Browsing by Subject "X-ray diffraction measurements"

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Open Access
Buffer effects on the mosaic structure of the HR-GaN grown on 6H-SiC substrate by MOCVD
(Springer New York LLC, 2017) Arslan, E.; Öztürk, M. K.; Tıraş, E.; Tıraş, T.; Özçelik, S.; Özbay, Ekmel
High-resistive GaN (>108 Ω cm) layers have been grown with different buffer structures on 6H-SiC substrate using metalorganic chemical vapor deposition reactor. Different combination of the GaN/AlN super lattice, low temperature AlN, high temperature AlN and AlxGa1−xN (x ≈ 0.67) layers were used in the buffer structures. The growth parameters of the buffer layers were optimized for obtaining a high-resistive GaN epilayer. The mosaic structure parameters, such as lateral and vertical coherence lengths, tilt and twist angle (and heterogeneous strain), and dislocation densities (edge and screw dislocations) of the high-resistive GaN epilayers have been investigated using x-ray diffraction measurements. In addition, the residual stress behaviors in the high-resistive GaN epilayers were determined using both x-ray diffraction and Raman measurements. It was found that the buffer structures between the HR-GaN and SiC substrate have been found to have significant effect on the surface morphology and the mosaic structures parameters. On the other hand, both XRD and Raman results confirmed that there is low residual stress in the high-resistive GaN epilayers grown on different buffer structures.
Open Access
Excitation dependent recombination studies on SnO2/TiO2 electrospun nanofibers
(Royal Society of Chemistry, 2015) Babu, V. J.; Vempati S.; Ertas Y.; Uyar, Tamer
Poly(vinyl acetate) (PVAc)/TiO2 nanofibers, PVAc/SnO2 nanoribbons and PVAc/SnO2-TiO2 nanoribbons were produced via electrospinning. TiO2 nanofibers and SnO2 nanoribbons were obtained by removal of the polymeric matrix (PVAc) after calcination at 450 °C. Interestingly, PVAc/SnO2-TiO2 nanoribbons were transformed into SnO2-TiO2 nanofibers after calcination under the similar conditions. Fiber morphology and elemental mapping confirmed through SEM and TEM microscope techniques respectively. The X-ray diffraction measurements suggested the presence of anatase TiO2 and rutile SnO2 and both were present in the SnO2-TiO2 mixed system. Systematic photoluminescence studies were performed on the electrospun nanostructures at different excitation wavelengths (λex1 = 325, λex2 = 330, λex3 = 350, λex4 = 397 and λex5 = 540 nm). We emphasize that the defects in the SnO2-TiO2 based on the defect levels present in TiO2 and SnO2 and anticipate that these defect levels may have great potential in understanding and characterizing various semiconducting nanostructures.
Open Access
Low-temperature self-limiting atomic layer deposition of wurtzite InN on Si(100)
(American Institute of Physics Inc., 2016) Haider, A.; Kizir, S.; Bıyıklı, Necmi
In this work, we report on self-limiting growth of InN thin films at substrate temperatures as low as 200 °C by hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD). The precursors used in growth experiments were trimethylindium (TMI) and N2 plasma. Process parameters including TMI pulse time, N2 plasma exposure time, purge time, and deposition temperature have been optimized for self-limiting growth of InN with in ALD window. With the increase in exposure time of N2 plasma from 40 s to 100 s at 200 °C, growth rate showed a significant decrease from 1.60 to 0.64 Å/cycle. At 200 °C, growth rate saturated as 0.64 Å/cycle for TMI dose starting from 0.07 s. Structural, optical, and morphological characterization of InN were carried out in detail. X-ray diffraction measurements revealed the hexagonal wurtzite crystalline structure of the grown InN films. Refractive index of the InN film deposited at 200 °C was found to be 2.66 at 650 nm. 48 nm-thick InN films exhibited relatively smooth surfaces with Rms surface roughness values of 0.98 nm, while the film density was extracted as 6.30 g/cm3. X-ray photoelectron spectroscopy (XPS) measurements depicted the peaks of indium, nitrogen, carbon, and oxygen on the film surface and quantitative information revealed that films are nearly stoichiometric with rather low impurity content. In3d and N1s high-resolution scans confirmed the presence of InN with peaks located at 443.5 and 396.8 eV, respectively. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) further confirmed the polycrystalline structure of InN thin films and elemental mapping revealed uniform distribution of indium and nitrogen along the scanned area of the InN film. Spectral absorption measurements exhibited an optical band edge around 1.9 eV. Our findings demonstrate that HCPA-ALD might be a promising technique to grow crystalline wurtzite InN thin films at low substrate temperatures.