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Published Journal Articles



Science Journal of University of Zakho (Issue : 4) (Volume : 8)
This paper reports the fabrication and electrical characterization of hybrid organic-inorganic solar cell based on the deposition of polyaniline (PANI) on n-type GaAs substrate with three different crystal orientations namely Au/PANI/(100) n-GaAs/(Ni-Au), Au/PANI/(110) n-GaAs/(Ni-Au), and Au/PANI/(311)B n-GaAs/(Ni-Au) using spin coating technique. The effect of crystallographic orientation of n-GaAs on solar cell efficiency of the hybrid solar cell devices has been studied utilizing current density-voltage (J-V) measurements under illumination conditions. Additionally, the influence of planes of n-GaAs on the diode parameters of the same devices has been investigated by employing current-voltage (I-V) characteristics in the dark conditions at room temperature. The experimental observations showed that the best performance was obtained for solar cells fabricated with the structure of Au/PANI/(311)B n-GaAs/(Ni-Au). The open-circuit voltage (Voc), short circuit current density (Jsc), and solar cell efficiency (𝜂) of the same device were shown the values of 342 mV, 0.294 mAcm-2, 0.0196%, respectively under illuminated condition. All the solar cell characteristics were carried out under standard AM 1.5 at room temperature. Also, diode parameters of PANI/(311)B n-GaAs heterostructures were calculated from the dark I-V measurements revealed the lower reverse saturation current (Io) of 3.0×10-9 A, higher barrier height (𝜙!) of 0.79 eV and lower ideality factor (n) of 3.16.

Electrical Properties of Sulfonated Polyaniline Thin Film Grown on Different GaAs Substrates

e-Journal of Surface Science and Nanotechnology (Volume : 18)
The paper describes the impact of the crystallographic orienta-tion of an n-type GaAs substrate on the electrical properties of a sulfonated polyaniline (SPAN) thin film with a thickness of 120 nm grown on different n-type GaAs substrates orientation, which are (100), (311)A, and (311)B GaAs planes. Electrical characterization was performed by using current density-voltage (J−V) at room temperature and different temperatures (60−360 K). An ideality factor (n), a Schottky barrier height (Φb), and an activation energy (Ea) were extracted from forward J−V characteristics. From the J−V results, it was obtained that the rectification value at 0.5 V for the SPAN/(311)B GaAs hybrid device is higher than those for SPAN grown on the (100) and (311)A GaAs planes. Furthermore, as the temperature of the three heterojunction devices rises, the value of Φb increases, n drops, and Ea rises. The Ea measurements revealed that Ea for the SPAN/(311)B n-type GaAs heterostructure is lower than those for SPAN samples grown on the (100) and (311)A n-type GaAs planes. This could be related to the low number of defects in SPAN/(311)B than the other two samples. These results make SPAN with a thickness of 120 nm grown on the high index GaAs planes an interesting hybrid device for future devices applications.

Investigation of the effects of GaAs substrate orientations on the electrical properties of sulfonated polyaniline based heterostructures

Applied Surface Science (Volume : 504)
In this work we present a detailed study of the influence of the GaAs substrate orientation on the electrical properties of heterojunctions based on GaAs and sulfonated polyaniline (SPAN) using Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep-Level Transient Spectroscopy (DLTS) and Laplace DLTS techniques. Three different GaAs substrate orientations have been investigated, namely (1 0 0), (3 1 1)A and (3 1 1)B. The I-V results revealed that the turn-on voltage (Von) of SPAN/(3 1 1)B GaAs heterojunction is higher than that for SPAN/(1 0 0) GaAs and SPAN/(3 1 1)A GaAs heterojunctions. The DLTS results showed that the number of electrically active defects present in devices based on the lower index (1 0 0) plane of GaAs substrate is higher than those of higher index (3 1 1)A and (3 1 1)B GaAs substrates, corroborating with I-V results. In order to investigate the role of interface states, capacitance-frequency measurements were performed in forward bias on all three devices.

Characterisation of temperature dependent parameters of multi-quantum well (MQW) Ti/Au/n-AlGaAs/n-GaAs/n-AlGaAs Schottky diodes

Journal of Superlattices and Microstructures (Volume : 111)
Forward and reverse current-voltage (I V) of Ti/Au/n-Al?0.33Ga?0.67As/n-GaAs/n-Al?0.33Ga?0.67As multi-quantum well (MQW) Schottky diodes were measured over a range of temperatures from 20 to 400 K by a step of 20 K. The Schottky diodes parameters were then extracted from these characteristics. The Cheung method is used for this purpose, assuming a thermionic conduction mechanism. The extracted ideality factor decrease with increasing temperatures. But their values at low temperatures were found to be unrealistic. In order to explain this uncertainty, three assumptions were explored. Firstly an assumed inhomogeneous barrier height gave better parameters especially the Richardson constant but the ideality factor is still unrealistic at low temperatures. Secondly, by using numerical simulation, it was demonstrated that defects including interface states are not responsible for the apparent unrealistic Schottky diode parameters. The third assumption is the tunnelling mechanism through the barrier in the low temperature range. At these lower temperatures, the tunnelling mechanism was more suitable to explain the extracted parameters values.

The Effect of Different Thicknesses of Evaporated CdTe Thin Films on The Electrical, Optical and Structural properties

The Journal of The University of Duhok
A different thickness of CdTe thin films were prepared from high purity Cd and Te blended powders by the way and Te blended powders by the way of thermal evaporation technique at a vacuum of 2 of 2*10 -5 mbar. Thin films were prepared on cleaned glass substrates at room temp temperature. The X-ray diffraction patterns for as prepared samples have an amorphous structure. The optical energy gap of the prepared CdTe thin films showed an increase in its value its value as the thickness increases . The minimum optical energy gap of the prepared samples was 1.60 eV for (1.612 nm ) and ) and the maximum optical energy for the sample was 2.226 eV for (2.226 nm).The electrical properties show .The electrical properties show .The electrical properties show.The electrical properties show .The electrical properties show .The electrical properties shows that all samples had an Ohmic contact.

SiC polytypes and doping nature effects on electrical properties of ZnO-SiC Schottky diodes

Journal of Microelectronic Engineering (Volume : 171)
Electrical properties of ZnO/SiC Schottky diodes with two SiC polytypes and N and P doping are investigated. Characterization was performed through I–V and C–V–f measurements. Schottky barrier height (Φb), ideality factor (n), and series resistance (Rs) were extracted from forward I–V characteristics. (Φb), carrier's concentrations (Nd-Na) and (Rs) frequency dependence were extracted from C–V–f characteristics. The extracted n values suggest that current transport is dominated by interface generation-recombination and/or barrier tunneling mechanisms. When changing SiC polytypes, the rectifying ratio of ZnO/n-4HSiC is found to be twice that of ZnO/n-6HSiC. A change in doping nature gave a leakage current ratio of 40 between ZnO/p-4HSiC and ZnO/n-4HSiC. These results indicate that ZnO/p-4HSiC diodes have a complex current transport compared to diodes on n-type SiC. From I-V measurements, barrier height values are 0.63 eV, 0.65 eV and 0.71 eV for heterojunction grown on n-6HSiC, n-4HSiC and p-4HSiC, respectively. C-V measurements gave higher values indicating the importance of interface density of states. Nss values at 1 MHz frequency are 4.54 × 1011 eV−1 cm−2, 3 × 1012 eV−1 cm−2 and 8.13 × 1010 eV−1 cm−2 for ZnO/n-6HSiC, ZnO/n-4HSiC and ZnO/p-4HSiC, respectively. Results indicate the importance of SiC poly types and its doping nature.

Investigation of Electrically Active Defects in InGaAs Quantum Wires Intermediate-Band Solar Cells Using Deep-Level Transient Spectroscopy Technique

Journal of Nanotechnology (Volume : 28)
InGaAs quantum wire (QWr) intermediate-band solar cell–based nanostructures grown by molecular beam epitaxy are studied. The electrical and interface properties of these solar cell devices, as determined by current–voltage (I–V) and capacitance–voltage (C-V) techniques, were found to change with temperature over a wide range of 20–340 K. The electron and hole traps present in these devices have been investigated using deep-level transient spectroscopy (DLTS). The DLTS results showed that the traps detected in the QWr-doped devices are directly or indirectly related to the insertion of the Si δ-layer used to dope the wires. In addition, in the QWr-doped devices, the decrease of the solar conversion efficiencies at low temperatures and the associated decrease of the integrated external quantum efficiency through InGaAs could be attributed to detected traps E1QWR_D, E2QWR_D, and E3QWR_D with activation energies of 0.0037, 0.0053, and 0.041 eV, respectively.

Investigation of defects in indium doped TiO2 thin films using electrical and optical techniques

Journal of Alloys and Compounds (Volume : 698)
Existence of defect levels into the band gap of titanium oxide (TiO2) due to indium (In) doping was investigated by Deep level transition spectroscopy (DLTS), Raman Spectroscopy and photoluminescence (PL). Particularly, two distinct e-beam grown TiO2 thin film (TF) samples on Si substrates were doped using In films with thicknesses of 5 nm and 50 nm instantaneous source. It was observed that the increasing in In doping concentration has changed the TiO2 crystal structure from anatase to rutile phase. In addition, the low doped Ti/Au/5 nm In/TiO2 TF samples showed at 5 V reverse-bias lower leakage current (3.0 x 10-7 A) as compared to the highly doped Ti/Au/50 nm In/TiO2 TF devices (7.0  105 A). The free carrier concentration was increased from about 1014 cm3 to 1015 cm3 for 5 nm In/TiO2 TF to 50 nm In/TiO2 TF devices, respectively. DLTS results have revealed a unique behaviour where a substantial reduction in deep trap concentration was observed in the samples having larger In doping. A PL band around 2.4 eV and 1.9 eV was observed for 5 nm and 50 nm In/TiO2 TF samples, respectively A blue shift of photoluminescence (PL) energy peak with the increase of temperature was also observed for both samples and was associated to defect related emissions. Finally, the shallow activation energy was determined from the temperature dependence of PL spectra. It was observed that the activation energy increased from 25 meV for the low In-doped TiO2 TF samples to 65 meV for the highly In-doped TiO2 TFs.

Electrical performance of conducting polymer (SPAN) grown on GaAs with different substrate orientations

Applied Surface Science (Issue : 386) (Volume : 4)
This article reports the effect of n-type GaAs substrate orientation, namely (100), (311)A and (311)B, onthe electrical properties of sulfonated polyaniline (SPAN)/GaAs heterojunction devices. In addition, the inhomogeneity of the interface between various GaAs substrates and SPAN is investigated in terms of barrier height and ideality factor by performing I–V measurements at different temperatures (20–420 K).The I–V results indicate that the value of the rectification ratio (IF/IR) at 0.5 V is higher for SPAN/(311)B GaAs samples than for SPAN/(100) GaAs and SPAN/(311)A GaAs samples. Moreover, the barrier height decreases and the ideality factor increases with decreasing temperature for all three heterostructure devices. The high value of mean barrier¯˚bof SPAN/(311)B (calculated from the plots of ˚b0as a function of 1/2kT) confirms that the GaAs substrate orientation results in an increase of barrier homogeneities. Furthermore, the C-V characteristics were obtained at room temperature. The C-V measurements showed that the carrier distributions at the interface and away from the interface in high index (311) GaAs orientations are more uniform and have better barrier homogeneity than those grown on the conventional(100) GaAs substrates.

High-performance organic/inorganic hybrid heterojunction based on Gallium Arsenide (GaAs) substrates and a conjugated polymer

Applied Surface Science (Issue : 4) (Volume : 387)
In this paper, we present an extensive study of the electrical properties of organic-inorganic hybridheterojunctions. Polyaniline (PANI) thin films were deposited by a very simple technique on (1 0 0)and (3 1 1)B n-type Gallium Arsenide (GaAs) substrates to fabricate hybrid devices with excellentelectrical properties. The hybrid devices were electrically characterized using current–voltage (I–V),capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) measurements in the temper-ature range 20–440 K. The analysis of I–V characteristics based on the thermionic emission mechanismhas shown a decrease of the barrier height and an increase of the ideality factor at lower temperatures forboth hybrid devices. The interface states were analyzed by series resistance obtained using the C–G–Vmethods. The interface state density (Dit) of PANI/(1 0 0) GaAs devices is approximately one order ofmagnitude higher than that of PANI/(3 1 1)B GaAs devices. This behaviour is attributed to the effect ofcrystallographic orientation of the substrates, and was confirmed by DLTS results as well. Additionally,the devices show excellent air stability, with rectification ratio values almost unaltered after two years ofstorage under ambient conditions, making the polyaniline an interesting conductor polymer for futuredevices applications.

Hyperfine interaction and tuning of magnetic anisotropy of cu doped CoFe2O4 ferrite nanoparticles

Journal of Magnetism and Magnetic Materials (Volume : 411)
Ferrimagnetic oxides may contain single or multi domain particles which get converted into superparamagnetic state near a critical size. To explore the existence of these particles, we have made Mössbauer and magnetic studies of Cu2þ substitution effect in CoFe2xO4 Ferrites (0.0, 0.1, 0.2, 0.3, 0.4, and 0.5). All the samples have a cubic spinel structure with lattice parameters increasing linearly with increase in Cu content. The hysteresis loops yield a saturation magnetization, coercive field, and remanent magnetization that vary significantly with Cu content. The magnetic hysteresis curves shows a reduction in saturation magnetization and an increase in coercitivity with Cu2þ ion substitution. The anisotropy constant, K1, is found strongly dependent on the composition of Cu2þ ions. The variation of saturation magnetization with increasing Cu2þ ion content has been explained in the light of Neel's molecular field theory. Mössbauer spectra at room temperature shows two ferrimagnetically relaxed Zeeman sextets. The dependence of Mössbauer parameters such as isomer shift, quadrupole splitting, line width and hyperfine magnetic field on Cu2þ ion concentration have been discussed.

Electrical Behavior of MBE Grown Interfacial Misfit GaSb/GaAs Heterostructures With and Without Te-Doped Interfaces

IEEE Transactions on Electron Devices (Volume : 62)
A detailed study of interface states in interfacial misfit (IMF) grown GaSb on GaAs substrates is presented. Two types of structures, namely, uncompensated and Te compensated, are investigated using current–voltage, capacitance–frequency, conductance–frequency, and deep level transient spectroscopy techniques. Our studies reveal that incorporation of Te at the interface (IMF) causes a degradation of the Te-compensated devices. A higher number of electrical active defects and higher value of interface states are detected in Te-compensated IMF GaSb/GaAs devices compared with as-grown IMF GaSb/GaAs devices.

Analysis of deep level defects in GaN p-i-n diodes after beta particle irradiation

Electronics (Issue : 4) (Volume : 4)
The effect of beta particle irradiation (electron energy 0.54 MeV) on the electrical characteristics of GaN p-i-n diodes is investigated by current-voltage (I-V), capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) measurements. The experimental studies show that, for the as-grown samples, three electron traps are found with activation energies ranging from 0.06 to 0.81 eV and concentrations ranging from 1.2 × 1014 to 3.6 × 1015 cm−3, together with one hole trap with energy depth of 0.83 eV and concentration of 8 × 1014 cm−3. It has been found that the irradiation has no effect on these intrinsic defects. The irradiation affected only a shallow donor level close to Ec [0.06 eV-0.18 eV] on the p-side of the p-i-n junction.

12. Thin Film Deposition Processes

International Journal of Modern Physics and Applications (Volume : 1)
small thickness that produces by physical vapour deposition (PVD) and chemical vapour deposition (CVD). Despite the PVD technique has a few drawbacks, it remains an important method and more beneficial than CVD technique for depositing thin films materials. This project examines some remarkable similarities and differences between PVD and CVD systems as well as evaluates the different techniques of depositing thin film. The majority of researchers have attempted to explain and justify the most precise system for depositing thin film since it is important in several applications such as surgical/medical and automotive. It is concluded that the most efficient method of depositing is PVD process. In addition, it has been found that there are more differences than similarities between PVD and CVD processes.

Rapid thermal annealing: An efficient method to improve the electrical properties of tellurium compensated Interfacial Misfit GaSb/GaAs heterostructures

Superlattices and Microstructures (Volume : 88)
The effect of thermal annealing on Te compensated Interfacial Misfit GaSb/GaAs heterostructures is investigated by using two different thermal annealing procedures, namely rapid thermal annealing and furnace annealing. The electrical properties of the devices are studied by using Current-Voltage, Capacitance-Voltage and Deep Level Transient Spectroscopy techniques. It is observed that rapid thermal annealing treatment is superior in terms of improvement of the electrical characteristics compared to furnace annealing treatment. The lowest leakage current and defect concentration are obtained when rapid thermal annealing is employed.

Modeling the effect of deep traps on the capacitance-voltage characteristics of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates

Materials Science in Semiconductor Processing (Issue : 8) (Volume : 36)
Numerical simulation, using SILVACO-TCAD, is carried out to explain experimentally observed effects of different types of deep levels on the capacitance–voltage characteristics of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates.Two diodes were grown on (311)A and (211)A oriented GaAs substrates using Molecular Beam Epitaxy (MBE).Although,deep levels were observed in both structures, the measured capacitance–voltage characteristics show a negative differential capacitance (NDC) for the (311)A diodes, while the (211)A devices display a usual behaviour. The NDC is related to the nature and spatial distribution of the deep levels, which are characterized by the Deep Level Transient Spectroscopy (DLTS) technique. In the (311)A structure only majority deep levels (hole traps) were observed while both majority and minority deep levels were present in the (211)A diodes. The simulation, which calculates the capacitance–voltage characteristics in the absence and presence of different types of deep levels, agrees well with the experimentally observed behaviour.

Effect of post growth annealing treatment on Interfacial Misfit GaSb/GaAs

Materials Science in Semiconductor Processing (Issue : 5) (Volume : 36)
Post-growth annealing treatments in the range 400–600 1C are performed on GaSb/GaAs Interfacial Misfit grown samples. Current density–voltage(J–V), Capacitance–voltage(C–V), capacitance–frequency (C–F) and Deep Level Transient Spectroscopy(DLTS) measurements are performed on as-grown and annealed samples.Ourstudiesshowthatpossibledefectcompensationisobservedwiththeannealing treatments, resulting in a significant improvement in the performances of the devices.

Investigation of the Effects of Gamma Radiation on the Electrical Properties of Dilute GaAs1-xNx Layers Grown by Molecular Beam Epitaxy

Current Applied Physics (Volume : 15)
This work reports the effect of gamma (g-) irradiation on dilute GaAsN with nitrogen concentrations ranging from 0.2 to 1.2% with post-irradiation stability using Current-Voltage (I-V) and Deep Level Transient Spectroscopy (DLTS) measurements in the temperature range from 10 K to 450 K. The I-V results indicate that the irradiation effect was more pronounced in the samples with nitrogen concentration of 0.4%. Additionally, the irradiated samples showed an ideality factor higher than the as-grown samples. On the other hand, for temperatures above 265 K the barrier height of the irradiated samples with 0.8% nitrogen is higher than the as-grown samples. The DLTS measurements revealed that after irradiation the number of traps either decreased remained constant, or new traps are created depending on the concentration of nitrogen. For samples with N ¼ 0.2% e 0.4% the number of traps after irradiation decreased, whereas for samples with N ¼ 0.8%  1.2 % the number of traps remained the same. However, the properties of some traps such as capture cross-sections and density increased by about 2 orders of magnitude. The origin of the defects present before and after irradiation are discussed and correlated.

X-Ray Diffraction and DC Electrical Conductivity for Te61.8Se38.2 Thin Films

International Journal of Science and Research (IJSR) (Issue : 8) (Volume : 3)
Vacuum alloying system was designed and built up to alloy (Te61.8Se38.2). Te61.8Se38.2thin films were prepared by thermal evaporating system under pressure about (5×10-5) mbar. Three thin films samples were prepared in one evaporation run, one in the center of the evaporation source and the other two beside it (using flat substrate holder) to study the effect of evaporation angle on properties of Te61.8Se38.2 thin film. X-ray fluorescence (XRF) has been used to investigate the purity of the primary materials and Te61.8Se38.2 alloy.Also (XRD) system has been used to investigate the structure of the Te61.8Se38.2 alloy and Te61.8Se38.2thin films.The electrical measurements of thin film samples, showed that the center sample hasan activation energy (0.575eV and its thickness 415 nm) and for sided sample has an activation energy (0.61eV and its thickness 340 nm).

Deep traps and temperature effects on the capacitance of p-type Si-doped GaAs Schottky diodes on (211) and (311) oriented GaAs substrates

Superlattices and Microstructures (Issue : 8) (Volume : 65)
The SILVACO-TCAD numerical simulator is used to explain the effect of different types of deep levels on the temperature dependence of the capacitance of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates, namely (311)A and (211)A oriented GaAs substrates. For the (311)A diodes, the measured capacitance–temperature characteristics at different reverse biases show a large peak while the (211)A devices display a much smaller one. This peak is related to the presence of different types of deep levels in the two structures. These deep levels are characterized by the Deep Level Transient Spectroscopy (DLTS) technique. In the (311)A structure only majority deep levels (hole deep levels) were observed while both majority and minority deep levels were present in the (211)A diodes. The simulation software, which calculates the capacitance–voltage and the capacitance–temperature characteristics in the absence and presence of different types of deep levels, agrees well with the experimentally observed behavior of the capacitance–temperature properties. A further evidence to confirm that deep levels are responsible for the observed phenomenon is provided by a simulation of the capacitance–temperature characteristics as a function of the ac-signal frequency.

Deep-level transient spectroscopy of interfacial states in "buffer-free" p-i-n GaSb/GaAs devices

Applied Physics (Issue : 13) (Volume : 14)
A systematic study was carried out on defect states in Interfacial Misfit (IMF) unpassivated and Tepassivated IMF in p-i-n GaSb/GaAs devices using Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS. Additionally, Current-Voltage (I–V) measurements were performed, which showed that the turn-on voltage (Von) of passivated samples is lower than that for unpassivated samples; an effect which can be explained by the introduction of new defects states near to the interface of GaSb/GaAs, where Te was incorporated to passivate the IMF. The Capacitance-Voltage (C-V) analysis demonstrates that these new states are the consequence of adding Te at the misfit of GaSb/GaAs. Furthermore, DLTS measurements reveal a distribution of states including a main midgap energy level, namely the well documented EL2 trap, with some peculiar behaviour. Most of these levels are related to interface states that are generated by the mismatch between GaAs and GaSb. Originally, the addition of Te atoms was thought to passivate these interface states. On the contrary, this paper, which attempts at correlating the current-voltage and capacitance-voltage characteristics to the DLTS results, shows clearly that Te atoms increase the density of interface states.