Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 5Citation - Scopus: 5Self-Powered Photodetector Array Based on Individual Graphene Electrode and Silicon-On Integration(Elsevier, 2023) Yanılmaz, Alper; Ünverdi, Özhan; Çelebi, CemOne of the key limitations for the device performance of the silicon (Si) based photodetector arrays is the optical crosstalk effect encountered between photoactive elements as well. The scope of this work is to reduce optical crosstalk and thus increasing the device performances with graphene and Si integration. This paper presents the design, fabrication process, and performance evaluation of self-powered individual Graphene/Silicon on Insulator (GSOI) based Schottky barrier photodiode array (PDA) devices. A 4-element GSOI Schottky barrier PDA with separate graphene electrodes is fabricated to examine possible optical crosstalk encountered between each diode in the array structure. Here, monolayer graphene is utilized as hole collecting separate electrode on individually arrayed n-type Si on SOI substrate by photolithography technique. Each diode in the array exhibited a clear rectifying Schottky character. Photoresponse characterizations revealed that all diodes had excellent device performance even in self-powered mode in terms of an Ilight/Idark ratio up to 104, a responsivity of ∼0.12 A/W, a specific detectivity of around 1.6 × 1012 Jones, and a response speed of ∼1.32 μs at 660 nm wavelength. As revealed by optical crosstalk measurement, the device with pixel pitch of 1.5 mm had a total crosstalk of about 0.10% (−60 dB) per array. These results showed that the optical crosstalk between neighboring n-Si elements can be greatly minimized when graphene is used as separated electrode on arrayed Si on SOI substrate. Our study is expected give an insight into the performance characteristics of GSOI PDA devices which have great potential to be used in many technological applications such as multi-wavelength light measurement, level metering, high-speed photometry and position/motion detection. © 2023 Elsevier B.V.Article Citation - WoS: 11Citation - Scopus: 10Intercalation Leads To Inverse Layer Dependence of Friction on Chemically Doped Mos2(IOP Publishing, 2023) Açıkgöz, Oğulcan; Guerrero, Enrique; Yanılmaz, Alper; Dağdeviren, Ömür E.; Çelebi, Cem; Strubbe, David A.; Baykara, Mehmet Z.We present results of atomic-force-microscopy-based friction measurements on Re-doped molybdenum disulfide (MoS2). In stark contrast to the widespread observation of decreasing friction with increasing number of layers on two-dimensional (2D) materials, friction on Re-doped MoS2 exhibits an anomalous, i.e. inverse, dependence on the number of layers. Raman spectroscopy measurements combined with ab initio calculations reveal signatures of Re intercalation. Calculations suggest an increase in out-of-plane stiffness that inversely correlates with the number of layers as the physical mechanism behind this remarkable observation, revealing a distinctive regime of puckering for 2D materials.Article Citation - WoS: 4Citation - Scopus: 4Graphene/Soi-based Self-Powered Schottky Barrier Photodiode Array(American Institute of Physics, 2022) Yanılmaz, Alper; Fidan, Mehmet; Ünverdi, Özhan; Çelebi, CemWe have fabricated a four-element graphene/silicon on insulator (SOI) based Schottky barrier photodiode array (PDA) and investigated its optoelectronic device performance. In our device design, monolayer graphene is utilized as a common electrode on a lithographically defined linear array of n-type Si channels on a SOI substrate. As revealed by wavelength resolved photocurrent spectroscopy measurements, each element in the PDA structure exhibited a maximum spectral responsivity of around 0.1 A/W under a self-powered operational mode. Time-dependent photocurrent spectroscopy measurements showed excellent photocurrent reversibility of the device with ∼1.36 and ∼1.27 μs rise time and fall time, respectively. Each element in the array displayed an average specific detectivity of around 1.3 × 1012 Jones and a substantially small noise equivalent power of ∼0.14 pW/Hz-1/2. The study presented here is expected to offer exciting opportunities in terms of high value-added graphene/Si based PDA device applications such as multi-wavelength light measurement, level metering, high-speed photometry, and position/motion detection.Article Citation - WoS: 4Citation - Scopus: 4Light-Induced Modification of the Schottky Barrier Height in Graphene/Si Based Near-Infrared Photodiodes(Elsevier, 2022) Fidan, Mehmet; Dönmez, Gülçin; Yanılmaz, Alper; Ünverdi, Özhan; Çelebi, CemThe impact of light on the Schottky barrier height (SBH) in p-type graphene/n-type Si (p-Gr/n-Si) based near-infrared photodiodes is investigated. Hall effect and optoelectronic transport measurements carried out under illumination of 905 nm wavelength light showed that zero-bias SBH in such photodiodes can be effectively tuned in a range between 0.7 and 0.9 eV consistent with the variation in their open-circuit voltage. Shockley-Read-Hall model, which considers the charge recombination through mid-gap and interface states at the p-Gr/n-Si heterojunction, is used to explain the experimentally observed nonlinear dependence of SBH on the incident light. Light induced tunability of SBH at the graphene/semiconductor heterojunction is of great importance especially for the development of new generation optically driven devices in which graphene acts as a functioning element.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.Article Citation - WoS: 22Citation - Scopus: 22Zinc Oxide and Metal Halide Perovskite Nanostructures Having Tunable Morphologies Grown by Nanosecond Laser Ablation for Light-Emitting Devices(American Chemical Society, 2020) Demirci Sankir, Nurdan; Abdullayeva, Nazrin; Altaf, Çiğdem Tuç; Kumtepe, Alihan; Yılmaz, Nazmi; Coşkun, Özlem; Sankir, Mehmet; Kurt, Hamza; Çelebi, Cem; Yanılmaz, AlperThis work reports a one-pot chemical bath deposition (CBD) method for the preparation of selectively grown, morphology-tunable zinc oxide (ZnO) nanostructures provided via straightforward nanosecond fiber laser ablation. Nanosecond fiber laser ablation is different from lithographic methods due to its simple, time saving, and efficient film scribing abilities. Here, multiple morphologies of the ZnO nanostructures on the same substrate have been grown via laser ablation of the ZnO seeding layer. Selective and controlled ablation of the titanium layer, ZnO growth inhibitor, resulted in systematic growth of nanorod arrays, while the application of extensive fluence energies resulted in the penetration of the laser beam until the glass substrate induced the nanoflake growth within the same CBD environment. The laser penetration depth has been numerically investigated via COMSOL Multiphysics heat module simulations, and the optical variations between two nanostructures (nanorod and nanoflake) have been examined via Lumerical FDTD. The simultaneous growth of two morphologies served as an efficient tool for the enhancement of photoluminescence intensities. It increased the average charge carrier lifetimes of the thin films from approximately 2.01 to 9.07 ns under the same excitation wavelengths. The amplification in PL performances has been accomplished via the capstone of all-inorganic halide perovskite (IHP) deposition that brought a successful conclusion to lifetime responses, which have been increased by 1.4-fold. The development of IHP sensitized nanoscaled multimorphological ZnO thin films can, therefore, be used as potential nanomaterials for light-emitting-device applications. © 2020 American Chemical Society.Article Citation - WoS: 6Citation - Scopus: 6Few-Layer Mos2 as Nitrogen Protective Barrier(IOP Publishing Ltd., 2017) Akbalı, Barış; Yanılmaz, Alper; Tomak, Aysel; Tongay, Sefaattin; Çelebi, Cem; Şahin, HasanWe report experimental and theoretical investigations of the observed barrier behavior of few-layer MoS2 against nitrogenation. Owing to its low-strength shearing, low friction coefficient, and high lubricity, MoS2 exhibits the demeanor of a natural N-resistant coating material. Raman spectroscopy is done to determine the coating capability of MoS2 on graphene. Surface morphology of our MoS2/graphene heterostructure is characterized by using optical microscopy, scanning electron microscopy, and atomic force microscopy. In addition, density functional theory-based calculations are performed to understand the energy barrier performance of MoS2 against nitrogenation. The penetration of nitrogen atoms through a defect-free MoS2 layer is prevented by a very high vertical diffusion barrier, indicating that MoS2 can serve as a protective layer for the nitrogenation of graphene. Our experimental and theoretical results show that MoS2 material can be used both as an efficient nanocoating material and as a nanoscale mask for selective nitrogenation of graphene layer.