Browsing by Author "Fidan, Mehmet"

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Citation - WoS: 38
Citation - Scopus: 38
CVD graphene/SiC UV photodetector with enhanced spectral responsivity and response speed
(Elsevier B.V., 2023) Ala K. Jehad; Mehmet Fidan; Özhan Ünverdi; Cem Celebi; Fidan, Mehmet; Celebi, Cem; Jehad, Ala K.; Unverdi, Ozhan
A self-powered high-performance graphene/Silicon Carbide (G/4H-SiC) ultraviolet Schottky junction photodetector has been fabricated and the effect of using monolayer and bilayer graphene on the device performance parameters was investigated. P-type graphene sheets were grown by the chemical vapor deposition (CVD) method while 4H-SiC material consists of an epilayer structure of n-/n+ on bulk n-SiC. Two photodetector devices have been studied one with monolayer graphene (MLG) and the other with bilayer graphene (BLG). The proposed photodetector structure reveals the highest spectral responsivity known of a G/4H-SiC UV photodetector so far. Electronic and optoelectronic characterizations were done under an ultraviolet wavelength range from 240 to 350 nm. The results show two spectral responsivity maxima (Rmax) at 285 nm and 300 nm wavelengths. Exhibiting two maxima in spectral responsivity and detectivity is caused by the constructive and destructive interference effects of multiple reflections at the SiC epilayer's interfaces. The photodetector devices exhibit high spectral responsivity (R ∼ 0.09 AW−1) maximum detectivity (D* ∼ 2.9 × 1012 Jones) and minimum noise equivalent power (NEP ∼ 0.17 pWHz-1/2) in both devices. Using bilayer graphene instead of monolayer showed no significant change in both the photogenerated current and the spectral responsivity due to the higher absorption coefficient of bilayer graphene however it exhibited a significant improvement in the response speed. The response speed was found to increase by 50 % when bilayer graphene was used as a hole collecting electrode in the G/4H-SiC junction. This is because bilayer graphene creates a narrower depletion layer and higher electric field which promotes efficient charge separation and recombination. © 2023 Elsevier B.V. All rights reserved.
Citation - WoS: 3
Citation - Scopus: 3
Enhancing the photo-response characteristics of graphene/n-Si based Schottky barrier photodiodes by increasing the number of graphene layers
(AVS Science and Technology Society, 2022) Mehmet Fidan; Özhan Ünverdi; Cem Celebi; Fidan, Mehmet; celebi, Cem; uenverdi, Oezhan; Ünverdi, Özhan
The 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. © 2022 Elsevier B.V. All rights reserved.
Citation - WoS: 14
Citation - Scopus: 19
Junction area dependent performance of graphene/silicon based self-powered Schottky photodiodes
(ELSEVIER SCIENCE SA, 2021) Mehmet Fidan; Ozhan Unverdi; Cem Celebi; Unverdi, Ozhan; Fidan, Mehmet; Celebi, Cem
This work reports the impact of junction area on the device performance parameters of Graphene/n-Silicon (Gr/n-Si) based Schottky photodiodes. Herein three batches of Gr/n-Si photodiode samples were produced based on various sized CVD grown monolayer graphene layers transferred on individual n-Si substrates. The fabricated devices exhibited strong Schottky diode character and had high spectral sensi-tivity at 905 nm peak wavelength. The optoelectronic measurements showed that the spectral response of Gr/n-Si Schottky photodiodes has a linear dependence on the active junction area. The sample with 20 mm(2) junction area reached a spectral response of 0.76 AW(-1) which is the highest value reported in the literature for self-powered Gr/n-Si Schottky photodiodes without the modification of graphene electrode. In contrast to their spectral responsivities the response speed of the samples were found to be lowered as a function of the junction area. The experimental results demonstrated that the device performance of Gr/n-Si Schottky photodiodes can be modified simply by changing the size of the graphene electrode on n-Si without need of external doping of graphene layer or engineering Gr/n-Si interface. This study may serve towards the standardization of junction area for the development of high performance Gr/Si based optoelectronic devices such as solar cells and photodetectors operating in between the ultraviolet and near-infrared spectral region. (C) 2021 Elsevier B.V. All rights reserved.