Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Conference Object Citation - WoS: 33Citation - Scopus: 35Effects of Physical Growth Conditions on the Structural and Optical Properties of Sputtered Grown Thin Hfo2 Films(Elsevier Ltd., 2011) Aygün, Gülnur; Cantaş, Ayten; Şimşek, Yılmaz; Turan, RaşitHfO2 thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O2/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO2 grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiOx suboxide layer at the HfO2/Si interface is unavoidable. The HfO2 thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O 2/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO 2, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO2 to form HfO2, leaving Si-Si bonds behind. © 2010 Elsevier B.V. All rights reserved.Article Citation - WoS: 10Citation - Scopus: 10Evolution of Sio2/Ge Multilayer Structure During High Temperature Annealing(Elsevier Ltd., 2010) Şahin, D.; Yıldız, İlker; Gençer İmer, Arife; Aygün, Gülnur; Slaoui, A.; Turan, RaşitUse of germanium as a storage medium combined with a high-k dielectric tunneling oxide is of interest for non-volatile memory applications. The device structure consists of a thin HfO2 tunneling oxide with a Ge layer either in the form of continuous layer or discrete nanocrystals and relatively thicker SiO2 layer functioning as a control oxide. In this work, we studied interface properties and formation kinetics in SiO2/Ge/HfO2(Ge) multilayer structure during deposition and annealing. This material structure was fabricated by magnetron sputtering and studied by depth profiling with XPS and by Raman spectroscopy. It was observed that Ge atoms penetrate into HfO2 layer during the deposition and segregate out with annealing. This is related to the low solubility of Ge in HfO2 which is observed in other oxides as well. Therefore, Ge out diffusion might be an advantage in forming well controlled floating gate on top of HfO2. In addition we observed the Ge oxidation at the interfaces, where HfSiOx formation is also detected. © 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 25Citation - Scopus: 26Structural and Optical Characteristics of Tantalum Oxide Grown by Pulsed Nd:yag Laser Oxidation(AVS Science and Technology Society, 2006) Atanassova, Elenada A.; Aygün, Gülnur; Turan, Raşit; Babeva, T.Tantalum pentoxide (Ta2 O5) thin films (20-50 nm) have been grown by 1064 nm Nd:YAG laser oxidation of Ta film deposited on Si. The chemical bonding, structure, and optical properties of the films have been studied by Fourier transform infrared spectroscopy, x-ray diffraction, and reflectance measurements at normal light incidence in the spectral range of 350-800 nm. The effect of the substrate temperature (250-400 °C) during oxidation and its optimization with respect to the used laser beam energy density (3.2-3.4 J cm2 per pulse) is discussed. It is established that the substrate temperature is a critical factor for the effectiveness of the oxidation process and can be used to control the composition and amorphous status of the films. The film density explored by refractive index is improved with increasing film thickness. The refractive index of the layers grown under the higher laser beam energy density and at substrate temperature of 350-400 °C was found to be close to the value of bulk Ta2 O5. The films are amorphous at substrate temperature below 350 °C and possessed an orthorhombic (Β- Ta2 O5) crystal structure at higher temperatures. The thinner layers crystallize at a little higher temperature.Article Citation - WoS: 14Citation - Scopus: 18Xps Study of Pulsed Nd:yag Laser Oxidized Si(Elsevier Ltd., 2006) Özyüzer, Gülnur Aygün; Aygün, Gülnur; Atanassova, Elenada A.; Kostov, K.; Turan, RaşitX-ray photoelectron spectra (XPS) of thin SiO2 layers grown by pulsed Nd:YAG laser at a substrate temperature of 748 K are presented. The peak decomposition technique combined with depth profiling is employed to identify the composition and chemical states of the film structure. It is established that the oxide is non-stoichiometric, and contains all oxidation states of Si in different amounts throughout the film. The interface Si/laser-grown oxide is not abrupt, and the coexistence of Si2O3 and Si2O suboxides in a relatively wide interfacial region is found. It is concluded that post-oxidation annealing is necessary in order to improve the microstructure of both oxide and near interface region.Article Citation - WoS: 24Citation - Scopus: 24Electrical and Dielectrical Properties of Tantalum Oxide Films Grown by Nd:yag Laser Assisted Oxidation(Elsevier Ltd., 2008) Aygün, Gülnur; Turan, RaşitTantalum pentoxide (Ta2O5) thin films (20 to 44 nm) have been grown by 1064 nm Nd:YAG laser oxidation of Ta deposited films with various thickness on Si. Fourier Transform Infrared (FTIR) spectrum, thickness distribution, dielectric and electrical properties of laser grown oxide layers have been studied. The effect of the sputtered Ta film thickness, laser beam energy density and the substrate temperature on the final Ta2O5 film structure has been determined. It is shown that the oxide layers obtained for the laser beam energy density in the range from 3.26 to 3.31 J/cm2 and the substrate temperature around 350 °C have superior properties. FTIR measurement demonstrates that the Ta2O5 layers are obtained with the laser assisted oxidation technique. Metal Oxide Semiconductor capacitors fabricated on the grown oxide layers exhibits typical Capacitance-Voltage, Conductance-Voltage and Current-Voltage characteristics. However, the density of oxide charges is found to be slightly higher than the typical values of thermally grown oxides. The conduction mechanism studied by Current-Voltage measurements of the capacitors indicated that the current flow through the oxide layer is modified Poole-Frenkel type. It is concluded that the Ta2O5 films formed by the technique of Nd:YAG laser-enhanced oxidation at relatively low substrate temperatures are potentially useful for device applications and their properties can be further improved by post oxidation annealing processes. © 2008 Elsevier B.VArticle Developing a Trilayer Processing Technique for Superconducting Yba 2cu3o7-? Thin Films by Using Ge Ion Implantation(IOP Publishing Ltd., 2005) Avcı, İlbeyi; Tepe, Mustafa; Öktem, Bülent; Serincan, Uğur; Turan, Raşit; Abukay, DoğanFor making trilayer superconducting devices based on YBa2Cu 3O7-δ (YBCO) thin film processing, we developed a new technique by employing Ge ion implantation. A YBCO thin film of 150 nm thickness having high c-axis orientation and a transition temperature, T c, of 90 K was implanted with 80 keV, 1 × 1016 Ge ions cm-2 at room temperature. By the result of TRIM calculation, Ge ions were found to penetrate into the YBCO thin film approximately 60 nm below the surface of the film, thus leaving the lower part of the film as a superconductor. Upon implantation with Ge ions, the implanted upper part of the sample lost its electrical conductivity and diamagnetism while its original crystalline structure was preserved. The implanted ions we found did not alter the overall crystal structure of the YBCO thin film; this allowed us to grow an epitaxial superconducting upper layer of YBCO on top of the implanted area, leaving no need to use any buffer layer. The superconducting properties of the upper layer were similar to those of the pure YBCO base layer with an increased room temperature resistivity and a lowered Tc (88 K). This process provides an effective method for fabrication of a trilayer HTS device structure.Article Citation - WoS: 22Citation - Scopus: 22Oxidation of Si Surface by a Pulsed Nd: Yag Laser(IOP Publishing Ltd., 2004) Özyüzer, Gülnur Aygün; Atanassova, Elenada A.; Alaçakır, Ali; Özyüzer, Lütfi; Turan, RaşitSiO2 thin films have been obtained by 1064 nm Nd: YAG laser oxidation of p-Si in the presence of O2. The thickness uniformity, dielectric and electrical properties of the layers have been studied. The effect of both the laser beam energy density and the substrate temperature on the oxide growth is also discussed. It was established that there exists an interval of laser beam energy density in which the oxidation occurs without surface melting. The oxidation process is controlled by the laser beam energy density rather than by the substrate temperature (673-748 K) and the higher laser power results in a thicker oxide. X-ray photoelectron spectroscopy (XPS) was used to provide information on the oxide composition. XPS results revealed that the as-grown oxide is a mixed layer of SiO2 and Si2O, which are distributed nonuniformly through the depth. MOS capacitors fabricated on the grown oxide exhibited typical capacitance-voltage, conductance-voltage characteristics. However, the density of interface states and oxide charge density were found to be higher than the typical values of thermally grown oxides. The quality of the oxide layers can be further improved by optimization of the process parameters and/or by post-processing of the grown films. It is concluded that the SiO2 films formed by the technique of Nd: YAG laser-enhanced oxidation at low temperature are potentially useful for device applications.Article Citation - WoS: 1Citation - Scopus: 1Electrical and Magnetic Properties of Si Ion Implanted Yba 2cu3o7-? Thin Films and Microbridges(Elsevier Ltd., 2004) Avcı, İlbeyi; Tepe, Mustafa; Serincan, Uğur; Öktem, Bülent; Turan, Raşit; Abukay, DoğanFabrication of superconducting bilayer YBa2Cu3O 7-δ (YBCO) thin film structure by Si ion implantation and properties of microbridge patterned on that are presented. YBCO thin film of 150 nm thickness was grown on single crystal (100) SrTiO3 substrate by inverted cylindrical magnetron sputtering. The sample was implanted with 100 keV, 1×1016 Si ions/cm2. Upon implantation with Si, the sample lost its electrical conductivity and diamagnetism while its crystalline structure was preserved after the annealing of the sample. The implanted ions do not alter the overall crystal structure of high temperature superconductor film. This allows the growth of epitaxial superconducting second layer YBCO film on top of the implanted area without using any buffer layer, thus providing an effective method of fabricating multilayer structures. The second layer film and the microbridge patterned by laser writing technique, showed the superconducting properties similar to those of pure YBCO base layer with a reduced critical current density.