investigated by in situ reflection high-energy electron diffraction and atomic force microscopy observations. A stepped and (9×9) reconstructed surface structures are formed on the sapphire substrates annealed at 900°C before deposition of the GaN buffer layer. It is found that no nitridation of the sapphire surface occurred under radio frequency plasma-enhanced nitrogen gas irradiation at 900°C for 10min. It has been found that the amorphous GaN buffer layer deposited at room temperature changes to the single crystal by annealing at 700°C. It is concluded that the GaN epilayer with the flat surface is successfully grown on sapphire(0001) by using the amorphous GaN buffer layer.

Morphology and Interface chemistry of the Initial Growth of GAN and ALN on α-SIC and Sapphire

ABSTRACTThe morphology and interface chemistry occurring during the initial stages of growth of GaN and A1N layers has been obtained. Films were grown using gas source MBE equipment containing an ECR plasma source to activate molecular nitrogen. The experiments consisted of sequential depositions of about one monolayer thick films and XPS analysis. Evidence for silicon nitride formation on the SiC surface was obtained from the studies of both the Si oxidation states and the substrate peak intensity dependence on film thickness. The growth of GaN on sapphire appeared to occur via the Stranski-Krastanov mode, while the growth on SiC showed characteristics of three-dimensional growth. AlN grew in a layer-by-layer mode on both substrates.