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Ag-doped HfO2 thin films via sol–gel dip coating method
(Springer Nature, 2019-10-01) Pakma, Osman; Kaval, Şehmus; Kari̇per, İshak Afşin
In this study, undoped and Ag-doped HfO2 thin films were deposited on glass substrates by means of sol–gel dip coating method. These films were then thermally annealed at 500 °C for 1 h. The structural and optical properties of undoped and Ag-doped HfO2 thin films were characterized by X-ray diffraction, UV–Vis spectrometry and scanning electron microscope. The results of this analysis were compared and interpreted with the results obtained in literature by various methods of coating with HfO2. The X-ray diffraction peaks of the films paired with monoclinic HfO2 crystalline peaks. The refractive indices of the films decreased with doping Ag, at 500 nm wavelengths. The optical band gap values of Ag-doped HfO2 thin films increased with doping Ag. The porous structures were observed on the surface films, especially with 5% Ag doping.
Analysis of electrical and photoelectrical properties of ZnO/p-InP heterojunction
(Elsevier, 2011-06) Ocak, Yusuf Selim; Kulakçı, Mustafa; Turan, Raşit; Kılıçoğlu, Tahsin; Güllü, Ömer
A ZnO/p-InP heterojunction has been fabricated by dc sputtering of ZnO on p-InP. It has been observed that the device has a good rectification. The electrical properties of the device such as ideality factor, barrier height, series resistance have been calculated using its current-voltage (I-V) measurements between 300 and 380 K with 20 K intervals. The short current density (Jsc) and open circuit voltage (Voc) parameters have been determined between 40 and 100 mW/cm2. The photovoltaic parameters of the device have been also determined under 100 mW/cm2 and AM1.5 illumination condition.
Analysis of interface states of Al/DNA/p-Si MIS photovoltaic structures with DNA biomolecules using the conductance technique
(Taylor & Francis, 2017-03-29) Güllü, Ömer
In this study, we report on the calculation of interface charge distribution of metal–interlayer–semiconductor (MIS) photovoltaic diodes containing DNA biomolecules and Si semiconductor based on the conductance technique. DNA biofilms were deposited at room temperature using a simple cast method on p-type Si. Interface parameters of the Al/DNA/p-Si structures were investigated by using capacitance–voltage (C–V) and conductance–voltage (G–V) measurements as a function of frequency. The distributions of interfacial charge states and the trap relaxation times were reported. Also, photoelectric and photocapacitance properties of the diode were measured at room temperature.
The analysis of lateral distribution of barrier height in identically prepared Co/n-Si Schottky diodes
(Elsevier, 2009-11-03) Güllü, Ömer; Karataş, Şükrü; Güler, Gülşen; Bakkaloğlu, Ömer Faruk
We have studied the experimental linear relationship between ideality factors and barrier heights (BHs) for Co/n-Si metal–semiconductor (MS) structures with a doping density of about 1015 cm−3. The barrier heights for the Co/n-type Si metal–semiconductor structures from the current–voltage (I–V) characteristics varied from 0.64 to 0.70 eV, the ideality factor n varied from 1.18 to 1.26, and from reverse bias capacitance–voltage (C−2–V) characteristics the barrier height varied from 0.68 to 0.81 eV. The experimental barrier height distributions obtained from the I–V and C−2–V characteristics were fitted by a Gaussian distribution function, and their mean values were found to be 0.67 and 0.75 eV, respectively. Furthermore, the lateral homogeneous BH value of approximately 0.81 eV for Co/n-Si metal–semiconductor structures was obtained from the linear relationship between experimental effective BHs and ideality factors.
The analysis of the charge transport mechanism of n-Si/MEH-PPV device structure using forward bias I-V-T characteristics
(Elsevier, 2010-03-04) Kavasoğlu, Abdülkadir Sertap; Yakuphanoğlu, Fahrettin; Kavasoğlu, Neşe; Pakma, Osman; Birgi, Özcan; Oktik, Şener
In this study, temperature dependent current-voltage (I-V) measurements and investigation of the dc current transport mechanism of n-Si/MEH-PPV device have been performed. While the series resistance value displayed strongly temperature dependent behaviour, the ideality factor varied between 3.2 and 1.8 in the temperature range 110-330 K. The temperature dependent ideality factor behaviour at low temperature region (110-220 K) shows that tunnelling enhanced recombination is valid rather than thermionic emission theory and the characteristic tunnelling energy is calculated as 30 meV. There is a slightly linear relationship between the ideality factor and temperature at region II (230-330 K) which is attributed to drift-diffusion current transport in the n-Si/MEH-PPV device as stated already by Osvald.
Analysis of the series resistance and interface state densities in metal semiconductor structures
(Journal of Physics: Conference Series, 2009-03) Güllü, Ömer; Karataş, Şükrü; Güler, Gülşen; Bakkaloğlu, Ömer Faruk
The electrical properties of Co/n-Si metal-semiconductor (MS) Schottky structure investigated at room temperature using current-voltage (I-V) characteristics. The characteristic parameters of the structure such as barrier height, ideality factor and series resistance have been determined from the I-V measurements. The values of barrier height obtained from Norde’s function were compared with those from Cheung functions, and it was seen that there was a good agreement between barrier heights from both methods. The series resistance values calculated with Cheung’s two methods were compared and seen that there was an agreement with each other. However, the values of series resistance obtained from Cheung functions and Norde’s functions are not agreeing with each other. Because, Cheung functions are only applied to the non-linear region (high voltage region) of the forward bias I–V characteristics. Furthermore, the energy distribution of interface state density was determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height. The results show that the presence of thin interfacial layer between the metal and semiconductor
Barrier enhancement of Al/n-InP Schottky diodes by graphene oxide thin layer
(Scientific Publishers, 2019) Güllü, Ömer; Çankaya, Murat; Rajagopal Reddy, Varra
In the present work, the surface morphology, structural and optical features of graphene oxide (GO) films are investigated. The Al/GO/n-InP MIS diode is formed by depositing GO layer on n-InP wafer for the barrier enhancement. Interfacial properties of the MIS diode with GO interlayer are extracted from current–voltage (I–V) measurement. The simple diode parameters such as barrier height and ideality factor are extracted from I–V plots, and the values are compared with those of conventional Al/n-InP MS contact. The value of barrier height (BH) for the Al/GO/n-InP contact is found as 0.85 eV. The BH value of 0.85 eV of the Al/GO/n-InP MIS structure is as high as around 100% compared to the value of 0.43 eV of the Al/n-InP reference contacts. We have showed that the value of 0.85 eV is one of the highest values presented for reference contacts with an interlayer.
The characteristic diode parameters in Ti/p-InP contacts prepared by DC sputtering and evaporation processes over a wide measurement temperature
(World Scientific, 2017-06) Ejderha, Kadir; Asubay, Sezai; Yıldırım, Nezir; Güllü, Ömer; Türüt, Abdülmecit; Abay, Bahattin
The titanium/p-indium phosphide (Ti/p-InP) Schottky diodes (SDs) have been prepared by thermal evaporation and DC magnetron sputtering deposition. Then, their current-voltage (I-V) characteristics have been measured in the sample temperature range of 100-400K with steps of 20K. The characteristic parameters of both Ti/p-InP SDs have been compared with each other. The barrier height (BH) values of 0.824 and 0.847 at 300K have been obtained for the sputtered and the evaporated SDs, respectively. This low BH value for the sputtered SD has been attributed to some defects introduced by the sputtered deposition technique over a limited depth in to the p-type substrate. The BH of the evaporated and sputtered diodes has decreased with the standard deviations of 58 and 64mV obeying to double-Gaussian distribution (GD) in 220-400K range, respectively, and it has seen a more sharper reduction for the BHs with the standard deviations of 93 and 106 mV in 100-220K range. The Richardson constant values of 89.72 and 53.24A(Kcm)-2 (in 220-400K range) for the evaporated and sputtered samples, respectively, were calculated from the modified ln(I0/T2)-q2σs2/2k2T2 vs (kT)-1 curves by GD of the BHs. The value 53.24A(Kcm)-2 for the sputtered sample in high temperatures range is almost the same as the known Richardson constant value of 60A(Kcm)-2 for p-type InP.
Characterization of an Au/n-Si photovoltaic structure with an organic thin film
(Elsevier, 2013-08) Özaydın, Cihat; Akkılıç, Kemal; İlhan, Salih; Rüzgar, Şerif; Güllü, Ömer; Temel, Hamdi
We demonstrate that a copper(II) organic complex can control the electrical characteristics of conventional Au/n-Si metal-semiconductor (MS) contacts. We investigated the electronic and photovoltaic properties of a Cu(II) complex/n-Si heterojunction diode. The ideality factor n and barrier height Φb of the diode were 2.22 and 0.736 eV, respectively. An ideality factor greater than unity indicates that the diode exhibits non-ideal current-voltage behavior. This behavior results from the effect of series resistance and the presence of an interfacial layer. The series resistance and barrier height determined using Norde's method were 6.7 kΩ and 0.77 eV, respectively. The device showed photovoltaic behavior, with a maximum open-circuit voltage of 0.24 V and a short circuit current of 1.7 μA under light of 8 mW/cm2.
Current density-voltage analyses and interface characterization in Ag/DNA/p-InP structures
(American Institute of Physics, 2012-02-15) Güllü, Ömer; Pakma, Osman; Türüt, Abdülmecit
The current density-voltage (J-V) characteristics of Ag/DNA/p-InP metal-insulator-semiconductor (MIS) structures have been investigated in room temperature. We have observed that the Ag/DNA/p-InP structure shows an excellent rectifying behavior and that this structure increases the barrier height (φ b0). The main electrical parameters of these structures, such as ideality factor (n), barrier height, and average series resistance values were found to be 1.087, 0.726 eV, and 66.92Ω. This value of n was attributed to the presence of an interfacial insulator layer at the Ag/p-InP interface and the density of interface states (N ss) localized at the InP/DNA interface. The values of N ss localized at the InP/DNA interface were found at 0.675-E v in the 1.38 × 10 12 eV -1 cm -2.
Current mechanism in HfO 2-gated metal-oxide-semiconductor devices
(Hindawi, 2012-06-19) Pakma, Osman
The present study aimed to examine the current density-voltage (J-V) characteristics of Al/HfO2/p-Si (MOS) structure at temperatures ranging between 100 and 320 K and to determine the structure’s current transport mechanism. The HfO2 film was coated on a single side of the p-Si (111) crystal using the spin coating method. The J-V measurements of the obtained structure at the temperatures between 100 and 320 K revealed that the current transport mechanism in the structure was compatible with the Schottky emission theory. The Schottky emission theory was also used to calculate the structure’s Schottky barrier heights (φB), dielectric constants (εr) and refractive index values of the thin films at each temperature value. The dielectric constant and refractive index values were observed to decrease at decreasing temperatures. The capacitance-voltage (C-V) and conductancevoltage (G/ω-V) characteristics of Al/HfO2/p-Si (MOS) structure was measured in the temperature range of 100–320 K. The values of measured C and G/ω decrease in accumulation and depletion regions with decreasing temperature due to localized Nss at Si/HfO2 interface.
Determination of the laterally homogeneous barrier height of thermally annealed and unannealed Au/p-InP/Zn-Au Schottky barrier diodes
(Elsevier, 2008-03-25) Güllü, Ömer; Turut, Abdulmecit; Asubay, Sezai
We have identically prepared Au/p-InP Schottky barrier diodes (SBDs). The diodes were annealed up to 400 °C thermally. The barrier height (BH) for the as-deposited Au/p-InP/Zn-Au SBDs from the current–voltage characteristics have varied from 0.58 to 0.72 eV, and ideality factor n from 1.14 to 1.47. The BH for the annealed SBDs from the current–voltage characteristics have varied from 0.76 to 0.82 eV, and ideality factor n from 1.17 to 1.39. As a result of the thermal annealing, it has been seen that the BH values of the annealed SBDs are larger than those of the as-deposited SBDs. We have determined a lateral homogeneous BH value of 0.72 eV for the as-deposited Au/p-InP SBD from the experimental linear relationship between barrier heights and ideality factors, and a value of 0.85 eV for the annealed Au/p-InP SBD. The increase of 0.13 eV in the BH value by means of 400 °C annealing has been ascribed to the formation of the excess charges that electrically actives on the semiconductor surface.
Electrical analysis of organic dye based MIS Schottky contacts
(Microelectronic Engineering, 2010-05-25) Güllü, Ömer; Turut, Abdulmecit
In this work, we prepared metal/interlayer/semiconductor (MIS) diodes by coating of an organic film onp-Si substrate. Metal(Al)/interlayer(Orange G@OG)/semiconductor(p-Si) MIS structure had a good recti-fying behavior. By using the forward-biasI–Vcharacteristics, the values of ideality factor (n) and barrierheight (BH) for the Al/OG/p-Si MIS diode were obtained as 1.73 and 0.77 eV, respectively. It was seen thatthe BH value of 0.77 eV calculated for the Al/OG/p-Si MIS diode was significantly larger than the value of0.50 eV of conventional Al/p-Si Schottky diodes. Modification of the potential barrier of Al/p-Si diode wasachieved by using thin interlayer of the OG organic material. This was attributed to the fact that the OGorganic interlayer increased the effective barrier height by influencing the space charge region of Si. Theinterface-state density of the MIS diode was found to vary from 2.79x1013to 5.80x1012eVx1cmx2.
Electrical analysis of organic interlayer based metal/interlayer/semiconductor diode structures
(Journal of Applied Physics, 2009-01) Güllü, Ömer; Turut, Abdulmecit
In this work, metal/interlayer/semiconductor (MIS) diodes formed by coating of an organic film to p-Si semiconductor substrate were prepared. Metal(Al)/interlayer (phenolsulfonphthalein=PSP)/semiconductor(p-Si) MIS device had a good rectifying behavior. By using the forward bias I-V characteristics, the values of ideality factor (n) and barrier height (Phi(b)) for the Al/PSP/p-Si MIS diode were obtained as 1.45 and 0.81 eV, respectively. It was seen that the Phi(b) value of 0.81 eV calculated for the Al/PSP/p-Si MIS diode was significantly larger than value of 0.50 eV of conventional Al/p-Si Schottky diodes. Modification of the interfacial potential barrier of Al/p-Si diode was achieved by using a thin interlayer of the PSP organic material. This has been attributed to the fact that the PSP organic interlayer increases the effective barrier height by influencing the space-charge region of Si. The interface-state density of the MIS diode was determined, and the interface-state density was found to vary from 3.00 x 10(13) to 2.99 x 10(12) eV(-1) cm(-2). (C) 2009 American Institute of Physics.
Electrical characteristics of Co/n-Si schottky barrier diodes using I – V and C – V measurements electrical characteristics of Co/n-Si schottky barrier diodes using I – V and C – V measurements
(Chinese Physics Letters, 2009-06) Güllü, Ömer; Güler, Gülşen; Karataş, Şükrü; Bakkaloğlu, Ömer Faruk
Electrical characteristics of Co/n-Si Schottky barrier diodes are analysed by current-voltage (I – V) and capacitance-voltage (C – V) techniques at room temperature. The electronic parameters such as ideality factor, barrier height and average series resistance are determined. The barrier height 0.76eV obtained from the C – V measurements is higher than that of the value 0.70eV obtained from the I – V measurements. The series resistance RS and the ideality factor n are determined from the d ln(I)/dV plot and are found to be 193.62Ω, and 1.34, respectively. The barrier height and the RS value are calculated from the H(I) – I plot and are found to be 0.71 eV and 205.95Ω. Furthermore, the energy distribution of the interface state density is determined from the forward bias I – V characteristics by taking into account the bias dependence of the effective barrier height. The interface state density Nss ranges from 6.484 × 1011 cm−2eV−1 in (EC – 0.446) eV to 2.801 × 1010 cm−2eV−1 in (EC – 0.631) eV, of the Co/n-Si Schottky barrier diode. The results show the presence of a thin interfacial layer between the metal and the semiconductor.
Electrical characterization of the Al/new fuchsin/n-Si organic-modified device
(Elsevier, 2010-03) Güllü, Ömer; Asubay, Sezai; Turut, Abdulmecit; Aydoğan, Şakir
The current–voltage (I–V) and the capacitance–voltage (C–V) characteristics of the Al/new fuchsin (NF)/n-Si device have been investigated at room temperature. The I–V characteristic of the device shows a good rectification. The ideality factor and the barrier height from the I–V characteristics have been determined as 3.14 and 0.80 eV, respectively. A modified Norde's function combined with the conventional I–V method has been used to extract the parameters including the barrier height and the series resistance. The barrier height and the series resistance obtained from Norde's function have been compared with those from Cheung functions, and it has been seen that there was a good agreement between those from both method. It has also been seen that the values of diode capacitance increased up to the constant values for the forward bias.
Electrical properties of organic–ınorganic semiconductor device based on rhodamine-101
(SpringerLink, 2009-05) Güllü, Ömer; Turut, Abdulmecit; Yıldırım, Nezir; Çakar, Muzaffer
Rhodamine-101 (Rh101) thin films on n-type Si substrates have been formed by means of evaporation, thus Sn/Rh101/n-Si heterojunctions have been fabricated. The Sn/Rh101/n-Si devices are rectifying. The optical energy gaps have been determined from the absorption spectra in the wavelength range of 400 nm to 700 nm. Rh101 has been characterized by direct optical absorption with an optical edge at 2.05 ± 0.05 eV and by indirect optical absorption with␣an optical edge at 1.80 ± 0.05 eV. It was demonstrated that trap-charge-limited current is the dominant transport mechanism at large forward bias. A␣mobility value of μ = 7.31 × 10−6 cm2 V−1 s−1 for Rh101 has been obtained from the forward-bias current–voltage characteristics.
Electrical properties of safranine T p Si organic inorganic semiconductor devices
(Cambridge University, 2010-04-25) Güllü, Ömer; Asubay, Sezai; Biber, Mehmet; Kılıçoğlu, Tahsin; Turut, Abdulmecit
We investigated the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of identically prepared safranine T/p-Si organic/inorganic Schottky devices (total 26 diodes) formed by evaporation of organic compound solution on p-Si semiconductor substrate. It was seen that the safranine T organic thin film on the p-Si substrate showed a good rectifying behavior. The barrier heights and ideality factors of all devices were extracted from the electrical characteristics. The mean barrier height and mean ideality factor from I-V measurements were calculated as 0.59±0.02 eV and 1.80±0.20, respectively. Also, the mean barrier height and mean acceptor doping concentration from C-V measurements were calculated as 0.67±0.10 eV and (6.96±0.37)×1014 cm-3, respectively. The discrepancy in the barrier height values obtained from I-V and C-V characteristics has been attributed to different nature of the measurements. The discrepancy between these values can also be due to the existence of the interfacial native oxide and the organic safranine T thin layer between the semiconductor substrate and top contact metal.
Electronic parameters of high barrier Au/Rhodamine-101/n-Inp Schottky diode with organic interlayer
(Elsevier, 2012-01) Güllü, Ömer; Aydoğan, Şakir; Türüt, Abdülmecit
In this work, we present that Rhodamine-101 (Rh-101) organic molecules can control the electrical characteristics of conventional Au/n-InP metal-semiconductor contacts. An Au/n-InP Schottky junction with Rh-101 interlayer has been formed by using a simple cast process. A potential barrier height as high as 0.88 eV has been achieved for Au/Rh-101/n-InP Schottky diodes, which have good current-voltage (I-V) characteristics. This good performance is attributed to the effect of formation of interfacial organic thin layer between Au and n-InP. By using capacitance-voltage measurement of the Au/Rh-101/n-InP Schottky diode the diffusion potential and the barrier height have been calculated as 0.78 V and 0.88 eV, respectively. From the I-V measurement of the diode under illumination, short circuit current and open circuit voltage have been extracted as 1.70 μA and 240 mV, respectively.
Electronic parameters of MIS Schottky diodes with DNA biopolymer interlayer
(Walter de Gruyter, 2015-09-01) Güllü, Ömer; Türüt, Abdülmecit
In this work, we prepared an ideal Cu/DNA/n-InP biopolymer-inorganic Schottky sandwich device formed by coating a n-InP semiconductor wafer with a biopolymer DNA. The Cu/DNA/n-InP contact showed a good rectifying behavior. The ideality factor value of 1.08 and the barrier height (Φb) value of 0.70 eV for the Cu/DNA/n-InP device were determined from the forward ias I-V characteristics. It was seen that the Φb value of 0.70 eV obtained for the Cu/DNA/n-InP contact was significantly larger tan the value of 0.48 eV of conventional Cu/n-InP Schottky diodes. Modification of the interfacial potential barrier of Cu/n-InP iode was achieved using a thin interlayer of DNA biopolymer. This was attributed to the fact that DNA biopolymer interlayer increased the effective barrier height by influencing the space charge region of InP.

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