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Publication 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(A V S AMER INST PHYSICS, 2016-01) ALEVLİ, MUSTAFA; Alevli, Mustafa; Haider, Ali; Kizir, Seda; Leghari, Shahid A.; Biyikli, NecmiGaN 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. (C) 2015 American Vacuum Society.Publication Metadata only Effect of N-2/H-2 plasma on the growth of InN thin films on sapphire by hollow-cathode plasma-assisted atomic layer deposition(A V S AMER INST PHYSICS, 2020) ALEVLİ, MUSTAFA; Alevli, Mustafa; Gungor, NeseIn this work, we have studied the influence of N-2/H-2 plasma gas flow rates on the hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD) growth of indium nitride (InN) films. The influence of N-2/H-2 plasma gas flow rates on crystallinity, lattice distortion, phonon properties, and bandgap was analyzed. We found that the strain can be relieved fully or partially through the incorporation of H-2 in plasma. We present Raman scattering measurements on HCPA-ALD grown InN films. We found that the E-2-high phonon relaxation time increases with decreasing H-2 plasma flow. Atomic force microscopy (AFM) topography measurements revealed high surface roughness for InN films deposited with N-2/H-2. The spectroscopic ellipsometry analysis revealed that InN surface layers are thick and contain large void structures with the incorporation of H-2 in N-2 plasma. Combining the AFM surface morphology analysis with spectroscopic ellipsometry analysis, we propose a possible surface reaction mechanism for hydrogen incorporation on an InN surface. A clear shift of the absorption edge and a decrease in the absorption coefficient were observed when H-2 was introduced into N-2 flow. These results may provide a useful guide for understanding the HCPA-ALD growth mechanism of InN and In-rich nitrides.Publication Metadata only Influence of N-2/H-2 and N-2 plasma on binary III-nitride films prepared by hollow-cathode plasma-assisted atomic layer deposition(A V S AMER INST PHYSICS, 2018) ALEVLİ, MUSTAFA; Alevli, Mustafa; Gungor, NeseThe authors reported the hollow-cathode plasma-assisted atomic layer deposition of AlN, GaN, and InN films using N-2-only and N-2/H-2 plasma. In this study, the authors analyzed the effect of plasma gas composition on the properties of deposited binary III-nitride thin films. Toward this goal, AlN, GaN, and InN films were deposited on Si (100) substrates using N-2-only (50 sccm), as well as N-2/H-2 (50+50, 50+25 sccm) plasma to investigate the impact of H-2 flow. Grazingincidence x-ray diffraction (GIXRD) patterns of AlN and GaN thin films deposited with N-2/H-2 plasma remained almost unchanged when H-2 flow decreased from 50 to 25 sccm. On the other hand, the use of N-2 plasma without any H-2 resulted in amorphous GaN thin films with significant carbon impurity within the bulk film. In the case of AlN, similar behavior was observed as the crystal structure is significantly altered to amorphouslike material. Thicknesses of AlN and GaN thin films increased tremendously when N-2-only was used as the plasma gas. Furthermore, refractive index values of both AlN and GaN films decreased upon the use of N-2-only plasma, which confirm the deterioration of the film quality. Structural weaknesses of GaN and AlN films deposited with N-2-only plasma are due to presences of carbon impurities that are trapped inside the growing film. Interestingly, the authors did not observe similar results in InN films grown with N-2/H-2 plasma. For InN, GIXRD and spectroscopic ellipsometry results show that the phases of deposited films change from InN to In+InN as H-2 content in the plasma gas is increased. On the other hand, InN films grown with N-2-only plasma show improved structural properties. However, significantly higher N-2 plasma exposure times are needed to minimize the residual carbon content in deposited InN layers. Published by the AVS.Publication Open Access Optical properties of AlN thin films grown by plasma enhanced atomic layer deposition(A V S AMER INST PHYSICS, 2012-03) ALEVLİ, MUSTAFA; Alevli, Mustafa; Ozgit, Cagla; Donmez, Inci; Biyikli, NecmiCrystalline aluminum nitride (AlN) films have been prepared by plasma enhanced atomic layer deposition within the temperature range of 100 and 500 degrees 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 similar to 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. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3687937]Publication Metadata only Role of film thickness on the structural and optical properties of GaN on Si (100) grown by hollow-cathode plasma-assisted atomic layer deposition(A V S AMER INST PHYSICS, 2018) ALEVLİ, MUSTAFA; Gungor, Nese; Alevli, MustafaIn this study, the authors report on the evolution of crystallinity, chemical composition, surface morphology, and optical properties of highly oriented (002) GaN films as a function of film thickness, ranging from 5.37 to 81.40 nm deposited on Si substrates via low-temperature hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD). GaN thin films were prepared using a sequential injection of triethyl gallium and N-2/H-2 plasma within the self-limited growth regime, i.e., ALD window at 200 degrees C. The grazing-incidence x-ray diffraction (GIXRD) analysis reveals that GaN films have a (002) preferential growth direction and the crystalline quality of GaN films was improved with the increase in thickness. GIXRD and atomic force microscopy confirmed the presence of GaN grains, and the grain size increases when the thickness of the GaN layer increases from 5.37 to 48.65 nm. From the x-ray photoelectron spectra, it was shown that the amount of oxygen incorporated in the GaN film decreases as the thickness increases. The spectroscopic ellipsometry analysis reveals that the optical film density and local crystallinity was improved with increasing film thickness to 48.65 nm, but further increase in the film thickness does not seem to improve these features. The optical band edge results suggested that bandgap widening is valid for all HCPA-ALD grown GaN samples. The overall results suggested that GaN films with thicknesses above 48.65 nm have different behavior compared to the thinner GaN films. Published by the AVS.Publication Open Access Substrate temperature influence on the properties of GaN thin films grown by hollow-cathode plasma-assisted atomic layer deposition(A V S AMER INST PHYSICS, 2016-01) ALEVLİ, MUSTAFA; Alevli, Mustafa; Gungor, Nese; Haider, Ali; Kizir, Seda; Leghari, Shahid A.; Biyikli, NecmiGallium nitride films were grown by hollow cathode plasma-assisted atomic layer deposition using triethylgallium and N-2/H-2 plasma. An optimized recipe for GaN film was developed, and the effect of substrate temperature was studied in both self-limiting growth window and thermal decomposition-limited growth region. With increased substrate temperature, film crystallinity improved, and the optical band edge decreased from 3.60 to 3.52 eV. The refractive index and reflectivity in Reststrahlen band increased with the substrate temperature. Compressive strain is observed for both samples, and the surface roughness is observed to increase with the substrate temperature. Despite these temperature dependent material properties, the chemical composition, E-1(TO), phonon position, and crystalline phases present in the GaN film were relatively independent from growth temperature. (C) 2015 American Vacuum Society.Publication Metadata only Visible/infrared refractive index and phonon properties of GaN films grown on sapphire by hollow-cathode plasma-assisted atomic layer deposition(A V S AMER INST PHYSICS, 2019) ALEVLİ, MUSTAFA; Gungor, Nese; Alevli, MustafaUsing Raman spectroscopy and spectroscopic ellipsometry, the authors report on the refractive index and optical phonon modes of GaN layers with thicknesses from 6.57 to 84.35 nm, grown on sapphire (0001) substrates by hollow-cathode plasma-assisted atomic layer deposition at low temperature (200 degrees C). The crystalline nature of the GaN films was confirmed by Raman spectroscopy and spectroscopic ellipsometry. The dispersion of the refractive index of GaN films in the UV-visible and infrared part of the spectrum is determined. The finding of this work indicates that the film thickness has important effects on the refractive index in the wavelength range of 300-1000 nm. On the other hand, the refractive index in the infrared region does not obviously change with increasing thickness. The authors compare the results of infrared ellipsometry with Raman spectra. They have identified E-1(TO), E-1(LO), A(1)(LO), and E2High phonon modes. The dependencies of their frequencies on the stress state of GaN films were analyzed and discussed. Published by the AVS.