Browsing by Subject "Leakage currents"
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Item Open Access Dual-color ultraviolet metal-semiconductor-metal AlGaN photodetectors(AIP Publishing LLC, 2006) Gökkavas, M.; Bütün, S.; Yu, H.; Tut, T.; Bütün, B.; Özbay, EkmelBackilluminated ultraviolet metal-semiconductor-metal photodetectors with different spectral responsivity bands were demonstrated on a single Alx Ga1-x N heterostructure. This was accomplished by the incorporation of an epitaxial filter layer and the recess etching of the surface. The 11 nm full width at half maximum (FWHM) responsivity peak of the detector that was fabricated on the as-grown surface was 0.12 AW at 310 nm with 10 V bias, whereas the 22 nm FWHM responsivity peak of the detector fabricated on the recess-etched surface was 0.1 AW at 254 nm with 25 V bias. Both detectors exhibited excellent dark current characteristics with less than 10 fA leakage current. © 2006 American Institute of Physics.Item Open Access Electrical characteristics of β-Ga2O3 thin films grown by PEALD(Elsevier, 2014) Altuntas, H.; Donmez, I.; Ozgit Akgun, C.; Bıyıklı, NecmiIn this work, 7.5 nm Ga2O3 dielectric thin films have been deposited on p-type (1 1 1) silicon wafer using plasma enhanced atomic layer deposition (PEALD) technique. After the deposition, Ga2O 3 thin films were annealed under N2 ambient at 600, 700, and 800 C to obtain β-phase. The structure and microstructure of the β-Ga2O3 thin films was carried out by using grazing-incidence X-ray diffraction (GIXRD). To show effect of annealing temperature on the microstructure of β-Ga2O3 thin films, average crystallite size was obtained from the full width at half maximum (FWHM) of Bragg lines using the Scherrer formula. It was found that crystallite size increased with increasing annealing temperature and changed from 0.8 nm to 9.1 nm with annealing. In order to perform electrical characterization on the deposited films, Al/β-Ga2O3/p-Si metal-oxide- semiconductor (MOS) type Schottky barrier diodes (SBDs) were fabricated using the β-Ga2O3 thin films were annealed at 800 C. The main electrical parameters such as leakage current level, reverse breakdown voltage, series resistance (RS), ideality factor (n), zero-bias barrier height (Bo), and interface states (NSS) were obtained from the current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. The RS values were calculated by using Cheung methods. The energy density distribution profile of the interface states as a function of (ESS-EV) was obtained from the forward bias I-V measurements by taking bias dependence of ideality factor, effective barrier height (e), and RS into account. Also using the Norde function and C-V technique, e values were calculated and cross-checked. Results show that β-Ga2O3 thin films deposited by PEALD technique at low temperatures can be used as oxide layer for MOS devices and electrical properties of these devices are influenced by some important parameters such as NSS, RS, and β-Ga2O3 oxide layer.Item Open Access Estimation of Spurious Radiation from Microstrip Etches Using Closed-Form Green’s Functions(IEEE, 1992) Aksun, M.I.; Mittra, R.The problem of spurious radiation from electronic packages is considered in this paper by investigating the power radiated from microstrip etches that are excited by arbitrarily-located current sources, and terminated by complex loads at both ends. The first step in the procedure is to compute the current distribution on the microstrip line by using the method of moments (MoM). Two novel contributions of this paper are: (i) employing the recently-derived closed-form Green’s functions in the spatial domain that permit an efficient computation of the elements of the MoM matrix; (ii) incorporating complex load terminations in a convenient manner with virtually no increase in the computation time. The computed current distribution is subsequently used to calculate the spurious radiated power and the result is compared with that derived by using an approximate, transmission line analysis. © 1992 IEEEItem Open Access High bandwidth-efficiency solar-blind AlGaN Schottky photodiodes with low dark current(Pergamon Press, 2005-01) Tut, T.; Bıyıklı, Necmi; Kimukin, I.; Kartaloglu, T.; Aytur, O.; Unlu, M. S.; Özbay, EkmelAl0.38Ga0.62N/GaN heterojunction solar-blind Schottky photodetectors with low dark current, high responsivity, and fast pulse response were demonstrated. A five-step microwave compatible fabrication process was utilized to fabricate the devices. The solarblind detectors displayed extremely low dark current values: 30 μm diameter devices exhibited leakage current below 3fA under reverse bias up to 12V. True solar-blind operation was ensured with a sharp cut-off around 266nm. Peak responsivity of 147mA/W was measured at 256nm under 20V reverse bias. A visible rejection more than 4 orders of magnitude was achieved. The thermally-limited detectivity of the devices was calculated as 1.8 × 1013cm Hz1/2W-1. Temporal pulse response measurements of the solar-blind detectors resulted in fast pulses with high 3-dB bandwidths. The best devices had 53 ps pulse-width and 4.1 GHz bandwidth. A bandwidth-efficiency product of 2.9GHz was achieved with the AlGaN Schottky photodiodes. © 2004 Elsevier Ltd. All rights reserved.Item Open Access High-performance solar-blind AlGaN photodetectors(SPIE, 2005) Özbay, Ekmel; Tut, Turgut; Bıyıklı, N.Design, fabrication, and characterization of high-performance Al xGa1-xN-based photodetectors for solar-blind applications are reported. AlxGa1-xN heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3 fA leakage currents at 6 V and 12 V reverse bias were measured on p-i-n and Schottky photodiode samples respectively. The excellent current-voltage (I-V) characteristics led to a detectivity performance of 4.9×1014 cmHz1/2W-1. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.15 A/W and 0.11 A/W peak responsivity values at 267 nm and 261 nm respectively. All samples displayed true solar-blind response with cut-off wavelengths smaller than 280 nm. A visible rejection of 4×104 was achieved with Schottky detector samples. High speed measurements at 267 nm resulted in fast pulse responses with >GHz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.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.Item Open Access Thiol passivation of MWIR Type II superlattice photodetectors(SPIE, 2013) Salihoğlu, Ömer; Muti, Abdullah; Aydınlı, AtillaPoor passivation on photodetectors can result in catastrophic failure of the device. Abrupt termination of mesa side walls during pixel definition generates dangling bonds that lead to inversion layers and surface traps leading to surface leakage currents that short circuit diode action. Good passivation, therefore, is critical in the fabrication of high performance devices. Silicondioxide has been the main stay of passivation for commercial photodetectors, deposited at high temperatures and high RF powers using plasma deposition techniques. In photodetectors based on III-V compounds, sulphur passivation has been shown to replace oxygen and saturate the dangling bonds. Despite its effectiveness, it degrades over time. More effort is required to create passivation layers which eliminate surface leakage current. In this work, we propose the use of sulphur based octadecanethiol (ODT), CH3(CH2)17SH, as a passivation layer for the InAs/GaSb superlattice photodetectors that acts as a self assembled monolayer (SAM). ODT SAMs consist of a chain of 18 carbon atoms with a sulphur atom at its head. ODT Thiol coating is a simple process that consist of dipping the sample into the solution for a prescribed time. Excellent electrical performance of diodes tested confirm the effectiveness of the sulphur head stabilized by the intermolecular interaction due to van der Walls forces between the long chains of ODT SAM which results in highly stable ultrathin hydrocarbon layers without long term degradation. © 2013 SPIE.Item Open Access Variable temperature-scanning Hall probe microscopy with GaN/AlGaN two-dimensional electron gas (2DEG) micro Hall sensors in 4.2-425 K range using novel quartz tuning fork AFM feedback(IEEE, 2008) Akram, Rizwan; Dede, Münir; Oral, AhmetIn this paper, we present the fabrication and variable temperature (VT) operation of Hall sensors, based on GaN/AlGaN heterostructure with a two-dimensional electron gas (2DEG) as an active layer, integrated with quartz tuning fork (QTF) in atomic force-guided (AFM) scanning Hall probe microscopy (SHPM). Physical strength and a wide bandgap of GaN/AlGaN heterostructure makes it a better choice to be used for SHPM at elevated temperatures, compared to other compound semiconductors (AlGaAs/GaAs and InSb), which are unstable due to their narrower bandgap and physical degradation at high temperatures. GaN/AlGaN micro Hall probes were produced using optical lithography and reactive ion etching. The active area, Hall coefficient, carrier concentration, and series resistance of the Hall sensors were ∼1 × 1 μm, 10 mΩ/G at 4.2 K, 6.3 × 10 12 cm -2 and 12 kΩ at room temperature and 7 mΩ/G, 8.9 × 10 12 cm -2 and 24 kΩ at 400 K, respectively. A novel method of AFM feedback using QTF has been adopted. This method provides an advantage over scanning tunneling-guided feedback, which limits the operation of SHPM the conductive samples and failure of feedback due to high leakage currents at high temperatures. Simultaneous scans of magnetic and topographic data at various pressures (from atmospheric pressure to high vacuum) from 4. to 425K will be presented for different samples to illustrate the capability of GaN/AlGaN Hall sensors in VT-SHPM.