Browsing by Subject "Zinc oxide (ZnO)"

Now showing 1 - 6 of 6

Open Access
Fabrication and characterization of zinc oxide based surface acoustic wave devices
(2013) Noyan, Mehmet Alican
Surface acoustic wave (SAW) devices, as applied to today’s technology, were first described in 1965. Since then, these devices were applied to a wide variety of fields. Bandpass filter is their most common application, which is an important component in consumer products such as televisions and mobile phones. SAW devices can also be utilized as chemical and biological sensors. Driving force behind the development of SAW sensors is their small size, high sensitivity, reliability, and durability. This thesis presents the development and characterization of ZnO/Si based SAW devices. ZnO thin films with c-axis orientation were deposited using rfmagnetron sputtering. Effect of post deposition annealing on the structure of ZnO and on the SAW device performance was studied. It was found that annealing ZnO above 600o C is detrimental for SAW device performance. Surface roughness of ZnO increases as the annealing temperature increases. In literature, roughness increase is presented as one of the reasons behind device breakdown. This work shows that roughness is not the primary cause for the breakdown. In addition, effect of SiO2 interlayer insertion between ZnO/Si structure on the device performance was examined together with the effect of ZnO thickness.
Open Access
Flexible organic-inorganic core-shell nanofibers by electrospinning and atomic layer deposition
(CRC Press, 2012) Kayacı, Fatma; Çağla, Özgit-Akgün; Dönmez, İnci; Bıyıklı, Necmi; Uyar, Tamer
Organic-inorganic core-shell nanofibers were fabricated by combining electrospinning and atomic layer deposition (ALD). In the first step, nylon66 (polymeric organic core) nanofibers having different average fiber diameters (∼100 nm, ∼250 nm and ∼650 nm) were electrospun by using different solvent systems and polymer concentrations. In the second step, uniform and conformal layer of zinc oxide (ZnO) (inorganic shell) with precise thickness (∼90 nm) and composition on the round surface of the nylon nanofibers were deposited by ALD. The core-shell nylon66-ZnO nanofibers have shown unique properties such as structural flexibility due to the polymeric core and photocatalytic activity due to the ZnO shell layer.
Open Access
Growth of ∼3-nm ZnO nano-islands using Atomic layer deposition
(IEEE, 2016) El-Atab, N.; Chowdhury, F. I.; Ulusoy, Türkan Gamze; Ghobadi, Amir; Nazirzadeh, Amin; Okyay, Ali Kemal; Nayfeh, A.
In this work, the deposition of 3-nm dispersed Zinc-Oxide (ZnO) nanislands by thermal Atomic Layer Deposition (ALD) is demonstrated. The physical and electronic properties of the islands are studied using Atomic Force Microscopy, UV-Vis-NIR spectroscopy, and X-ray Photoelectron Spectroscopy. The results show that there is quantum confinement in 1D in the nanoislands which is manifested by the increase of the bandgap and the reduction of the electron affinity of the ZnO islands. The results are promising for the fabrication of future electronic and optoelectronic devices by single ALD step.
Open Access
Investigation of photodetectors based on iii-nitride and metal oxide thin films deposited by atomic layer deposition
(2015-05) Tekcan, Burak
Gallium Nitride (GaN), one of the most attractive optoelectronic materials today with a direct wide band gap of 3.4eV and high electron saturation velocity of, has found many applications from blue/UV LEDs to UV photodetectors, from high electron mobility transistors (HEMT) to solar cells. Traditional techniques to grow GaN films require high temperature (over 600C) processes. Such techniques cannot be used to synthesize GaN films on temperature sensitive substrates such as plastics or even paper for large area optoelectronic applications. To circumvent this setback, atomic layer deposition (ALD) stands out with its unique features such as low temperature process, precise thickness control and step coverage. Our work marks the demonstration of the first optical device on hollow cathode plasma assisted atomic layer deposition (HCPA-ALD) grown GaN films. The fabricated devices showed promising electrical and optical performance. A UV/VIS contrast ratio of 15 is obtained with very low dark current of 14pA at 20V applied bias. Annealing the films improved the device performance. Dark current was reduced more than two orders of magnitude while the responsivity was increased by two times. In the second part of the thesis, optoelectronic device applications on ALD grown ZnO layers will be presented. ZnO is also an attractive wide direct band gap semiconductor. It is utilized in many optical devices such as photodetectors and solar cells as well as thin film transistors and biomedical applications. In this work, device applications of ZnO on Silicon heterojunctions are investigated. A high rectification ratio of 103 is achieved with 80C grown ZnO-Si heterojunction photodiodes. High responsivity values are also recorded for these devices. At 350nm incident wavelength maximum responsivity of 35mA/W and at 585nm incident wavelength maximum responsivity of 90mA/W are obtained.
Open Access
Light trapping in inverted organic photovoltaics with nanoimprinted ZnO photonic crystals
(IEEE Electron Devices Society, 2017) Nirmal A.; Kyaw A.K.K.; Jianxiong, W.; Dev K.; Sun, X.; Demir, Hilmi Volkan
Zinc oxide photonic crystal (ZnO PC) formed via facile nanoimprinting was employed on the ZnO electron selective layer of inverted organic photovoltaics (OPV). Optimized inverted OPV fabricated with these highly ordered periodic structures provided effective light trapping, which resulted in increased incident light absorption in the active layer. Consequently, OPVs with the ZnO PC layers show a 23% current density improvement compared with OPVs with planar ZnO layer. Finite-difference time-domain simulation studies show that the electric field intensity is significantly higher in the active layer for devices with ZnO PC structures in comparison with reference devices with planar ZnO electron selective layer. Nanoimprinted ZnO PC is, thus, a viable method for light absorption and efficiency enhancement in OPVs. ï¿½ 2011-2012 IEEE.
Open Access
Low power Zinc-Oxide based charge trapping memory with embedded silicon nanoparticles
(ECS, 2014) Nayfeh, A.; Okyay, Ali Kemal; El-Atab, N.; Özcan, Ayşe; Alkış, Sabri
In this work, a bottom-gate charge trapping memory device with Zinc-Oxide (ZnO) channel and 2-nm Si nanoparticles (Si-NPs) embedded in ZnO charge trapping layer is demonstrated. The active layers of the memory device are deposited by atomic layer deposition (ALD) and the Si-NPs are deposited by spin coating. The Si-NPs memory exhibits a threshold voltage (Vt) shift of 6.3 V at an operating voltage of -10/10 V while 2.6 V Vt shift is obtained without nanoparticles confirming that the Si-NPs act as energy states within the bandgap of the ZnO layer. In addition, a 3.4 V Vt is achieved at a very low operating voltage of -1 V/1 V due to the charging of the Si-NPs through Poole-Frenkel emission mechanism at an electric field across the tunnel oxide E > 0.36 MV/cm. The results highlight a promising technology for future ultra-low power memory devices.