Güneş, Mehmet
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Gunes, M
Gunes, M.
Güneş, M.
Gunes, Mehmet
Gunes, M.
Güneş, M.
Gunes, Mehmet
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04.05. Department of Pyhsics
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414
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242
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8.34
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29
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7
| Journal | Count |
|---|---|
| Journal of Materials Science: Materials in Electronics | 5 |
| Journal of Optoelectronics and Advanced Materials | 5 |
| IEE Proceedings: Circuits, Devices and Systems | 3 |
| Journal of Non-Crystalline Solids | 3 |
| Thin Solid Films | 2 |
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Article Citation - WoS: 13Citation - Scopus: 14Electronic Transport Properties of Microcrystalline Silicon Thin Films Prepared by Vhf-Pecvd(Springer Verlag, 2004) Okur, Salih; Güneş, Mehmet; Göktaş, Oktay; Finger, Friedhelm; Carius, ReinhardSteady-state photocarrier grating (SSPG) and steady-state photoconductivity, σph, experiments have been carried out to investigate the electronic transport properties of undoped hydrogenated microcrystalline silicon (μc-Si: H) films prepared with very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Material with different crystalline volume fractions was obtained by variation of the silane concentration (SC) in the process gas mixture. Pure amorphous silicon material was investigated for comparison. The ambipolar diffusion length, L amb, which is dominated by the minority carrier properties, is obtained both from the best fit to the experimental photocurrents ratio, β, versus grating period (Λ), and from the "Balberg plot" for the generation rates between 1019 and 1021 cm -3 s-1. Lamb increases from 86 nm with increasing SC and peaks around 200 nm for the SC = 5.6% and decreases again for higher SCs. Lamb values obtained from the intercept of the Balberg plot result in a small difference of around 5% for most of the samples. Minority carrier mobility-lifetime (μτ)-products are much lower than those of majority carriers, however, both majority and minority carrier μτ-products in microcrystalline silicon are higher than those of undoped hydrogenated amorphous silicon. The grating quality factor (γ 0) changes from 0.70 to 1.0 indicating almost negligible surface roughness present in the samples.Article Citation - WoS: 37Citation - Scopus: 41Differences in the Densities of Charged Defect States and Kinetics of Staebler-Wronski Effect in Undoped (nonintrinsic) Hydrogenated Amorphous Silicon Thin Films(American Institute of Physics, 1997) Güneş, Mehmet; Wronski, Christopher R.A variety of undoped (nonintrinsic) hydrogenated amorphous silicon (a-Si:H) thin films was studied in greater detail using steady-state photoconductivity, σph, subband-gap absorption, α(hν), steady-state photocarrier grating (SSPG), and electron-spin-resonance (ESR) techniques both in the annealed and stabilized light soaked states. The experimental results were self-consisiently modeled using a detailed numerical analysis. It was found that large differences in the optoelectronic properties of device quality a-Si:H thin films can only be explained using a gap slate distribution which consists of positively charged D+ defect states above the Fermi level, the neutral D0 defect states, and the negatively charged D- defect states below the Fermi level. There are large differences both in the densities of neutral and charged defect states and R ratios in different a-Si:H films in the annealed state. The densities of both neutral and charged defect states increased, however, R ratios decreased in the stabilized light soaked state. Very good agreement was obtained between the densities of neutral defect states measured by ESR and those derived from the numerical analysis in the stabilized light soaked state. The kinetics of the Staebler-Wronski effect was also investigated. There was no direct correlation between the decrease of steady-state photoconductivity and increase of subband-gap absorption. The self-consistent fits to wide range of experimental results obtained with the three Gaussian distributions of charged defect states imply that this model is much better representation of the bulk defect states in undoped hydrogenated amorphous silicon thin films.Conference Object Citation - WoS: 2Citation - Scopus: 3The Effects of Oxide Thickness on the Interface and Oxide Properties of Metal-Tantalum Pentoxide-Si (mos) Capacitors(National Institute of Optoelectronics, 2005) Özdağ, Pınar; Atanassova, Elena; Güneş, MehmetHigh dielectric constant tantalum-pentoxide insulating layers were prepared on p-type (100) crystalline silicon wafers using an RF magnetron sputtering technique. Then, metal-oxide-semiconductor (Al-Ta 2O 5-Si) structures were formed with various oxide thickness from 15 to 25 nm. Devices were characterized using the high frequency capacitance-voltage (C-V) spectroscopy method. From the analysis of the high frequency C-V curves, non-ideal effects such as oxide charges and interface trap densities have been evaluated. The results for Ta 2O 5 layers have been compared with those for conventional SiO 2 layers. Interface trap densities were found to be 1.6 ± 0.4×10 12 eV -1 cm -2 for Ta 2O 5 and about 2×10 11 eV -1 cm -2 for SiO 2 insulating layers. There was no clear thickness dependence of the interface trap densities for the Ta 2O 5 insulating layers.Conference Object Citation - WoS: 16Citation - Scopus: 17Instability Phenomena in Microcrystalline Silicon Films(National Institute of Optoelectronics, 2005) Finger, Friedhelm; Carius, Reinhard; Dylla, Thorsten; Klein, Stefan; Okur, Salih; Güneş, MehmetMicrocrystalline silicon (μc-Si:H) for solar cell applications is investigated with respect to the material stability upon treatment of the material in various environments, followed by annealing. The material can be separated into two groups: (i) material with high crystalline volume fractions and pronounced porosity which is susceptible to in-diffusion of atmospheric gases, which, through adsorption or oxidation affect the electronic properties and (ii) compact material with high or low crystalline volume fractions which show considerably less or no influence of treatment in atmospheric gases. We report the investigation of such effects on the stability of μc-Si:H films prepared by plasma enhanced chemical vapour deposition and hot wire chemical vapour deposition.Master Thesis Capacitance-voltage spectroscopy in metal-tantalum pentoxide (Ta-O)-silicon mos capacitors(Izmir Institute of Technology, 2005) Özdağ, Pınar; Güneş, MehmetThe electronic properties of Al-Ta2O5-Si MOS capacitors with oxide layers prepared by RF magnetron sputtering with or without a prior nitridation process in N2O or NH3 gas environments at temperature ranges between 700 °C to 850 °C were investigated using Capacitance-Voltage (C-V) Spectroscopy to determine the quality of oxide layer and oxide-silicon interface. The theoretical ideal capacitance-voltage calculations were compared with the experimental capacitance-voltage results in order to evaluate effective oxide charges, Qeff , present inside Ta2O5 insulating layer and density of interface trap states, Dit, present at the Ta2O5-Si interface. In addition,dielectric constant, doping concentration, flat band voltage values were determined by using the experimental data. Finally, the effects of deposition conditions on Ta2O5 MOS capacitors were compared by using a reference sample of a MOS capacitor with native oxide SiO2. It has been found that dielectric constant value up to 12 have been reached for Ta2O5 insulating layers which increases the capacitance value several times than that of MOS capacitor with native oxide SiO2. The density of interface trap states, Dit, for unnitrided Ta2O5 MOS capacitors, values around 1.6x1012 cm-2 eV-1 have been detected which is much higher than that of MOS capacitor with native oxide SiO2. However, prior nitridation process enhances the interface properties and Dit values down to 2-5x1011 cm-2 eV-1 have been reached for the nitrided samples which is in the limits for MOS capacitors with high quality insulating layers. In addition, the effective oxide charges, Qeff, for unnitrided samples, values as high as 3x1012 cm-2 were detected. Even though nitridation process enhances interface properties, the effective oxide charges are found to be higher for nitrided samples. Best electrical and interface properties are obtained by nitridation process at 800 °C in N2O and NH3. It can be inferred that samples nitrided in N2O gas at 800 °C improves the dielectric constant above the level of SiO2 and decreases both Qeff and Dit levels to that of native oxide SiO2. These results show that a prior nitridation of p-silicon surface is a promising approach to improve both oxide and interface properties of Al-Ta2O5-Si MOS devices. However, further investigation is necessary to understand the nature of these oxide charges and interface properties of MOS devices with high dielectric constant oxide layers before integration into large scale fabrication.Article Citation - WoS: 13Noise in Hydrogenated Amorphous Silicon(Institute of Electrical and Electronics Engineers, 2002) Johanson, Robert E.; Güneş, Mehmet; Kasap, Safa O.Published work on conductance fluctuations in hydrogenated amorphous silicon is surveyed. There are many reports of 1/f noise. some describing unusual features Such as non-Gaussian statistics. The relative insensitivity to doping and temperature is highlighted. In addition to the 1/f noise. random-telegraph-like noise is often reported. The successes and failures of generation-recombination models for 1 f noise and current filament models for the telegraph noise are summarised.Master Thesis The Effects of Deposition Conditions on the Low Energy Absorption Spectrum of Microcrystalline Silicon Thin Films Prepared by Hwcvd Method(Izmir Institute of Technology, 2005) Işık, Nebile; Güneş, MehmetThe optical and electronic properties of hydrogenated microcrystalline silicon films deposited by HWCVD method were investigated using steady state photoconductivity (SSPC), dual beam photoconductivity (DBP) and transmission spectroscopy methods to understand the effects of deposition conditions such as silane concentration and filament temperature on the low absorption coefficient spectrum, alpha (h.). The alpha (h.) spectrum obtained from the detailed optical calculation using the relative DBP and transmission spectra were compared with that independently measured on the same samples using photothermal deflection spectroscopy (PDS) and constant photocurrent method (CPM) techniques. The results were found to be in agreement with those of PDS and CPM at higher energy part of spectrum. On the other hand some differences exist among the spectra at lower energies. These differences were discussed to be consistent with underlying the physics of these methods.The effect of silane concentration on the sub-bandgap alpha (h.) spectrum was found to be substantial. At highest SC of 10% the alpha (h.) spectrum similar to that of a-Si: H is obtained. As SC decreases to 7%, microcrystalline phase becomes dominant.Further decrease of SC, the low energy alpha (h.) decreases and given a minimum around SC of 5%. For the lower SC.s, highly crystalline .c-Si: H films are obtained but the alpha (h.) values increases to higher values indicating an increase in the defect densities present in the microstructure.The effect of filament temperature was investigated for a constant SC of 10%. It was found that at 1700 C and 1800 C, fully amorphous films are obtained but 1800 C results in higher alpha (h.) values at lower energies. At 1880 C, microcrystalline phase becomes dominant and the alpha (h.) spectrum becomes similar to that of single crystal silicon.Finally, due to inhomogeneous microstructure of uec-Si: H, there are left fringes on calculated alpha(h.) spectrum on same samples. The degree of the inhomogeneity was investigated by front and back ac illumination of DBP measurements. It was found that there exists a substantial differences on the spectra measured on the same sample indicating importance of inhomogeneous film growth on optoelectronic measurements and its evaluation.Master Thesis The Effects of Prior Nitridation Process of Silicon Surface and Different Metal Gates on the Capacitance Voltage Characteristics of Metal-Ta2o5 Mos Capacitor(Izmir Institute of Technology, 2007) Özben, Eylem Durğun; Güneş, MehmetAccording to the 2004 International Technology Roadmap of Semiconductor (ITRS), for sub-micron technology, an equivalent oxide thickness (EOT) less than 1 nm is required. However, for such thickness levels, the native oxide SiO2 is unacceptable since it does not posses its inherited physical properties and results in high leakage current density resulting in reduced device performance. The replacement of SiO2 with high dielectric constant material (high-k) may eliminate such problems since it will allow the usage of thicker dielectric material. The leakage current will be reduced while maintaining the same levels of inversion charge. In this study, the electrical properties of metal-Ta2O5-Si MOS capacitor were investigated for devices prepared with different conditions. A prior nitridation process of silicon surface in N2O and NH3 gas before Ta2O5 was carried out to improve interface quality. In addition, different metal gates formed on the Ta2O5 oxide layer were also used in order to see the effects of top oxide-metal gate on the electrical properties of MOS capacitors. The metal gates used are Al, TiN and W. High frequency (1MHz) Capacitance-Voltage Spectroscopy was used to understand the effects of prior nitridation process and metal gates on the Ta2O5 high-k oxide properties. From the analysis of high frequency C-V curves, oxide capacitance, dielectric constant, EOT, leakage current density, conductance, flat band voltage VFB shift, mobile charge density, effective oxide charge and interface trap density Dit were obtained and compared with those of reference samples. Reference sample -1 has native oxide SiO2 and Al metal gate and Reference sample-2 has Ta2O5 oxide layer with unnitrided silicon surface. It has been found that, the replacement of SiO2 gate oxide with Ta2O5 oxide layer results in an increase in dielectric constant by several factors and using nitridation process prior to Ta2O5 oxide layer improves the interface properties. Many promising results were obtained for samples with W metal gates and nitrided silicon surface prior to formation of Ta2O5 oxide layer. It is potentially applicable to future MOS devices.Conference Object Citation - WoS: 8Citation - Scopus: 9Diffusion Length Measurements of Microcrystalline Silicon Thin Films Prepared by Hot-wire/Catalytic Chemical Vapor Deposition (hwcvd)(Elsevier Ltd., 2006) Okur, Salih; Güneş, Mehmet; Finger, Friedhelm; Carius, ReinhardHydrogenated microcrystalline silicon (μc-Si:H) films prepared by using the hot-wire/catalytic chemical vapor deposition (HWCVD) technique at low substrate temperatures between 185 °C and 220 °C with different silane concentrations (SC) were investigated using steady-state photocarrier grating (SSPG) and the steady-state photoconductivity methods (SSPC). Crystalline volume fractions (IC RS) obtained from Raman spectroscopy change from 0.22 to 0.77. The diffusion length (LD) is measured at generation rates between G = 1019 and 1021 cm- 3 s- 1. LD changes from 27 nm to 270 nm, with maximum values around SC = 5%. The dependence of LD on SC is similar to that observed for similar quality microcrystalline silicon films prepared using the VHF-PECVD technique. The grating quality factor, γ0, drops from about 0.9 to 0.5 after transition to the microcrystalline regime as indication of scattering from surface patterns.Conference Object Citation - WoS: 5Citation - Scopus: 5Photoconductivity Spectroscopy in Hydrogenated Microcrystalline Silicon Thin Films(Springer Verlag, 2003) Güneş, Mehmet; Akdaş, Deniz; Göktaş, Oktay; Carius, Reinhard; Klomfaß, Josef; Finger, FriedhelmSteady-state photoconductivity and sub-bandgap absorption measurements by the dual-beam photoconductivity (DBF) method were carried out on undoped hydrogenated microcrystalline silicon thin films prepared by VHF-PECVD and hot-wire chemical vapor deposition. The results are compared with those of the constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS). It is found that DBP, CPM, and PDS provide complementary data on the optoelectronic processes in microcrystalline silicon.
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