GCRIS

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Fabrication and Characterization of Soi Based Photodetectors With Graphene Electrode
(01. Izmir Institute of Technology, 2023) Yanılmaz, Alper; Çelebi, Cem; Balcı, Sinan
This thesis presents the pioneering methods for the design, fabrication process, and performance evaluation of graphene (G) and n-type silicon (n-Si) based self-powered one dimensional (1D) and two dimensional (2D) photodetector arrays (PDAs) on a silicon on insulator (SOI) substrate. In the device structure, monolayer G is utilized as hole collecting transparent conductive electrode (TCE) and n-Si is used as light absorbing material, respectively. After analyzing the photo-response characteristics of single pixel G/n-Si diode on SOI, we fabricated G/n-Si based Schottky barrier 1D PDAs with common G electrode, separate G electrode and 2D PDA with individual G electrodes on linearly arrayed n-Si channels, respectively. Each G/n-Si diodes exhibited a clear rectifying Schottky character with low dark current and diode parameters were analyzed using the current-voltage measurement. Besides, all diodes demonstrated a clear photovoltaic activity under the light illumination and maximum responsivity at 660 nm peak wavelength. Each diode in PDA revealed similar device performances under self-powered mode in terms of an Ilight/Idark ratio up to 104, a responsivity of ~0.1 A/W and a response speed of ~1.3 μs at 660 nm wavelength. The optical crosstalk was extremely low between neighboring diodes and also it could be greatly minimized when G is used as separated electrode on arrayed Si up to ~0.10% (-60 dB) per array. Time dependent photocurrent spectroscopy measurements revealed an excellent photocurrent reversibility of both device types. In the diode structure, the homogeneity of the graphene film transferred on n-Si were examined by Raman mapping and correlated with the sensitivity of diode to incoming light. This thesis paves the way for the new generation of optoelectronic devices with various potential by integrating G and SOI technology to PDA devices with ease of fabrication.
Two Dimensional Material Based Field Effect Transistor for Biosensing Applications
(01. Izmir Institute of Technology, 2023) İnanç, Dilce; Yıldız, Ümit Hakan; Çelebi, Cem
This thesis presents research on the use of two-dimensional material graphene as an area-effective transistor and its application in biological fields. The formation of wrinkled and flat structures on the surface of a single-layer graphene area-effective transistor, epitaxially grown for determining the bio-membrane dynamics of graphene, was examined using two different methods of deposition (thermal evaporation and pulsed electron accumulation) of a silicon dioxide (SiO2) layer. The investigation aimed to evaluate the pH and lipid bilayer formation performance of both wrinkled and flat GFETs. Increased sensitivity was determined through electrical measurements, as the oxide layer becomes thinner due to the existence of wrinkles, thus providing electrostatic coating on graphene. A sensor platform of chemiresistor type was developed for the differential determination of volatile organic compounds (VOCs) by synthesizing single-layer, bilayer, and multilayer graphene, enabling the analysis of ethanol (EtOH) and methanol (MetOH). Sensors produced using three different graphene morphologies demonstrated differential MeOH-EtOH responses attributed to the differential intercalation phenomenon in multilayer graphene morphologies when compared to ethanol. For the detection of VOCs such as acetone, ethanol, and hexane in human breath, a polymer nanofiber/multi-walled carbon nanotube or poly (3,4-ethylenedioxythiophene)/gold (Au) and iron oxide (Fe) hybrid bioelectronic interface was developed. Sensitivity studies were conducted by applying pure VOCs at different concentrations to the sensor platforms, and the behavior of the sensor platforms against interfering elements was evaluated by recharacterizing them under CO2 and humidity conditions. Considering the responses of MWCNT-PLLCL-Fe-based sensors to acetone, ethanol, and hexane, the tendency of water molecules to adhere to the Fe surface was shown to decrease water condensation on the conductive layer compared to other sensor configurations, indicating that the humidity effect was minimized in MWCNT-PLLCL-Fe-based sensors.

Phd Degree / Doktora

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