Browsing by Author "Yu, H. Y."
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Item Open Access High quality single-crystal germanium-on-insulator on bulk Si substrates based on multistep lateral over-growth with hydrogen annealing(American Institute of Physics, 2010-08-09) Yu, H. Y.; Cheng, S. L.; Park, J. H.; Okyay, Ali Kemal; Onbal, M. C.; Ercan, B.; Nishi, Y.; Saraswat, K. C.Germanium-on-insulator (GOI) is desired for high performance metal-oxide-semiconductor transistors and monolithically integrated optoelectronics. We demonstrate a promising approach to achieve single-crystal defect-free GOI by using lateral over-growth through SiO2 window. The dislocations due to the lattice mismatch are effectively terminated and reduced in SiO2 trench by selective area heteroepitaxy combined with hydrogen annealing. Low defect density of 4× 106 cm-2 and low surface roughness of 0.7 nm (root-mean-square) on GOI are confirmed by plan-view transmission electron microscopy and atomic force microscopy analysis. In addition, the excellent metal-semiconductor-metal diode electrical characteristics fabricated on this GOI confirm Ge crystal quality. The selectively grown GOI structure can provide the monolithic integration of SiGe based devices on a Si very large scale integration (VLSI) platformItem Open Access An indium-free transparent resistive switching random access memory(IEEE, 2011-02-28) Zheng, K.; Sun, X. W.; Zhao, J. L.; Wang, Y.; Yu, H. Y.; Demir, Hilmi Volkan; Teo, K. L.We report an indium-free transparent resistive switching random access memory device based on GZO-Ga(2)O(3)-ZnO-Ga(2)O(3)-GZO structure by metal-organic chemical vapor deposition. The memory device shows good transmittance in the visible region and bipolar resistive switching behavior with good cycling characteristics and retention time under room temperature. The conduction and resistive switching mechanism was discussed based on filament theory.Item Open Access Influence of channel layer thickness on the electrical performances of inkjet-printed In-Ga-Zn oxide thin-film transistors(IEEE, 2010-12-10) Wang, Y.; Sun, X. W.; Goh, G. K. L.; Demir, Hilmi Volkan; Yu, H. Y.Inkjet-printed In-Ga-Zn oxide (IGZO) thin-film transistors (TFTs) with bottom-gate bottom-contact device architecture are studied in this paper. The impact of the IGZO film thickness on the performance of TFTs is investigated. The threshold voltage, field-effect mobility, on and off drain current, and subthreshold swing are strongly affected by the thickness of the IGZO film. With the increase in film thickness, the threshold voltage shifted from positive to negative, which is related to the depletion layer formed by the oxygen absorbed on the surface. The field-effect mobility is affected by the film surface roughness, which is thickness dependent. Our results show that there is an optimum IGZO thickness, which ensures the best TFT electrical performance. The best result is from a 55-nm-thick IGZO TFT, which showed a field-effect mobility in the saturation region of 1.41 cm(2)/V . s, a threshold voltage of 1 V, a drain current on/off ratio of approximately 4.3 x 10(7), a subthreshold swing of 384 mV/dec, and an off-current level lower than 1 pA.Item Open Access Low temperature atomic layer deposited ZnO photo thin film transistors(AVS Science and Technology Society, 2014) Oruc, F. B.; Aygun, L. E.; Donmez, I.; Bıyıklı, Necmi; Okyay, Ali Kemal; Yu, H. Y.ZnO thin film transistors (TFTs) are fabricated on Si substrates using atomic layer deposition technique. The growth temperature of ZnO channel layers are selected as 80, 100, 120, 130, and 250°C. Material characteristics of ZnO films are examined using x-ray photoelectron spectroscopy and x-ray diffraction methods. Stoichiometry analyses showed that the amount of both oxygen vacancies and interstitial zinc decrease with decreasing growth temperature. Electrical characteristics improve with decreasing growth temperature. Best results are obtained with ZnO channels deposited at 80°C; Ion/Ioff ratio is extracted as 7.8 × 109 and subthreshold slope is extracted as 0.116 V/dec. Flexible ZnO TFT devices are also fabricated using films grown at 80°C. ID-VGS characterization results showed that devices fabricated on different substrates (Si and polyethylene terephthalate) show similar electrical characteristics. Sub-bandgap photo sensing properties of ZnO based TFTs are investigated; it is shown that visible light absorption of ZnO based TFTs can be actively controlled by external gate bias. © 2014 American Vacuum Society.Item Open Access Selective-area high-quality germanium growth for monolithic integrated optoelectronics(Institute of Electrical and Electronics Engineers, 2012-03-02) Yu, H. Y.; Park, J. H.; Okyay, Ali Kemal; Saraswat, K. C.Selective-area germanium (Ge) layer on silicon (Si) is desired to realize the advanced Ge devices integrated with Si very-large-scale-integration (VLSI) components. We demonstrate the area-dependent high-quality Ge growth on Si substrate through SiO 2 windows. The combination of area-dependent growth and multistep deposition/hydrogen annealing cycles has effectively reduced the surface roughness and the threading dislocation density. Low root-mean-square surface roughness of 0.6 nm is confirmed by atomic-force-microscope analysis. Low defect density in the area-dependent grown Ge layer is measured to be as low as 1 × 10 7cm -2 by plan-view transmission-electron-miscroscope analysis. In addition, the excellent metal-semiconductor-metal photodiode characteristics are shown on the grown Ge layer to open up a possibility to merge Ge optoelectronics with Si VLSI.Item Open Access Silicon-Germanium multi-quantum well photodetectors in the near infrared(Optical Society of American (OSA), 2012) Onaran, E.; Onbasli, M. C.; Yesilyurt, A.; Yu, H. Y.; Nayfeh, A. M.; Okyay, Ali KemalSingle crystal Silicon-Germanium multi-quantum well layers were epitaxially grown on silicon substrates. Very high quality films were achieved with high level of control utilizing recently developed MHAH epitaxial technique. MHAH growth technique facilitates the monolithic integration of photonic functionality such as modulators and photodetectors with low-cost silicon VLSI technology. Mesa structured p-i-n photodetectors were fabricated with low reverse leakage currents of ∼10 mA/cm2 and responsivity values exceeding 0.1 A/W. Moreover, the spectral responsivity of fabricated detectors can be tuned by applied voltage. © 2012 Optical Society of America.