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Optimization of Zinc Oxide Based Metal - Semiconductor Junction Interface Properties and Applications for Optoelectronic Devices
(01. Izmir Institute of Technology, 2024) Güzelaydın, Abdurrahman Halis; Tarhan, Enver
This thesis manifests an experimental investigation on the optoelectronic characteristics of wide band gap thin film zinc oxide semiconductor – metal junction and performance enhancement of ultraviolet photo detectors fabricated utilizing this metal-semiconductor interface. Pristine zinc oxide, aluminum doped zinc oxide and amorphous In-Ga-Zn-O thin film samples with thicknesses varying between 50-250 nm were fabricated from 2' ceramic targets via magnetron sputtering method. Surface properties and thus the zinc oxide – metal junction interface was optimized by altering sputtering parameters. Sputtering gas pressure, power and temperature was varied between 1.5 – 5 mTorr, 50 – 120 W and 25 – 500 °C, respectively. To determine the effects of energetic ion bombardment on the films' surface properties, biases ranging from 5 to 15 W were applied to the substrates during depositions. A 5 nm thick silicon dioxide passivation layer was deposited on zinc oxide thin films to suppress persistent photoconductivity effect. Furthermore, a thermal treatment under ultraviolet irradiation and was applied specifically to amorphous In-Ga-Zn-O thin films after device fabrication to improve their ultraviolet sensing capabilities. Optoelectronic spectral responses of devices were assessed experimentally by using transient photocurrent spectroscopy method. An ultraviolet light source with a 275 nm peak wavelength at 500 µW power was used as illumination source. All devices exhibited photoconductor behavior with ohmic metal-semiconductor junctions under 5 V bias. Amorphous In-Ga-Zn-O Sample 10 attained a dark current of 140 nA and reached a photocurrent level of 3.8 µA with a photo-to-dark current ratio of 27, yielding a spectral response of 1830 A/W. The calculated external quantum efficiency for this device was 825000%.
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.

Phd Degree / Doktora

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