We have studied the surface kinetics of N-face GaN during molecular-beam epitaxial growth by investigating the Ga wetting and the surface morphology. In the case of N-face GaN, it is not possible to establish the self-regulated Ga bilayer that is used as a surfactant for molecular-beam-epitaxy growth of Ga-face GaN. Indeed, to prevent the accumulation of Ga droplets, growth of the N-face GaN must be performed with less than one monolayer of excess Ga on the growing surface. Optimum surface morphology is achieved when growth is performed at the Ga accumulation limit.

We report on the effect of vertical correlation on GaN/AlN quantum dots grown by plasma-assisted molecular-beam epitaxy using the modified Stranski–Krastanow growth mode. When increasing the number of GaN periods, we observe a homogenization of the island distribution and a redshift of the luminescence line. This redshift is attributed to an increase of the quantum Stark effect due to the increase of the piezoelectric contribution to the internal electric field.

Molecular beam epitaxy as a method for the growth of freestanding zinc-blende (cubic) GaN layers and substrates J.We have investigated the polytype conversion of a GaN film from N-face wurtzite ͑2H u ͒ to zinc-blende ͑3C u ͒ structure due to Mg doping during growth by plasma-assisted molecular-beam epitaxy. Structural analysis by high-resolution transmission electron microscopy and high-resolution x-ray diffraction measurement revealed alignment of the cubic phase with the [111] axis perpendicular to the substrate surface. The optical characteristics of GaN:Mg layers are shown to be very sensitive to the presence of the cubic polytype. For low Mg doping, photoluminescence is dominated by a phonon-replicated donor-acceptor pair at ϳ3.25 eV, related to the shallow Mg acceptor level, accompanied by a narrow excitonic emission. For high Mg doping, the photoluminescence spectra are also dominated by a line around 3.25 eV, but this emission displays the behavior of excitonic luminescence from cubic GaN. A cubic-related donor-acceptor transition at ϳ3.16 eV is also observed, together with a broad blue band around 2.9 eV, previously reported in heavily Mg-doped 3C-GaN(001).

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International audienceThick polycrystalline AlN layers were grown at low pressure using high temperature chemical vapor deposition (HTCVD). The experimental setup consists of a graphite susceptor heated by an induction coil surrounding a vertical cold wall reactor. The reactants used were ammonia (NH(3)) and aluminum chloride (AlCl(x)) species formed in situ via chlorine (Cl(2)) reaction with high purity aluminum wire. AlN films were deposited on a 55 mm diameter graphite susceptor between 1200 and 1600 degrees C. AlN layers have been characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and electron backscattered diffraction. The influence of temperature on growth rate, surface morphology, grain size, and crystalline structure is presented. Growth rates of up to 230 mu m/h have been reached. A nonpolar preferred orientation of AlN films is stabilized at a higher temperature. The potential of investigation in this new range of experimental conditions, i.e., high temperature and high growth rate, as well as deposition of nonpolar AlN crystals, is very promising for epitaxial growth and extends the field of applications. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3536477] All rights reserve