Browsing by Subject "Current voltage characteristics"

Now showing 1 - 12 of 12

Open Access
Capacitance-conductance-current-voltage characteristics of atomic layer deposited Au/Ti/Al2O3/n-GaAs MIS structures
(Elsevier Ltd, 2015) Turut, A.; Karabulut, A.; Ejderha, K.; Bıyıklı, Necmi
We have studied the admittance and current–voltage characteristics of the Au/Ti/Al2O3/nGaAs structure. The Al2O3 layer of about 5 nm was formed on the n-GaAs by atomic layer deposition. The barrier height (BH) and ideality factor values of 1.18 eV and 2.45 were obtained from the forward-bias ln I vs V plot at 300 K. The BH value of 1.18 eV is larger than the values reported for conventional Ti/n-GaAs or Au/Ti/n-GaAs diodes. The barrier modification is very important in metal semiconductor devices. The use of an increased barrier diode as the gate can provide an adequate barrier height for FET operation while the decreased barrier diodes also show promise as small signal zero-bias rectifiers and microwave. The experimental capacitance and conductance characteristics were corrected by taking into account the device series resistance Rs. It has been seen that the noncorrection characteristics cause a serious error in the extraction of the interfacial properties. Furthermore, the device behaved more capacitive at the reverse bias voltage range rather than the forward bias voltage range because the phase angle in the reverse bias has remained unchanged as 901 independent of the measurement frequency.
Open Access
Current transport mechanisms and trap state investigations in (Ni/Au)-AlN/GaN Schottky barrier diodes
(Elsevier, 2010-10-13) Arslan, E.; Bütün, S.; Şafak, Y.; Çakmak, H.; Yu, H.; Özbay, Ekmel
The current transport mechanisms in (Ni/Au)-AlN/GaN Schottky barrier diodes (SBDs) were investigated by the use of current-voltage characteristics in the temperature range of 80-380 K. In order to determine the true current transport mechanisms for (Ni/Au)-AlN/GaN SBDs, by taking the Js(tunnel), E 0, and Rs as adjustable fit parameters, the experimental J-V data were fitted to the analytical expressions given for the current transport mechanisms in a wide range of applied biases and at different temperatures. Fitting results show the weak temperature dependent behavior in the saturation current and the temperature independent behavior of the tunneling parameters in this temperature range. Therefore, it has been concluded that the mechanism of charge transport in (Ni/Au)-AlN/GaN SBDs, along the dislocations intersecting the space charge region, is performed by tunneling. In addition, in order to analyze the trapping effects in (Ni/Au)-AlN/GaN SBDs, the capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics were measured in the frequency range 0.7-50 kHz. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming the models in which traps are located at the heterojunction interface. The density (Dt) and time constants (τt) of the trap states have been determined as a function of energy separation from the conduction-band edge (Ec - Et) as Dt≅ (5-8)×10 12eV-1 cm-2andτt≅(43-102) μs, respectively.
Open Access
Electric breakdown in polycrystalline semiconductors with highly nonlinear I-V characteristics: Simulations for simple barrier height models
(1997) Yildirim H.E.; Tanatar, Bilal; Canessa, E.
An extension of the Canessa and Nguyen binary model for the nonlinear current-voltage (I-V) characteristics of polycrystalline semiconductors, based on the electrical properties of individual grains, is presented. Simple analytical models for the nonuniform distribution of barrier heights at grain boundaries are assumed. The set of nonlinear Kirchhoff equations, that determine the macroscopic current across the specimen, and the nonlinearity coefficient α are solved numerically. The applied voltage dependence of the barrier height models gives α values reaching ≈ 50, indicating high nonlinearity as required by potential commercial applications. © Tübi̇tak.
Open Access
Electronic properties of polypyrrole/polyindene composite/metal junctions
(Elsevier, 1997) Bozkurt, A.; Ercelebi, C.; Toppare, L.
Junction properties between conducting polymer composites of polypyrrole/polyindene (PPy/PIn) with different conductivities and metals like Pt, Au, Al and In have been investigated. Rectifying junctions were observed for low work function metals, In and Al; however, high work function metals, Pt and Au, were observed to form ohmic contacts to PPy/PIn composite in the sandwich geometry. The rectifying behavior of the metal/composite/Pt junctions improved when the conductivity of the composite was decreased from 1 to 0.01 S/cm. Using the ideal Schottky theory various junction parameters have been determined. All planar junctions were ohmic regardless of the conductivities of the samples.
Open Access
High-performance solar-blind AlGaN photodetectors
(IEEE, 2004) Özbay, Ekmel; Bıyıklı, Necmi; Kimukin, İbrahim; Tut, Turgut; Kartaloğlu, Tolga; Aytür, Orhan
High-performance aluminum gallium nitride (AlGaN)-based solar-blind (SB) photodetectors were demonstrated using different device structures. The Al x-Ga1-xN layers structure were grown by metalorganic chemical vapor deposition (MOCVD) on sapphire structures. n+ and p+ ohmic contacts on GaN were formed with non-annealed titanium (Ti)/aluminum (Al) and nickel (Ni)/ gold (Au) alloys. Spectral UV photoresponse measurements confirmed the solar-blind response of the devices.
Open Access
High-speed solar-blind AlGaN Schottky photodiodes
(Cambridge University Press, 2003) Bıyıklı, Necmi; Kimukin, İbrahim; Kartaloğlu, Tolga; Aytür, Orhan; Özbay, Ekmel
We report high-speed solar-blind AlGaN-based Schottky photodiodes. AlGaN/GaN heterostructure device layers were grown on sapphire substrate. The devices were fabricated on AlGaN/GaN heterostructuresusing a microwave compatible fabrication process. Schottky photodiodes with Au and indium-tin-oxide (ITO) Schottky contacts were fabricated. Current-voltage, spectral responsivity, and high-speed measurements were performed. Both Schottky samples exhibited very low sub-pA dark currents at high reverse bias. A bias dependent spectral responsivity was observed with a peak responsivity of 89 mA/W at 267 nm, and 44 mA/W at 263 nm for Au and ITO-Schottky devices respectively. Time-based high-frequency measurements at 267 nm resulted in pulse responses with rise times and pulse-widths as short as 13 ps and 74 ps respectively. The fastest solar-blind detector had a record 3-dB bandwidth of 1.10 GHz.
Open Access
High-speed solar-blind photodetectors with indium-tin-oxide Schottky contacts
(American Institute of Physics, 2003) Bıyıklı, Necmi; Kimukin, I.; Kartaloglu, T.; Aytur, O.; Özbay, Ekmel
AlGaN/GaN-based high-speed solar-blind photodetectors were discussed. Current-voltage, spectral responsivity, and high-frequency response characterizations were performed. Breakdown voltages larger than 40 V were obtained. A maximum responsivity of 44 mA/W at 263 nm was measured. True solar-blind detection was also ensured.
Open Access
High-speed visible-blind GaN-based ITO-Schottky photodiodes
(SPIE, 2002) Bıyıklı, Necmi; Kimukin, İbrahim; Kartaloğlu, Tolga; Aytür, Orhan; Özbay, Ekmel
In this paper we present our efforts on the design, fabrication and characterization of high-speed, visible-blind, GaN-based ultra-violet (UV) photodiodes using indium-tin-oxide (ITO) Schottky contacts. ITO is known as a transparent conducting material for the visible and near infrared part of the electromagnetic spectrum. We have investigated the optical properties of thin ITO films in the ultraviolet spectrum The transmission and reflection measurements showed that thin ITO films had better transparencies than thin Au films for wavelengths greater than 280 mn. Using a microwave compatible fabrication process, we have fabricated Au and ITO based Schottky photediodes on n-/n+ GaN epitaxial layers. We have made current-voltage (I-V), spectral quantum efficiency, and high-speed characterization of the fabricated devices. I-V characterization showed us that the Au-Schottky samples had better electrical characteristics mainly due to the larger Schottky barrier. However, due to the better optical transparency, ITO-Schottky devices exhibited higher quantum efficiencies compared to Au-Schottky devices. ITO-Schottky photodiodes with ∼80 nm thick ITO films resulted in a maximum quantum efficiency of 47%, whereas Au-Schottky photodiode samples with ∼10 nm thick Au films displayed a maximum efficiency of 27% in the visible-blind spectrum. UV/visible rejection ratios over three orders of magnitude were obtained for both samples. High-frequency characterization of the devices was performed via pulse-response measurements at 360 nm. ITO-Schottky photodiodes showed excellent high-speed characteristics with rise times as small as 12 psec and RC-time constant limited pulse-widths of 60 psec.
Open Access
Junction characteristics and magnetic field dependencies of low noise step edge junction Rf-SQUIDs for unshielded applications
(IEEE, 2003-06) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Bozbey, Ali; Bick, M.; Banzet, M.; Lomparski, D.; Zander, W.; Zhang, Y.; Krause, H-J.
Step edge grain boundary (GB) junctions and rf-SQUIDs have been made using pulsed laser deposited Y-Ba-Cu-O films on crystalline LaAlO3 substrates. The steps were developed using various ion-beam etching processes resulting in sharp and ramp type step structures. Sharp step based GB junctions showed behavior of serial junctions with resistively shunted junction (RSJ)-like I-V characteristics. The ramped type step structures resulted in relatively high critical current, Ic, junctions and noisy SQUIDs. The sharp steps resulted in low noise rf-SQUIDs with a noise level below 140 fT/Hz12/ down to few Hz at 77 K while measured with conventional tank circuits. The Ic of the junctions and hence the operating temperature range of the SQUIDs made using sharp steps was controlled by both the step height and the junction widths. The junction properties of the SQUIDs were also characterized showing RSJ-like characteristics and magnetic field sensitivities correlated to that of the SQUIDs. Two major low and high background magnetic field sensitivities have been observed for our step edge junctions and the SQUIDs made on sharp steps. High quality step edge junctions with low magnetic field sensitivities made on clean sharp steps resulted in low 1/f noise rf-SQUIDs proper for applications in unshielded environment.
Open Access
Noise, junction characteristics, and magnetic field dependencies of bicrystal grain boundary junction Rf-SQUIDs
(IEEE, 2003) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Bick, M.; Banzet, M.; Zander, W.; Zhang, Y.; Krause, H-J.
Bicrystal grain boundary (GB) Josephson junctions and rf-SQUID's were made of 200 nm thick PLD YBCO films on bi-crystal SrTiO3 substrates. The junction characteristics were studied to investigate optimal parameters in the rf-SQUID) layout designs and the limits imposed by the technology. The I c of 3 to 8 μm wide test junctions scaled with the junction widths, showing clear linear RSJ-like I-V characteristics at 77 K. All the junctions showed hysteretic RCSJ-like behavior at very low temperatures. Classical Josephson flux motion type (long junction) nonlinearity in I-V curves of all the junctions was also observed at lower temperatures with systematic dependence on the junction widths. Measurements of the magnetic field dependence of the Ic of the junctions resulted in junction width dependent well-defined Fraunhofer-pattern like characteristics. The obtained characteristics of the junctions led to feasible criteria for the rf-SQUID layouts with desired device characteristics. Rf-SQUID's were made using designs for optimal performance at 77 K while avoiding large superconducting weak links across the substrate GB. Devices with low noise characteristics and junction field sensitivities proper for operation in environmental background magnetic fields were obtained. A nonsystematic spread of optimal working temperature of the SQUID's were also observed which is associated to the spread of the junction parameters caused by the defects at the GB of substrates.
Open Access
Solar-blind A1GaN-based p-i-n photodiodes with low dark current and high detectivity
(IEEE, 2004) Bıyıklı, Necmi; Kimukin, I.; Aytur, O.; Özbay, Ekmel
We report solar-blind AlxGal1-xN-based heterojunction p-i-n photodiodes with low dark current and high detectivity. After the p+ GaN cap layer was recess etched, measured dark current was below 3 fA for reverse bias values up to 6 V. The device responsivity increased with reverse bias and reached 0.11 A/W at 261 nm under 10-V reverse bias. The detectors exhibited a cutoff around 283 nm, and a visible rejection of four orders of magnitude at zero bias. Low dark current values led to a high differential resistance of 9.52 × 1015 Ω. The thermally limited detectivity of the devices was calculated as 4.9 × 1014 cm · Hz1/2W-1. © 2004 IEEE.
Open Access
Spintronic properties of zigzag-edged triangular graphene flakes
(AIP Publishing LLC, 2010) Şahin, H.; Senger, R. T.; Çıracı, Salim
We investigate quantum transport properties of triangular graphene flakes with zigzag edges by using first principles calculations. Triangular graphene flakes have large magnetic moments which vary with the number of hydrogen atoms terminating its edge atoms and scale with its size. Electronic transmission and current-voltage characteristics of these flakes, when contacted with metallic electrodes, reveal spin valve and remarkable rectification features. The transition from ferromagnetic to antiferromagnetic state under bias voltage can, however, terminate the spin polarizing effects for specific flakes. Geometry and size dependent transport properties of graphene flakes may be crucial for spintronic nanodevice applications.