Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 2Citation - Scopus: 2Enhancing the Photo-Response Characteristics of Graphene/N-si Based Schottky Barrier Photodiodes by Increasing the Number of Graphene Layers(AVS, 2022) Fidan, Mehmet; Ünverdi, Özhan; Çelebi, CemThe impact of the number of graphene layers on the spectral responsivity and response speed of graphene/n-type Si (Gr/n-Si)-based Schottky barrier photodiodes is investigated. Gr/n-Si photodiode devices are fabricated by transferring chemical vapor deposition-grown graphene layers one by one on n-Si substrates, reaching up to three graphene layers. The devices show a clear rectifying Schottky character and have a maximum responsivity at a peak wavelength of 905 nm. Wavelength-resolved and time-dependent photocurrent measurements demonstrated that both spectral responsivity and response speed are enhanced as the number of graphene layers is increased from 1 to 3 on n-Si substrates. For example, the spectral responsivity and the response speed of the fabricated device were found to be improved by about 15% (e.g., from 0.65 to 0.75 AW-1) and 50% (e.g., 14 to 7 μs), respectively, when three graphene layers are used as the hole-collecting cathode electrode. The experimentally obtained results showed that the device parameters, such as spectral responsivity and response speed of Gr/n-Si Schottky barrier photodiodes, can be boosted simply by increasing the number of graphene layers on n-Si substrates.Article Citation - WoS: 3Citation - Scopus: 4Lipid Bilayer on Wrinkled-Interfaced Graphene Field Effect Transistor(Elsevier Ltd., 2021) Özkendir İnanç, Dilce; Çelebi, Cem; Yıldız, Ümit HakanThis study describes lipid bilayer-based sensor interface on SiO2 encapsulated graphene field effect transistors (GFET). The SiO2 layer was utilized as a lipid compatible surface that drives bilayer formation. The two types of surface morphologies i) wrinkled morphology by thermal evaporation (TE) and ii) flat morphology by pulsed electron deposition (PED) were obtained. The sensing performance of wrinkled and flat interfaced-GFETs were investigated, pH sensitivity of wrinkled interfaced-GFETs were found to be ten fold larger than the flat ones. The enhanced sensitivity is attributed to thinning of the oxide layer by formation of wrinkles thereby facilitating electrostatic gating on graphene. We foresee that described wrinkled SiO2 interfaced-GFET holds promise as a cell membrane mimicking sensing platform for novel bioelectronic applications. © 2020Article Citation - WoS: 10Citation - Scopus: 10The Comparison of Transient Photocurrent Spectroscopy Measurements of Pulsed Electron Deposited Zno Thin Film for Air and Vacuum Ambient Conditions(Elsevier, 2019) Özdoğan, Mehmet; Yiğen, Serap; Çelebi, Cem; Utlu, GökhanPhotoconduction mechanism of ZnO thin films that produced by Pulsed Electron Deposition method is systematically investigated by taking Transient Photocurrent Spectroscopy measurements for different atmospheres including high vacuum and air environments. Response and recovery rates of photocurrent in the air are faster than the rates in high vacuum condition. The results in the presented work clearly indicate that the photoconduction of ZnO thin films with high surface-area-to-volume ratio are surface-related and mostly governed by adsorption/desorption of oxygen and water molecules in the atmosphere. Therefore, the high surface interaction tendency of ZnO surface with the atmosphere inevitably leads to charge transfer from surface to adsorbates and/or vice versa.Article Citation - WoS: 2Citation - Scopus: 2Impact of Encapsulation Method on the Adsorbate Induced Electrical Instability of Monolayer Graphene(AVS Science and Technology Society, 2019) Kalkan, Sırrı Batuhan; Yanılmaz, Alper; Çelebi, CemMonolayer graphene transferred onto a set of silicon carbide (SiC) substrates was encapsulated with a thin SiO2 film in order to prevent its interaction with atmospheric adsorbates. The encapsulation of graphene samples was realized by using two different thin film growth methods such as thermal evaporation (TE) and state-of-the-art pulsed electron deposition (PED). The encapsulation efficiency of these two techniques on the structural and electrical characteristics of graphene was compared with each other. Scanning electron microscopy (SEM) analysis showed that unlike the SiO2 thin film grown with PED, structural defects like cracks were readily formed on TE grown films due to the lack of surface wettability. The electronic transport measurements revealed that the electrical resistivity of graphene has been increased by two orders of magnitude, and the carrier mobility has been subsequently decreased upon the encapsulation process with the PED method. However, in-vacuum transient photocurrent spectroscopy (TPS) measurements conducted for short periods and a few cycles showed that the graphene layer encapsulated with the PED grown SiO2 film is electrically far more stable than the one encapsulated with TE grown SiO2 film. The results of TPS measurements were related to the SEM images to unravel the mechanism behind the improved electrical stability of graphene samples encapsulated with the PED grown SiO2 film.