Browsing by Author "Bolat, S."
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Item Open Access Atomic Layer Deposition for Vertically Integrated ZnO Thin Film Transistors: Toward 3D High Packing Density Thin Film Electronics(Wiley-VCH Verlag, 2017) Sisman, Z.; Bolat, S.; Okyay, Ali KemalWe report on the first demonstration of the atomic layer deposition (ALD) based three dimensional (3D) integrated ZnO thin film transistors (TFTs) on rigid substrates. Devices exhibit high on-off ratio (∼106) and high effective mobility (∼11.8 cm2 V−1 s−1). It has also been demonstrated that the steps of fabrication result in readily stable electrical characteristics in TFTs, eliminating the need for post-production steps. These results mark the potential of our fabrication method for the semiconducting metal oxide-based vertical-integrated circuits requiring high packing density and high functionality. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Open Access Atomic-layer-deposited zinc oxide as tunable uncooled infrared microbolometer material(Wiley-VCH Verlag, 2014) Battal, E.; Bolat, S.; Tanrikulu, M. Y.; Okyay, Ali Kemal; Akin, T.ZnO is an attractive material for both electrical and optical applications due to its wide bandgap of 3.37 eV and tunable electrical properties. Here, we investigate the application potential of atomic-layer-deposited ZnO in uncooled microbolometers. The temperature coefficient of resistance is observed to be as high as-10.4% K-1 near room temperature with the ZnO thin film grown at 120 °C. Spectral noise characteristics of thin films grown at various temperatures are also investigated and show that the 120 °C grown ZnO has a corner frequency of 2 kHz. With its high TCR value and low electrical noise, atomic-layer-deposited (ALD) ZnO at 120 °C is shown to possess a great potential to be used as the active layer of uncooled microbolometers. The optical properties of the ALD-grown ZnO films in the infrared region are demonstrated to be tunable with growth temperature from near transparent to a strong absorber. We also show that ALD-grown ZnO can outperform commercially standard absorber materials and appears promising as a new structural material for microbolometer-based applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Open Access Demonstration of flexible thin film transistors with GaN channels(American Institute of Physics Inc., 2016) Bolat, S.; Sisman, Z.; Okyay, Ali KemalWe report on the thin film transistors (TFTs) with Gallium Nitride (GaN) channels directly fabricated on flexible substrates. GaN thin films are grown by hollow cathode plasma assisted atomic layer deposition (HCPA-ALD) at 200 °C. TFTs exhibit 103 on-to-off current ratios and are shown to exhibit proper transistor saturation behavior in their output characteristics. Gate bias stress tests reveal that flexible GaN TFTs have extremely stable electrical characteristics. Overall fabrication thermal budget is below 200 °C, the lowest reported for the GaN based transistors so far. © 2016 Author(s)Item Open Access Electronic and optical device applications of hollow cathode plasma assisted atomic layer deposition based GaN thin films(A I P Publishing LLC, 2015) Bolat, S.; Tekcan, B.; Ozgit Akgun, C.; Bıyıklı, Necmi; Okyay, Ali KemalElectronic and optoelectronic devices, namely, thin film transistors (TFTs) and metal-semiconductor-metal (MSM) photodetectors, based on GaN films grown by hollow cathode plasma-assisted atomic layer deposition (PA-ALD) are demonstrated. Resistivity of GaN thin films and metal-GaN contact resistance are investigated as a function of annealing temperature. Effect of the plasma gas and postmetallization annealing on the performances of the TFTs as well as the effect of the annealing on the performance of MSM photodetectors are studied. Dark current to voltage and responsivity behavior of MSM devices are investigated as well. TFTs with the N2/H2 PA-ALD based GaN channels are observed to have improved stability and transfer characteristics with respect to NH3 PA-ALD based transistors. Dark current of the MSM photodetectors is suppressed strongly after high-temperature annealing in N2:H2 ambient. © 2014 American Vacuum Society.Item Open Access Electronic and optical properties of atomic layer-deposited ZnO and TiO2(Springer New York LLC, 2018) Ates, H.; Bolat, S.; Oruc, F.; Okyay, Ali KemalMetal oxides are attractive for thin film optoelectronic applications. Due to their wide energy bandgaps, ZnO and TiO2 are being investigated by many researchers. Here, we have studied the electrical and optical properties of ZnO and TiO2 as a function of deposition and post-annealing conditions. Atomic layer deposition (ALD) is a novel thin film deposition technique where the growth conditions can be controlled down to atomic precision. ALD-grown ZnO films are shown to exhibit tunable optical absorption properties in the visible and infrared region. Furthermore, the growth temperature and post-annealing conditions of ZnO and TiO2 affect the electrical properties which are investigated using ALD-grown metal oxide as the electron transport channel on thin film field-effect devices.Item Open Access Low temperature thin films transistors with hollow cathode plasma-assisted atomic layer deposition based GaN channels(AIP Publishing LLC, 2014) Bolat, S.; Ozgit Akgun, C.; Tekcan, B.; Bıyıklı, Necmi; Okyay, Ali KemalWe report GaN thin film transistors (TFT) with a thermal budget below 250 °C. GaN thin films are grown at 200 °C by hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD). HCPA-ALD-based GaN thin films are found to have a polycrystalline wurtzite structure with an average crystallite size of 9.3 nm. TFTs with bottom gate configuration are fabricated with HCPA-ALD grown GaN channel layers. Fabricated TFTs exhibit n-type field effect characteristics. N-channel GaN TFTs demonstrated on-to-off ratios (ION/I OFF) of 103 and sub-threshold swing of 3.3 V/decade. The entire TFT device fabrication process temperature is below 250 °C, which is the lowest process temperature reported for GaN based transistors, so far. © 2014 AIP Publishing LLC.Item Open Access Low-temperature hollow cathode plasma-assisted atomic layer deposition of crystalline III-nitride thin films and nanostructures(Wiley - V C H Verlag GmbH & Co. KGaA, 2015) Ozgit Akgun, C.; Goldenberg, E.; Bolat, S.; Tekcan, B.; Kayaci, F.; Uyar, Tamer; Okyay, Ali Kemal; Bıyıklı, NecmiHollow cathode plasma-assisted atomic layer deposition (HCPA-ALD) is a promising technique for obtaining III-nitride thin films with low impurity concentrations at low temperatures. Here we report our previous and current efforts on the development of HCPA-ALD processes for III-nitrides together with the properties of resulting thin films and nanostructures. The content further includes nylon 6,6-GaN core-shell nanofibers, proof-of-concept thin film transistors and UV photodetectors fabricated using HCPA-ALD-grown GaN layers, as well as InN thin films deposited by HCPA-ALD using cyclopentadienyl indium and trimethylindium precursors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Open Access Metal-semiconductor-metal ultraviolet photodetectors based on gallium nitride grown by atomic layer deposition at low temperatures(SPIE, 2014) Tekcan, B.; Ozgit Akgun, C.; Bolat, S.; Bıyıklı, Necmi; Okyay, Ali KemalProof-of-concept, first metal-semiconductor-metal ultraviolet photodetectors based on nanocrystalline gallium nitride (GaN) layers grown by low-temperature hollow-cathode plasma-assisted atomic layer deposition are demonstrated. Electrical and optical characteristics of the fabricated devices are investigated. Dark current values as low as 14 pA at a 30 V reverse bias are obtained. Fabricated devices exhibit a 15× UV/VIS rejection ratio based on photoresponsivity values at 200 nm (UV) and 390 nm (VIS) wavelengths. These devices can offer a promising alternative for flexible optoelectronics and the complementary metal oxide semiconductor integration of such devices. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).