G. Nouet

Chemical ordering in wurtzite InxGa1−xN layers grown on (0001) sapphire by metalorganic vapor phase epitaxy

A diffraction analysis in the transmission electron microscope was carried out on InxGa1−xN layers grown on (0001) sapphire by metalorganic vapor phase epitaxy on top of thick GaN buffer layers. It is found that the ternary InxGa1−xN layers can be chemically ordered. The In and Ga atoms occupy, respectively, the two simple hexagonal sublattice sites related by the glide mirrors and helicoidal axes of the P63 mc symmetry group of the wurtzite GaN. The symmetry of the ordered ternary is subsequently lowered by the disappearance of these operations, and it is shown to agree with the P3ml space group.

An empirical potential for the calculation of the atomic structure of extended defects in wurtzite GaN

Abstract The Stillinger–Weber potential has been parametrized for GaN with bond-type dependent parameters to allow efficient atomic simulations of large systems containing wrong, dangling and extra bonds. The input data for the fit are the experimental elastic constants of wurtzite structure and wrong bond energies deduced from ab initio calculation. The potential in then applied to zincblende structure and to planar defects. The predicted values are compared to experimental observation and previous computations.

Structure of the carrot defect in 4H-SiC epitaxial layers

Transmission electron microscopy and KOH etching were used to determine the structure of the carrot defect in 4H-SiC epilayers. The defect consists of two intersecting planar faults on prismatic {11¯00} and basal {0001} planes. Both faults are connected by a stair-rod dislocation with Burgers vector 1∕n [101¯0] with n>3 at the crossover. A Frank-partial dislocation with b=1∕12[44¯03] terminates the basal fault.

Vitrification of lead-rich solid ashes from incineration of hazardous industrial wastes

Lead-rich solid industrial wastes were vitrified by the addition of glass formers in various concentrations, to produce non-toxic vitreous stabilized products that can be freely disposed or used as construction materials. Toxicity of both the as-received industrial solid waste and the stabilized products was determined using standard leaching test procedures. The chemically stable vitreous products were subjected to thermal annealing in order to investigate the extent of crystal separation that could occur during cooling of large pieces of glass. Leaching tests were repeated to investigate the relation between annealing process and chemical stability. X-ray, scanning and transmission electron microscopy techniques were employed to identify the microstructure of stabilized products before and after thermal treatment. Relation between synthesis and processing, chemical stability and microstructure was investigated.

Misfit accommodation of compact and columnar InN epilayers grown on Ga-face GaN (0001) by molecular-beam epitaxy

The interfacial structural properties of compact InN films and of noncoalesced three-dimensional InN islands, grown by molecular-beam epitaxy on Ga-face GaN/Al2O3 (0001) substrates, were investigated by transmission electron microscopy. Compact film growth was accomplished employing an InN nucleation layer, grown at low substrate temperatures. A 60° misfit dislocation network effectively accommodated the lattice mismatch in the InN/GaN interface in both cases of epilayers. The lattice constants of InN were determined by electron diffraction analysis, revealing a 0.28% larger in-plane parameter of the compact InN film relative to the corresponding lattice parameter of the InN islands. This is attributed to thermal tensile strain developed during post-growth cooling down of the epilayers, which also compensated the remaining compressive strain originating from the in-plane lattice mismatch of InN and GaN.

Contacts of titanium nitride to n- and p-type gallium nitride films

Abstract The electrical characteristics of titanium nitride (TiN x ) contacts to n- and p-type GaN films, deposited by reactive magnetron sputtering at room temperature, are investigated. The contacts of TiN x to n-type GaN are ohmic and to p-type GaN are rectifying, while their properties are strongly dependent on the stoichiometry of the deposited titanium nitride layer. It is shown that the ohmic behavior of the contacts is associated with the presence of a high density of interface states and not to the low Schottky barrier.

A modified empirical potential for energetic calculations of planar defects in GaN

Abstract The Stillinger–Weber empirical potential was modified and its parameters were determined to achieve a realistic description of the microscopic structure and the energetics of different planar defects and their interactions in wurtzite GaN. The formulation was based on the adjustment of the parameters in order to represent the Ga–Ga, N–N and Ga–N bonds. The input data comprises of the different crystalline phases of gallium, nitrogen and GaN. A satisfactory agreement on the values of the energy versus atomic volume per atom was obtained compared to those derived by ab initio calculations and experimental data for all the cases studied. By employing the modified Stillinger–Weber potential the energy of translation domain boundaries, which have been observed experimentally in GaN thin films, was calculated providing results comparable with ab initio calculations.

Boron-rich boron nitride (BN) films prepared by a single spin-coating process of a polymeric precursor

Abstract Crack-free and highly smooth boron-rich boron nitride (BN) films with a thickness of up to 2 μm have been prepared on Si and SiO 2 /Si substrates by vacuum or inert atmosphere pyrolysis at 900–1100°C of single spin-coated polyborazine films. The thickness of the BN films depends on the polymerization time of the borazine monomer and the polymer concentration, and the surface morphology on pyrolytic conditions. As the pyrolytic temperatures increase, the films displayed lower IR absorption for residual NH bonds and higher crystallinity with better preferential orientation along the substrate surface, but severe inter-diffusion phenomena at the interface. Microstructural development of the prepared films was thoroughly characterized by SEM, XRD, SPM, IR, SIMS and high resolution TEM.

Electrical and structural studies of copper and nickel precipitates in a Σ=25 silicon bicrystal

Deep‐level transient spectroscopy measurements of electronic defect states in a coincidence Σ=25 grain boundary (GB) in silicon have been performed after quenching of heat‐treated samples (900 °C, 2 h) containing copper and/or nickel. These elements are usually suspected to be nonintentionally contaminating impurities. The special care supplied to get processed samples free from transition‐metal impurities (particularly copper) has led to the measurement of a continuous distribution of boundary levels between Ec−0.20 eV and Ec−0.38 eV which shift toward deeper energies (between Ec−0.25 eV and Ec−0.42 eV) with a gradual increase of the copper content. The heavily contaminated samples with Cu or with both Cu and Ni exhibit a single interface trap at Ec−0.54 eV. According to transmission electron microscopy (TEM) and energy‐dispersive x‐ray (EDX) analyses, as well as comparable data reported earlier, this interface state seems characteristic of copper precipitates obtained by quenching from 900 °C; however, ...

Optical and electrical properties of TiN/n-GaN contacts in correlation with their structural properties

The optical and electrical properties of TiN contacts on Si-doped GaN were investigated in correlation with their structural properties. Stoichiometric TiN films were directly deposited on 2.5 µm thick n-GaN by dc reactive magnetron sputtering at room temperature, while the stoichiometry and the structural characteristics of the TiN films were determined by in situ spectroscopic ellipsometry (SE). SE was also used for characterization of the GaN surface and for chemical etching of gallium oxide. Current–voltage measurements showed an ohmic behaviour for the as-deposited and annealed TiN/GaN samples. The specific contact resistivity was found to be 4.5 × 10−3 Ω cm2 for the as-deposited TiN film, becoming as low as 5.9 × 10−4 Ω cm2 after annealing at 400 °C. Further thermal treatment over 500 °C resulted in significant TiN oxidation and poor adhesion of the TiN film on the GaN, leading to an increase in specific contact resistivity. Transmission electron microscopy revealed structural and interfacial contact changes after high thermal treatment.