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Citation - WoS: 2
Citation - Scopus: 3
Electrical Characterization of Zninse₂ Thin-Film Heterojunction
(Springer, 2019) Gullu, H. H.; Parlak, M.
ZnInSe2/Cu0.5Ag0.5InSe2 diode structures have been fabricated by thermal evaporation of stacked layers on indium tin oxide-coated glass substrates. Temperature-dependent dark current-voltage measurements were carried out to extract the diode parameters and to determine the dominant conduction mechanisms in the forward- and reverse-bias regions. The heterostructure showed three order of magnitude rectifying behavior with a barrier height of 0.72 eV and ideality factor of 2.16 at room temperature. In the high forward-bias region, the series and shunt resistances were calculated with the help of parasitic resistance relations, yielding room-temperature values of 9.54 x 10(2) Omega cm(2) and 1.23 x 10(3) Omega cm(2), respectively. According to the analysis of the current flow in the forward-bias region, abnormal thermionic emission due to the variation of the ideality factor with temperature and space-charge-limited current processes were determined to be the dominant conduction mechanisms in this heterostructure. In the reverse-bias region, the tunneling mechanism was found to be effective in the leakage current flow with trap density of 10(6) cm(-3). Spectral photocurrent measurements were carried out to investigate the spectral working range of the device structure. The main photocurrent peaks observed in the spectrum corresponded to the band-edge values of the active thin-film layers.
Citation - WoS: 11
Citation - Scopus: 10
Optical Conduction in Amorphous Gase Thin Films
(Elsevier Gmbh, 2016) Qasrawi, A. F.; Khanfar, Hazem. K.; Kmail, Renal R. N.
In this work, the optical conduction mechanism in GaSe thin films was explored by means of dielectric spectral analysis in the 270-1000 THz range of frequency. The GaSe films which are found to be amorphous in nature are observed to follow the Lorentz approach for optical conduction. The modeling of the optical conductivity which takes into account the damped electronic motion resulting from the collision of photogenerated carriers with impurities, phonons and other damping sources allowed determining the optical conduction parameters. Particularly, an average carrier scattering time, a free carrier density, a reduced resonant frequency, a field effect mobility and an electron bounded plasma frequency of 0.142 (fs), 1.7 x 10(19) (cm(-3)), 875.8 (THz), 1.25 (cm(2)/Vs) and 82.8 (THz), respectively, were determined. These parameters are promising as they indicate the applicability of GaSe in the technology of mid-infrared plasmonic nanoantennas. In addition, the dielectric optical signal which displayed a resonance peak at 500 THz seems to be attractive for use in passive modes operating optoelectronic devices like field effect transistors as they exhibit an increasing signal quality factor with decreasing incident light frequency (C) 2016 Elsevier GmbH. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 5
Structural and Optical Properties of Thermally Evaporated (gase)0.75-(gas)0.25 Thin Films
(Elsevier Gmbh, 2021) Isik, M.; Işık, Mehmet; Emir, C.; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics Engineering
GaSe and GaS binary semiconducting compounds are layered structured and have been an attractive research interest in two-dimensional material research area. The present paper aims at growing (GaSe)0.75 - (GaS)0.25 (or simply GaSe0.75S0.25) thin film and investigating its structural and optical properties. Thin films were prepared by thermal evaporation technique using evaporation source of its single crystal grown by Bridgman method. The structural properties were revealed using x-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. XRD pattern and EDS analyses indicated that thin films annealed at 300 ?C were successfully deposited and its structural characteristics are well-consistent with its single crystal form. Surface morphology was studied by means of SEM and AFM measurements. Optical properties were investigated by transmission and Raman spectroscopy techniques. Raman spectrum exhibited three peaks around 172, 242 and 342 cm-1. Analyses of transmission spectrum revealed the direct band gap energy as 2.34 eV. The mixed compounds of GaSe0.75S0.25 were prepared for the first time in a thin film form and the results of the present paper would provide valuable information to research area in which layered compounds have been studied in detail.
Citation - WoS: 4
Citation - Scopus: 4
Physical Characterization of Thermally Evaporated Sn-Sb Thin Films for Solar Cell Applications
(Springer Heidelberg, 2023) Bektas, Tunc; Surucu, Ozge; Terlemezoglu, Makbule; Parlak, Mehmet
The substitution of Sb in binary SnSe structure may lead to tailoring the physical properties of both SnSe and SbSe, promising absorber layers for thin film solar cells. The resulting Sn-Sb-Se structure could be an outstanding material for photovoltaic applications. In this study, Sn-Sb-Se thin films were deposited by thermal evaporation, and the effect of annealing on the films' structural, optical, and electrical properties were reported. XRD measurement shows that annealing at 300 degrees C yields the best crystalline quality, and structural parameters were calculated using XRD data. SEM and AFM measurements indicate deformation in the film surface after annealing at 400 degrees C. UV-Vis spectroscopy measurement provides a high absorption coefficient which indicates a direct band gap. The band gap and activation energies of the as-grown sample were found as 1.59 eV and 106.1 meV, respectively. The results of SEM, AFM, XRD, Raman, UV-Vis spectroscopy and temperature-dependent photoconductivity measurements were discussed throughout the paper.
Citation - WoS: 8
Citation - Scopus: 9
Investigation of Electrical Properties of In/Znin_{2< Diode}
(indian Acad Sciences, 2019) Gullu, H. H.
In/ZnIn2Te4/n-Si/Ag diode structure was fabricated by the thermal deposition of a ZnIn2Te4 thin film on n-Si wafer substrate with Ag metal back contact. The structural characteristics of the film were investigated in terms of composition, X-ray diffraction and topographic measurements. The diode structure was completed by evaporating In metal on the film surface as a top contact. The diode parameters as saturation current, barrier height, ideality factor and series resistance values were determined from the semi-logarithmic forward bias current-voltage characteristics of the diode. According to the assumption of the thermionic emission model, the ideality factor was found higher than unity and it was also observed that the barrier height and ideality factor showed a temperature-dependent profile resulting from the non-ideality in the current-voltage behaviour of the diode. As a result, the model was modified by considering inhomogeneous barrier formation and Gaussian distribution was expected to be dominant on 1.37 eV mean barrier height with a deviation of 0.18. In addition, the voltage dependence of these Gaussian diode parameters was investigated. The forward and reverse bias capacitance and conductance measurements showed that there was a slight change in capacitance values with frequency whereas the conductance values decreased with increase in frequency. In addition to the current-voltage analysis, the distribution of density of interface states and the values of series resistance were evaluated as a function of bias voltage and frequency.
Citation - WoS: 5
Citation - Scopus: 5
Improvement of Electrical Characteristics of Snse/Si Heterostructure by Integration of Si Nanowires
(Elsevier, 2021) Coskun, E.; Gullu, H. H.; Emir, C.; Parlak, M.
In this study, the effects of the nanowire geometry on Si wafer substrate were investigated for the SnSe/Si-nanowire heterojunction device and the obtained results were compared with the one fabricated on planar Si surface. Nanowires on Si surface were produced by metal-assisted etching method and the SnSe film layer was deposited by thermal evaporation technique. On both Si and glass surfaces, deposited film shows polycrystalline and single SnSe phase. From optical transmission measurements, optical band gap of this film was determined as 1.36 eV in a good agreement with the literature. All SnSe/Si heterostructures were found in a p-n diode behavior and the ideality factor and series resistance values were calculated as 2.40, 547 Omega, and 3.71, 1.57 x 10(3) Omega, for SnSe/Si-nanowire and SnSe/Si heterojunctions, respectively. As a result, an improvement in device characteristics concerning the planar Si structure was found by utilizing Si nanowire structure.
Citation - WoS: 25
Citation - Scopus: 26
Determination of Current Transport Characteristics in Au-cu/Cuo Schottky Diodes
(Elsevier, 2019) Surucu, O. Bayrakli; Gullu, H. H.; Terlemezoglu, M.; Yildiz, D. E.; Parlak, M.
In this study, the material properties of CuO thin films fabricated by sputtering technique and electrical properties of CuO/n-Si structure were reported. Temperature-dependent current-voltage (I-V) measurement was carried out to determine the detail electrical characteristics of this structure. The anomaly in thermionic emission (TE) model related to barrier height inhomogeneity at the interface was obtained from the forward bias I-V analysis. The current transport mechanism at the junction was determined under the assumption of TE with Gaussian distribution of barrier height. In this analysis, standard deviation and mean zero bias barrier height were evaluated as 0.176 and 1.48 eV, respectively. Depending on the change in the diode parameters with temperature, Richardson constant was recalculated as 110.20 Acm(-2)K(-2) with the help of modified Richardson plot. In addition, density of states at the interface were determined by using the forward bias I-V results.
Citation - WoS: 10
Citation - Scopus: 10
Electrical Characterization of Cdznte/Si Diode Structure
(Springer Heidelberg, 2020) Balbasi, C. Dogru; Terlemezoglu, M.; Gullu, H. H.; Yildiz, D. E.; Parlak, M.
Temperature-dependent current-voltage (I - V), and frequency dependent capacitance-voltage (C - V) and conductance-voltage (G - V) measurements were performed in order to analyze characteristics of CdZnTe/Si structure. Obtained profiles enable us to understand the different characteristics of the diode structure such as the carrier conduction mechanism and the nature of the interfacial layer. Over the temperature range between 220 and 340 K, taking consideration of the disparity in the forward-biased current, the diode parameters such as saturation current (I-0), zero-bias barrier height (Phi(B0)) and ideality factor (n) have been obtained. The barrier height increased (0.53 to 0.80 eV) while the ideality factor decreased (4.63 to 2.79) with increasing temperature from 220 to 340 K, indicating an improvement in the junction characteristics at high temperatures. Due to the inhomogeneity in barrier height, the conduction mechanism was investigated by Gaussian distribution analysis. Hence, the mean zero-bias barrier height ((Phi) over bar (B0)) and zero-bias standard deviation (sigma(0)) were calculated as 1.31 eV and 0.18, respectively. Moreover, for holes in p-type Si, Richardson constant was found to be 32.09 A cm(-2) K-2 via modified Richardson plot. Using the capacitance-voltage (C - V) and conductance-voltage (G - V) characteristics, series resistance (R-s) and density of interfacial traps (D-it) have been also investigated in detail. A decreasing trend for R-s and D-it profiles with increasing frequency was observed due to the impurities at the CdZnTe/Si interface and interfacial layer between the front metal contact and CdZnTe film.
Citation - WoS: 1
Citation - Scopus: 1
Material Characterization of Thermally Evaporated Znsn₂te_{4< Thin Films}
(Elsevier Gmbh, Urban & Fischer verlag, 2019) Gullu, H. H.
Polycrystalline and stoichiometric ZnSn2Te4 (ZST) thin films were deposited on glass substrates by sequential evaporation of elemental powder sources. The deposited films were annealed in nitrogen atmosphere at annealing temperature ranging 100-300 degrees C. Under post-annealing treatments, the composition, structural, surface morphological, optical and electrical characteristics of the films were investigated. Annealing treatments lead to maintain the structural characteristics with the possible change in atomic concentration of the constituent elements in limit of detection and crystallinity of the films increased with increasing annealing temperature. Grainy surface morphology was observed in as-grown and annealed films and densely packed appearance of the surface of the samples indicates uniform deposition of the film over the entire substrate surface. Under the aim of visible light harvesting in the applications of thin film photovoltaics, normal-incidence transmittance measurements were performed and the direct band gap values were found in the range of 1.8-2.1 eV. Temperature dependent conductivity characteristics of the films were investigated under dark condition and the observed conductivity profiles were found in Arrhenius behavior with temperature dominated by the thermionic emission model.
Citation - WoS: 22
Citation - Scopus: 24
Synthesis and Temperature-Tuned Band Gap Characteristics of Magnetron Sputtered Znte Thin Films
(Elsevier, 2020) Isik, M.; Gullu, H. H.; Parlak, M.; Gasanly, N. M.
Zinc telluride (ZnTe) is one of the attractive semiconducting compounds used in various optoelectronic devices. The usage of ZnTe in optoelectronic applications directs researchers to search its optical characteristics in great detail. For this purpose, structural and optical properties of magnetron sputtered ZnTe thin films were studied by means of x-ray diffraction and transmission spectroscopy measurements. Structural analyses indicated that ZnTe thin films having cubic crystalline structure were successfully grown on soda-lime glass substrates. Transmittance spectra in the 400-1000 nm were recorded in between 10 and 300 K temperature region. The analyses of absorption coefficient spectra resulted in band gap energies decreasing from around 2.31 (10 K) to 2.26 eV (300 K). Temperature dependency of gap energy was studied by Varshni and O'Donnell-Chen relations to determine various optical parameters like absolute zero temperature band gap energy, change of gap energy with temperature, phonon energy.

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