The authors report on the use of hollow cathode plasma for low-temperature plasma-assisted atomic layer deposition (PA-ALD) of crystalline AlN, GaN and AlxGa1−xN thin films with low impurity concentrations.

Hexagonal boron nitride (hBN) thin films were deposited on silicon and quartz substrates using sequential exposures of triethylboron and N 2 /H 2 plasma in a hollow-cathode plasmaassisted atomic layer deposition reactor at low temperatures (≤450°C). A non-saturating film deposition rate was observed for substrate temperatures above 250°C. BN films were characterized for their chemical composition, crystallinity, surface morphology, and optical properties. X-ray photoelectron spectroscopy (XPS) depicted the peaks of boron, nitrogen, carbon, and oxygen at the film surface. B 1s and N 1s high-resolution XPS spectra confirmed the presence of BN with peaks located at 190.8 and 398.3 eV, respectively. As deposited films were polycrystalline, single-phase hBN irrespective of the deposition temperature. Absorption spectra exhibited an optical band edge at~5.25 eV and an optical transmittance greater than 90% in the visible region of the spectrum. Refractive index of the hBN film deposited at 450°C was 1.60 at 550 nm, which increased to 1.64 after postdeposition annealing at 800°C for 30 min. These results represent the first demonstration of hBN deposition using low-temperature hollow-cathode plasma-assisted sequential deposition technique.G. Brennecka-contributing editor Manuscript No. 35104.

The problem of transmitting CO(2) laser radiation through metallic or metallic with inner dielectric coating (metallic-dielectric) bent hollow cylindrical waveguides is investigated using a ray model. Computer calculations of transmission as a function of the geometrical dimensions of the waveguide are performed. The coupling of laser radiation at the entrance of the waveguide is also taken into account. The theoretical calculated transmission is compared with previously published experimental data and good agreement is obtained for a large range of curvatures. The devised ray model contributes to a better understanding of the role of the dielectric layer in the metallic-dielectric waveguide, increasing the transmission of the radiation. The calculation of the transmission as a function of the radius of the cross section of the waveguide shows that, for a best metallic-dielectric waveguide, an optimal cross-sectional diameter appears where the transmitted energy is maximum. The method presented will be of value as a tool in the design of hollow cylindrical waveguides.

Hollow cathode plasma assisted atomic layer deposited InxGa1−xN alloys show successful tunability of the optical band gap by changing the In concentration in a wide range.

Hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD) is a promising technique for obtaining III-nitride thin films with low impurity concentrations at low temperatures. Here we report our previous and current efforts on the development of HCPA-ALD processes for III-nitrides together with the properties of resulting thin films and nanostructures. The content further includes nylon 6,6-GaN core-shell nanofibers, proof-of-concept thin film transistors and UV photodetectors fabricated using HCPA-ALD-grown GaN layers, as well as InN thin films deposited by HCPA-ALD using cyclopentadienyl indium and trimethylindium precursors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim