Browsing by Author "Ozgit, C."

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    Atomic layer deposition of GaN at low temperatures
    (A I P Publishing LLC, 2012) Ozgit, C.; Donmez, I.; Alevli, M.; Bıyıklı, Necmi
    The authors report on the self-limiting growth of GaN thin films at low temperatures. Films were deposited on Si substrates by plasma-enhanced atomic layer deposition using trimethylgallium (TMG) and ammonia (NH 3) as the group-III and -V precursors, respectively. GaN deposition rate saturated at 185 C for NH 3 doses starting from 90 s. Atomic layer deposition temperature window was observed from 185 to ∼385 C. Deposition rate, which is constant at ∼0.51 cycle within the temperature range of 250 - 350 C, increased slightly as the temperature decreased to 185 C. In the bulk film, concentrations of Ga, N, and O were constant at ∼36.6, ∼43.9, and ∼19.5 at. , respectively. C was detected only at the surface and no C impurities were found in the bulk film. High oxygen concentration in films was attributed to the oxygen impurities present in group-V precursor. High-resolution transmission electron microscopy studies revealed a microstructure consisting of small crystallites dispersed in an amorphous matrix. © 2012 American Vacuum Society.
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    The influence of N2/H2 and ammonia N source materials on optical and structural properties of AlN films grown by plasma enhanced atomic layer deposition
    (2011) Alevli, M.; Ozgit, C.; Donmez, I.; Bıyıklı, Necmi
    The influence of N2/H2 and ammonia as N source materials on the properties of AlN films grown by plasma enhanced atomic layer deposition using trimethylaluminum as metal source has been studied. The -2Θ grazing-incidence X-ray diffraction, high resolution transmission electron microscopy, and spectroscopic ellipsometry results on AlN films grown using either NH3 or N2/H2 plasma revealed polycrystalline and wurtzite AlN layers. The AlN growth rate per cycle was decreased from 0.84 to 0.54 Å/cycle when the N source was changed from NH3 to N2/H2. Growth rate of AlN remained constant within 100200 °C for both N precursors, confirming the self-limiting growth mode in the ALD window. AlAl bond was detected only near the surface in the AlN film grown with NH3 plasma. AFM analysis showed that the RMS roughness values for AlN films grown on Si(100) substrates using NH3 and N2/H2 plasma sources were 1.33 nm and 1.18 nm, respectively. The refractive indices of both AlN films are similar except for a slight difference in the optical band edge and position of optical phonon modes. The optical band edges of the grown AlN films are observed at 5.83 and 5.92 eV for ammonia and N2/H2 plasma, respectively. According to the FTIR data for both AlN films on sapphire substrates, the E1(TO) phonon mode position shifted from 671 cm -1 to 675 cm-1 when the plasma source was changed from NH3 to N2/H2. © 2011 Elsevier B.V. All Rights Reserved.
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    Low - temperature self - limiting growth of III - nitride thin films by plasma - enhanced atomic layer deposition
    (American Scientific Publishers, 2012) Bıyıklı, Necmi; Ozgit, C.; Donmez, I.
    We report on the low-temperature self-limiting growth and characterization of III-Nitride thin films. AlN and GaN films were deposited by plasma-enhanced atomic layer deposition (PEALD) on various substrates using trimethylaluminum (TMA), trimethylgallium (TMG) and triethylgallium (TEG) as group-III, and ammonia (NH3) as nitrogen precursor materials. Self-limiting growth behavior, which is the major characteristic of an ALD process, was achieved for both nitride films at temperatures below 200 °C. AlN deposition rate saturated around 0.86 Å/cycle for TMA and NH3 doses starting from 0.05 and 40 s, respectively, whereas GaN growth rate saturated at a lower value of 0.56 Å/cycle and 0.48 Å/cycle for TMG and TEG doses 0.015 s and 1 s, respectively. The saturation dose for NH3 was measured as 90 s and 120 s, for TMG and TEG experiments, respectively. Within the self-limiting growth temperature range (ALD window), film thicknesses increased linearly with the number of deposition cycles. At higher temperatures (≥225 °C and ≥350 °C for AlN and GaN respectively), deposition rate became temperature-dependent, with increasing growth rates. Chemical composition and bonding states of the films deposited within the self-limiting growth regime were investigated by X-ray photoelectron spectroscopy (XPS). GaN films exhibited high oxygen concentrations regardless of the precursors choice, either TMG or TEG, whereas low-oxygen incorporation in AlN films was confirmed by high resolution Al 2p and N 1s spectra of AlN films. AlN films were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction (GIXRD). GaN films showed amorphous-like XRD signature, confirming the highly defective layers. High-resolution transmission electron microscopy (HR-TEM) images of the AlN thin films revealed a microstructure consisting of several-nanometer sized crystallites, whereas GaN films exhibited sub-nm small crystallites dispersed in an amorphous matrix.
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    Optical properties of AlN thin films grown by plasma enhanced atomic layer deposition
    (A I P Publishing LLC, 2012) Alevli, M.; Ozgit, C.; Donmez, I.; Bıyıklı, Necmi
    Crystalline aluminum nitride (AlN) films have been prepared by plasma enhanced atomic layer deposition within the temperature range of 100 and 500 °C. The AlN films were characterized by x-ray diffraction, spectroscopic ellipsometry, Fourier transform infrared spectroscopy, optical absorption, and photoluminescence. The authors establish a relationship between growth temperature and optical properties and in addition, the refractive indices of the AlN films were determined to be larger than 1.9 within the 300-1000 nm wavelength range. Infrared reflectance spectra confirmed the presence of E 1(TO) and A 1(LO) phonon modes at ∼660 cm -1 and 895 cm -1, respectively. Analysis of the absorption spectroscopy show an optical band edge between 5.78 and 5.84 eV and the absorption and photoluminescence emission properties of the AlN layers revealed defect centers in the range of 250 and 300 nm at room temperature. © 2012 American Vacuum Society.
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    Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition
    (2012) Ozgit, C.; Donmez I.; Alevli, M.; Bıyıklı, Necmi
    We report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH 3). At 185 °C, deposition rate saturated for TMA and NH 3 doses starting from 0.05 and 40 s, respectively. Saturative surface reactions between TMA and NH 3 resulted in a constant growth rate of ∼ 0.86 Å/cycle from 100 to 200 °C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≤ 225 °C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185 °C were investigated by X-ray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185 °C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at ∼ 5.8 eV and an optical transmittance of > 95% in the visible region of the spectrum. © 2011 Elsevier B.V. All rights reserved.
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    Structural properties of AIN films deposited by plasma-enhanced atomic layer deposition at different growth temperatures
    (Wiley, 2012) Alevli, M.; Ozgit, C.; Donmez, I.; Bıyıklı, Necmi
    Crystalline aluminum nitride (AlN) films have been prepared by plasma-enhanced atomic layer deposition (PEALD) within the temperature range from 100 to 500 °C. A self-limiting, constant growth rate per cycle temperature window (100-200 °C) was established which is the major characteristic of an ALD process. At higher temperatures (>225 °C), deposition rate increased with temperature. Chemical composition, crystallinity, surface morphology, mass density, and spectral refractive index were studied for AlN films. X-ray photoelectron spectroscopy (XPS) analyses indicated that besides main Al-N bond, the films contained Al-O-N, Al-O complexes, and Al-Al metallic aluminum bonds as well. Crystalline hexagonal AlN films were obtained at remarkably low growth temperatures. The mass density increased from 2.65 to 2.96 g/cm 3 and refractive index of the films increased from 1.88 to 2.08 at 533 nm for film growth temperatures of 100 and 500 °C, respectively. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.