Browsing by Author "Celebi, Cem"

Now showing 1 - 5 of 5

Citation - WoS: 1
Citation - Scopus: 1
Comparison of the Photoresponse Characteristics for 4H-SiC Schottky Barrier UV Photodetector with Graphene and Ni/Cr Electrode
(Elsevier, 2026) Dulcel, Atilla Mert; Gozek, Melike; Celebi, Cem; Unverdi, Ozhan
Gr/4H-SiC and Ni/Cr/4H-SiC Schottky junction UV photodetectors were fabricated and investigated to reveal the effect of electrode materials on the device performance such as spectral response and response speed. I-V characterization, spectral response, and response speed (on-off) measurements were conducted for the UV wavelength range between 200 and 400 nm. The maximum photo-responsivity was obtained as 0.081 A/W for Gr/4H-SiC and 0.041 A/W for Ni/Cr/4H-SiC at a wavelength of 260 nm. This result was attributed to the higher optical transmittance of the graphene electrode compared to the semitransparent Ni/Cr electrode. Zero bias response speed measurements were done under 280 nm wavelength UV light pulsed at different frequencies such as 100 Hz, 500 Hz, and 1000 Hz. The Gr/4H-SiC and Ni/Cr/4H-SiC photodetectors show distinctly different decay times of 5.04 ms and 305.1 mu s, respectively, while their rise times were found to be similar. This observation has been explained by the inclination of graphene to act as a trap site for photogenerated holes.
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: 10
Citation - Scopus: 9
High voltage response of graphene/4H-SiC UV photodetector with low level detection
(Elsevier Ltd, 2023) Ala K. Jehad; Özhan Ünverdi; Cem Celebi; Unverdi, Ozhan; Celebi, Cem; Jehad, Ala K.
A self-powered graphene/silicon carbide (G/4H-SiC) ultraviolet photodetector of a p-i-n like-structure with high voltage response has been fabricated to detect and measure low intensity ultraviolet (UV) radiation. Bilayer graphene sheet grown by chemical vapor deposition (CVD) method was transferred on the top of an epilayer structure of n-/n+ 4 H-SiC. In this structure two Schottky contacts were formed: one at G/ n- 4H-SiC interface and the other at bulk-4 H-SiC/Cr/Au interface. The photodetector's characteristic measurements revealed low dark current of ∼ 0.58 nA and spectral voltage responsivity of ∼ 0.75 V/W at 300 nm wavelength. Under low level UV illumination of 300 nm wavelength the photodetector exhibited a leakage current and a photogenerated response voltage of 1.1 nA and 10 mV respectively. The time-dependent photovoltage measurements displayed a rapid photovoltage response with rise and decay times of ∼74 ns and ∼ 580 ns respectively. This novel device holds promise for applications requiring sensitive and self-powered UV detection. © 2023 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.
Citation - WoS: 5
Citation - Scopus: 5
Self-powered photodetector array based on individual graphene electrode and silicon-on-insulator integration
(Elsevier B.V., 2023) Alper Yanilmaz; Özhan Ünverdi; Cem Celebi; Yanilmaz, Alper; Unverdi, Ozhan; Celebi, Cem
One 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. All rights reserved.