Mohamed Fathallah - Academia.edu (original) (raw)

Papers by Mohamed Fathallah

Journal of Non-Crystalline Solids

The electrical properties were extracted by I-V and C-V analysis, performed from 10 K to 450 K. W... more The electrical properties were extracted by I-V and C-V analysis, performed from 10 K to 450 K. When the annealing temperature varied to 400 °C, the Schottky barrier height (SBH) increased from 0.85 Ev to 1.20 eV in Ti/4H-SiC whereas in the Mo/4H-SiC the SBH varied from 1.04 eV to 1.10 eV. Deformation of J-V-T characteristics was observed in two types of devices when the temperature decreases from 300 K to 10 K. The electrical properties and the stability of the devices have been correlated to the fabrication processes and to the metal/semiconductor interfaces. Mo-based contacts show better behaviour in forward polarization when compared to the Ti-based Schottky contacts, with ideality factors close to the unity even after the annealing process. However, Mo-based contacts show leakage currents higher than that measured on the more optimized Ti-based Schottky.

Annales de Chimie Science des Matériaux

Philosophical Magazine B: Physics of Condensed Matter

The constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS) have been u... more The constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS) have been used as complementary techniques to measure the density-of-states distribution and the different optical parameters in hydrogenated amorphous silicon-nitrogen alloy (a-SiN : H). Constants such as the optical gap Eg, the Urbach edge EU or valence-band edge E0V were obtained directly from the CPM or photothermal deflection spectra. The height of the midgap-defect density of states, its wideness or the conduction-band edge have been deduced by applying a deconvolution procedure to the measured absorption spectra. The density of surface states was also calculated. The results were based on the different sensitivities of the CPM and PDS to transitions involving unoccupied defects and surface states. We have studied the influence of nitrogen incorporation in a-SiN : H samples and the effect of hydrogen dilution.

We have synthesized and used several natural dyes such as extracted from: Spinach, Beet, Henna, S... more We have synthesized and used several natural dyes such as extracted from: Spinach, Beet, Henna, Strawberry, Red cabbage, and Mloukhia. The absorption of the extracted dyes diluted in ethanol or distilled water were measured using UV–Vis spectrophotometer. We have studied the topology of these films by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) patterns of synthesized TiO2. The contents of Ti and O of synthesized TiO are 30 % and 50 % corresponding to closely Ti4+ state. The absorption of the TiO2 thin films immersed in these dyes was also measured in order to tune the change. The absorption in Beet and Red cabbage is more significant compared to other natural dyes.

Journal of Non-Crystalline Solids

We present results on optical, structural and electrical properties of a-Si1−xCx:H films deposite... more We present results on optical, structural and electrical properties of a-Si1−xCx:H films deposited by plasma enhanced chemical vapor deposition in the low power regime, with C fraction from 0 to 0.28. The absorption coefficient has been obtained in the region 0.73–4.5eV by means of ellipsometry, reflectance–transmittance and photothermal deflection spectroscopy. The addition of carbon in the alloy increases the disorder and the density of defects: samples deposited with high carbon content have poorer optoelectronic properties. Two conduction regimes are observed: extended state conduction and hopping conduction in the conduction band tail. A visible PL peak that widens and shifts to higher energies as the carbon content increases has been observed.

Materials Science Forum, 2005

The optical and electrical properties of undoped and low doped polycrystalline silicon films depo... more The optical and electrical properties of undoped and low doped polycrystalline silicon films deposited by LPCVD technique are analysed. Photothermal deflexion spectroscopy, and electrical conductivity in the temperature range 50-475 K are used. The effect of low phosphorus doping on the density of defects, electrical parameters and hopping conduction are examined and interpreted in conjunction with the passivation of defects by the introduction of phosphorus atoms. The density of states at the Fermi level is also calculated.

Materials Science and Engineering: C, 2008

Typical power switching devices such as diodes, thyristors, and transistors are based on a monocr... more Typical power switching devices such as diodes, thyristors, and transistors are based on a monocrystalline silicon semiconductor or silicon carbide. Silicon is less expensive, more widely used, and a more versatile processing material than silicon carbide. The silicon carbide (SiC) has ...

2013 International Conference on Electrical Engineering and Software Applications, 2013

:H) at AM1.5. All parameters are determined such as efficiency and filling factor. In the dark, t... more :H) at AM1.5. All parameters are determined such as efficiency and filling factor. In the dark, the static and dynamic parameters of diode are deduced. Defects in the intrinsic layer are evaluated by photothermal deflexion spectroscopy technique. All the measured parameters are used by the solar cell capacitance simulator (SCAPS 3.2). The structure of solar cells and the experimental conditions were introduced in simulator. The experimental I-V and spectral response characteristics were correlated to the simulated ones. The simulation shows that increase in defects density, reduces the electrical parameters of amorphous solar cells. The effect of the gap value is more important to define the efficiency of the solar cell made by a-SiC:H materials.

Philosophical Magazine Part B, 2002

Wide-bandgap hydrogenated amorphous silicon-carbon and silicon-nitrogen films having optical gaps... more Wide-bandgap hydrogenated amorphous silicon-carbon and silicon-nitrogen films having optical gaps in the range 1.9-4.0 eV have been deposited by the 13.56 MHz plasma-enhanced chemical vapour deposition technique from SiH4 + C2H2 (+H2), SiH4 + NH3 (+H2), gas mixtures. The deposition conditions have been chosen so as to obtain device-quality films already successfully applied in optoelectronic technology. The films have been

Materials Science Forum, 2010

Optical and electrical properties amorphous carbon nitride (a-CN) has been investigated on films ... more Optical and electrical properties amorphous carbon nitride (a-CN) has been investigated on films deposited by reactive R.F. sputtering source with a graphite target. The amorphous carbon nitride samples were prepared under a gas mixture of nitrogen (N 2 ) and /or Argon (Ar).The optical transitions are governed by the π and π* electronic state distributions, related to sp 2 -and sp 1hybridized C and N atoms. Specific lonepair electronic states arise from groups (CN) with sp 1hybridized C atoms, which may form C≡N triple bonds or -N=C=N-longer chains. Photoluminescence spectra show a maximum around 650 nm. Two conduction regimes at high and low temperature are found in a-CN samples. The corresponding activation energies decrease with the increase of target voltage.

2012 16th IEEE Mediterranean Electrotechnical Conference, 2012

The wide band gap (3.2 eV) allows the silicon carbide (SiC) to work at high temperatures with hig... more The wide band gap (3.2 eV) allows the silicon carbide (SiC) to work at high temperatures with high voltages and currents, to switch large power densities and reduce losses. The 4H-SiC polytype is the most widely used material for electronic applications. Despite the development of manufacturing technology of SiC wafers, this material has structural defects, such as micropipes, dislocations and inclusions of polytypes. In this paper, the defects and dynamic performance of the SiC Schottky diodes is studied and the obtained maximum reverse voltage is 600V. The reverse recovery time is evaluated to 135ns. The results demonstrate the effectiveness of the SiC devices in reducing the overall system losses generated by switching transitions compared to silicon based diodes. We introduced the parameters found in the Ti/4H-SiC Schottky diode in the Pspice model for simulation. We compared these results with the model using Matlab-Simulink to see the behavior of the switching cell and to deduce the equivalent circuit of diode in dynamic transitions.

Solid-State Electronics, 2006

UV photosensors based on a-Si:H/a-SiC:H were deposited by ultra high vacuum plasma enhanced chemi... more UV photosensors based on a-Si:H/a-SiC:H were deposited by ultra high vacuum plasma enhanced chemical vapour deposition system (UHV-PECVD) over a large area (10 cm · 10 cm) in p-i-n configuration.

Solid-State Electronics, 2007

p-i-n Heterostructures deposited by ultra high vacuum plasma enhanced chemical vapour deposition ... more p-i-n Heterostructures deposited by ultra high vacuum plasma enhanced chemical vapour deposition (UHV-PECVD) using silane and methane gases with and without hydrogen dilution of the i-layer have been studied. Amorphous silicon carbon alloy (a-SiC:H) has been used in the p + and i-layers and amorphous silicon (a-Si:H) in the n layer. The effect of hydrogen dilution on the defect properties of i-layer films has been studied by photothermal deflection spectroscopy and constant photocurrent method. Hydrogen dilution of the ilayer changes the J (V) characteristics and notably under illumination: the fill factor decreases, the short-circuit current density J sc increases and, moreover, a cross over was observed between J (V) characteristics in dark and under illumination of the diluted cells. A two diodes model has been used to explain this phenomenon. Measurements of the diode junction capacity show higher capacitance in the diluted i-layer p-i-n structure than in the undiluted ones at low frequencies. This effect is due to the decrease of the defects density induced mainly by the increase of the capture reemission time (or delay time) of charges.

Solid-State Electronics, 2007

The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in ... more The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in amorphous silicon and its compounds are the object of intense research works. By starting on the concept that such p-i-n structures can be compared to p + -n and n-n + junctions in series, and by referring to Shockley's model in one modified diode, we propose an equivalent electrical circuit in dynamic state of the considered structure resulting from a series association of Shockley's model. A simulation study by PSPICE of the equivalent electrical circuit so obtained is in good agreement with the experimental results, and physical interpretations connected to this model are discussed.

Philosophical Magazine, 2007

The local microstructure and optical and electrical properties were investigated of amorphous car... more The local microstructure and optical and electrical properties were investigated of amorphous carbon nitride (a-CN) films deposited by reactive radio-frequency (RF) sputtering. Two series prepared in nitrogen or in a nitrogen and argon mixture were studied. The optical properties were investigated by transmittance/reflectance and photothermal deflection spectroscopies. Combined infrared measurements and Raman scattering spectroscopies were used to investigate the microstructure of a-CN films in terms of nitrogen incorporation within the films and C sp content. These experiments were completed by dark electrical conductivity measurements performed in coplanar configuration in the temperature range 50–450 K. The films exhibit semiconductor behaviour and the temperature dependence suggests two types of conduction. An increase in nitrogen incorporation induces an increase with clustering of sp phase replacing C=C olefinic groups with aromatic groups.

Microelectronic Engineering, 2013

We have studied and compared two types of Schottky diodes prepared by the evaporation of molybden... more We have studied and compared two types of Schottky diodes prepared by the evaporation of molybdenum (Mo) and titanium (Ti) on a 4H-SiC semiconductor. The electrical characteristics of these diodes are analyzed based on the standard thermionic emission model. The main electrical parameters including the series resistance R s , the ideality factor n and the barrier height U B are extracted from current-voltage-temperature (I-V-T) measurements. In the Ti/4H-SiC structure, the series resistance increases from 1.51 mO cm 2 to 27.68 mO cm 2 when the temperature is varied from 70 K to 450 K. In contrast, the series resistance does not exceed a 6.17 mO cm 2 at 450 K in the Mo/4H-SiC Schottky diode. We have decomposed the series resistance into three components. The deduced static and dynamic parameters were used to define an electrical model. The switching behavior of the equivalent circuit indicates a reverse recovery time (Trr) of 1.412 ns for Ti/4H-SiC and 3.27 ns for Mo/4H-SiC.

Materials Science and Engineering: C, 2006

The optical and electrical properties of amorphously deposited and then post-crystallized silicon... more The optical and electrical properties of amorphously deposited and then post-crystallized silicon films are studied as a function of the deposition pressure and the phosphorus doping. Amorphous silicon films are deposited in a high pressure regime by SAPCVD (Sub-Atmospheric ...

Materials Science and Engineering: C, 2008

The paper deals with the effect of slightly phosphorus atoms introduced during deposition of poly... more The paper deals with the effect of slightly phosphorus atoms introduced during deposition of polysilicon films. Polysilicon films are used as an active layer in thin film transistors (TFTs) fabricated on glass substrates at a maximum temperature of 600 °C.Three phosphorus atoms contents, determined by the value of the phosphine to silane ratio: Γ (3.7×10−7, 8×10−7, 26×10−6), are used to optimize

Journal of Non-Crystalline Solids

The electrical properties were extracted by I-V and C-V analysis, performed from 10 K to 450 K. W... more The electrical properties were extracted by I-V and C-V analysis, performed from 10 K to 450 K. When the annealing temperature varied to 400 °C, the Schottky barrier height (SBH) increased from 0.85 Ev to 1.20 eV in Ti/4H-SiC whereas in the Mo/4H-SiC the SBH varied from 1.04 eV to 1.10 eV. Deformation of J-V-T characteristics was observed in two types of devices when the temperature decreases from 300 K to 10 K. The electrical properties and the stability of the devices have been correlated to the fabrication processes and to the metal/semiconductor interfaces. Mo-based contacts show better behaviour in forward polarization when compared to the Ti-based Schottky contacts, with ideality factors close to the unity even after the annealing process. However, Mo-based contacts show leakage currents higher than that measured on the more optimized Ti-based Schottky.

Annales de Chimie Science des Matériaux

Philosophical Magazine B: Physics of Condensed Matter

The constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS) have been u... more The constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS) have been used as complementary techniques to measure the density-of-states distribution and the different optical parameters in hydrogenated amorphous silicon-nitrogen alloy (a-SiN : H). Constants such as the optical gap Eg, the Urbach edge EU or valence-band edge E0V were obtained directly from the CPM or photothermal deflection spectra. The height of the midgap-defect density of states, its wideness or the conduction-band edge have been deduced by applying a deconvolution procedure to the measured absorption spectra. The density of surface states was also calculated. The results were based on the different sensitivities of the CPM and PDS to transitions involving unoccupied defects and surface states. We have studied the influence of nitrogen incorporation in a-SiN : H samples and the effect of hydrogen dilution.

We have synthesized and used several natural dyes such as extracted from: Spinach, Beet, Henna, S... more We have synthesized and used several natural dyes such as extracted from: Spinach, Beet, Henna, Strawberry, Red cabbage, and Mloukhia. The absorption of the extracted dyes diluted in ethanol or distilled water were measured using UV–Vis spectrophotometer. We have studied the topology of these films by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) patterns of synthesized TiO2. The contents of Ti and O of synthesized TiO are 30 % and 50 % corresponding to closely Ti4+ state. The absorption of the TiO2 thin films immersed in these dyes was also measured in order to tune the change. The absorption in Beet and Red cabbage is more significant compared to other natural dyes.

Journal of Non-Crystalline Solids

We present results on optical, structural and electrical properties of a-Si1−xCx:H films deposite... more We present results on optical, structural and electrical properties of a-Si1−xCx:H films deposited by plasma enhanced chemical vapor deposition in the low power regime, with C fraction from 0 to 0.28. The absorption coefficient has been obtained in the region 0.73–4.5eV by means of ellipsometry, reflectance–transmittance and photothermal deflection spectroscopy. The addition of carbon in the alloy increases the disorder and the density of defects: samples deposited with high carbon content have poorer optoelectronic properties. Two conduction regimes are observed: extended state conduction and hopping conduction in the conduction band tail. A visible PL peak that widens and shifts to higher energies as the carbon content increases has been observed.

Materials Science Forum, 2005

The optical and electrical properties of undoped and low doped polycrystalline silicon films depo... more The optical and electrical properties of undoped and low doped polycrystalline silicon films deposited by LPCVD technique are analysed. Photothermal deflexion spectroscopy, and electrical conductivity in the temperature range 50-475 K are used. The effect of low phosphorus doping on the density of defects, electrical parameters and hopping conduction are examined and interpreted in conjunction with the passivation of defects by the introduction of phosphorus atoms. The density of states at the Fermi level is also calculated.

Materials Science and Engineering: C, 2008

Typical power switching devices such as diodes, thyristors, and transistors are based on a monocr... more Typical power switching devices such as diodes, thyristors, and transistors are based on a monocrystalline silicon semiconductor or silicon carbide. Silicon is less expensive, more widely used, and a more versatile processing material than silicon carbide. The silicon carbide (SiC) has ...

2013 International Conference on Electrical Engineering and Software Applications, 2013

:H) at AM1.5. All parameters are determined such as efficiency and filling factor. In the dark, t... more :H) at AM1.5. All parameters are determined such as efficiency and filling factor. In the dark, the static and dynamic parameters of diode are deduced. Defects in the intrinsic layer are evaluated by photothermal deflexion spectroscopy technique. All the measured parameters are used by the solar cell capacitance simulator (SCAPS 3.2). The structure of solar cells and the experimental conditions were introduced in simulator. The experimental I-V and spectral response characteristics were correlated to the simulated ones. The simulation shows that increase in defects density, reduces the electrical parameters of amorphous solar cells. The effect of the gap value is more important to define the efficiency of the solar cell made by a-SiC:H materials.

Philosophical Magazine Part B, 2002

Wide-bandgap hydrogenated amorphous silicon-carbon and silicon-nitrogen films having optical gaps... more Wide-bandgap hydrogenated amorphous silicon-carbon and silicon-nitrogen films having optical gaps in the range 1.9-4.0 eV have been deposited by the 13.56 MHz plasma-enhanced chemical vapour deposition technique from SiH4 + C2H2 (+H2), SiH4 + NH3 (+H2), gas mixtures. The deposition conditions have been chosen so as to obtain device-quality films already successfully applied in optoelectronic technology. The films have been

Materials Science Forum, 2010

Optical and electrical properties amorphous carbon nitride (a-CN) has been investigated on films ... more Optical and electrical properties amorphous carbon nitride (a-CN) has been investigated on films deposited by reactive R.F. sputtering source with a graphite target. The amorphous carbon nitride samples were prepared under a gas mixture of nitrogen (N 2 ) and /or Argon (Ar).The optical transitions are governed by the π and π* electronic state distributions, related to sp 2 -and sp 1hybridized C and N atoms. Specific lonepair electronic states arise from groups (CN) with sp 1hybridized C atoms, which may form C≡N triple bonds or -N=C=N-longer chains. Photoluminescence spectra show a maximum around 650 nm. Two conduction regimes at high and low temperature are found in a-CN samples. The corresponding activation energies decrease with the increase of target voltage.

2012 16th IEEE Mediterranean Electrotechnical Conference, 2012

The wide band gap (3.2 eV) allows the silicon carbide (SiC) to work at high temperatures with hig... more The wide band gap (3.2 eV) allows the silicon carbide (SiC) to work at high temperatures with high voltages and currents, to switch large power densities and reduce losses. The 4H-SiC polytype is the most widely used material for electronic applications. Despite the development of manufacturing technology of SiC wafers, this material has structural defects, such as micropipes, dislocations and inclusions of polytypes. In this paper, the defects and dynamic performance of the SiC Schottky diodes is studied and the obtained maximum reverse voltage is 600V. The reverse recovery time is evaluated to 135ns. The results demonstrate the effectiveness of the SiC devices in reducing the overall system losses generated by switching transitions compared to silicon based diodes. We introduced the parameters found in the Ti/4H-SiC Schottky diode in the Pspice model for simulation. We compared these results with the model using Matlab-Simulink to see the behavior of the switching cell and to deduce the equivalent circuit of diode in dynamic transitions.

Solid-State Electronics, 2006

UV photosensors based on a-Si:H/a-SiC:H were deposited by ultra high vacuum plasma enhanced chemi... more UV photosensors based on a-Si:H/a-SiC:H were deposited by ultra high vacuum plasma enhanced chemical vapour deposition system (UHV-PECVD) over a large area (10 cm · 10 cm) in p-i-n configuration.

Solid-State Electronics, 2007

p-i-n Heterostructures deposited by ultra high vacuum plasma enhanced chemical vapour deposition ... more p-i-n Heterostructures deposited by ultra high vacuum plasma enhanced chemical vapour deposition (UHV-PECVD) using silane and methane gases with and without hydrogen dilution of the i-layer have been studied. Amorphous silicon carbon alloy (a-SiC:H) has been used in the p + and i-layers and amorphous silicon (a-Si:H) in the n layer. The effect of hydrogen dilution on the defect properties of i-layer films has been studied by photothermal deflection spectroscopy and constant photocurrent method. Hydrogen dilution of the ilayer changes the J (V) characteristics and notably under illumination: the fill factor decreases, the short-circuit current density J sc increases and, moreover, a cross over was observed between J (V) characteristics in dark and under illumination of the diluted cells. A two diodes model has been used to explain this phenomenon. Measurements of the diode junction capacity show higher capacitance in the diluted i-layer p-i-n structure than in the undiluted ones at low frequencies. This effect is due to the decrease of the defects density induced mainly by the increase of the capture reemission time (or delay time) of charges.

Solid-State Electronics, 2007

The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in ... more The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in amorphous silicon and its compounds are the object of intense research works. By starting on the concept that such p-i-n structures can be compared to p + -n and n-n + junctions in series, and by referring to Shockley's model in one modified diode, we propose an equivalent electrical circuit in dynamic state of the considered structure resulting from a series association of Shockley's model. A simulation study by PSPICE of the equivalent electrical circuit so obtained is in good agreement with the experimental results, and physical interpretations connected to this model are discussed.

Philosophical Magazine, 2007

The local microstructure and optical and electrical properties were investigated of amorphous car... more The local microstructure and optical and electrical properties were investigated of amorphous carbon nitride (a-CN) films deposited by reactive radio-frequency (RF) sputtering. Two series prepared in nitrogen or in a nitrogen and argon mixture were studied. The optical properties were investigated by transmittance/reflectance and photothermal deflection spectroscopies. Combined infrared measurements and Raman scattering spectroscopies were used to investigate the microstructure of a-CN films in terms of nitrogen incorporation within the films and C sp content. These experiments were completed by dark electrical conductivity measurements performed in coplanar configuration in the temperature range 50–450 K. The films exhibit semiconductor behaviour and the temperature dependence suggests two types of conduction. An increase in nitrogen incorporation induces an increase with clustering of sp phase replacing C=C olefinic groups with aromatic groups.

Microelectronic Engineering, 2013

We have studied and compared two types of Schottky diodes prepared by the evaporation of molybden... more We have studied and compared two types of Schottky diodes prepared by the evaporation of molybdenum (Mo) and titanium (Ti) on a 4H-SiC semiconductor. The electrical characteristics of these diodes are analyzed based on the standard thermionic emission model. The main electrical parameters including the series resistance R s , the ideality factor n and the barrier height U B are extracted from current-voltage-temperature (I-V-T) measurements. In the Ti/4H-SiC structure, the series resistance increases from 1.51 mO cm 2 to 27.68 mO cm 2 when the temperature is varied from 70 K to 450 K. In contrast, the series resistance does not exceed a 6.17 mO cm 2 at 450 K in the Mo/4H-SiC Schottky diode. We have decomposed the series resistance into three components. The deduced static and dynamic parameters were used to define an electrical model. The switching behavior of the equivalent circuit indicates a reverse recovery time (Trr) of 1.412 ns for Ti/4H-SiC and 3.27 ns for Mo/4H-SiC.

Materials Science and Engineering: C, 2006

The optical and electrical properties of amorphously deposited and then post-crystallized silicon... more The optical and electrical properties of amorphously deposited and then post-crystallized silicon films are studied as a function of the deposition pressure and the phosphorus doping. Amorphous silicon films are deposited in a high pressure regime by SAPCVD (Sub-Atmospheric ...

Materials Science and Engineering: C, 2008

The paper deals with the effect of slightly phosphorus atoms introduced during deposition of poly... more The paper deals with the effect of slightly phosphorus atoms introduced during deposition of polysilicon films. Polysilicon films are used as an active layer in thin film transistors (TFTs) fabricated on glass substrates at a maximum temperature of 600 °C.Three phosphorus atoms contents, determined by the value of the phosphine to silane ratio: Γ (3.7×10−7, 8×10−7, 26×10−6), are used to optimize