Browsing by Subject "Bias voltage"

Now showing 1 - 6 of 6

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
Dual-color ultraviolet metal-semiconductor-metal AlGaN photodetectors
(AIP Publishing LLC, 2006) Gökkavas, M.; Bütün, S.; Yu, H.; Tut, T.; Bütün, B.; Özbay, Ekmel
Backilluminated 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.
Open Access
Femtosecond pulse generation from a Ti3+: Sapphire laser near 800 nm with voltage reconfigurable graphene saturable absorbers
(OSA - The Optical Society, 2017) Baylam, Işınsu; Özharar, Sarper; Kakenov, Nurbek; Kocabaş, Coşkun; Sennaroglu, Alphan
We experimentally show that a voltage-controlled graphene-gold supercapacitor saturable absorber (VCG-gold-SA) can be operated as a fast saturable absorber with adjustable linear absorption at wavelengths as low as 795 nm. This was made possible by the use of a novel supercapacitor architecture, consisting of a high-dielectric electrolyte sandwiched between a graphene and a gold electrode. The high-dielectric electrolyte allowed continuous, reversible adjustment of the Fermi level and, hence, the optical loss of the VCG-gold-SA up to the visible wavelengths at low bias voltages of the order of a few volts (0-2 V). The fast saturable absorber action of the VCG-gold-SA and the bias-dependent reduction of its loss were successfully demonstrated inside a femtosecond Ti3+:sapphire laser operating near 800 nm. Dispersion compensation was employed by using dispersion control mirrors and a prism pair. At a bias voltage of 1.2 V, the laser operated with improved power performance in comparison with that at zero bias, and the VCG-gold-SA initiated the generation of nearly transform-limited pulses as short as 48 fs at a pulse repetition rate of 131.7 MHz near 830 nm. To the best of our knowledge, this represents the shortest wavelength where a VCG-gold-SA has been employed as a mode locker with adjustable loss. © 2017 Optical Society of America.
Open Access
On the profile of frequency and voltage dependent interface states and series resistance in (Ni/Au)/Al0.22Ga0.78N/AlN/GaN heterostructures by using current-voltage (I-V) and admittance spectroscopy methods
(Elsevier, 2011-06-08) Demirezen, S.; Altindal, S.; Özelik, S.; Özbay, Ekmel
In order to explain the experimental effect of interface states (N ss) and series resistance (Rs) of device on the non-ideal electrical characteristics, current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of (Ni/Au)/Al 0.22Ga0.78N/AlN/GaN heterostructures were investigated at room temperature. Admittance measurements (C-V and G/ω-V) were carried out in frequency and bias voltage ranges of 2 kHz-2 MHz and (-5 V)-(+5 V), respectively. The voltage dependent Rs profile was determined from the I-V data. The increasing capacitance behavior with the decreasing frequency at low frequencies is a proof of the presence of interface states at metal/semiconductor (M/S) interface. At various bias voltages, the ac electrical conductivity (σac) is independent from frequencies up to 100 kHz, and above this frequency value it increases with the increasing frequency for each bias voltage. In addition, the high-frequency capacitance (C m) and conductance (Gm/ω) values measured under forward and reverse bias were corrected to minimize the effects of series resistance. The results indicate that the interfacial polarization can more easily occur at low frequencies. The distribution of Nss and R s is confirmed to have significant effect on non-ideal I-V, C-V and G/ω-V characteristics of (Ni/Au)/Al0.22Ga0.78N/AlN/ GaN heterostructures.
Open Access
Voltage contrast X-ray photoelectron spectroscopy reveals graphene-substrate interaction in graphene devices fabricated on the C-and Si-faces of SiC
(American Institute of Physics Inc., 2015) Aydogan, P.; Arslan, E.; Cakmakyapan, S.; Özbay, Ekmel; Strupinski, W.; Süzer, Şefik
We report on an X-ray photoelectron spectroscopy (XPS) study of two graphene based devices that were analyzed by imposing a significant current under +3 V bias. The devices were fabricated as graphene layers(s) on hexagonal SiC substrates, either on the C- or Si-terminated faces. Position dependent potential distributions (IR-drop), as measured by variations in the binding energy of a C1s peak are observed to be sporadic for the C-face graphene sample, but very smooth for the Si-face one, although the latter is less conductive. We attribute these sporadic variations in the C-face device to the incomplete electrical decoupling between the graphene layer(s) with the underlying buffer and/or substrate layers. Variations in the Si2p and O1s peaks of the underlayer(s) shed further light into the electrical interaction between graphene and other layers. Since the potential variations are amplified only under applied bias (voltage-contrast), our methodology gives unique, chemically specific electrical information that is difficult to obtain by other techniques.
Open Access
X-ray photoelectron spectroscopy for identification of morphological defects and disorders in graphene devices
(AIP Publishing, 2016) Aydogan, P.; Polat, E. O.; Kocabas, C.; Süzer, Şefik
The progress in the development of graphene devices is promising, and they are now considered as an option for the current Si-based electronics. However, the structural defects in graphene may strongly influence the local electronic and mechanical characteristics. Although there are well-established analytical characterization methods to analyze the chemical and physical parameters of this material, they remain incapable of fully understanding of the morphological disorders. In this study, x-ray photoelectron spectroscopy (XPS) with an external voltage bias across the sample is used for the characterization of morphological defects in large area of a few layers graphene in a chemically specific fashion. For the XPS measurements, an external +6 V bias applied between the two electrodes and areal analysis for three different elements, C1s, O1s, and Au4f, were performed. By monitoring the variations of the binding energy, the authors extract the voltage variations in the graphene layer which reveal information about the structural defects, cracks, impurities, and oxidation levels in graphene layer which are created purposely or not. Raman spectroscopy was also utilized to confirm some of the findings. This methodology the authors offer is simple but provides promising chemically specific electrical and morphological information.