Ribbon and rod sapphire pulling has been performed in three different crystal growth equipments in order to study the effect of the installation, of the atmosphere, of the die shape, of the feed material and of the pulling rate on the distribution, number and diameter of the characteristic voids (micro-bubbles) in the crystals. The location of the bubbles in the crystals depends on the die geometry; however, in most cases they are essentially located close to the crystal periphery and then can be efficiently removed by lapping. After statistical analysis of the results, it is demonstrated that the number of gas moles incorporated in the crystals, inside the voids, is totally independent of any growth parameter. It is also shown that the bubble diameter depends only on the pulling rate. Consequently, for a given pulling rate, the number of bubbles auto-adjusts in order to satisfy the constant molar gas incorporation.

Fourier transform deep level transient spectroscopy has been performed between 80 K and 550 K in five n−type ZnO samples grown by different techniques. The capture cross section and ionization energy of four electron traps have been deduced from Arrhenius diagrams. A trap 1 eV below the conduction band edge is systematically observed in the five samples with a large apparent capture cross section for electrons (1.6 ± 0.4 × 10 −13 cm 2 ) indicating a donor character. The assignment of this deep level to the oxygen vacancy is discussed on the basis of available theoretical predictions. * julien.pernot@neel.cnrs.fr 1 arXiv:1401.6851v1 [cond-mat.mtrl-sci]

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International audienceDeep level transient spectroscopy measurements were per- formed on three non-intentionally doped n-type ZnO samples grown by different techniques in order to investigate the electronic properties of E3 electron trap. The ionization energy and the capture cross-section are found respectively at 0.275 eV from the conduction band and 2.3×10^−16 cm2 with no electric field dependence. This center is present irrespective of the synthesis method. In view of its physical properties and recent works published in the literature, its physical origin is discussed. Based mainly on its insensibility to the macroscopic electric field, the best candidates turn out to be dual defects with opposite charges on adjacent sites, like the dual vacancy VO -VZn

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Blue light-emitting diodes (LEDs) grown on ZnO substrates were fabricated owing to the monolithic integration of an entire nitride-based LED structure including a GaN p–n junction and an (In,Ga)N/GaN multiple quantum well active region. The surface preparation of the ZnO substrate, as well as the GaN nucleation process, was developed to grow the structures and limit the inter diffusion of O from the substrate, which are the key points for the fabrication of a light-emitting device on ZnO. LEDs with a clear rectification behavior and electroluminescence over the blue range, from 415 to 450 nm, were demonstrated.

The electrical properties of ZnO mono-crystalline materials, either in the form of bulk crystals or epitaxial films, were investigated for a large range of un-intentional or intentional doping concentrations extending from 4.0×1015 cm−3 up to 1.3×1020 cm−3. Hall and resistivity measurements were carried out from 10 K to 300 K, yielding the temperature dependent carrier densities and carrier mobilities. This allowed for an unambiguous determination of the dopant ionization energies, taking into account the concentration of compensation centers. The ionization energy variation as a function of dopant concentration was found to follow Mott's law, being consistent with the hydrogenic behavior of all involved donors; an effective critical Mott's concentration for the insulator to metal transition was found to be around 4.2×1018 cm−3, while the apparent value of the isolated donor ionization energy was determined as being 60 meV.

A transient finite‐element numerical simulation of the heat transfer and melt convection has been performed for the vertical Bridgman growth configuration in order to investigate the solid‐liquid interface deflection. The numerical simulation is realized with the help of the finite element software FIDAPTM. A free surface model is applied for the description of the moving solid‐liquid interface. By a dimensional analysis of the factors which affect the interface deflection, the influence of the nondimensional ratio δ = VIH/(kLGL) on the interface curvature is studied. The dimensionless interface curvatures are computed for different values of the interface rate VI, the latent heat of fusion H, the liquid thermal gradient GL and the thermal conductivity of liquid kL. Finally a simple expression which contains the quantity δ is proposed for the interface deflection.