Browsing by Subject "Spectroscopic ellipsometry"

Now showing 1 - 4 of 4

Open Access
Comparison of trimethylgallium and triethylgallium as "ga" source materials for the growth of ultrathin GaN films on Si (100) substrates via hollow-cathode plasma-assisted atomic layer deposition
(AVS Science and Technology Society, 2016-02) Alevli, M.; Haider A.; Kizir S.; Leghari, S. A.; Bıyıklı, Necmi
GaN films grown by hollow cathode plasma-assisted atomic layer deposition using trimethylgallium (TMG) and triethylgallium (TEG) as gallium precursors are compared. Optimized and saturated TMG/TEG pulse widths were used in order to study the effect of group-III precursors. The films were characterized by grazing incidence x-ray diffraction, atomic force microscopy, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Refractive index follows the same trend of crystalline quality, mean grain, and crystallite sizes. GaN layers grown using TMG precursor exhibited improved structural and optical properties when compared to GaN films grown with TEG precursor.
Open Access
Nanoscale selective area atomic layer deposition of TiO2 using e-beam patterned polymers
(Royal Society of Chemistry, 2016) Haider A.; Yilmaz, M.; Deminskyi, P.; Eren, H.; Bıyıklı, Necmi
Here, we report nano-patterning of TiO2via area selective atomic layer deposition (AS-ALD) using an e-beam patterned growth inhibition polymer. Poly(methylmethacrylate) (PMMA), polyvinylpyrrolidone (PVP), and octafluorocyclobutane (C4F8) were the polymeric materials studied where PMMA and PVP were deposited using spin coating and C4F8 was grown using inductively coupled plasma (ICP) polymerization. TiO2 was grown at 150 °C using tetrakis(dimethylamido) titanium (TDMAT) and H2O as titanium and oxygen precursors, respectively. Contact angle, scanning electron microscopy (SEM), spectroscopic ellipsometry, and X-ray photoelectron spectroscopy (XPS) measurements were performed to investigate the blocking/inhibition effectiveness of polymer layers for AS-ALD of TiO2. TiO2 was grown with different numbers of growth cycles (maximum = 1200 cycles) on PMMA, PVP, and C4F8 coated substrates, where PMMA revealed complete growth inhibition up to the maximum number of growth cycles. On the other hand, PVP was able to block TiO2 growth up to 300 growth cycles only, whereas C4F8 showed no TiO2-growth blocking capability. Finally, mm-, μm-, and nm-scale patterned selective deposition of TiO2 was demonstrated exploiting a PMMA masking layer that has been patterned using e-beam lithography. SEM, energy-dispersive X-ray spectroscopy (EDX) line scan, EDX elemental mapping, and XPS line scan measurements cumulatively confirmed the self-aligned deposition of TiO2 features. The results presented for the first time demonstrate the feasibility of achieving self-aligned TiO2 deposition via TDMAT/H2O precursor combination and e-beam patterned PMMA blocking layers with a complete inhibition for >50 nm-thick films.
Open Access
Optical characteristics of nanocrystalline AlxGa1-xN thin films deposited by hollow cathode plasma-assisted atomic layer deposition
(AVS Science and Technology Society, 2014) Goldenberg, E.; Ozgit-Akgun, C.; Bıyıklı, Necmi; Kemal Okyay, A.
Gallium nitride (GaN), aluminum nitride (AlN), and AlxGa 1-xN films have been deposited by hollow cathode plasma-assisted atomic layer deposition at 200 °C on c-plane sapphire and Si substrates. The dependence of film structure, absorption edge, and refractive index on postdeposition annealing were examined by x-ray diffraction, spectrophotometry, and spectroscopic ellipsometry measurements, respectively. Well-adhered, uniform, and polycrystalline wurtzite (hexagonal) GaN, AlN, and Al xGa1-xN films were prepared at low deposition temperature. As revealed by the x-ray diffraction analyses, crystallite sizes of the films were between 11.7 and 25.2 nm. The crystallite size of as-deposited GaN film increased from 11.7 to 12.1 and 14.4 nm when the annealing duration increased from 30 min to 2 h (800 °C). For all films, the average optical transmission was ∼ 85% in the visible (VIS) and near infrared spectrum. The refractive indices of AlN and AlxGa1-xN were lower compared to GaN thin films. The refractive index of as-deposited films decreased from 2.33 to 2.02 (λ = 550 nm) with the increased Al content x (0 ≤ x ≤ 1), while the extinction coefficients (k) were approximately zero in the VIS spectrum (>400 nm). Postdeposition annealing at 900 °C for 2 h considerably lowered the refractive index value of GaN films (2.33-1.92), indicating a significant phase change. The optical bandgap of as-deposited GaN film was found to be 3.95 eV, and it decreased to 3.90 eV for films annealed at 800 °C for 30 min and 2 h. On the other hand, this value increased to 4.1 eV for GaN films annealed at 900 °C for 2 h. This might be caused by Ga 2O3 formation and following phase change. The optical bandgap value of as-deposited AlxGa1-xN films decreased from 5.75 to 5.25 eV when the x values decreased from 1 to 0.68. Furthermore, postdeposition annealing did not affect the bandgap of Al-rich films. © 2014 American Vacuum Society.
Open Access
Spectroscopic ellipsometric study of Ge nanocrystals embedded in SiO 2 using parametric models
(Wiley, 2008-05) Basa, P.; Petrik, P.; Fried, M.; Dâna, Aykutlu; Aydınlı, Atilla; Foss, S.; Finstad, T. G.
Ge-rich SiO2 layers on top of Si substrates were deposited using plasma enhanced chemical vapour deposition. Ge nanocrystals embedded in the SiO2 layers were formed by high temperature annealing. The samples were measured and evaluated by spectroscopic ellipsometry. Effective medium theory (EMT) and parametric semiconductor models have been used to model the dielectric function of the layers. Systematic dependences of the layer thickness and the oscillator parameters have been found on the annealing temperature (nanocrystal size).