Browsing by Subject "Schottky diodes"
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Item Open Access Au/TiO2 nanorod-based Schottky-type UV photodetectors(Wiley, 2012-10-12) Karaagac, H.; Aygun, L. E.; Parlak, M.; Ghaffari, M.; Bıyıklı, Necmi; Okyay, Ali KemalTiO2 nanorods (NRs) were synthesized on fluorine-doped tin oxide (FTO) pre-coated glass substrates using hydrothermal growth technique. Scanning electron microscopy studies have revealed the formation of vertically-aligned TiO2 NRs with length of similar to 2 mu m and diameter of 110128 nm, homogenously distributed over the substrate surface. 130 nm thick Au contacts using thermal evaporation were deposited on the n-type TiO2 NRs at room temperature for the fabrication of NR-based Schottky-type UV photodetectors. The fabricated Schottky devices functioned as highly sensitive UV photodetectors with a peak responsivity of 134.8 A/W (lambda = 350 nm) measured under 3 V reverse bias. (c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Open Access Design and optimization of high-speed resonant cavity enhanced Schottky photodiodes(Institute of Electrical and Electronics Engineers, 1999-02) Gökkavas, M.; Onat, B. M.; Özbay, Ekmel; Ata, E. P.; Xu, J.; Towe, E.; Ünlü, M. S.Resonant cavity enhanced (RCE) photodiodes (PD's) are promising candidates for applications in optical communications and interconnects where high-speed high-efficiency photodetection is desirable. In RCE structures, the electrical properties of the photodetector remain mostly unchanged; however, the presence of the microcavity causes wavelength selectivity accompanied by a drastic increase of the optical field at the resonant wavelengths. The enhanced optical field allows to maintain a high efficiency for faster transit-time limited PD's with thinner absorption regions. The combination of an RCE detection scheme with Schottky PD's allows for the fabrication of high-performance photodetectors with relatively simple material structures and fabrication processes. In top-illuminated RCE Schottky PD's, a semitransparent Schottky contact can also serve as the top reflector of the resonant cavity. We present theoretical and experimental results on spectral and high-speed properties of GaAs-AlAs-InGaAs RCE Schottky PD's designed for 900-nm wavelength.Item Open Access Fabrication of high-speed resonant cavity enhanced schottky photodiodes(Institute of Electrical and Electronics Engineers, 1997-05) Özbay, Ekmel; Islam, M. S.; Onat, B.; Gökkavas, M.; Aytür, O.; Tuttle, G.; Towe, E.; Henderson, R. H.; Ünlü, M. S.We report the fabrication and testing of a GaAs-based high-speed resonant cavity enhanced (RCE) Schottky photodiode. The top-illuminated RCE detector is constructed by integrating a Schottky contact, a thin absorption region (In0.8Ga0.92As) and a distributed AlAs-GaAs Bragg mirror. The Schottky contact metal serves as a high-reflectivity top mirror in the RCE detector structure. The devices were fabricated by using a microwave-compatible fabrication process. The resulting spectral photo response had a resonance around 895 nm, in good agreement with our simulations. The full-width-at-half-maximum (FWHM) was 15 nm, and the enhancement factor was in excess of 6. The photodiode had an experimental setup limited temporal response of 18 ps FWHM, corresponding to a 3-dB bandwidth of 20 GHz.Item Open Access On-chip characterization of THz Schottky diodes using non-contact probes(IEEE Computer Society, 2016) Khan, T. M.; Ghobadi, A.; Celik, O.; Caglayan, C.; Bıyıklı, Necmi; Okyay, Ali Kemal; Topalli, K.; Sertel, K.We present non-contact characterization of GaAs Schottky contacts in the 140-220 GHz band. The non-contact probing technique utilizes planar on-chip antennas that are monolithically integrated with the coplanar waveguide environment housing the Schottky diode under test. The diode contact is fabricated through a 6 mask lithographic process with a 5 μm deep-trench under the contact to minimize parasitics and extend operation into the THz band. A quasi-optical link between the VNA ports and on-chip probe antennas enables efficient signal coupling into the test device. The non-contact probe station is calibrated using on-chip quick-offset-short method and the effectiveness of this approach is demonstrated for integrated diodes for under various bias conditions.Item Open Access A performance-enhanced planar Schottky diode for Terahertz applications: an electromagnetic modeling approach(Cambridge University Press, 2017) Ghobadi, Amir; Khan, Talha Masood; Celik, Ozan Onur; Biyikli, Necmi; Okyay, Ali Kemal; Topalli, KaganIn this paper, we present the electromagnetic modeling of a performance-enhanced planar Schottky diode for applications in terahertz (THz) frequencies. We provide a systematic simulation approach for analyzing our Schottky diode based on finite element method and lumped equivalent circuit parameter extraction. Afterward, we use the developed model to investigate the effect of design parameters of the Schottky diode on parasitic capacitive and resistive elements. Based on this model, device design has been improved by deep-trench formation in the substrate and using a closed-loop junction to reduce the amount of parasitic capacitance and spreading resistance, respectively. The results indicate that cut-off frequency can be improved from 4.1 to 14.1 THz. Finally, a scaled version of the diode is designed, fabricated, and well characterized to verify the validity of this modeling approach.Item Open Access Ta/Si Schottky diodes fabricated by magnetron sputtering technique(2010) Ocak, Y.S.; Genisel, M.F.; Kiliçoǧlu, T.Electrical properties of Ta/n-Si and Ta/p-Si Schottky barrier diodes obtained by sputtering of tantalum (Ta) metal on semiconductors have been investigated. The characteristic parameters of these contacts like barrier height, ideality factor and series resistance have been calculated using current voltage (I-V) measurements. It has seen that the diodes have ideality factors more than unity and the sum of their barrier heights is 1.21 eV which is higher than the band gap of the silicon (1.12 eV). The results have been attributed the effects of inhomogeneities at the interface of the devices and native oxide layer. In addition, the barrier height values determined using capacitance-voltage (C-V) measurements have been compared the ones obtained from I-V measurements. It has seen that the interface states have strong effects on electrical properties of the diodes such as C-V and Rs-V measurements. © 2010 Elsevier Ltd. All rights reserved.Item Open Access Ultra-low-cost near-infrared photodetectors on silicon(SPIE, 2015-02) Nazirzadeh, M. Amin; Atar, Fatih B.; Turgut, B. Berkan; Okyay, Ali KemalWe demonstrate Silicon-only near-infrared (NIR) photodetectors (sensitive up to 2000 nm) that meet large-scale ultralow-cost fabrication requirements. For the detection of infrared photons, we use metal nanoislands that form Schottky contact with Silicon. NIR photons excite plasmon resonances at metal nanoislands and plasmons decay into highly energetic charge carriers (hot electrons). These hot electrons get injected into Silicon (internal photoemission), resulting in photocurrent. Several groups have studied plasmonic nanoantennas using high resolution lithography techniques. In this work, we make use of randomly formed nanoislands for broad-band photoresponse at NIR wavelengths. We observe photoresponse up to 2000 nm wavelength with low dark current density about 50 pA/μm2. The devices exhibit photoresponsivity values as high as 2 mA/W and 600 μA/W at 1.3 μm and 1.55 μm wavelengths, respectively. Thin metal layer was deposited on low-doped n-type Silicon wafer. Rapid thermal annealing results in surface reconstruction of the metal layer into nanoislands. Annealing conditions control the average size of the nanoislands and photoresponse of the devices. An Al-doped Zinc Oxide (AZO) layer was deposited on the nanoislands using thermal atomic layer deposition (ALD) technique to acts as a transparent conductive oxide (TCO) and patterned using photolithography. AZO film creates electrical connection between the nanoislands and also makes a heterojunction to Silicon. Simple and scalable fabrication on Si substrates without the need for any sub-micron lithography or high temperature epitaxy process make these devices good candidates for ultra-low-cost broad-band NIR imaging and spectroscopy applications. © 2015 SPIE.