Reactive sputtering was used to grow thin films of BexZnyO on Si (100) substrates. X-ray diffraction patterns of the films revealed no structure, suggesting that the films have an amorphous nature. The optical “bandgap” energy of the amorphous BexZnyO (a-BexZnyO) films was derived from vacuum ultraviolet variable angle spectroscopic ellipsometry measurements. The value of the energy bandgap of the films can be efficiently engineered to vary from the amorphous ZnO bandgap of 3.35to7.91eV by changing the Be doping level in the a-BeZnO. The a-BeZnO films could be used for fabricating excellent a-ZnO based electronic devices.
Amorphous silicon-nitrogen (a-SiN) thin films have been independently doped with Sm, Tb, and Sm + Tb. The films were prepared by reactive cosputtering and characterized by energy dispersive x-ray analysis, optical transmission, and photo-and cathodoluminescence techniques. All films display roomtemperature visible luminescence after excitation with either photon or electron sources. The present results indicate that the luminescence intensity is highly susceptible to thermal annealing treatments as well as to the combination of rare-earth ions. In fact, an improvement of about 500% was achieved in the overall optical emission after annealing the films up to 1050 • C for 15 min. Also, the presence of Tb 3+ ions in the Sm + Tb-doped a-SiN films enhanced the Sm 3+ -related emission, and spectrally sharp optical transitions could be verified at 485, 545, and 650 nm. The likely mechanisms behind the optical activation of the Sm 3+ and Tb 3+ ions and the energy transfer processes between these ions and the amorphous SiN matrix, are presented and discussed. In order to improve the blue light emission of the present samples, one a-SiN film simultaneously doped with Sm + Tb + Tm has also been prepared and investigated in detail.
Magneto-optical properties of Ni-and Co-doped amorphous AlN thin films were investigated as a function of post grown annealing temperature using magneto-optical Kerr effect (MOKE) spectroscopy. The x-ray diffraction spectra confirmed that the as-grown material is amorphous and retained its morphology after thermal treatment; however the sample morphology strongly depends on the concentration of incorporated transition metals. We observed with help of transmission electron microscopy and atomic force microscopy that the films surface containing TMs with concentrations larger than ~10 at.% undergo morphological changes suggesting possible Ni and Co atom clustering. Significant enhancement of the polar Kerr rotation signal was observed for Ni-and Co-doped a-AlN materials annealed above 300 °C in nitrogen. The studied materials have shown strong magnetic isotropy in polar geometry whereas the MOKE measurements in longitudinal geometry did not show an explicit signal for the transition metals doped a-AlN studied.
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This paper presents an analysis of the characteristics of two gallium nitride (GaN) films grown on (0001) plane sapphire substrates by low-pressure metalorganic chemical vapor deposition (MOCVD) is presented. The GaN films were characterized by a variety of methods, including scanning electron microscopy (SEM), x-ray diffraction (XRD), photoluminescence (PL), and Raman scattering. SEM micrographs revealed that different growth conditions will lead to different surface morphology of the films. XRD measurements indicated that both films were highly oriented and mono crystalline. PL spectra for both samples exhibited an intense and sharp band edge peak at 3.42 eV with full width at half maximum (FWHM) of 15 and 35 meV respectively. Raman scattering showed that the peaks of E2(high) phonon mode were observed at 568.1 and 570.1 cm-1 respectively. The different growth mode of these films were linked to the growth conditions, in which the growth mechanism could be correlated with the shift of E2(high) phonon mode in Raman scattering.
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