Andreas Wohlfart

A Study of Bisazido(dimethylamino‐propyl)gallium as a Precursor for the OMVPE of Gallium Nitride Thin Films in a Cold‐Wall Reactor System under Reduced Pressure

The use of alternative nitrogen sources for growing GaN materials by organometallic vapor phase epitaxy (OMVPE) is being continuously investigated in the hope of achieving device-quality films under moderate conditions, in comparison to conventional methods. Employing the single molecule precursor (N 3 ) 2 Ga[(CH 2 ) 3 NMe 2 ], and using a cold-wall CVD reactor, epitaxial films of GaN, transparent in appearance and stoichiometric in composition, were deposited on c-plane sapphire, in the absence of ammonia, above 1073 K, under low pressures (between 0.080 and 100.0 mbar). Dense, amorphous, and very smooth films were grown at temperatures as low as 773 K. The influence of substrate temperature, reactor pressure, and the effect of small quantities of additional ammonia, on the growth rate and the film properties, were studied in some detail. The films were characterized by high-resolution X-ray diffraction (XRD) (e.g., full width at half maximum (FWHM) of the 0002 GaN rocking curve of 130 arcsec), X-ray reflectometry, scanning electron microscopy (SEM), atomic force microscopy (AFM) (root mean square roughness of 1.9 nm), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Rutherford backscattering (RBS) (Ga/N = 1:1 ± 0.05), and photoluminescence (PL) measurements (band edge luminescence at 3.45 eV and FWHM of 0.22 eV at 300 K).

Low-temperature approach to high surface ZnO nanopowders and a non-aqueous synthesis of ZnO colloids using the single-source precursor [MeZnOSiMe3]4 and related zinc siloxides

We present the temperature-dependent thermolysis of siloxy-substituted ZnO single-source precursors into zinc and zinc oxide, respectively. The solid-state pyrolysis at low temperatures leads to the formation of ZnO powder with a very high surface area whereas the thermolysis in solution yields ZnO colloids. The materials are characterized by UV/VIS, photoluminescence, X-Ray Diffraction (XRD), and Transmission Electron Microscopy (TEM).

MOCVD of gallium nitride nanostructures using (N3)2Ga{(CH2)3NR2}, R = Me, Et, as a single molecule precursor: morphology control and materials characterization

Gallium nitride nanostructures such as nanopillars, nanorods and nanowires were grown by metal organic chemical vapor deposition (MOCVD) on a c-plane sapphire substrate using the single molecule precursors (SMPs) bisazido(dimethylaminopropyl)gallium (BAZIGA, 1) and its ethyl derivative bisazido(diethylaminopropyl)gallium (E-BAZIGA, 2) in horizontal and vertical stagnation flow cold-wall reactors. It has been found that, at a given growth temperature, H2 and the total pressure have a profound influence on the morphology of the GaN nanostructure, which changes from self-organized nanopillars to randomly oriented nanowires through dense, ordered nanorods. The GaN nanopillars grown by SMPs 1 and 2 in the presence of N2 were most likely to follow a vapor–liquid–solid (VLS) autocatalytic growth process and exhibit a surface distribution density of 3.8 × 1010–4.5 × 1012 cm−2, whereas GaN nanorods and nanowires were produced in the presence of various amounts of H2. The surface distribution density in the case of the nanorods was dependent on the H2 flow. X-Ray diffraction and selected area electron diffraction revealed that the nanostructures were a single crystalline and hexagonal modification of GaN. The nanostructures were easily detached from the substrate and dispersed in organic solvents and showed strong photoluminescence in the near UV region (2.7–3.0 eV).

An Efficient Chemical Solution Deposition Method for Epitaxial Gallium Nitride Layers Using a Single-Molecule Precursor

An efficient chemical solution deposition (CSD) approach to growing epitaxial GaN layers at relatively low temperatures using a single-molecule precursor (SMP) is described. The precursor employed was bisazido diethylaminopropyl gallium, which exists as a dimer in the solid state and decomposes at relatively low temperatures. Using this precursor, epitaxial GaN layers were grown and characterized for their morphology, microstructure, and composition by X-ray diffraction (XRD), X-ray rocking curve (XRC) analysis, pole figure measurements, reciprocal space mappings, scanning electron microscopy (SEM), Rutherford backscattering (RBS), X-ray photoelectron spectroscopy (XPS), and room temperature photoluminescence (PL) measurements.

A novel preparation of nano-Cu/ZnO by photo-reduction of Cu(OCH(Me)CH2NMe2)2 on ZnO at room temperature

Room-temperature preparation of nano-Cu on ZnO by UV light induced photo-reduction of Cu(OCH(Me)CH2NMe2)2 precursor was achieved, indicating a novel method of nano-Cu/ZnO synthesis from an organometallic copper precursor in non-aqueous media without further chemical reduction.

A study on the thermal properties and the solid state pyrolysis of the Lewis acid/base adducts [X3M·N(SnMe3)3](X = Cl, Br; M = Al, Ga, In) and [Cl2MeM·N(SnMe3)3](M = Al, Ga) as molecular precursors for group 13 nitride materials

The Lewis acid/base adducts [X3M·N(SnMe3)3] (1–3: X = Cl, Br; M = Al, Ga, In) and [Cl2MeM·N(SnMe3)3] (4: M = Al, 5: M = Ga) were studied as precursors for group 13 nitride materials. The compounds were prepared by the 1∶1 mole reaction of MX3 and MCl2Me with N(SnMe3)3 at room temperature in diethyl ether and crystallised from CH2Cl2 at −20 °C. As shown by thermal analysis and the analysis of the volatile by-products, the precursors of the type [X3M·N(SnMe3)3] decompose between 100 and 350 °C predominantly in two steps via dehalostannylation by partly releasing Me3SnCl. Polycrystalline powders of AlN, GaN and InN were obtained after prolonged pyrolysis under inert conditions (argon, and in vacuo) above 350 °C and were contaminated with metallic tin according to the X-ray powder diffraction patterns. The pyrolysis of the organometallic precursors [Cl2MeM·N(SnMe3)3] (4, 5) yielded tin-free nitride materials at temperatures below 350 °C due to the parallel elimination of SnMe4 and Me3SnCl, as evidenced by X-ray powder diffraction, elemental analysis, NMR and IR spectroscopy of the products.

Morphology controlled growth of arrays of GaN nanopillars and randomly distributed GaN nanowires on sapphire using (N3)2Ga[(CH2)3NMe2] as a single molecule precursor

Controlled growth of oriented GaN nanopillars and randomly distributed nanowires is accomplished by MOCVD using (N3)2Ga[(CH2)3NMe2] as a single molecule precursor.