Effect of O 2 /Ni ratio on structure and surface morphology of atmospheric pressure MOCVD grown NiO thin films
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Effect of O2/Ni ratio on structure and surface morphology of atmospheric pressure MOCVD grown NiO thin films
Teuku M. Roffi, Motohiko Nakamura, Kazuo Uchida, and Shinji Nozaki Department of Engineering Science, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan.
ABSTRACT Effect of oxygen to nickel molar ratio (O2/Ni) on the crystallinity of atmospheric pressure metal organic chemical vapor deposition (APMOCVD) grown NiO at 500°C is reported. X-ray diffraction (XRD) analysis including grazing incident angle θ of 0.6°, θ-2θ, ɸ and rocking curve scan are employed for crystallographic characterization. Furthermore, surface roughness is studied by atomic force microscopy (AFM). No evidence of diffraction peaks in X-ray grazing incident angle measurement confirms that all the grown NiO films are well oriented along a certain direction. θ-2θ scan results further indicate that the samples are highly oriented only along [111] direction on (0001) sapphire substrates. The analysis of full width at half maximum (FWHM) of rocking curve scan of (111) plane shows that higher O2/Ni ratio results in better crystallinity. The best crystallinity is achieved with FWHM as low as 0.106° at (111) rocking curve scan corresponding to 82.57nm grain size. AFM measurement shows that NiO films grown with higher O2/Ni ratio have smoother surface morphology.
INTRODUCTION Nickel oxide films have been extensively studied due to their characteristics enabling various applications such as diode ultraviolet detectors pairing with zinc oxide1 and transparent conducting oxides.2 It is reported that undoped NiO has p-type semiconductor characteristics3 with a wide bandgap energy ranging from 3.8 to 4.3eV.4 Various methods have been employed for the fabrication of NiO thin film including sputtering,5 atomic layer deposition,6 pulsed laser deposition,7 molecular beam epitaxy8 and metal organic chemical vapor deposition (MOCVD) 9 including one of our previous works.10 This study reports the growth of NiO films on sapphire substrates with emphasis on the effect of oxygen to nickel ratio on the crystallinity and surface morphology of APMOCVD grown NiO films. Oxygen was varied with molar ratio to nickel ranged from 542:1 to 5641:1. Formation of NiO films with better crystallinity is expected. XRD and AFM are employed for crystallographic and surface morphology characterization.
EXPERIMENTAL DETAILS NiO was grown on sapphire substrates by APMOCVD at 500°C. This APMOCVD with a horizontal reactor was specially made for the growth of oxide thin films. Various oxygen to nickel ratio as of 542:1, 1354:1, 2617:1 and 5641:1 were employed in the growth and are
represented here as 0.5k, 1k, 2k, and 5k samples respectively. Allylcyclopentadienylnickel (C8H10Ni) was used as nickel precursor and was kept at 30°C to obtain vapor pressure of 0.84torr. Pure O2 gas was used as an oxygen source and N2 was used as a carrier gas. PANalytical X'Pert PRO MRD was employed for all XRD measurements including grazing incident angle, θ-2θ, ɸ a
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